This is ../info/elisp, produced by makeinfo version 4.8 from elisp.texi.

INFO-DIR-SECTION Emacs
START-INFO-DIR-ENTRY
* Elisp: (elisp).       The Emacs Lisp Reference Manual.
END-INFO-DIR-ENTRY

   This is edition 2.9 of the GNU Emacs Lisp Reference Manual,
corresponding to Emacs version 22.3.

   Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999,
2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008  Free Software
Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
     Foundation; with the Invariant Sections being "GNU General Public
     License," with the Front-Cover texts being "A GNU Manual," and
     with the Back-Cover Texts as in (a) below.  A copy of the license
     is included in the section entitled "GNU Free Documentation
     License."

     (a) The FSF's Back-Cover Text is: "You are free to copy and modify
     this GNU Manual. Buying copies from GNU Press supports the FSF in
     developing GNU and promoting software freedom."


File: elisp,  Node: Top,  Next: Introduction,  Prev: (dir),  Up: (dir)

Emacs Lisp
**********

This Info file contains edition 2.9 of the GNU Emacs Lisp Reference
Manual, corresponding to GNU Emacs version 22.3.

* Menu:

* Introduction::            Introduction and conventions used.

* Lisp Data Types::         Data types of objects in Emacs Lisp.
* Numbers::                 Numbers and arithmetic functions.
* Strings and Characters::  Strings, and functions that work on them.
* Lists::                   Lists, cons cells, and related functions.
* Sequences Arrays Vectors::  Lists, strings and vectors are called sequences.
                                Certain functions act on any kind of sequence.
                                The description of vectors is here as well.
* Hash Tables::             Very fast lookup-tables.
* Symbols::                 Symbols represent names, uniquely.

* Evaluation::              How Lisp expressions are evaluated.
* Control Structures::      Conditionals, loops, nonlocal exits.
* Variables::               Using symbols in programs to stand for values.
* Functions::               A function is a Lisp program
                              that can be invoked from other functions.
* Macros::                  Macros are a way to extend the Lisp language.
* Customization::           Writing customization declarations.

* Loading::                 Reading files of Lisp code into Lisp.
* Byte Compilation::        Compilation makes programs run faster.
* Advising Functions::      Adding to the definition of a function.
* Debugging::               Tools and tips for debugging Lisp programs.

* Read and Print::          Converting Lisp objects to text and back.
* Minibuffers::             Using the minibuffer to read input.
* Command Loop::            How the editor command loop works,
                              and how you can call its subroutines.
* Keymaps::                 Defining the bindings from keys to commands.
* Modes::                   Defining major and minor modes.
* Documentation::           Writing and using documentation strings.

* Files::                   Accessing files.
* Backups and Auto-Saving:: Controlling how backups and auto-save
                              files are made.
* Buffers::                 Creating and using buffer objects.
* Windows::                 Manipulating windows and displaying buffers.
* Frames::		    Making multiple system-level windows.
* Positions::               Buffer positions and motion functions.
* Markers::                 Markers represent positions and update
                              automatically when the text is changed.

* Text::                    Examining and changing text in buffers.
* Non-ASCII Characters::    Non-ASCII text in buffers and strings.
* Searching and Matching::  Searching buffers for strings or regexps.
* Syntax Tables::           The syntax table controls word and list parsing.
* Abbrevs::                 How Abbrev mode works, and its data structures.

* Processes::               Running and communicating with subprocesses.
* Display::	            Features for controlling the screen display.
* System Interface::        Getting the user id, system type, environment
                              variables, and other such things.

Appendices

* Antinews::                Info for users downgrading to Emacs 21.
* GNU Free Documentation License:: The license for this documentation
* GPL::                     Conditions for copying and changing GNU Emacs.
* Tips::                    Advice and coding conventions for Emacs Lisp.
* GNU Emacs Internals::     Building and dumping Emacs;
                              internal data structures.
* Standard Errors::         List of all error symbols.
* Standard Buffer-Local Variables::
                            List of variables buffer-local in all buffers.
* Standard Keymaps::        List of standard keymaps.
* Standard Hooks::          List of standard hook variables.

* Index::                   Index including concepts, functions, variables,
                              and other terms.



 --- The Detailed Node Listing ---
 ---------------------------------

Here are other nodes that are inferiors of those already listed,
mentioned here so you can get to them in one step:

Introduction

* Caveats::                 Flaws and a request for help.
* Lisp History::            Emacs Lisp is descended from Maclisp.
* Conventions::             How the manual is formatted.
* Version Info::            Which Emacs version is running?
* Acknowledgements::        The authors, editors, and sponsors of this manual.

Conventions

* Some Terms::              Explanation of terms we use in this manual.
* nil and t::               How the symbols `nil' and `t' are used.
* Evaluation Notation::     The format we use for examples of evaluation.
* Printing Notation::       The format we use for examples that print output.
* Error Messages::          The format we use for examples of errors.
* Buffer Text Notation::    The format we use for buffer contents in examples.
* Format of Descriptions::  Notation for describing functions, variables, etc.

Format of Descriptions

* A Sample Function Description::  A description of an imaginary
                                     function, `foo'.
* A Sample Variable Description::  A description of an imaginary
                                     variable, `electric-future-map'.

Lisp Data Types

* Printed Representation::  How Lisp objects are represented as text.
* Comments::                Comments and their formatting conventions.
* Programming Types::       Types found in all Lisp systems.
* Editing Types::           Types specific to Emacs.
* Circular Objects::            Read syntax for circular structure.
* Type Predicates::         Tests related to types.
* Equality Predicates::     Tests of equality between any two objects.

Programming Types

* Integer Type::        Numbers without fractional parts.
* Floating Point Type:: Numbers with fractional parts and with a large range.
* Character Type::      The representation of letters, numbers and
                          control characters.
* Symbol Type::         A multi-use object that refers to a function,
                        variable, property list, or itself.
* Sequence Type::       Both lists and arrays are classified as sequences.
* Cons Cell Type::      Cons cells, and lists (which are made from cons cells).
* Array Type::          Arrays include strings and vectors.
* String Type::         An (efficient) array of characters.
* Vector Type::         One-dimensional arrays.
* Char-Table Type::     One-dimensional sparse arrays indexed by characters.
* Bool-Vector Type::    One-dimensional arrays of `t' or `nil'.
* Hash Table Type::     Super-fast lookup tables.
* Function Type::       A piece of executable code you can call from elsewhere.
* Macro Type::          A method of expanding an expression into another
                          expression, more fundamental but less pretty.
* Primitive Function Type::     A function written in C, callable from Lisp.
* Byte-Code Type::      A function written in Lisp, then compiled.
* Autoload Type::       A type used for automatically loading seldom-used
                          functions.

Character Type

* Basic Char Syntax::       Syntax for regular characters.
* General Escape Syntax::   How to specify characters by their codes.
* Ctl-Char Syntax::         Syntax for control characters.
* Meta-Char Syntax::        Syntax for meta-characters.
* Other Char Bits::         Syntax for hyper-, super-, and alt-characters.

Cons Cell and List Types

* Box Diagrams::            Drawing pictures of lists.
* Dotted Pair Notation::    An alternative syntax for lists.
* Association List Type::   A specially constructed list.

String Type

* Syntax for Strings::      How to specify Lisp strings.
* Non-ASCII in Strings::    International characters in strings.
* Nonprinting Characters::  Literal unprintable characters in strings.
* Text Props and Strings::  Strings with text properties.

Editing Types

* Buffer Type::             The basic object of editing.
* Marker Type::             A position in a buffer.
* Window Type::             What makes buffers visible.
* Frame Type::		    Windows subdivide frames.
* Window Configuration Type::  Recording the way a frame is subdivided.
* Frame Configuration Type::   Recording the status of all frames.
* Process Type::            A process running on the underlying OS.
* Stream Type::             Receive or send characters.
* Keymap Type::             What function a keystroke invokes.
* Overlay Type::            How an overlay is represented.

Numbers

* Integer Basics::          Representation and range of integers.
* Float Basics::	    Representation and range of floating point.
* Predicates on Numbers::   Testing for numbers.
* Comparison of Numbers::   Equality and inequality predicates.
* Numeric Conversions::	    Converting float to integer and vice versa.
* Arithmetic Operations::   How to add, subtract, multiply and divide.
* Rounding Operations::     Explicitly rounding floating point numbers.
* Bitwise Operations::      Logical and, or, not, shifting.
* Math Functions::          Trig, exponential and logarithmic functions.
* Random Numbers::          Obtaining random integers, predictable or not.

Strings and Characters

* String Basics::           Basic properties of strings and characters.
* Predicates for Strings::  Testing whether an object is a string or char.
* Creating Strings::        Functions to allocate new strings.
* Modifying Strings::         Altering the contents of an existing string.
* Text Comparison::         Comparing characters or strings.
* String Conversion::       Converting characters to strings and vice versa.
* Formatting Strings::      `format': Emacs's analogue of `printf'.
* Case Conversion::         Case conversion functions.
* Case Tables::		    Customizing case conversion.

Lists

* Cons Cells::              How lists are made out of cons cells.
* List-related Predicates:: Is this object a list?  Comparing two lists.
* List Elements::           Extracting the pieces of a list.
* Building Lists::          Creating list structure.
* List Variables::          Modifying lists stored in variables.
* Modifying Lists::         Storing new pieces into an existing list.
* Sets And Lists::          A list can represent a finite mathematical set.
* Association Lists::       A list can represent a finite relation or mapping.
* Rings::                   Managing a fixed-size ring of objects.

Modifying Existing List Structure

* Setcar::                  Replacing an element in a list.
* Setcdr::                  Replacing part of the list backbone.
                              This can be used to remove or add elements.
* Rearrangement::           Reordering the elements in a list; combining lists.

Sequences, Arrays, and Vectors

* Sequence Functions::      Functions that accept any kind of sequence.
* Arrays::                  Characteristics of arrays in Emacs Lisp.
* Array Functions::         Functions specifically for arrays.
* Vectors::                 Special characteristics of Emacs Lisp vectors.
* Vector Functions::        Functions specifically for vectors.
* Char-Tables::             How to work with char-tables.
* Bool-Vectors::            How to work with bool-vectors.

Hash Tables

* Creating Hash::           Functions to create hash tables.
* Hash Access::             Reading and writing the hash table contents.
* Defining Hash::           Defining new comparison methods
* Other Hash::              Miscellaneous.

Symbols

* Symbol Components::       Symbols have names, values, function definitions
                              and property lists.
* Definitions::             A definition says how a symbol will be used.
* Creating Symbols::        How symbols are kept unique.
* Property Lists::          Each symbol has a property list
                              for recording miscellaneous information.

Property Lists

* Plists and Alists::       Comparison of the advantages of property
                              lists and association lists.
* Symbol Plists::           Functions to access symbols' property lists.
* Other Plists::            Accessing property lists stored elsewhere.

Evaluation

* Intro Eval::              Evaluation in the scheme of things.
* Forms::                   How various sorts of objects are evaluated.
* Quoting::                 Avoiding evaluation (to put constants in
                              the program).
* Eval::                    How to invoke the Lisp interpreter explicitly.

Kinds of Forms

* Self-Evaluating Forms::   Forms that evaluate to themselves.
* Symbol Forms::            Symbols evaluate as variables.
* Classifying Lists::       How to distinguish various sorts of list forms.
* Function Indirection::    When a symbol appears as the car of a list,
			      we find the real function via the symbol.
* Function Forms::          Forms that call functions.
* Macro Forms::             Forms that call macros.
* Special Forms::           "Special forms" are idiosyncratic primitives,
                              most of them extremely important.
* Autoloading::             Functions set up to load files
                              containing their real definitions.

Control Structures

* Sequencing::              Evaluation in textual order.
* Conditionals::            `if', `cond', `when', `unless'.
* Combining Conditions::    `and', `or', `not'.
* Iteration::               `while' loops.
* Nonlocal Exits::          Jumping out of a sequence.

Nonlocal Exits

* Catch and Throw::         Nonlocal exits for the program's own purposes.
* Examples of Catch::       Showing how such nonlocal exits can be written.
* Errors::                  How errors are signaled and handled.
* Cleanups::                Arranging to run a cleanup form if an
                              error happens.

Errors

* Signaling Errors::        How to report an error.
* Processing of Errors::    What Emacs does when you report an error.
* Handling Errors::         How you can trap errors and continue execution.
* Error Symbols::           How errors are classified for trapping them.
* Standard Errors::         List of all error symbols.

Variables

* Global Variables::        Variable values that exist permanently, everywhere.
* Constant Variables::      Certain "variables" have values that never change.
* Local Variables::         Variable values that exist only temporarily.
* Void Variables::          Symbols that lack values.
* Defining Variables::      A definition says a symbol is used as a variable.
* Tips for Defining::       Things you should think about when you
                              define a variable.
* Accessing Variables::     Examining values of variables whose names
                              are known only at run time.
* Setting Variables::       Storing new values in variables.
* Variable Scoping::        How Lisp chooses among local and global values.
* Buffer-Local Variables::  Variable values in effect only in one buffer.
* Future Local Variables::  New kinds of local values we might add some day.
* File Local Variables::    Handling local variable lists in files.
* Variable Aliases::        Variables that are aliases for other variables.
* Variables with Restricted Values::  Non-constant variables whose value can
                                        _not_ be an arbitrary Lisp object.
* Standard Buffer-Local Variables::
                            List of variables buffer-local in all buffers.

Scoping Rules for Variable Bindings

* Scope::                   Scope means where in the program a value
                              is visible.  Comparison with other languages.
* Extent::                  Extent means how long in time a value exists.
* Impl of Scope::           Two ways to implement dynamic scoping.
* Using Scoping::           How to use dynamic scoping carefully and
                              avoid problems.

Buffer-Local Variables

* Intro to Buffer-Local::   Introduction and concepts.
* Creating Buffer-Local::   Creating and destroying buffer-local bindings.
* Default Value::           The default value is seen in buffers
                              that don't have their own buffer-local values.

Functions

* What Is a Function::      Lisp functions vs primitives; terminology.
* Lambda Expressions::      How functions are expressed as Lisp objects.
* Function Names::          A symbol can serve as the name of a function.
* Defining Functions::      Lisp expressions for defining functions.
* Calling Functions::       How to use an existing function.
* Mapping Functions::       Applying a function to each element of a list, etc.
* Anonymous Functions::     Lambda-expressions are functions with no names.
* Function Cells::          Accessing or setting the function definition
                              of a symbol.
* Obsolete Functions::      Declaring functions obsolete.
* Inline Functions::	    Defining functions that the compiler will open code.
* Function Safety::         Determining whether a function is safe to call.
* Related Topics::          Cross-references to specific Lisp primitives
                              that have a special bearing on how
                              functions work.

Lambda Expressions

* Lambda Components::       The parts of a lambda expression.
* Simple Lambda::           A simple example.
* Argument List::           Details and special features of argument lists.
* Function Documentation::  How to put documentation in a function.

Macros

* Simple Macro::            A basic example.
* Expansion::               How, when and why macros are expanded.
* Compiling Macros::        How macros are expanded by the compiler.
* Defining Macros::         How to write a macro definition.
* Backquote::               Easier construction of list structure.
* Problems with Macros::    Don't evaluate the macro arguments too many times.
                              Don't hide the user's variables.
* Indenting Macros::        Specifying how to indent macro calls.

Common Problems Using Macros

* Wrong Time::             Do the work in the expansion, not in the macro.
* Argument Evaluation::    The expansion should evaluate each macro arg once.
* Surprising Local Vars::  Local variable bindings in the expansion
                              require special care.
* Eval During Expansion::  Don't evaluate them; put them in the expansion.
* Repeated Expansion::     Avoid depending on how many times expansion is done.

Writing Customization Definitions

* Common Keywords::         Common keyword arguments for all kinds of
                              customization declarations.
* Group Definitions::       Writing customization group definitions.
* Variable Definitions::    Declaring user options.
* Customization Types::     Specifying the type of a user option.

Customization Types

* Simple Types::            Simple customization types: sexp, integer, number,
                              string, file, directory, alist.
* Composite Types::         Build new types from other types or data.
* Splicing into Lists::     Splice elements into list with `:inline'.
* Type Keywords::           Keyword-argument pairs in a customization type.
* Defining New Types::      Give your type a name.

Loading

* How Programs Do Loading:: The `load' function and others.
* Load Suffixes::           Details about the suffixes that `load' tries.
* Library Search::          Finding a library to load.
* Loading Non-ASCII::       Non-ASCII characters in Emacs Lisp files.
* Autoload::                Setting up a function to autoload.
* Repeated Loading::        Precautions about loading a file twice.
* Named Features::          Loading a library if it isn't already loaded.
* Where Defined::           Finding which file defined a certain symbol.
* Unloading::		    How to "unload" a library that was loaded.
* Hooks for Loading::	    Providing code to be run when
			      particular libraries are loaded.

Byte Compilation

* Speed of Byte-Code::      An example of speedup from byte compilation.
* Compilation Functions::   Byte compilation functions.
* Docs and Compilation::    Dynamic loading of documentation strings.
* Dynamic Loading::         Dynamic loading of individual functions.
* Eval During Compile::     Code to be evaluated when you compile.
* Compiler Errors::         Handling compiler error messages.
* Byte-Code Objects::	    The data type used for byte-compiled functions.
* Disassembly::             Disassembling byte-code; how to read byte-code.

Advising Emacs Lisp Functions

* Simple Advice::           A simple example to explain the basics of advice.
* Defining Advice::         Detailed description of `defadvice'.
* Around-Advice::           Wrapping advice around a function's definition.
* Computed Advice::         ...is to `defadvice' as `fset' is to `defun'.
* Activation of Advice::    Advice doesn't do anything until you activate it.
* Enabling Advice::         You can enable or disable each piece of advice.
* Preactivation::           Preactivation is a way of speeding up the
                              loading of compiled advice.
* Argument Access in Advice:: How advice can access the function's arguments.
* Advising Primitives::     Accessing arguments when advising a primitive.
* Combined Definition::     How advice is implemented.

Debugging Lisp Programs

* Debugger::                How the Emacs Lisp debugger is implemented.
* Edebug::                  A source-level Emacs Lisp debugger.
* Syntax Errors::           How to find syntax errors.
* Test Coverage::           Ensuring you have tested all branches in your code.
* Compilation Errors::      How to find errors that show up in
                              byte compilation.

The Lisp Debugger

* Error Debugging::         Entering the debugger when an error happens.
* Infinite Loops::	    Stopping and debugging a program that doesn't exit.
* Function Debugging::      Entering it when a certain function is called.
* Explicit Debug::          Entering it at a certain point in the program.
* Using Debugger::          What the debugger does; what you see while in it.
* Debugger Commands::       Commands used while in the debugger.
* Invoking the Debugger::   How to call the function `debug'.
* Internals of Debugger::   Subroutines of the debugger, and global variables.

Edebug

* Using Edebug::	    Introduction to use of Edebug.
* Instrumenting::	    You must instrument your code
			      in order to debug it with Edebug.
* Edebug Execution Modes::  Execution modes, stopping more or less often.
* Jumping::		    Commands to jump to a specified place.
* Edebug Misc::		    Miscellaneous commands.
* Breaks::		    Setting breakpoints to make the program stop.
* Trapping Errors::	    Trapping errors with Edebug.
* Edebug Views::	    Views inside and outside of Edebug.
* Edebug Eval::		    Evaluating expressions within Edebug.
* Eval List::		    Expressions whose values are displayed
			      each time you enter Edebug.
* Printing in Edebug::	    Customization of printing.
* Trace Buffer::	    How to produce trace output in a buffer.
* Coverage Testing::	    How to test evaluation coverage.
* The Outside Context::	    Data that Edebug saves and restores.
* Edebug and Macros::       Specifying how to handle macro calls.
* Edebug Options::	    Option variables for customizing Edebug.

Debugging Invalid Lisp Syntax

* Excess Open::             How to find a spurious open paren or missing close.
* Excess Close::            How to find a spurious close paren or missing open.

Reading and Printing Lisp Objects

* Streams Intro::           Overview of streams, reading and printing.
* Input Streams::           Various data types that can be used as
                              input streams.
* Input Functions::         Functions to read Lisp objects from text.
* Output Streams::          Various data types that can be used as
                              output streams.
* Output Functions::        Functions to print Lisp objects as text.
* Output Variables::        Variables that control what the printing
                              functions do.

Minibuffers

* Intro to Minibuffers::    Basic information about minibuffers.
* Text from Minibuffer::    How to read a straight text string.
* Object from Minibuffer::  How to read a Lisp object or expression.
* Minibuffer History::	    Recording previous minibuffer inputs
			      so the user can reuse them.
* Initial Input::           Specifying initial contents for the minibuffer.
* Completion::              How to invoke and customize completion.
* Yes-or-No Queries::       Asking a question with a simple answer.
* Multiple Queries::	    Asking a series of similar questions.
* Reading a Password::	    Reading a password from the terminal.
* Minibuffer Commands::     Commands used as key bindings in minibuffers.
* Minibuffer Contents::     How such commands access the minibuffer text.
* Minibuffer Windows::      Operating on the special minibuffer windows.
* Recursive Mini::          Whether recursive entry to minibuffer is allowed.
* Minibuffer Misc::         Various customization hooks and variables.

Completion

* Basic Completion::        Low-level functions for completing strings.
                              (These are too low level to use the minibuffer.)
* Minibuffer Completion::   Invoking the minibuffer with completion.
* Completion Commands::     Minibuffer commands that do completion.
* High-Level Completion::   Convenient special cases of completion
                              (reading buffer name, file name, etc.)
* Reading File Names::      Using completion to read file names.
* Programmed Completion::   Finding the completions for a given file name.

Command Loop

* Command Overview::    How the command loop reads commands.
* Defining Commands::   Specifying how a function should read arguments.
* Interactive Call::    Calling a command, so that it will read arguments.
* Distinguish Interactive::     Making a command distinguish interactive calls.
* Command Loop Info::   Variables set by the command loop for you to examine.
* Adjusting Point::     Adjustment of point after a command.
* Input Events::	What input looks like when you read it.
* Reading Input::       How to read input events from the keyboard or mouse.
* Special Events::      Events processed immediately and individually.
* Waiting::             Waiting for user input or elapsed time.
* Quitting::            How C-g works.  How to catch or defer quitting.
* Prefix Command Arguments::    How the commands to set prefix args work.
* Recursive Editing::   Entering a recursive edit,
                          and why you usually shouldn't.
* Disabling Commands::  How the command loop handles disabled commands.
* Command History::     How the command history is set up, and how accessed.
* Keyboard Macros::     How keyboard macros are implemented.

Defining Commands

* Using Interactive::       General rules for `interactive'.
* Interactive Codes::       The standard letter-codes for reading arguments
                              in various ways.
* Interactive Examples::    Examples of how to read interactive arguments.

Input Events

* Keyboard Events::         Ordinary characters--keys with symbols on them.
* Function Keys::           Function keys--keys with names, not symbols.
* Mouse Events::            Overview of mouse events.
* Click Events::            Pushing and releasing a mouse button.
* Drag Events::             Moving the mouse before releasing the button.
* Button-Down Events::      A button was pushed and not yet released.
* Repeat Events::           Double and triple click (or drag, or down).
* Motion Events::           Just moving the mouse, not pushing a button.
* Focus Events::            Moving the mouse between frames.
* Misc Events::             Other events the system can generate.
* Event Examples::          Examples of the lists for mouse events.
* Classifying Events::      Finding the modifier keys in an event symbol.
* Accessing Mouse::	    Functions to extract info from mouse events.
* Accessing Scroll::        Functions to get info from scroll bar events.
* Strings of Events::       Special considerations for putting
                              keyboard character events in a string.

Reading Input

* Key Sequence Input::      How to read one key sequence.
* Reading One Event::       How to read just one event.
* Event Mod::               How Emacs modifies events as they are read.
* Invoking the Input Method::   How reading an event uses the input method.
* Quoted Character Input::  Asking the user to specify a character.
* Event Input Misc::        How to reread or throw away input events.

Keymaps

* Key Sequences::           Key sequences as Lisp objects.
* Keymap Basics::           Basic concepts of keymaps.
* Format of Keymaps::       What a keymap looks like as a Lisp object.
* Creating Keymaps::        Functions to create and copy keymaps.
* Inheritance and Keymaps:: How one keymap can inherit the bindings
                              of another keymap.
* Prefix Keys::             Defining a key with a keymap as its definition.
* Active Keymaps::          How Emacs searches the active keymaps
                              for a key binding.
* Searching Keymaps::       A pseudo-Lisp summary of searching active maps.
* Controlling Active Maps:: Each buffer has a local keymap
                               to override the standard (global) bindings.
                               A minor mode can also override them.
* Key Lookup::              How extracting elements from keymaps works.
* Functions for Key Lookup::    How to request key lookup.
* Changing Key Bindings::   Redefining a key in a keymap.
* Remapping Commands::      A keymap can translate one command to another.
* Translation Keymaps::     Keymaps for translating sequences of events.
* Key Binding Commands::    Interactive interfaces for redefining keys.
* Scanning Keymaps::        Looking through all keymaps, for printing help.
* Menu Keymaps::            A keymap can define a menu for X
                              or for use from the terminal.
* Standard Keymaps::        List of standard keymaps.

Major and Minor Modes

* Hooks::                   How to use hooks; how to write code that
                              provides hooks.
* Major Modes::             Defining major modes.
* Minor Modes::             Defining minor modes.
* Mode Line Format::        Customizing the text that appears in the mode line.
* Imenu::                   How a mode can provide a menu
                              of definitions in the buffer.
* Font Lock Mode::          How modes can highlight text according to syntax.
* Desktop Save Mode::       How modes can have buffer state saved between
                              Emacs sessions.

Menu Keymaps

* Defining Menus::          How to make a keymap that defines a menu.
* Mouse Menus::             How users actuate the menu with the mouse.
* Keyboard Menus::          How users actuate the menu with the keyboard.
* Menu Example::            Making a simple menu.
* Menu Bar::                How to customize the menu bar.
* Tool Bar::                A tool bar is a row of images.
* Modifying Menus::         How to add new items to a menu.

Defining Menus

* Simple Menu Items::       A simple kind of menu key binding,
                              limited in capabilities.
* Extended Menu Items::     More powerful menu item definitions
                              let you specify keywords to enable
                              various features.
* Menu Separators::         Drawing a horizontal line through a menu.
* Alias Menu Items::        Using command aliases in menu items.

Major and Minor Modes

* Hooks::              How to use hooks; how to write code that provides hooks.
* Major Modes::        Defining major modes.
* Minor Modes::        Defining minor modes.
* Mode Line Format::   Customizing the text that appears in the mode line.
* Imenu::              How a mode can provide a menu
                         of definitions in the buffer.
* Font Lock Mode::     How modes can highlight text according to syntax.
* Desktop Save Mode::  How modes can have buffer state saved between
                         Emacs sessions.

Major Modes

* Major Mode Basics::
* Major Mode Conventions::  Coding conventions for keymaps, etc.
* Example Major Modes::     Text mode and Lisp modes.
* Auto Major Mode::         How Emacs chooses the major mode automatically.
* Mode Help::               Finding out how to use a mode.
* Derived Modes::           Defining a new major mode based on another major
                              mode.
* Generic Modes::           Defining a simple major mode that supports
                              comment syntax and Font Lock mode.
* Mode Hooks::              Hooks run at the end of major mode functions.

Minor Modes

* Minor Mode Conventions::  Tips for writing a minor mode.
* Keymaps and Minor Modes:: How a minor mode can have its own keymap.
* Defining Minor Modes::    A convenient facility for defining minor modes.

Mode Line Format

* Mode Line Basics::
* Mode Line Data::          The data structure that controls the mode line.
* Mode Line Variables::     Variables used in that data structure.
* %-Constructs::            Putting information into a mode line.
* Properties in Mode::      Using text properties in the mode line.
* Header Lines::            Like a mode line, but at the top.
* Emulating Mode Line::     Formatting text as the mode line would.

Font Lock Mode

* Font Lock Basics::        Overview of customizing Font Lock.
* Search-based Fontification::  Fontification based on regexps.
* Customizing Keywords::    Customizing search-based fontification.
* Other Font Lock Variables::   Additional customization facilities.
* Levels of Font Lock::     Each mode can define alternative levels
                              so that the user can select more or less.
* Precalculated Fontification:: How Lisp programs that produce the buffer
                                  contents can also specify how to fontify it.
* Faces for Font Lock::     Special faces specifically for Font Lock.
* Syntactic Font Lock::     Fontification based on syntax tables.
* Setting Syntax Properties::   Defining character syntax based on context
                                  using the Font Lock mechanism.
* Multiline Font Lock::     How to coerce Font Lock into properly
                              highlighting multiline constructs.

Multiline Font Lock Constructs

* Font Lock Multiline::     Marking multiline chunks with a text property
* Region to Fontify::       Controlling which region gets refontified
                              after a buffer change.

Documentation

* Documentation Basics::    Good style for doc strings.
                              Where to put them.  How Emacs stores them.
* Accessing Documentation:: How Lisp programs can access doc strings.
* Keys in Documentation::   Substituting current key bindings.
* Describing Characters::   Making printable descriptions of
                              non-printing characters and key sequences.
* Help Functions::          Subroutines used by Emacs help facilities.

Files

* Visiting Files::          Reading files into Emacs buffers for editing.
* Saving Buffers::          Writing changed buffers back into files.
* Reading from Files::      Reading files into other buffers.
* Writing to Files::        Writing new files from parts of buffers.
* File Locks::              Locking and unlocking files, to prevent
                              simultaneous editing by two people.
* Information about Files:: Testing existence, accessibility, size of files.
* Changing Files::          Renaming files, changing protection, etc.
* File Names::              Decomposing and expanding file names.
* Contents of Directories:: Getting a list of the files in a directory.
* Create/Delete Dirs::	    Creating and Deleting Directories.
* Magic File Names::	    Defining "magic" special handling
			      for certain file names.
* Format Conversion::       Conversion to and from various file formats.

Visiting Files

* Visiting Functions::      The usual interface functions for visiting.
* Subroutines of Visiting:: Lower-level subroutines that they use.

Information about Files

* Testing Accessibility::   Is a given file readable?  Writable?
* Kinds of Files::          Is it a directory?  A symbolic link?
* Truenames::		    Eliminating symbolic links from a file name.
* File Attributes::         How large is it?  Any other names?  Etc.
* Locating Files::          How to find a file in standard places.

File Names

* File Name Components::    The directory part of a file name, and the rest.
* Relative File Names::     Some file names are relative to a
                              current directory.
* Directory Names::         A directory's name as a directory
                              is different from its name as a file.
* File Name Expansion::     Converting relative file names to absolute ones.
* Unique File Names::       Generating names for temporary files.
* File Name Completion::    Finding the completions for a given file name.
* Standard File Names::     If your package uses a fixed file name,
                              how to handle various operating systems simply.

Backups and Auto-Saving

* Backup Files::            How backup files are made; how their names
                              are chosen.
* Auto-Saving::             How auto-save files are made; how their
                              names are chosen.
* Reverting::               `revert-buffer', and how to customize
                              what it does.

Backup Files

* Making Backups::          How Emacs makes backup files, and when.
* Rename or Copy::          Two alternatives: renaming the old file
                              or copying it.
* Numbered Backups::        Keeping multiple backups for each source file.
* Backup Names::            How backup file names are computed; customization.

Buffers

* Buffer Basics::           What is a buffer?
* Current Buffer::          Designating a buffer as current
                              so primitives will access its contents.
* Buffer Names::            Accessing and changing buffer names.
* Buffer File Name::        The buffer file name indicates which file
                              is visited.
* Buffer Modification::     A buffer is "modified" if it needs to be saved.
* Modification Time::       Determining whether the visited file was changed
                              ``behind Emacs's back''.
* Read Only Buffers::       Modifying text is not allowed in a
                              read-only buffer.
* The Buffer List::         How to look at all the existing buffers.
* Creating Buffers::        Functions that create buffers.
* Killing Buffers::         Buffers exist until explicitly killed.
* Indirect Buffers::        An indirect buffer shares text with some
                              other buffer.
* Buffer Gap::              The gap in the buffer.

Windows

* Basic Windows::           Basic information on using windows.
* Splitting Windows::       Splitting one window into two windows.
* Deleting Windows::        Deleting a window gives its space to other windows.
* Selecting Windows::       The selected window is the one that you edit in.
* Cyclic Window Ordering::  Moving around the existing windows.
* Buffers and Windows::     Each window displays the contents of a buffer.
* Displaying Buffers::      Higher-level functions for displaying a buffer
                              and choosing a window for it.
* Choosing Window::	    How to choose a window for displaying a buffer.
* Window Point::            Each window has its own location of point.
* Window Start::            The display-start position controls which text
                              is on-screen in the window.
* Textual Scrolling::       Moving text up and down through the window.
* Vertical Scrolling::      Moving the contents up and down on the window.
* Horizontal Scrolling::    Moving the contents sideways on the window.
* Size of Window::          Accessing the size of a window.
* Resizing Windows::        Changing the size of a window.
* Coordinates and Windows:: Converting coordinates to windows.
* Window Tree::             The layout and sizes of all windows in a frame.
* Window Configurations::   Saving and restoring the state of the screen.
* Window Hooks::            Hooks for scrolling, window size changes,
                              redisplay going past a certain point,
                              or window configuration changes.

Frames

* Creating Frames::	    Creating additional frames.
* Multiple Displays::       Creating frames on other displays.
* Frame Parameters::	    Controlling frame size, position, font, etc.
* Frame Titles::            Automatic updating of frame titles.
* Deleting Frames::	    Frames last until explicitly deleted.
* Finding All Frames::	    How to examine all existing frames.
* Frames and Windows::	    A frame contains windows;
			      display of text always works through windows.
* Minibuffers and Frames::  How a frame finds the minibuffer to use.
* Input Focus::		    Specifying the selected frame.
* Visibility of Frames::    Frames may be visible or invisible, or icons.
* Raising and Lowering::    Raising a frame makes it hide other windows;
			      lowering it puts it underneath the others.
* Frame Configurations::    Saving the state of all frames.
* Mouse Tracking::	    Getting events that say when the mouse moves.
* Mouse Position::	    Asking where the mouse is, or moving it.
* Pop-Up Menus::	    Displaying a menu for the user to select from.
* Dialog Boxes::            Displaying a box to ask yes or no.
* Pointer Shape::           Specifying the shape of the mouse pointer.
* Window System Selections::Transferring text to and from other windows.
* Drag and Drop::               Internals of Drag-and-Drop implementation.
* Color Names::	            Getting the definitions of color names.
* Text Terminal Colors::    Defining colors for text-only terminals.
* Resources::		    Getting resource values from the server.
* Display Feature Testing:: Determining the features of a terminal.

Frame Parameters

* Parameter Access::        How to change a frame's parameters.
* Initial Parameters::	    Specifying frame parameters when you make a frame.
* Window Frame Parameters:: List of frame parameters for window systems.
* Size and Position::       Changing the size and position of a frame.
* Geometry::                Parsing geometry specifications.

Window Frame Parameters

* Basic Parameters::        Parameters that are fundamental.
* Position Parameters::     The position of the frame on the screen.
* Size Parameters::         Frame's size.
* Layout Parameters::       Size of parts of the frame, and
                              enabling or disabling some parts.
* Buffer Parameters::       Which buffers have been or should be shown.
* Management Parameters::   Communicating with the window manager.
* Cursor Parameters::       Controlling the cursor appearance.
* Color Parameters::        Colors of various parts of the frame.

Positions

* Point::                   The special position where editing takes place.
* Motion::                  Changing point.
* Excursions::              Temporary motion and buffer changes.
* Narrowing::               Restricting editing to a portion of the buffer.

Motion

* Character Motion::        Moving in terms of characters.
* Word Motion::             Moving in terms of words.
* Buffer End Motion::       Moving to the beginning or end of the buffer.
* Text Lines::              Moving in terms of lines of text.
* Screen Lines::            Moving in terms of lines as displayed.
* List Motion::             Moving by parsing lists and sexps.
* Skipping Characters::     Skipping characters belonging to a certain set.

Markers

* Overview of Markers::     The components of a marker, and how it relocates.
* Predicates on Markers::   Testing whether an object is a marker.
* Creating Markers::        Making empty markers or markers at certain places.
* Information from Markers::Finding the marker's buffer or character
                              position.
* Marker Insertion Types::  Two ways a marker can relocate when you
                              insert where it points.
* Moving Markers::          Moving the marker to a new buffer or position.
* The Mark::                How "the mark" is implemented with a marker.
* The Region::              How to access "the region".

Text

* Near Point::              Examining text in the vicinity of point.
* Buffer Contents::         Examining text in a general fashion.
* Comparing Text::          Comparing substrings of buffers.
* Insertion::               Adding new text to a buffer.
* Commands for Insertion::  User-level commands to insert text.
* Deletion::                Removing text from a buffer.
* User-Level Deletion::     User-level commands to delete text.
* The Kill Ring::           Where removed text sometimes is saved for
                              later use.
* Undo::                    Undoing changes to the text of a buffer.
* Maintaining Undo::        How to enable and disable undo information.
			      How to control how much information is kept.
* Filling::                 Functions for explicit filling.
* Margins::                 How to specify margins for filling commands.
* Adaptive Fill::           Adaptive Fill mode chooses a fill prefix
                              from context.
* Auto Filling::            How auto-fill mode is implemented to break lines.
* Sorting::                 Functions for sorting parts of the buffer.
* Columns::                 Computing horizontal positions, and using them.
* Indentation::             Functions to insert or adjust indentation.
* Case Changes::            Case conversion of parts of the buffer.
* Text Properties::         Assigning Lisp property lists to text characters.
* Substitution::            Replacing a given character wherever it appears.
* Transposition::           Swapping two portions of a buffer.
* Registers::               How registers are implemented.  Accessing
                              the text or position stored in a register.
* Base 64::                 Conversion to or from base 64 encoding.
* MD5 Checksum::            Compute the MD5 "message digest"/"checksum".
* Atomic Changes::          Installing several buffer changes "atomically".
* Change Hooks::            Supplying functions to be run when text is changed.

The Kill Ring

* Kill Ring Concepts::      What text looks like in the kill ring.
* Kill Functions::          Functions that kill text.
* Yanking::                 How yanking is done.
* Yank Commands::           Commands that access the kill ring.
* Low-Level Kill Ring::	    Functions and variables for kill ring access.
* Internals of Kill Ring::  Variables that hold kill-ring data.

Indentation

* Primitive Indent::        Functions used to count and insert indentation.
* Mode-Specific Indent::    Customize indentation for different modes.
* Region Indent::           Indent all the lines in a region.
* Relative Indent::         Indent the current line based on previous lines.
* Indent Tabs::             Adjustable, typewriter-like tab stops.
* Motion by Indent::        Move to first non-blank character.

Text Properties

* Examining Properties::    Looking at the properties of one character.
* Changing Properties::	    Setting the properties of a range of text.
* Property Search::	    Searching for where a property changes value.
* Special Properties::	    Particular properties with special meanings.
* Format Properties::       Properties for representing formatting of text.
* Sticky Properties::       How inserted text gets properties from
                              neighboring text.
* Saving Properties::       Saving text properties in files, and reading
                              them back.
* Lazy Properties::         Computing text properties in a lazy fashion
                              only when text is examined.
* Clickable Text::          Using text properties to make regions of text
                              do something when you click on them.
* Links and Mouse-1::       How to make <Mouse-1> follow a link.
* Fields::                  The `field' property defines
                              fields within the buffer.
* Not Intervals::	    Why text properties do not use
			      Lisp-visible text intervals.

Non-ASCII Characters

* Text Representations::    Unibyte and multibyte representations
* Converting Representations::  Converting unibyte to multibyte and vice versa.
* Selecting a Representation::  Treating a byte sequence as unibyte or multi.
* Character Codes::         How unibyte and multibyte relate to
                                codes of individual characters.
* Character Sets::          The space of possible character codes
                                is divided into various character sets.
* Chars and Bytes::         More information about multibyte encodings.
* Splitting Characters::    Converting a character to its byte sequence.
* Scanning Charsets::       Which character sets are used in a buffer?
* Translation of Characters::   Translation tables are used for conversion.
* Coding Systems::          Coding systems are conversions for saving files.
* Input Methods::           Input methods allow users to enter various
                                non-ASCII characters without special keyboards.
* Locales::                 Interacting with the POSIX locale.

Coding Systems

* Coding System Basics::    Basic concepts.
* Encoding and I/O::        How file I/O functions handle coding systems.
* Lisp and Coding Systems:: Functions to operate on coding system names.
* User-Chosen Coding Systems::  Asking the user to choose a coding system.
* Default Coding Systems::  Controlling the default choices.
* Specifying Coding Systems::   Requesting a particular coding system
                                    for a single file operation.
* Explicit Encoding::       Encoding or decoding text without doing I/O.
* Terminal I/O Encoding::   Use of encoding for terminal I/O.
* MS-DOS File Types::       How DOS "text" and "binary" files
                                relate to coding systems.

Searching and Matching

* String Search::           Search for an exact match.
* Searching and Case::      Case-independent or case-significant searching.
* Regular Expressions::     Describing classes of strings.
* Regexp Search::           Searching for a match for a regexp.
* POSIX Regexps::           Searching POSIX-style for the longest match.
* Match Data::              Finding out which part of the text matched,
                              after a string or regexp search.
* Search and Replace::	    Commands that loop, searching and replacing.
* Standard Regexps::        Useful regexps for finding sentences, pages,...

Regular Expressions

* Syntax of Regexps::       Rules for writing regular expressions.
* Regexp Example::          Illustrates regular expression syntax.
* Regexp Functions::        Functions for operating on regular expressions.

Syntax of Regular Expressions

* Regexp Special::          Special characters in regular expressions.
* Char Classes::            Character classes used in regular expressions.
* Regexp Backslash::        Backslash-sequences in regular expressions.

The Match Data

* Replacing Match::	    Replacing a substring that was matched.
* Simple Match Data::       Accessing single items of match data,
			      such as where a particular subexpression started.
* Entire Match Data::       Accessing the entire match data at once, as a list.
* Saving Match Data::       Saving and restoring the match data.

Syntax Tables

* Syntax Basics::           Basic concepts of syntax tables.
* Syntax Descriptors::      How characters are classified.
* Syntax Table Functions::  How to create, examine and alter syntax tables.
* Syntax Properties::       Overriding syntax with text properties.
* Motion and Syntax::	    Moving over characters with certain syntaxes.
* Parsing Expressions::     Parsing balanced expressions
                              using the syntax table.
* Standard Syntax Tables::  Syntax tables used by various major modes.
* Syntax Table Internals::  How syntax table information is stored.
* Categories::              Another way of classifying character syntax.

Syntax Descriptors

* Syntax Class Table::      Table of syntax classes.
* Syntax Flags::            Additional flags each character can have.

Parsing Expressions

* Motion via Parsing::      Motion functions that work by parsing.
* Position Parse::          Determining the syntactic state of a position.
* Parser State::            How Emacs represents a syntactic state.
* Low-Level Parsing::       Parsing across a specified region.
* Control Parsing::         Parameters that affect parsing.

Abbrevs And Abbrev Expansion

* Abbrev Mode::             Setting up Emacs for abbreviation.
* Abbrev Tables::           Creating and working with abbrev tables.
* Defining Abbrevs::        Specifying abbreviations and their expansions.
* Abbrev Files::            Saving abbrevs in files.
* Abbrev Expansion::        Controlling expansion; expansion subroutines.
* Standard Abbrev Tables::  Abbrev tables used by various major modes.

Processes

* Subprocess Creation::     Functions that start subprocesses.
* Shell Arguments::         Quoting an argument to pass it to a shell.
* Synchronous Processes::   Details of using synchronous subprocesses.
* Asynchronous Processes::  Starting up an asynchronous subprocess.
* Deleting Processes::      Eliminating an asynchronous subprocess.
* Process Information::     Accessing run-status and other attributes.
* Input to Processes::      Sending input to an asynchronous subprocess.
* Signals to Processes::    Stopping, continuing or interrupting
                              an asynchronous subprocess.
* Output from Processes::   Collecting output from an asynchronous subprocess.
* Sentinels::               Sentinels run when process run-status changes.
* Query Before Exit::       Whether to query if exiting will kill a process.
* Transaction Queues::      Transaction-based communication with subprocesses.
* Network::                 Opening network connections.
* Network Servers::         Network servers let Emacs accept net connections.
* Datagrams::               UDP network connections.
* Low-Level Network::       Lower-level but more general function
                              to create connections and servers.
* Misc Network::            Additional relevant functions for network connections.
* Byte Packing::            Using bindat to pack and unpack binary data.

Receiving Output from Processes

* Process Buffers::         If no filter, output is put in a buffer.
* Filter Functions::        Filter functions accept output from the process.
* Decoding Output::         Filters can get unibyte or multibyte strings.
* Accepting Output::        How to wait until process output arrives.

Low-Level Network Access

* Proc: Network Processes.  Using `make-network-process'.
* Options: Network Options.  Further control over network connections.
* Features: Network Feature Testing.
                            Determining which network features work on
                              the machine you are using.

Packing and Unpacking Byte Arrays

* Bindat Spec::             Describing data layout.
* Bindat Functions::        Doing the unpacking and packing.
* Bindat Examples::         Samples of what bindat.el can do for you!

Emacs Display

* Refresh Screen::          Clearing the screen and redrawing everything on it.
* Forcing Redisplay::       Forcing redisplay.
* Truncation::              Folding or wrapping long text lines.
* The Echo Area::           Displaying messages at the bottom of the screen.
* Warnings::                Displaying warning messages for the user.
* Invisible Text::          Hiding part of the buffer text.
* Selective Display::       Hiding part of the buffer text (the old way).
* Temporary Displays::      Displays that go away automatically.
* Overlays::		    Use overlays to highlight parts of the buffer.
* Width::                   How wide a character or string is on the screen.
* Line Height::             Controlling the height of lines.
* Faces::		    A face defines a graphics style
                              for text characters: font, colors, etc.
* Fringes::                 Controlling window fringes.
* Scroll Bars::             Controlling vertical scroll bars.
* Display Property::        Enabling special display features.
* Images::                  Displaying images in Emacs buffers.
* Buttons::                 Adding clickable buttons to Emacs buffers.
* Abstract Display::        Emacs' Widget for Object Collections.
* Blinking::                How Emacs shows the matching open parenthesis.
* Usual Display::	    The usual conventions for displaying nonprinting chars.
* Display Tables::	    How to specify other conventions.
* Beeping::                 Audible signal to the user.
* Window Systems::          Which window system is being used.

The Echo Area

* Displaying Messages::     Explicitly displaying text in the echo area.
* Progress::                Informing user about progress of a long operation.
* Logging Messages::        Echo area messages are logged for the user.
* Echo Area Customization:: Controlling the echo area.

Reporting Warnings

* Warning Basics::          Warnings concepts and functions to report them.
* Warning Variables::       Variables programs bind to customize their warnings.
* Warning Options::         Variables users set to control display of warnings.

Overlays

* Managing Overlays::       Creating and moving overlays.
* Overlay Properties::      How to read and set properties.
			    What properties do to the screen display.
* Finding Overlays::        Searching for overlays.

Faces

* Defining Faces::          How to define a face with `defface'.
* Face Attributes::         What is in a face?
* Attribute Functions::     Functions to examine and set face attributes.
* Displaying Faces::        How Emacs combines the faces specified for
                              a character.
* Font Selection::          Finding the best available font for a face.
* Face Functions::          How to define and examine faces.
* Auto Faces::              Hook for automatic face assignment.
* Font Lookup::             Looking up the names of available fonts
                              and information about them.
* Fontsets::                A fontset is a collection of fonts
                              that handle a range of character sets.

Fringes

* Fringe Size/Pos::         Specifying where to put the window fringes.
* Fringe Indicators::       Displaying indicator icons in the window fringes.
* Fringe Cursors::          Displaying cursors in the right fringe.
* Fringe Bitmaps::          Specifying bitmaps for fringe indicators.
* Customizing Bitmaps::     Specifying your own bitmaps to use in the fringes.
* Overlay Arrow::           Display of an arrow to indicate position.

The `display' Property

* Specified Space::         Displaying one space with a specified width.
* Pixel Specification::     Specifying space width or height in pixels.
* Other Display Specs::     Displaying an image; magnifying text; moving it
                              up or down on the page; adjusting the width
                              of spaces within text.
* Display Margins::         Displaying text or images to the side of
                              the main text.

Images

* Image Descriptors::       How to specify an image for use in `:display'.
* XBM Images::              Special features for XBM format.
* XPM Images::              Special features for XPM format.
* GIF Images::              Special features for GIF format.
* PostScript Images::       Special features for PostScript format.
* Other Image Types::       Various other formats are supported.
* Defining Images::         Convenient ways to define an image for later use.
* Showing Images::          Convenient ways to display an image once
                              it is defined.
* Image Cache::             Internal mechanisms of image display.

Buttons

* Button Properties::       Button properties with special meanings.
* Button Types::            Defining common properties for classes of buttons.
* Making Buttons::          Adding buttons to Emacs buffers.
* Manipulating Buttons::    Getting and setting properties of buttons.
* Button Buffer Commands::  Buffer-wide commands and bindings for buttons.

Abstract Display

* Abstract Display Functions::  Functions in the Ewoc package.
* Abstract Display Example::    Example of using Ewoc.

Display Tables

* Display Table Format::    What a display table consists of.
* Active Display Table::    How Emacs selects a display table to use.
* Glyphs::                  How to define a glyph, and what glyphs mean.

Operating System Interface

* Starting Up::             Customizing Emacs start-up processing.
* Getting Out::             How exiting works (permanent or temporary).
* System Environment::      Distinguish the name and kind of system.
* User Identification::     Finding the name and user id of the user.
* Time of Day::		    Getting the current time.
* Time Conversion::         Converting a time from numeric form to a string, or
                              to calendrical data (or vice versa).
* Time Parsing::            Converting a time from numeric form to text
                              and vice versa.
* Processor Run Time::      Getting the run time used by Emacs.
* Time Calculations::       Adding, subtracting, comparing times, etc.
* Timers::		    Setting a timer to call a function at a certain time.
* Idle Timers::             Setting a timer to call a function when Emacs has
                              been idle for a certain length of time.
* Terminal Input::          Accessing and recording terminal input.
* Terminal Output::         Controlling and recording terminal output.
* Sound Output::            Playing sounds on the computer's speaker.
* X11 Keysyms::             Operating on key symbols for X Windows
* Batch Mode::              Running Emacs without terminal interaction.
* Session Management::      Saving and restoring state with X Session Management.

Starting Up Emacs

* Startup Summary::         Sequence of actions Emacs performs at start-up.
* Init File::               Details on reading the init file (`.emacs').
* Terminal-Specific::       How the terminal-specific Lisp file is read.
* Command-Line Arguments::  How command-line arguments are processed,
                              and how you can customize them.

Getting Out of Emacs

* Killing Emacs::           Exiting Emacs irreversibly.
* Suspending Emacs::        Exiting Emacs reversibly.

Terminal Input

* Input Modes::		    Options for how input is processed.
* Recording Input::	    Saving histories of recent or all input events.

Tips and Conventions

* Coding Conventions::      Conventions for clean and robust programs.
* Key Binding Conventions:: Which keys should be bound by which programs.
* Programming Tips::        Making Emacs code fit smoothly in Emacs.
* Compilation Tips::        Making compiled code run fast.
* Warning Tips::            Turning off compiler warnings.
* Documentation Tips::      Writing readable documentation strings.
* Comment Tips::	    Conventions for writing comments.
* Library Headers::         Standard headers for library packages.

GNU Emacs Internals

* Building Emacs::          How the dumped Emacs is made.
* Pure Storage::            A kludge to make preloaded Lisp functions sharable.
* Garbage Collection::      Reclaiming space for Lisp objects no longer used.
* Memory Usage::            Info about total size of Lisp objects made so far.
* Writing Emacs Primitives::  Writing C code for Emacs.
* Object Internals::        Data formats of buffers, windows, processes.

Object Internals

* Buffer Internals::        Components of a buffer structure.
* Window Internals::        Components of a window structure.
* Process Internals::       Components of a process structure.


File: elisp,  Node: Introduction,  Next: Lisp Data Types,  Prev: Top,  Up: Top

1 Introduction
**************

Most of the GNU Emacs text editor is written in the programming
language called Emacs Lisp.  You can write new code in Emacs Lisp and
install it as an extension to the editor.  However, Emacs Lisp is more
than a mere "extension language"; it is a full computer programming
language in its own right.  You can use it as you would any other
programming language.

   Because Emacs Lisp is designed for use in an editor, it has special
features for scanning and parsing text as well as features for handling
files, buffers, displays, subprocesses, and so on.  Emacs Lisp is
closely integrated with the editing facilities; thus, editing commands
are functions that can also conveniently be called from Lisp programs,
and parameters for customization are ordinary Lisp variables.

   This manual attempts to be a full description of Emacs Lisp.  For a
beginner's introduction to Emacs Lisp, see `An Introduction to Emacs
Lisp Programming', by Bob Chassell, also published by the Free Software
Foundation.  This manual presumes considerable familiarity with the use
of Emacs for editing; see `The GNU Emacs Manual' for this basic
information.

   Generally speaking, the earlier chapters describe features of Emacs
Lisp that have counterparts in many programming languages, and later
chapters describe features that are peculiar to Emacs Lisp or relate
specifically to editing.

   This is edition 2.9 of the GNU Emacs Lisp Reference Manual,
corresponding to Emacs version 22.3.

* Menu:

* Caveats::             Flaws and a request for help.
* Lisp History::        Emacs Lisp is descended from Maclisp.
* Conventions::         How the manual is formatted.
* Version Info::        Which Emacs version is running?
* Acknowledgements::    The authors, editors, and sponsors of this manual.


File: elisp,  Node: Caveats,  Next: Lisp History,  Up: Introduction

1.1 Caveats
===========

This manual has gone through numerous drafts.  It is nearly complete
but not flawless.  There are a few topics that are not covered, either
because we consider them secondary (such as most of the individual
modes) or because they are yet to be written.  Because we are not able
to deal with them completely, we have left out several parts
intentionally.  This includes most information about usage on VMS.

   The manual should be fully correct in what it does cover, and it is
therefore open to criticism on anything it says--from specific examples
and descriptive text, to the ordering of chapters and sections.  If
something is confusing, or you find that you have to look at the sources
or experiment to learn something not covered in the manual, then perhaps
the manual should be fixed.  Please let us know.

   As you use this manual, we ask that you send corrections as soon as
you find them.  If you think of a simple, real life example for a
function or group of functions, please make an effort to write it up
and send it in.  Please reference any comments to the node name and
function or variable name, as appropriate.  Also state the number of
the edition you are criticizing.

   Please mail comments and corrections to

     bug-lisp-manual@gnu.org

We let mail to this list accumulate unread until someone decides to
apply the corrections.  Months, and sometimes years, go by between
updates.  So please attach no significance to the lack of a reply--your
mail _will_ be acted on in due time.  If you want to contact the Emacs
maintainers more quickly, send mail to `bug-gnu-emacs@gnu.org'.


File: elisp,  Node: Lisp History,  Next: Conventions,  Prev: Caveats,  Up: Introduction

1.2 Lisp History
================

Lisp (LISt Processing language) was first developed in the late 1950s
at the Massachusetts Institute of Technology for research in artificial
intelligence.  The great power of the Lisp language makes it ideal for
other purposes as well, such as writing editing commands.

   Dozens of Lisp implementations have been built over the years, each
with its own idiosyncrasies.  Many of them were inspired by Maclisp,
which was written in the 1960s at MIT's Project MAC.  Eventually the
implementors of the descendants of Maclisp came together and developed a
standard for Lisp systems, called Common Lisp.  In the meantime, Gerry
Sussman and Guy Steele at MIT developed a simplified but very powerful
dialect of Lisp, called Scheme.

   GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common
Lisp.  If you know Common Lisp, you will notice many similarities.
However, many features of Common Lisp have been omitted or simplified
in order to reduce the memory requirements of GNU Emacs.  Sometimes the
simplifications are so drastic that a Common Lisp user might be very
confused.  We will occasionally point out how GNU Emacs Lisp differs
from Common Lisp.  If you don't know Common Lisp, don't worry about it;
this manual is self-contained.

   A certain amount of Common Lisp emulation is available via the `cl'
library.  *note Overview: (cl)Top.

   Emacs Lisp is not at all influenced by Scheme; but the GNU project
has an implementation of Scheme, called Guile.  We use Guile in all new
GNU software that calls for extensibility.


File: elisp,  Node: Conventions,  Next: Version Info,  Prev: Lisp History,  Up: Introduction

1.3 Conventions
===============

This section explains the notational conventions that are used in this
manual.  You may want to skip this section and refer back to it later.

* Menu:

* Some Terms::               Explanation of terms we use in this manual.
* nil and t::                How the symbols `nil' and `t' are used.
* Evaluation Notation::      The format we use for examples of evaluation.
* Printing Notation::        The format we use when examples print text.
* Error Messages::           The format we use for examples of errors.
* Buffer Text Notation::     The format we use for buffer contents in examples.
* Format of Descriptions::   Notation for describing functions, variables, etc.


File: elisp,  Node: Some Terms,  Next: nil and t,  Up: Conventions

1.3.1 Some Terms
----------------

Throughout this manual, the phrases "the Lisp reader" and "the Lisp
printer" refer to those routines in Lisp that convert textual
representations of Lisp objects into actual Lisp objects, and vice
versa.  *Note Printed Representation::, for more details.  You, the
person reading this manual, are thought of as "the programmer" and are
addressed as "you."  "The user" is the person who uses Lisp programs,
including those you write.

   Examples of Lisp code are formatted like this: `(list 1 2 3)'.
Names that represent metasyntactic variables, or arguments to a function
being described, are formatted like this: FIRST-NUMBER.


File: elisp,  Node: nil and t,  Next: Evaluation Notation,  Prev: Some Terms,  Up: Conventions

1.3.2 `nil' and `t'
-------------------

In Lisp, the symbol `nil' has three separate meanings: it is a symbol
with the name `nil'; it is the logical truth value FALSE; and it is the
empty list--the list of zero elements.  When used as a variable, `nil'
always has the value `nil'.

   As far as the Lisp reader is concerned, `()' and `nil' are
identical: they stand for the same object, the symbol `nil'.  The
different ways of writing the symbol are intended entirely for human
readers.  After the Lisp reader has read either `()' or `nil', there is
no way to determine which representation was actually written by the
programmer.

   In this manual, we write `()' when we wish to emphasize that it
means the empty list, and we write `nil' when we wish to emphasize that
it means the truth value FALSE.  That is a good convention to use in
Lisp programs also.

     (cons 'foo ())                ; Emphasize the empty list
     (setq foo-flag nil)           ; Emphasize the truth value FALSE

   In contexts where a truth value is expected, any non-`nil' value is
considered to be TRUE.  However, `t' is the preferred way to represent
the truth value TRUE.  When you need to choose a value which represents
TRUE, and there is no other basis for choosing, use `t'.  The symbol
`t' always has the value `t'.

   In Emacs Lisp, `nil' and `t' are special symbols that always
evaluate to themselves.  This is so that you do not need to quote them
to use them as constants in a program.  An attempt to change their
values results in a `setting-constant' error.  *Note Constant
Variables::.

 -- Function: booleanp object
     Return non-nil if OBJECT is one of the two canonical boolean
     values: `t' or `nil'.


File: elisp,  Node: Evaluation Notation,  Next: Printing Notation,  Prev: nil and t,  Up: Conventions

1.3.3 Evaluation Notation
-------------------------

A Lisp expression that you can evaluate is called a "form".  Evaluating
a form always produces a result, which is a Lisp object.  In the
examples in this manual, this is indicated with `=>':

     (car '(1 2))
          => 1

You can read this as "`(car '(1 2))' evaluates to 1."

   When a form is a macro call, it expands into a new form for Lisp to
evaluate.  We show the result of the expansion with `==>'.  We may or
may not show the result of the evaluation of the expanded form.

     (third '(a b c))
          ==> (car (cdr (cdr '(a b c))))
          => c

   Sometimes to help describe one form we show another form that
produces identical results.  The exact equivalence of two forms is
indicated with `=='.

     (make-sparse-keymap) == (list 'keymap)


File: elisp,  Node: Printing Notation,  Next: Error Messages,  Prev: Evaluation Notation,  Up: Conventions

1.3.4 Printing Notation
-----------------------

Many of the examples in this manual print text when they are evaluated.
If you execute example code in a Lisp Interaction buffer (such as the
buffer `*scratch*'), the printed text is inserted into the buffer.  If
you execute the example by other means (such as by evaluating the
function `eval-region'), the printed text is displayed in the echo area.

   Examples in this manual indicate printed text with `-|',
irrespective of where that text goes.  The value returned by evaluating
the form (here `bar') follows on a separate line with `=>'.

     (progn (prin1 'foo) (princ "\n") (prin1 'bar))
          -| foo
          -| bar
          => bar


File: elisp,  Node: Error Messages,  Next: Buffer Text Notation,  Prev: Printing Notation,  Up: Conventions

1.3.5 Error Messages
--------------------

Some examples signal errors.  This normally displays an error message
in the echo area.  We show the error message on a line starting with
`error-->'.  Note that `error-->' itself does not appear in the echo
area.

     (+ 23 'x)
     error--> Wrong type argument: number-or-marker-p, x


File: elisp,  Node: Buffer Text Notation,  Next: Format of Descriptions,  Prev: Error Messages,  Up: Conventions

1.3.6 Buffer Text Notation
--------------------------

Some examples describe modifications to the contents of a buffer, by
showing the "before" and "after" versions of the text.  These examples
show the contents of the buffer in question between two lines of dashes
containing the buffer name.  In addition, `-!-' indicates the location
of point.  (The symbol for point, of course, is not part of the text in
the buffer; it indicates the place _between_ two characters where point
is currently located.)

     ---------- Buffer: foo ----------
     This is the -!-contents of foo.
     ---------- Buffer: foo ----------

     (insert "changed ")
          => nil
     ---------- Buffer: foo ----------
     This is the changed -!-contents of foo.
     ---------- Buffer: foo ----------


File: elisp,  Node: Format of Descriptions,  Prev: Buffer Text Notation,  Up: Conventions

1.3.7 Format of Descriptions
----------------------------

Functions, variables, macros, commands, user options, and special forms
are described in this manual in a uniform format.  The first line of a
description contains the name of the item followed by its arguments, if
any.  The category--function, variable, or whatever--appears at the
beginning of the line.  The description follows on succeeding lines,
sometimes with examples.

* Menu:

* A Sample Function Description::       A description of an imaginary
                                          function, `foo'.
* A Sample Variable Description::       A description of an imaginary
                                          variable,
                                          `electric-future-map'.


File: elisp,  Node: A Sample Function Description,  Next: A Sample Variable Description,  Up: Format of Descriptions

1.3.7.1 A Sample Function Description
.....................................

In a function description, the name of the function being described
appears first.  It is followed on the same line by a list of argument
names.  These names are also used in the body of the description, to
stand for the values of the arguments.

   The appearance of the keyword `&optional' in the argument list
indicates that the subsequent arguments may be omitted (omitted
arguments default to `nil').  Do not write `&optional' when you call
the function.

   The keyword `&rest' (which must be followed by a single argument
name) indicates that any number of arguments can follow.  The single
argument name following `&rest' will receive, as its value, a list of
all the remaining arguments passed to the function.  Do not write
`&rest' when you call the function.

   Here is a description of an imaginary function `foo':

 -- Function: foo integer1 &optional integer2 &rest integers
     The function `foo' subtracts INTEGER1 from INTEGER2, then adds all
     the rest of the arguments to the result.  If INTEGER2 is not
     supplied, then the number 19 is used by default.

          (foo 1 5 3 9)
               => 16
          (foo 5)
               => 14

     More generally,

          (foo W X Y...)
          ==
          (+ (- X W) Y...)

   Any argument whose name contains the name of a type (e.g., INTEGER,
INTEGER1 or BUFFER) is expected to be of that type.  A plural of a type
(such as BUFFERS) often means a list of objects of that type.
Arguments named OBJECT may be of any type.  (*Note Lisp Data Types::,
for a list of Emacs object types.)  Arguments with other sorts of names
(e.g., NEW-FILE) are discussed specifically in the description of the
function.  In some sections, features common to the arguments of
several functions are described at the beginning.

   *Note Lambda Expressions::, for a more complete description of
optional and rest arguments.

   Command, macro, and special form descriptions have the same format,
but the word `Function' is replaced by `Command', `Macro', or `Special
Form', respectively.  Commands are simply functions that may be called
interactively; macros process their arguments differently from functions
(the arguments are not evaluated), but are presented the same way.

   Special form descriptions use a more complex notation to specify
optional and repeated arguments because they can break the argument
list down into separate arguments in more complicated ways.
`[OPTIONAL-ARG]' means that OPTIONAL-ARG is optional and
`REPEATED-ARGS...' stands for zero or more arguments.  Parentheses are
used when several arguments are grouped into additional levels of list
structure.  Here is an example:

 -- Special Form: count-loop (VAR [FROM TO [INC]]) BODY...
     This imaginary special form implements a loop that executes the
     BODY forms and then increments the variable VAR on each iteration.
     On the first iteration, the variable has the value FROM; on
     subsequent iterations, it is incremented by one (or by INC if that
     is given).  The loop exits before executing BODY if VAR equals TO.
     Here is an example:

          (count-loop (i 0 10)
            (prin1 i) (princ " ")
            (prin1 (aref vector i))
            (terpri))

     If FROM and TO are omitted, VAR is bound to `nil' before the loop
     begins, and the loop exits if VAR is non-`nil' at the beginning of
     an iteration.  Here is an example:

          (count-loop (done)
            (if (pending)
                (fixit)
              (setq done t)))

     In this special form, the arguments FROM and TO are optional, but
     must both be present or both absent.  If they are present, INC may
     optionally be specified as well.  These arguments are grouped with
     the argument VAR into a list, to distinguish them from BODY, which
     includes all remaining elements of the form.


File: elisp,  Node: A Sample Variable Description,  Prev: A Sample Function Description,  Up: Format of Descriptions

1.3.7.2 A Sample Variable Description
.....................................

A "variable" is a name that can hold a value.  Although nearly all
variables can be set by the user, certain variables exist specifically
so that users can change them; these are called "user options".
Ordinary variables and user options are described using a format like
that for functions except that there are no arguments.

   Here is a description of the imaginary `electric-future-map'
variable.

 -- Variable: electric-future-map
     The value of this variable is a full keymap used by Electric
     Command Future mode.  The functions in this map allow you to edit
     commands you have not yet thought about executing.

   User option descriptions have the same format, but `Variable' is
replaced by `User Option'.


File: elisp,  Node: Version Info,  Next: Acknowledgements,  Prev: Conventions,  Up: Introduction

1.4 Version Information
=======================

These facilities provide information about which version of Emacs is in
use.

 -- Command: emacs-version &optional here
     This function returns a string describing the version of Emacs
     that is running.  It is useful to include this string in bug
     reports.

          (emacs-version)
            => "GNU Emacs 20.3.5 (i486-pc-linux-gnulibc1, X toolkit)
           of Sat Feb 14 1998 on psilocin.gnu.org"

     If HERE is non-`nil', it inserts the text in the buffer before
     point, and returns `nil'.  Called interactively, the function
     prints the same information in the echo area, but giving a prefix
     argument makes HERE non-`nil'.

 -- Variable: emacs-build-time
     The value of this variable indicates the time at which Emacs was
     built at the local site.  It is a list of three integers, like the
     value of `current-time' (*note Time of Day::).

          emacs-build-time
               => (13623 62065 344633)

 -- Variable: emacs-version
     The value of this variable is the version of Emacs being run.  It
     is a string such as `"20.3.1"'.  The last number in this string is
     not really part of the Emacs release version number; it is
     incremented each time you build Emacs in any given directory.  A
     value with four numeric components, such as `"20.3.9.1"',
     indicates an unreleased test version.

   The following two variables have existed since Emacs version 19.23:

 -- Variable: emacs-major-version
     The major version number of Emacs, as an integer.  For Emacs
     version 20.3, the value is 20.

 -- Variable: emacs-minor-version
     The minor version number of Emacs, as an integer.  For Emacs
     version 20.3, the value is 3.


File: elisp,  Node: Acknowledgements,  Prev: Version Info,  Up: Introduction

1.5 Acknowledgements
====================

This manual was written by Robert Krawitz, Bil Lewis, Dan LaLiberte,
Richard M. Stallman and Chris Welty, the volunteers of the GNU manual
group, in an effort extending over several years.  Robert J. Chassell
helped to review and edit the manual, with the support of the Defense
Advanced Research Projects Agency, ARPA Order 6082, arranged by
Warren A. Hunt, Jr. of Computational Logic, Inc.

   Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom,
Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R.
Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher,
David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob
Glickstein, Eric Hanchrow, George Hartzell, Nathan Hess, Masayuki Ida,
Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens,
Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Skip
Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potorti,
Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Per Starba"ck,
Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard
Westman, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty
Wright, and David D. Zuhn.


File: elisp,  Node: Lisp Data Types,  Next: Numbers,  Prev: Introduction,  Up: Top

2 Lisp Data Types
*****************

A Lisp "object" is a piece of data used and manipulated by Lisp
programs.  For our purposes, a "type" or "data type" is a set of
possible objects.

   Every object belongs to at least one type.  Objects of the same type
have similar structures and may usually be used in the same contexts.
Types can overlap, and objects can belong to two or more types.
Consequently, we can ask whether an object belongs to a particular type,
but not for "the" type of an object.

   A few fundamental object types are built into Emacs.  These, from
which all other types are constructed, are called "primitive types".
Each object belongs to one and only one primitive type.  These types
include "integer", "float", "cons", "symbol", "string", "vector",
"hash-table", "subr", and "byte-code function", plus several special
types, such as "buffer", that are related to editing.  (*Note Editing
Types::.)

   Each primitive type has a corresponding Lisp function that checks
whether an object is a member of that type.

   Note that Lisp is unlike many other languages in that Lisp objects
are "self-typing": the primitive type of the object is implicit in the
object itself.  For example, if an object is a vector, nothing can treat
it as a number; Lisp knows it is a vector, not a number.

   In most languages, the programmer must declare the data type of each
variable, and the type is known by the compiler but not represented in
the data.  Such type declarations do not exist in Emacs Lisp.  A Lisp
variable can have any type of value, and it remembers whatever value
you store in it, type and all.  (Actually, a small number of Emacs Lisp
variables can only take on values of a certain type.  *Note Variables
with Restricted Values::.)

   This chapter describes the purpose, printed representation, and read
syntax of each of the standard types in GNU Emacs Lisp.  Details on how
to use these types can be found in later chapters.

* Menu:

* Printed Representation::      How Lisp objects are represented as text.
* Comments::                    Comments and their formatting conventions.
* Programming Types::           Types found in all Lisp systems.
* Editing Types::               Types specific to Emacs.
* Circular Objects::            Read syntax for circular structure.
* Type Predicates::             Tests related to types.
* Equality Predicates::         Tests of equality between any two objects.


File: elisp,  Node: Printed Representation,  Next: Comments,  Up: Lisp Data Types

2.1 Printed Representation and Read Syntax
==========================================

The "printed representation" of an object is the format of the output
generated by the Lisp printer (the function `prin1') for that object.
Every data type has a unique printed representation.  The "read syntax"
of an object is the format of the input accepted by the Lisp reader
(the function `read') for that object.  This is not necessarily unique;
many kinds of object have more than one syntax.  *Note Read and Print::.

   In most cases, an object's printed representation is also a read
syntax for the object.  However, some types have no read syntax, since
it does not make sense to enter objects of these types as constants in
a Lisp program.  These objects are printed in "hash notation", which
consists of the characters `#<', a descriptive string (typically the
type name followed by the name of the object), and a closing `>'.  For
example:

     (current-buffer)
          => #<buffer objects.texi>

Hash notation cannot be read at all, so the Lisp reader signals the
error `invalid-read-syntax' whenever it encounters `#<'.  

   In other languages, an expression is text; it has no other form.  In
Lisp, an expression is primarily a Lisp object and only secondarily the
text that is the object's read syntax.  Often there is no need to
emphasize this distinction, but you must keep it in the back of your
mind, or you will occasionally be very confused.

   When you evaluate an expression interactively, the Lisp interpreter
first reads the textual representation of it, producing a Lisp object,
and then evaluates that object (*note Evaluation::).  However,
evaluation and reading are separate activities.  Reading returns the
Lisp object represented by the text that is read; the object may or may
not be evaluated later.  *Note Input Functions::, for a description of
`read', the basic function for reading objects.


File: elisp,  Node: Comments,  Next: Programming Types,  Prev: Printed Representation,  Up: Lisp Data Types

2.2 Comments
============

A "comment" is text that is written in a program only for the sake of
humans that read the program, and that has no effect on the meaning of
the program.  In Lisp, a semicolon (`;') starts a comment if it is not
within a string or character constant.  The comment continues to the
end of line.  The Lisp reader discards comments; they do not become
part of the Lisp objects which represent the program within the Lisp
system.

   The `#@COUNT' construct, which skips the next COUNT characters, is
useful for program-generated comments containing binary data.  The
Emacs Lisp byte compiler uses this in its output files (*note Byte
Compilation::).  It isn't meant for source files, however.

   *Note Comment Tips::, for conventions for formatting comments.


File: elisp,  Node: Programming Types,  Next: Editing Types,  Prev: Comments,  Up: Lisp Data Types

2.3 Programming Types
=====================

There are two general categories of types in Emacs Lisp: those having
to do with Lisp programming, and those having to do with editing.  The
former exist in many Lisp implementations, in one form or another.  The
latter are unique to Emacs Lisp.

* Menu:

* Integer Type::        Numbers without fractional parts.
* Floating Point Type:: Numbers with fractional parts and with a large range.
* Character Type::      The representation of letters, numbers and
                        control characters.
* Symbol Type::         A multi-use object that refers to a function,
                        variable, or property list, and has a unique identity.
* Sequence Type::       Both lists and arrays are classified as sequences.
* Cons Cell Type::      Cons cells, and lists (which are made from cons cells).
* Array Type::          Arrays include strings and vectors.
* String Type::         An (efficient) array of characters.
* Vector Type::         One-dimensional arrays.
* Char-Table Type::     One-dimensional sparse arrays indexed by characters.
* Bool-Vector Type::    One-dimensional arrays of `t' or `nil'.
* Hash Table Type::     Super-fast lookup tables.
* Function Type::       A piece of executable code you can call from elsewhere.
* Macro Type::          A method of expanding an expression into another
                          expression, more fundamental but less pretty.
* Primitive Function Type::     A function written in C, callable from Lisp.
* Byte-Code Type::      A function written in Lisp, then compiled.
* Autoload Type::       A type used for automatically loading seldom-used
                        functions.


File: elisp,  Node: Integer Type,  Next: Floating Point Type,  Up: Programming Types

2.3.1 Integer Type
------------------

The range of values for integers in Emacs Lisp is -268435456 to
268435455 (29 bits; i.e., -2**28 to 2**28 - 1) on most machines.  (Some
machines may provide a wider range.)  It is important to note that the
Emacs Lisp arithmetic functions do not check for overflow.  Thus `(1+
268435455)' is -268435456 on most machines.

   The read syntax for integers is a sequence of (base ten) digits with
an optional sign at the beginning and an optional period at the end.
The printed representation produced by the Lisp interpreter never has a
leading `+' or a final `.'.

     -1               ; The integer -1.
     1                ; The integer 1.
     1.               ; Also the integer 1.
     +1               ; Also the integer 1.
     536870913        ; Also the integer 1 on a 29-bit implementation.

   *Note Numbers::, for more information.


File: elisp,  Node: Floating Point Type,  Next: Character Type,  Prev: Integer Type,  Up: Programming Types

2.3.2 Floating Point Type
-------------------------

Floating point numbers are the computer equivalent of scientific
notation; you can think of a floating point number as a fraction
together with a power of ten.  The precise number of significant
figures and the range of possible exponents is machine-specific; Emacs
uses the C data type `double' to store the value, and internally this
records a power of 2 rather than a power of 10.

   The printed representation for floating point numbers requires either
a decimal point (with at least one digit following), an exponent, or
both.  For example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4'
are five ways of writing a floating point number whose value is 1500.
They are all equivalent.

   *Note Numbers::, for more information.


File: elisp,  Node: Character Type,  Next: Symbol Type,  Prev: Floating Point Type,  Up: Programming Types

2.3.3 Character Type
--------------------

A "character" in Emacs Lisp is nothing more than an integer.  In other
words, characters are represented by their character codes.  For
example, the character `A' is represented as the integer 65.

   Individual characters are used occasionally in programs, but it is
more common to work with _strings_, which are sequences composed of
characters.  *Note String Type::.

   Characters in strings, buffers, and files are currently limited to
the range of 0 to 524287--nineteen bits.  But not all values in that
range are valid character codes.  Codes 0 through 127 are ASCII codes;
the rest are non-ASCII (*note Non-ASCII Characters::).  Characters that
represent keyboard input have a much wider range, to encode modifier
keys such as Control, Meta and Shift.

   There are special functions for producing a human-readable textual
description of a character for the sake of messages.  *Note Describing
Characters::.

* Menu:

* Basic Char Syntax::
* General Escape Syntax::
* Ctl-Char Syntax::
* Meta-Char Syntax::
* Other Char Bits::


File: elisp,  Node: Basic Char Syntax,  Next: General Escape Syntax,  Up: Character Type

2.3.3.1 Basic Char Syntax
.........................

Since characters are really integers, the printed representation of a
character is a decimal number.  This is also a possible read syntax for
a character, but writing characters that way in Lisp programs is not
clear programming.  You should _always_ use the special read syntax
formats that Emacs Lisp provides for characters.  These syntax formats
start with a question mark.

   The usual read syntax for alphanumeric characters is a question mark
followed by the character; thus, `?A' for the character `A', `?B' for
the character `B', and `?a' for the character `a'.

   For example:

     ?Q => 81     ?q => 113

   You can use the same syntax for punctuation characters, but it is
often a good idea to add a `\' so that the Emacs commands for editing
Lisp code don't get confused.  For example, `?\(' is the way to write
the open-paren character.  If the character is `\', you _must_ use a
second `\' to quote it: `?\\'.

   You can express the characters control-g, backspace, tab, newline,
vertical tab, formfeed, space, return, del, and escape as `?\a', `?\b',
`?\t', `?\n', `?\v', `?\f', `?\s', `?\r', `?\d', and `?\e',
respectively.  (`?\s' followed by a dash has a different meaning--it
applies the "super" modifier to the following character.)  Thus,

     ?\a => 7                 ; control-g, `C-g'
     ?\b => 8                 ; backspace, <BS>, `C-h'
     ?\t => 9                 ; tab, <TAB>, `C-i'
     ?\n => 10                ; newline, `C-j'
     ?\v => 11                ; vertical tab, `C-k'
     ?\f => 12                ; formfeed character, `C-l'
     ?\r => 13                ; carriage return, <RET>, `C-m'
     ?\e => 27                ; escape character, <ESC>, `C-['
     ?\s => 32                ; space character, <SPC>
     ?\\ => 92                ; backslash character, `\'
     ?\d => 127               ; delete character, <DEL>

   These sequences which start with backslash are also known as "escape
sequences", because backslash plays the role of an "escape character";
this terminology has nothing to do with the character <ESC>.  `\s' is
meant for use in character constants; in string constants, just write
the space.

   A backslash is allowed, and harmless, preceding any character without
a special escape meaning; thus, `?\+' is equivalent to `?+'.  There is
no reason to add a backslash before most characters.  However, you
should add a backslash before any of the characters `()\|;'`"#.,' to
avoid confusing the Emacs commands for editing Lisp code.  You can also
add a backslash before whitespace characters such as space, tab,
newline and formfeed.  However, it is cleaner to use one of the easily
readable escape sequences, such as `\t' or `\s', instead of an actual
whitespace character such as a tab or a space.  (If you do write
backslash followed by a space, you should write an extra space after
the character constant to separate it from the following text.)


File: elisp,  Node: General Escape Syntax,  Next: Ctl-Char Syntax,  Prev: Basic Char Syntax,  Up: Character Type

2.3.3.2 General Escape Syntax
.............................

In addition to the specific excape sequences for special important
control characters, Emacs provides general categories of escape syntax
that you can use to specify non-ASCII text characters.

   For instance, you can specify characters by their Unicode values.
`?\uNNNN' represents a character that maps to the Unicode code point
`U+NNNN'.  There is a slightly different syntax for specifying
characters with code points above `#xFFFF'; `\U00NNNNNN' represents the
character whose Unicode code point is `U+NNNNNN', if such a character
is supported by Emacs.  If the corresponding character is not
supported, Emacs signals an error.

   This peculiar and inconvenient syntax was adopted for compatibility
with other programming languages.  Unlike some other languages, Emacs
Lisp supports this syntax in only character literals and strings.

   The most general read syntax for a character represents the
character code in either octal or hex.  To use octal, write a question
mark followed by a backslash and the octal character code (up to three
octal digits); thus, `?\101' for the character `A', `?\001' for the
character `C-a', and `?\002' for the character `C-b'.  Although this
syntax can represent any ASCII character, it is preferred only when the
precise octal value is more important than the ASCII representation.

     ?\012 => 10         ?\n => 10         ?\C-j => 10
     ?\101 => 65         ?A => 65

   To use hex, write a question mark followed by a backslash, `x', and
the hexadecimal character code.  You can use any number of hex digits,
so you can represent any character code in this way.  Thus, `?\x41' for
the character `A', `?\x1' for the character `C-a', and `?\x8e0' for the
Latin-1 character `a' with grave accent.


File: elisp,  Node: Ctl-Char Syntax,  Next: Meta-Char Syntax,  Prev: General Escape Syntax,  Up: Character Type

2.3.3.3 Control-Character Syntax
................................

Control characters can be represented using yet another read syntax.
This consists of a question mark followed by a backslash, caret, and the
corresponding non-control character, in either upper or lower case.  For
example, both `?\^I' and `?\^i' are valid read syntax for the character
`C-i', the character whose value is 9.

   Instead of the `^', you can use `C-'; thus, `?\C-i' is equivalent to
`?\^I' and to `?\^i':

     ?\^I => 9     ?\C-I => 9

   In strings and buffers, the only control characters allowed are those
that exist in ASCII; but for keyboard input purposes, you can turn any
character into a control character with `C-'.  The character codes for
these non-ASCII control characters include the 2**26 bit as well as the
code for the corresponding non-control character.  Ordinary terminals
have no way of generating non-ASCII control characters, but you can
generate them straightforwardly using X and other window systems.

   For historical reasons, Emacs treats the <DEL> character as the
control equivalent of `?':

     ?\^? => 127     ?\C-? => 127

As a result, it is currently not possible to represent the character
`Control-?', which is a meaningful input character under X, using
`\C-'.  It is not easy to change this, as various Lisp files refer to
<DEL> in this way.

   For representing control characters to be found in files or strings,
we recommend the `^' syntax; for control characters in keyboard input,
we prefer the `C-' syntax.  Which one you use does not affect the
meaning of the program, but may guide the understanding of people who
read it.


File: elisp,  Node: Meta-Char Syntax,  Next: Other Char Bits,  Prev: Ctl-Char Syntax,  Up: Character Type

2.3.3.4 Meta-Character Syntax
.............................

A "meta character" is a character typed with the <META> modifier key.
The integer that represents such a character has the 2**27 bit set.  We
use high bits for this and other modifiers to make possible a wide
range of basic character codes.

   In a string, the 2**7 bit attached to an ASCII character indicates a
meta character; thus, the meta characters that can fit in a string have
codes in the range from 128 to 255, and are the meta versions of the
ordinary ASCII characters.  (In Emacs versions 18 and older, this
convention was used for characters outside of strings as well.)

   The read syntax for meta characters uses `\M-'.  For example,
`?\M-A' stands for `M-A'.  You can use `\M-' together with octal
character codes (see below), with `\C-', or with any other syntax for a
character.  Thus, you can write `M-A' as `?\M-A', or as `?\M-\101'.
Likewise, you can write `C-M-b' as `?\M-\C-b', `?\C-\M-b', or
`?\M-\002'.


File: elisp,  Node: Other Char Bits,  Prev: Meta-Char Syntax,  Up: Character Type

2.3.3.5 Other Character Modifier Bits
.....................................

The case of a graphic character is indicated by its character code; for
example, ASCII distinguishes between the characters `a' and `A'.  But
ASCII has no way to represent whether a control character is upper case
or lower case.  Emacs uses the 2**25 bit to indicate that the shift key
was used in typing a control character.  This distinction is possible
only when you use X terminals or other special terminals; ordinary
terminals do not report the distinction to the computer in any way.
The Lisp syntax for the shift bit is `\S-'; thus, `?\C-\S-o' or
`?\C-\S-O' represents the shifted-control-o character.

   The X Window System defines three other modifier bits that can be set
in a character: "hyper", "super" and "alt".  The syntaxes for these
bits are `\H-', `\s-' and `\A-'.  (Case is significant in these
prefixes.)  Thus, `?\H-\M-\A-x' represents `Alt-Hyper-Meta-x'.  (Note
that `\s' with no following `-' represents the space character.)
Numerically, the bit values are 2**22 for alt, 2**23 for super and
2**24 for hyper.


File: elisp,  Node: Symbol Type,  Next: Sequence Type,  Prev: Character Type,  Up: Programming Types

2.3.4 Symbol Type
-----------------

A "symbol" in GNU Emacs Lisp is an object with a name.  The symbol name
serves as the printed representation of the symbol.  In ordinary Lisp
use, with one single obarray (*note Creating Symbols::), a symbol's
name is unique--no two symbols have the same name.

   A symbol can serve as a variable, as a function name, or to hold a
property list.  Or it may serve only to be distinct from all other Lisp
objects, so that its presence in a data structure may be recognized
reliably.  In a given context, usually only one of these uses is
intended.  But you can use one symbol in all of these ways,
independently.

   A symbol whose name starts with a colon (`:') is called a "keyword
symbol".  These symbols automatically act as constants, and are
normally used only by comparing an unknown symbol with a few specific
alternatives.

   A symbol name can contain any characters whatever.  Most symbol names
are written with letters, digits, and the punctuation characters
`-+=*/'.  Such names require no special punctuation; the characters of
the name suffice as long as the name does not look like a number.  (If
it does, write a `\' at the beginning of the name to force
interpretation as a symbol.)  The characters `_~!@$%^&:<>{}?' are less
often used but also require no special punctuation.  Any other
characters may be included in a symbol's name by escaping them with a
backslash.  In contrast to its use in strings, however, a backslash in
the name of a symbol simply quotes the single character that follows the
backslash.  For example, in a string, `\t' represents a tab character;
in the name of a symbol, however, `\t' merely quotes the letter `t'.
To have a symbol with a tab character in its name, you must actually
use a tab (preceded with a backslash).  But it's rare to do such a
thing.

     Common Lisp note: In Common Lisp, lower case letters are always
     "folded" to upper case, unless they are explicitly escaped.  In
     Emacs Lisp, upper case and lower case letters are distinct.

   Here are several examples of symbol names.  Note that the `+' in the
fifth example is escaped to prevent it from being read as a number.
This is not necessary in the fourth example because the rest of the name
makes it invalid as a number.

     foo                 ; A symbol named `foo'.
     FOO                 ; A symbol named `FOO', different from `foo'.
     char-to-string      ; A symbol named `char-to-string'.
     1+                  ; A symbol named `1+'
                         ;   (not `+1', which is an integer).
     \+1                 ; A symbol named `+1'
                         ;   (not a very readable name).
     \(*\ 1\ 2\)         ; A symbol named `(* 1 2)' (a worse name).
     +-*/_~!@$%^&=:<>{}  ; A symbol named `+-*/_~!@$%^&=:<>{}'.
                         ;   These characters need not be escaped.

   Normally the Lisp reader interns all symbols (*note Creating
Symbols::).  To prevent interning, you can write `#:' before the name
of the symbol.


File: elisp,  Node: Sequence Type,  Next: Cons Cell Type,  Prev: Symbol Type,  Up: Programming Types

2.3.5 Sequence Types
--------------------

A "sequence" is a Lisp object that represents an ordered set of
elements.  There are two kinds of sequence in Emacs Lisp, lists and
arrays.  Thus, an object of type list or of type array is also
considered a sequence.

   Arrays are further subdivided into strings, vectors, char-tables and
bool-vectors.  Vectors can hold elements of any type, but string
elements must be characters, and bool-vector elements must be `t' or
`nil'.  Char-tables are like vectors except that they are indexed by
any valid character code.  The characters in a string can have text
properties like characters in a buffer (*note Text Properties::), but
vectors do not support text properties, even when their elements happen
to be characters.

   Lists, strings and the other array types are different, but they have
important similarities.  For example, all have a length L, and all have
elements which can be indexed from zero to L minus one.  Several
functions, called sequence functions, accept any kind of sequence.  For
example, the function `elt' can be used to extract an element of a
sequence, given its index.  *Note Sequences Arrays Vectors::.

   It is generally impossible to read the same sequence twice, since
sequences are always created anew upon reading.  If you read the read
syntax for a sequence twice, you get two sequences with equal contents.
There is one exception: the empty list `()' always stands for the same
object, `nil'.


File: elisp,  Node: Cons Cell Type,  Next: Array Type,  Prev: Sequence Type,  Up: Programming Types

2.3.6 Cons Cell and List Types
------------------------------

A "cons cell" is an object that consists of two slots, called the CAR
slot and the CDR slot.  Each slot can "hold" or "refer to" any Lisp
object.  We also say that "the CAR of this cons cell is" whatever
object its CAR slot currently holds, and likewise for the CDR.

     A note to C programmers: in Lisp, we do not distinguish between
     "holding" a value and "pointing to" the value, because pointers in
     Lisp are implicit.

   A "list" is a series of cons cells, linked together so that the CDR
slot of each cons cell holds either the next cons cell or the empty
list.  The empty list is actually the symbol `nil'.  *Note Lists::, for
functions that work on lists.  Because most cons cells are used as part
of lists, the phrase "list structure" has come to refer to any
structure made out of cons cells.

   Because cons cells are so central to Lisp, we also have a word for
"an object which is not a cons cell."  These objects are called "atoms".

   The read syntax and printed representation for lists are identical,
and consist of a left parenthesis, an arbitrary number of elements, and
a right parenthesis.  Here are examples of lists:

     (A 2 "A")            ; A list of three elements.
     ()                   ; A list of no elements (the empty list).
     nil                  ; A list of no elements (the empty list).
     ("A ()")             ; A list of one element: the string `"A ()"'.
     (A ())               ; A list of two elements: `A' and the empty list.
     (A nil)              ; Equivalent to the previous.
     ((A B C))            ; A list of one element
                          ;   (which is a list of three elements).

   Upon reading, each object inside the parentheses becomes an element
of the list.  That is, a cons cell is made for each element.  The CAR
slot of the cons cell holds the element, and its CDR slot refers to the
next cons cell of the list, which holds the next element in the list.
The CDR slot of the last cons cell is set to hold `nil'.

   The names CAR and CDR derive from the history of Lisp.  The original
Lisp implementation ran on an IBM 704 computer which divided words into
two parts, called the "address" part and the "decrement"; CAR was an
instruction to extract the contents of the address part of a register,
and CDR an instruction to extract the contents of the decrement.  By
contrast, "cons cells" are named for the function `cons' that creates
them, which in turn was named for its purpose, the construction of
cells.

* Menu:

* Box Diagrams::                Drawing pictures of lists.
* Dotted Pair Notation::        A general syntax for cons cells.
* Association List Type::       A specially constructed list.


File: elisp,  Node: Box Diagrams,  Next: Dotted Pair Notation,  Up: Cons Cell Type

2.3.6.1 Drawing Lists as Box Diagrams
.....................................

A list can be illustrated by a diagram in which the cons cells are
shown as pairs of boxes, like dominoes.  (The Lisp reader cannot read
such an illustration; unlike the textual notation, which can be
understood by both humans and computers, the box illustrations can be
understood only by humans.)  This picture represents the three-element
list `(rose violet buttercup)':

         --- ---      --- ---      --- ---
        |   |   |--> |   |   |--> |   |   |--> nil
         --- ---      --- ---      --- ---
          |            |            |
          |            |            |
           --> rose     --> violet   --> buttercup

   In this diagram, each box represents a slot that can hold or refer to
any Lisp object.  Each pair of boxes represents a cons cell.  Each arrow
represents a reference to a Lisp object, either an atom or another cons
cell.

   In this example, the first box, which holds the CAR of the first
cons cell, refers to or "holds" `rose' (a symbol).  The second box,
holding the CDR of the first cons cell, refers to the next pair of
boxes, the second cons cell.  The CAR of the second cons cell is
`violet', and its CDR is the third cons cell.  The CDR of the third
(and last) cons cell is `nil'.

   Here is another diagram of the same list, `(rose violet buttercup)',
sketched in a different manner:

      ---------------       ----------------       -------------------
     | car   | cdr   |     | car    | cdr   |     | car       | cdr   |
     | rose  |   o-------->| violet |   o-------->| buttercup |  nil  |
     |       |       |     |        |       |     |           |       |
      ---------------       ----------------       -------------------

   A list with no elements in it is the "empty list"; it is identical
to the symbol `nil'.  In other words, `nil' is both a symbol and a list.

   Here is the list `(A ())', or equivalently `(A nil)', depicted with
boxes and arrows:

         --- ---      --- ---
        |   |   |--> |   |   |--> nil
         --- ---      --- ---
          |            |
          |            |
           --> A        --> nil

   Here is a more complex illustration, showing the three-element list,
`((pine needles) oak maple)', the first element of which is a
two-element list:

         --- ---      --- ---      --- ---
        |   |   |--> |   |   |--> |   |   |--> nil
         --- ---      --- ---      --- ---
          |            |            |
          |            |            |
          |             --> oak      --> maple
          |
          |     --- ---      --- ---
           --> |   |   |--> |   |   |--> nil
                --- ---      --- ---
                 |            |
                 |            |
                  --> pine     --> needles

   The same list represented in the second box notation looks like this:

      --------------       --------------       --------------
     | car   | cdr  |     | car   | cdr  |     | car   | cdr  |
     |   o   |   o------->| oak   |   o------->| maple |  nil |
     |   |   |      |     |       |      |     |       |      |
      -- | ---------       --------------       --------------
         |
         |
         |        --------------       ----------------
         |       | car   | cdr  |     | car     | cdr  |
          ------>| pine  |   o------->| needles |  nil |
                 |       |      |     |         |      |
                  --------------       ----------------


File: elisp,  Node: Dotted Pair Notation,  Next: Association List Type,  Prev: Box Diagrams,  Up: Cons Cell Type

2.3.6.2 Dotted Pair Notation
............................

"Dotted pair notation" is a general syntax for cons cells that
represents the CAR and CDR explicitly.  In this syntax, `(A . B)'
stands for a cons cell whose CAR is the object A and whose CDR is the
object B.  Dotted pair notation is more general than list syntax
because the CDR does not have to be a list.  However, it is more
cumbersome in cases where list syntax would work.  In dotted pair
notation, the list `(1 2 3)' is written as `(1 .  (2 . (3 . nil)))'.
For `nil'-terminated lists, you can use either notation, but list
notation is usually clearer and more convenient.  When printing a list,
the dotted pair notation is only used if the CDR of a cons cell is not
a list.

   Here's an example using boxes to illustrate dotted pair notation.
This example shows the pair `(rose . violet)':

         --- ---
        |   |   |--> violet
         --- ---
          |
          |
           --> rose

   You can combine dotted pair notation with list notation to represent
conveniently a chain of cons cells with a non-`nil' final CDR.  You
write a dot after the last element of the list, followed by the CDR of
the final cons cell.  For example, `(rose violet . buttercup)' is
equivalent to `(rose . (violet . buttercup))'.  The object looks like
this:

         --- ---      --- ---
        |   |   |--> |   |   |--> buttercup
         --- ---      --- ---
          |            |
          |            |
           --> rose     --> violet

   The syntax `(rose . violet . buttercup)' is invalid because there is
nothing that it could mean.  If anything, it would say to put
`buttercup' in the CDR of a cons cell whose CDR is already used for
`violet'.

   The list `(rose violet)' is equivalent to `(rose . (violet))', and
looks like this:

         --- ---      --- ---
        |   |   |--> |   |   |--> nil
         --- ---      --- ---
          |            |
          |            |
           --> rose     --> violet

   Similarly, the three-element list `(rose violet buttercup)' is
equivalent to `(rose . (violet . (buttercup)))'.  It looks like this:

         --- ---      --- ---      --- ---
        |   |   |--> |   |   |--> |   |   |--> nil
         --- ---      --- ---      --- ---
          |            |            |
          |            |            |
           --> rose     --> violet   --> buttercup


File: elisp,  Node: Association List Type,  Prev: Dotted Pair Notation,  Up: Cons Cell Type

2.3.6.3 Association List Type
.............................

An "association list" or "alist" is a specially-constructed list whose
elements are cons cells.  In each element, the CAR is considered a
"key", and the CDR is considered an "associated value".  (In some
cases, the associated value is stored in the CAR of the CDR.)
Association lists are often used as stacks, since it is easy to add or
remove associations at the front of the list.

   For example,

     (setq alist-of-colors
           '((rose . red) (lily . white) (buttercup . yellow)))

sets the variable `alist-of-colors' to an alist of three elements.  In
the first element, `rose' is the key and `red' is the value.

   *Note Association Lists::, for a further explanation of alists and
for functions that work on alists.  *Note Hash Tables::, for another
kind of lookup table, which is much faster for handling a large number
of keys.


File: elisp,  Node: Array Type,  Next: String Type,  Prev: Cons Cell Type,  Up: Programming Types

2.3.7 Array Type
----------------

An "array" is composed of an arbitrary number of slots for holding or
referring to other Lisp objects, arranged in a contiguous block of
memory.  Accessing any element of an array takes approximately the same
amount of time.  In contrast, accessing an element of a list requires
time proportional to the position of the element in the list.  (Elements
at the end of a list take longer to access than elements at the
beginning of a list.)

   Emacs defines four types of array: strings, vectors, bool-vectors,
and char-tables.

   A string is an array of characters and a vector is an array of
arbitrary objects.  A bool-vector can hold only `t' or `nil'.  These
kinds of array may have any length up to the largest integer.
Char-tables are sparse arrays indexed by any valid character code; they
can hold arbitrary objects.

   The first element of an array has index zero, the second element has
index 1, and so on.  This is called "zero-origin" indexing.  For
example, an array of four elements has indices 0, 1, 2, and 3.  The
largest possible index value is one less than the length of the array.
Once an array is created, its length is fixed.

   All Emacs Lisp arrays are one-dimensional.  (Most other programming
languages support multidimensional arrays, but they are not essential;
you can get the same effect with nested one-dimensional arrays.)  Each
type of array has its own read syntax; see the following sections for
details.

   The array type is a subset of the sequence type, and contains the
string type, the vector type, the bool-vector type, and the char-table
type.


File: elisp,  Node: String Type,  Next: Vector Type,  Prev: Array Type,  Up: Programming Types

2.3.8 String Type
-----------------

A "string" is an array of characters.  Strings are used for many
purposes in Emacs, as can be expected in a text editor; for example, as
the names of Lisp symbols, as messages for the user, and to represent
text extracted from buffers.  Strings in Lisp are constants: evaluation
of a string returns the same string.

   *Note Strings and Characters::, for functions that operate on
strings.

* Menu:

* Syntax for Strings::
* Non-ASCII in Strings::
* Nonprinting Characters::
* Text Props and Strings::


File: elisp,  Node: Syntax for Strings,  Next: Non-ASCII in Strings,  Up: String Type

2.3.8.1 Syntax for Strings
..........................

The read syntax for strings is a double-quote, an arbitrary number of
characters, and another double-quote, `"like this"'.  To include a
double-quote in a string, precede it with a backslash; thus, `"\""' is
a string containing just a single double-quote character.  Likewise,
you can include a backslash by preceding it with another backslash, like
this: `"this \\ is a single embedded backslash"'.

   The newline character is not special in the read syntax for strings;
if you write a new line between the double-quotes, it becomes a
character in the string.  But an escaped newline--one that is preceded
by `\'--does not become part of the string; i.e., the Lisp reader
ignores an escaped newline while reading a string.  An escaped space
`\ ' is likewise ignored.

     "It is useful to include newlines
     in documentation strings,
     but the newline is \
     ignored if escaped."
          => "It is useful to include newlines
     in documentation strings,
     but the newline is ignored if escaped."


File: elisp,  Node: Non-ASCII in Strings,  Next: Nonprinting Characters,  Prev: Syntax for Strings,  Up: String Type

2.3.8.2 Non-ASCII Characters in Strings
.......................................

You can include a non-ASCII international character in a string
constant by writing it literally.  There are two text representations
for non-ASCII characters in Emacs strings (and in buffers): unibyte and
multibyte.  If the string constant is read from a multibyte source,
such as a multibyte buffer or string, or a file that would be visited as
multibyte, then the character is read as a multibyte character, and that
makes the string multibyte.  If the string constant is read from a
unibyte source, then the character is read as unibyte and that makes the
string unibyte.

   You can also represent a multibyte non-ASCII character with its
character code: use a hex escape, `\xNNNNNNN', with as many digits as
necessary.  (Multibyte non-ASCII character codes are all greater than
256.)  Any character which is not a valid hex digit terminates this
construct.  If the next character in the string could be interpreted as
a hex digit, write `\ ' (backslash and space) to terminate the hex
escape--for example, `\x8e0\ ' represents one character, `a' with grave
accent.  `\ ' in a string constant is just like backslash-newline; it
does not contribute any character to the string, but it does terminate
the preceding hex escape.

   You can represent a unibyte non-ASCII character with its character
code, which must be in the range from 128 (0200 octal) to 255 (0377
octal).  If you write all such character codes in octal and the string
contains no other characters forcing it to be multibyte, this produces
a unibyte string.  However, using any hex escape in a string (even for
an ASCII character) forces the string to be multibyte.

   You can also specify characters in a string by their numeric values
in Unicode, using `\u' and `\U' (*note Character Type::).

   *Note Text Representations::, for more information about the two
text representations.


File: elisp,  Node: Nonprinting Characters,  Next: Text Props and Strings,  Prev: Non-ASCII in Strings,  Up: String Type

2.3.8.3 Nonprinting Characters in Strings
.........................................

You can use the same backslash escape-sequences in a string constant as
in character literals (but do not use the question mark that begins a
character constant).  For example, you can write a string containing the
nonprinting characters tab and `C-a', with commas and spaces between
them, like this: `"\t, \C-a"'.  *Note Character Type::, for a
description of the read syntax for characters.

   However, not all of the characters you can write with backslash
escape-sequences are valid in strings.  The only control characters that
a string can hold are the ASCII control characters.  Strings do not
distinguish case in ASCII control characters.

   Properly speaking, strings cannot hold meta characters; but when a
string is to be used as a key sequence, there is a special convention
that provides a way to represent meta versions of ASCII characters in a
string.  If you use the `\M-' syntax to indicate a meta character in a
string constant, this sets the 2**7 bit of the character in the string.
If the string is used in `define-key' or `lookup-key', this numeric
code is translated into the equivalent meta character.  *Note Character
Type::.

   Strings cannot hold characters that have the hyper, super, or alt
modifiers.


File: elisp,  Node: Text Props and Strings,  Prev: Nonprinting Characters,  Up: String Type

2.3.8.4 Text Properties in Strings
..................................

A string can hold properties for the characters it contains, in
addition to the characters themselves.  This enables programs that copy
text between strings and buffers to copy the text's properties with no
special effort.  *Note Text Properties::, for an explanation of what
text properties mean.  Strings with text properties use a special read
and print syntax:

     #("CHARACTERS" PROPERTY-DATA...)

where PROPERTY-DATA consists of zero or more elements, in groups of
three as follows:

     BEG END PLIST

The elements BEG and END are integers, and together specify a range of
indices in the string; PLIST is the property list for that range.  For
example,

     #("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))

represents a string whose textual contents are `foo bar', in which the
first three characters have a `face' property with value `bold', and
the last three have a `face' property with value `italic'.  (The fourth
character has no text properties, so its property list is `nil'.  It is
not actually necessary to mention ranges with `nil' as the property
list, since any characters not mentioned in any range will default to
having no properties.)


File: elisp,  Node: Vector Type,  Next: Char-Table Type,  Prev: String Type,  Up: Programming Types

2.3.9 Vector Type
-----------------

A "vector" is a one-dimensional array of elements of any type.  It
takes a constant amount of time to access any element of a vector.  (In
a list, the access time of an element is proportional to the distance of
the element from the beginning of the list.)

   The printed representation of a vector consists of a left square
bracket, the elements, and a right square bracket.  This is also the
read syntax.  Like numbers and strings, vectors are considered constants
for evaluation.

     [1 "two" (three)]      ; A vector of three elements.
          => [1 "two" (three)]

   *Note Vectors::, for functions that work with vectors.


File: elisp,  Node: Char-Table Type,  Next: Bool-Vector Type,  Prev: Vector Type,  Up: Programming Types

2.3.10 Char-Table Type
----------------------

A "char-table" is a one-dimensional array of elements of any type,
indexed by character codes.  Char-tables have certain extra features to
make them more useful for many jobs that involve assigning information
to character codes--for example, a char-table can have a parent to
inherit from, a default value, and a small number of extra slots to use
for special purposes.  A char-table can also specify a single value for
a whole character set.

   The printed representation of a char-table is like a vector except
that there is an extra `#^' at the beginning.

   *Note Char-Tables::, for special functions to operate on char-tables.
Uses of char-tables include:

   * Case tables (*note Case Tables::).

   * Character category tables (*note Categories::).

   * Display tables (*note Display Tables::).

   * Syntax tables (*note Syntax Tables::).


File: elisp,  Node: Bool-Vector Type,  Next: Hash Table Type,  Prev: Char-Table Type,  Up: Programming Types

2.3.11 Bool-Vector Type
-----------------------

A "bool-vector" is a one-dimensional array of elements that must be `t'
or `nil'.

   The printed representation of a bool-vector is like a string, except
that it begins with `#&' followed by the length.  The string constant
that follows actually specifies the contents of the bool-vector as a
bitmap--each "character" in the string contains 8 bits, which specify
the next 8 elements of the bool-vector (1 stands for `t', and 0 for
`nil').  The least significant bits of the character correspond to the
lowest indices in the bool-vector.

     (make-bool-vector 3 t)
          => #&3"^G"
     (make-bool-vector 3 nil)
          => #&3"^@"

These results make sense, because the binary code for `C-g' is 111 and
`C-@' is the character with code 0.

   If the length is not a multiple of 8, the printed representation
shows extra elements, but these extras really make no difference.  For
instance, in the next example, the two bool-vectors are equal, because
only the first 3 bits are used:

     (equal #&3"\377" #&3"\007")
          => t


File: elisp,  Node: Hash Table Type,  Next: Function Type,  Prev: Bool-Vector Type,  Up: Programming Types

2.3.12 Hash Table Type
----------------------

A hash table is a very fast kind of lookup table, somewhat like an
alist in that it maps keys to corresponding values, but much faster.
Hash tables have no read syntax, and print using hash notation.  *Note
Hash Tables::, for functions that operate on hash tables.

     (make-hash-table)
          => #<hash-table 'eql nil 0/65 0x83af980>


File: elisp,  Node: Function Type,  Next: Macro Type,  Prev: Hash Table Type,  Up: Programming Types

2.3.13 Function Type
--------------------

Lisp functions are executable code, just like functions in other
programming languages.  In Lisp, unlike most languages, functions are
also Lisp objects.  A non-compiled function in Lisp is a lambda
expression: that is, a list whose first element is the symbol `lambda'
(*note Lambda Expressions::).

   In most programming languages, it is impossible to have a function
without a name.  In Lisp, a function has no intrinsic name.  A lambda
expression can be called as a function even though it has no name; to
emphasize this, we also call it an "anonymous function" (*note
Anonymous Functions::).  A named function in Lisp is just a symbol with
a valid function in its function cell (*note Defining Functions::).

   Most of the time, functions are called when their names are written
in Lisp expressions in Lisp programs.  However, you can construct or
obtain a function object at run time and then call it with the primitive
functions `funcall' and `apply'.  *Note Calling Functions::.


File: elisp,  Node: Macro Type,  Next: Primitive Function Type,  Prev: Function Type,  Up: Programming Types

2.3.14 Macro Type
-----------------

A "Lisp macro" is a user-defined construct that extends the Lisp
language.  It is represented as an object much like a function, but with
different argument-passing semantics.  A Lisp macro has the form of a
list whose first element is the symbol `macro' and whose CDR is a Lisp
function object, including the `lambda' symbol.

   Lisp macro objects are usually defined with the built-in `defmacro'
function, but any list that begins with `macro' is a macro as far as
Emacs is concerned.  *Note Macros::, for an explanation of how to write
a macro.

   *Warning*: Lisp macros and keyboard macros (*note Keyboard Macros::)
are entirely different things.  When we use the word "macro" without
qualification, we mean a Lisp macro, not a keyboard macro.


File: elisp,  Node: Primitive Function Type,  Next: Byte-Code Type,  Prev: Macro Type,  Up: Programming Types

2.3.15 Primitive Function Type
------------------------------

A "primitive function" is a function callable from Lisp but written in
the C programming language.  Primitive functions are also called
"subrs" or "built-in functions".  (The word "subr" is derived from
"subroutine.")  Most primitive functions evaluate all their arguments
when they are called.  A primitive function that does not evaluate all
its arguments is called a "special form" (*note Special Forms::).

   It does not matter to the caller of a function whether the function
is primitive.  However, this does matter if you try to redefine a
primitive with a function written in Lisp.  The reason is that the
primitive function may be called directly from C code.  Calls to the
redefined function from Lisp will use the new definition, but calls
from C code may still use the built-in definition.  Therefore, *we
discourage redefinition of primitive functions*.

   The term "function" refers to all Emacs functions, whether written
in Lisp or C.  *Note Function Type::, for information about the
functions written in Lisp.

   Primitive functions have no read syntax and print in hash notation
with the name of the subroutine.

     (symbol-function 'car)          ; Access the function cell
                                     ;   of the symbol.
          => #<subr car>
     (subrp (symbol-function 'car))  ; Is this a primitive function?
          => t                       ; Yes.


File: elisp,  Node: Byte-Code Type,  Next: Autoload Type,  Prev: Primitive Function Type,  Up: Programming Types

2.3.16 Byte-Code Function Type
------------------------------

The byte compiler produces "byte-code function objects".  Internally, a
byte-code function object is much like a vector; however, the evaluator
handles this data type specially when it appears as a function to be
called.  *Note Byte Compilation::, for information about the byte
compiler.

   The printed representation and read syntax for a byte-code function
object is like that for a vector, with an additional `#' before the
opening `['.


File: elisp,  Node: Autoload Type,  Prev: Byte-Code Type,  Up: Programming Types

2.3.17 Autoload Type
--------------------

An "autoload object" is a list whose first element is the symbol
`autoload'.  It is stored as the function definition of a symbol, where
it serves as a placeholder for the real definition.  The autoload
object says that the real definition is found in a file of Lisp code
that should be loaded when necessary.  It contains the name of the file,
plus some other information about the real definition.

   After the file has been loaded, the symbol should have a new function
definition that is not an autoload object.  The new definition is then
called as if it had been there to begin with.  From the user's point of
view, the function call works as expected, using the function definition
in the loaded file.

   An autoload object is usually created with the function `autoload',
which stores the object in the function cell of a symbol.  *Note
Autoload::, for more details.


File: elisp,  Node: Editing Types,  Next: Circular Objects,  Prev: Programming Types,  Up: Lisp Data Types

2.4 Editing Types
=================

The types in the previous section are used for general programming
purposes, and most of them are common to most Lisp dialects.  Emacs Lisp
provides several additional data types for purposes connected with
editing.

* Menu:

* Buffer Type::         The basic object of editing.
* Marker Type::         A position in a buffer.
* Window Type::         Buffers are displayed in windows.
* Frame Type::		Windows subdivide frames.
* Window Configuration Type::   Recording the way a frame is subdivided.
* Frame Configuration Type::    Recording the status of all frames.
* Process Type::        A process running on the underlying OS.
* Stream Type::         Receive or send characters.
* Keymap Type::         What function a keystroke invokes.
* Overlay Type::        How an overlay is represented.


File: elisp,  Node: Buffer Type,  Next: Marker Type,  Up: Editing Types

2.4.1 Buffer Type
-----------------

A "buffer" is an object that holds text that can be edited (*note
Buffers::).  Most buffers hold the contents of a disk file (*note
Files::) so they can be edited, but some are used for other purposes.
Most buffers are also meant to be seen by the user, and therefore
displayed, at some time, in a window (*note Windows::).  But a buffer
need not be displayed in any window.

   The contents of a buffer are much like a string, but buffers are not
used like strings in Emacs Lisp, and the available operations are
different.  For example, you can insert text efficiently into an
existing buffer, altering the buffer's contents, whereas "inserting"
text into a string requires concatenating substrings, and the result is
an entirely new string object.

   Each buffer has a designated position called "point" (*note
Positions::).  At any time, one buffer is the "current buffer".  Most
editing commands act on the contents of the current buffer in the
neighborhood of point.  Many of the standard Emacs functions manipulate
or test the characters in the current buffer; a whole chapter in this
manual is devoted to describing these functions (*note Text::).

   Several other data structures are associated with each buffer:

   * a local syntax table (*note Syntax Tables::);

   * a local keymap (*note Keymaps::); and,

   * a list of buffer-local variable bindings (*note Buffer-Local
     Variables::).

   * overlays (*note Overlays::).

   * text properties for the text in the buffer (*note Text
     Properties::).

The local keymap and variable list contain entries that individually
override global bindings or values.  These are used to customize the
behavior of programs in different buffers, without actually changing the
programs.

   A buffer may be "indirect", which means it shares the text of
another buffer, but presents it differently.  *Note Indirect Buffers::.

   Buffers have no read syntax.  They print in hash notation, showing
the buffer name.

     (current-buffer)
          => #<buffer objects.texi>


File: elisp,  Node: Marker Type,  Next: Window Type,  Prev: Buffer Type,  Up: Editing Types

2.4.2 Marker Type
-----------------

A "marker" denotes a position in a specific buffer.  Markers therefore
have two components: one for the buffer, and one for the position.
Changes in the buffer's text automatically relocate the position value
as necessary to ensure that the marker always points between the same
two characters in the buffer.

   Markers have no read syntax.  They print in hash notation, giving the
current character position and the name of the buffer.

     (point-marker)
          => #<marker at 10779 in objects.texi>

   *Note Markers::, for information on how to test, create, copy, and
move markers.


File: elisp,  Node: Window Type,  Next: Frame Type,  Prev: Marker Type,  Up: Editing Types

2.4.3 Window Type
-----------------

A "window" describes the portion of the terminal screen that Emacs uses
to display a buffer.  Every window has one associated buffer, whose
contents appear in the window.  By contrast, a given buffer may appear
in one window, no window, or several windows.

   Though many windows may exist simultaneously, at any time one window
is designated the "selected window".  This is the window where the
cursor is (usually) displayed when Emacs is ready for a command.  The
selected window usually displays the current buffer, but this is not
necessarily the case.

   Windows are grouped on the screen into frames; each window belongs to
one and only one frame.  *Note Frame Type::.

   Windows have no read syntax.  They print in hash notation, giving the
window number and the name of the buffer being displayed.  The window
numbers exist to identify windows uniquely, since the buffer displayed
in any given window can change frequently.

     (selected-window)
          => #<window 1 on objects.texi>

   *Note Windows::, for a description of the functions that work on
windows.


File: elisp,  Node: Frame Type,  Next: Window Configuration Type,  Prev: Window Type,  Up: Editing Types

2.4.4 Frame Type
----------------

A "frame" is a screen area that contains one or more Emacs windows; we
also use the term "frame" to refer to the Lisp object that Emacs uses
to refer to the screen area.

   Frames have no read syntax.  They print in hash notation, giving the
frame's title, plus its address in core (useful to identify the frame
uniquely).

     (selected-frame)
          => #<frame emacs@psilocin.gnu.org 0xdac80>

   *Note Frames::, for a description of the functions that work on
frames.


File: elisp,  Node: Window Configuration Type,  Next: Frame Configuration Type,  Prev: Frame Type,  Up: Editing Types

2.4.5 Window Configuration Type
-------------------------------

A "window configuration" stores information about the positions, sizes,
and contents of the windows in a frame, so you can recreate the same
arrangement of windows later.

   Window configurations do not have a read syntax; their print syntax
looks like `#<window-configuration>'.  *Note Window Configurations::,
for a description of several functions related to window configurations.


File: elisp,  Node: Frame Configuration Type,  Next: Process Type,  Prev: Window Configuration Type,  Up: Editing Types

2.4.6 Frame Configuration Type
------------------------------

A "frame configuration" stores information about the positions, sizes,
and contents of the windows in all frames.  It is actually a list whose
CAR is `frame-configuration' and whose CDR is an alist.  Each alist
element describes one frame, which appears as the CAR of that element.

   *Note Frame Configurations::, for a description of several functions
related to frame configurations.


File: elisp,  Node: Process Type,  Next: Stream Type,  Prev: Frame Configuration Type,  Up: Editing Types

2.4.7 Process Type
------------------

The word "process" usually means a running program.  Emacs itself runs
in a process of this sort.  However, in Emacs Lisp, a process is a Lisp
object that designates a subprocess created by the Emacs process.
Programs such as shells, GDB, ftp, and compilers, running in
subprocesses of Emacs, extend the capabilities of Emacs.

   An Emacs subprocess takes textual input from Emacs and returns
textual output to Emacs for further manipulation.  Emacs can also send
signals to the subprocess.

   Process objects have no read syntax.  They print in hash notation,
giving the name of the process:

     (process-list)
          => (#<process shell>)

   *Note Processes::, for information about functions that create,
delete, return information about, send input or signals to, and receive
output from processes.


File: elisp,  Node: Stream Type,  Next: Keymap Type,  Prev: Process Type,  Up: Editing Types

2.4.8 Stream Type
-----------------

A "stream" is an object that can be used as a source or sink for
characters--either to supply characters for input or to accept them as
output.  Many different types can be used this way: markers, buffers,
strings, and functions.  Most often, input streams (character sources)
obtain characters from the keyboard, a buffer, or a file, and output
streams (character sinks) send characters to a buffer, such as a
`*Help*' buffer, or to the echo area.

   The object `nil', in addition to its other meanings, may be used as
a stream.  It stands for the value of the variable `standard-input' or
`standard-output'.  Also, the object `t' as a stream specifies input
using the minibuffer (*note Minibuffers::) or output in the echo area
(*note The Echo Area::).

   Streams have no special printed representation or read syntax, and
print as whatever primitive type they are.

   *Note Read and Print::, for a description of functions related to
streams, including parsing and printing functions.


File: elisp,  Node: Keymap Type,  Next: Overlay Type,  Prev: Stream Type,  Up: Editing Types

2.4.9 Keymap Type
-----------------

A "keymap" maps keys typed by the user to commands.  This mapping
controls how the user's command input is executed.  A keymap is actually
a list whose CAR is the symbol `keymap'.

   *Note Keymaps::, for information about creating keymaps, handling
prefix keys, local as well as global keymaps, and changing key bindings.


File: elisp,  Node: Overlay Type,  Prev: Keymap Type,  Up: Editing Types

2.4.10 Overlay Type
-------------------

An "overlay" specifies properties that apply to a part of a buffer.
Each overlay applies to a specified range of the buffer, and contains a
property list (a list whose elements are alternating property names and
values).  Overlay properties are used to present parts of the buffer
temporarily in a different display style.  Overlays have no read
syntax, and print in hash notation, giving the buffer name and range of
positions.

   *Note Overlays::, for how to create and use overlays.


File: elisp,  Node: Circular Objects,  Next: Type Predicates,  Prev: Editing Types,  Up: Lisp Data Types

2.5 Read Syntax for Circular Objects
====================================

To represent shared or circular structures within a complex of Lisp
objects, you can use the reader constructs `#N=' and `#N#'.

   Use `#N=' before an object to label it for later reference;
subsequently, you can use `#N#' to refer the same object in another
place.  Here, N is some integer.  For example, here is how to make a
list in which the first element recurs as the third element:

     (#1=(a) b #1#)

This differs from ordinary syntax such as this

     ((a) b (a))

which would result in a list whose first and third elements look alike
but are not the same Lisp object.  This shows the difference:

     (prog1 nil
       (setq x '(#1=(a) b #1#)))
     (eq (nth 0 x) (nth 2 x))
          => t
     (setq x '((a) b (a)))
     (eq (nth 0 x) (nth 2 x))
          => nil

   You can also use the same syntax to make a circular structure, which
appears as an "element" within itself.  Here is an example:

     #1=(a #1#)

This makes a list whose second element is the list itself.  Here's how
you can see that it really works:

     (prog1 nil
       (setq x '#1=(a #1#)))
     (eq x (cadr x))
          => t

   The Lisp printer can produce this syntax to record circular and
shared structure in a Lisp object, if you bind the variable
`print-circle' to a non-`nil' value.  *Note Output Variables::.


File: elisp,  Node: Type Predicates,  Next: Equality Predicates,  Prev: Circular Objects,  Up: Lisp Data Types

2.6 Type Predicates
===================

The Emacs Lisp interpreter itself does not perform type checking on the
actual arguments passed to functions when they are called.  It could
not do so, since function arguments in Lisp do not have declared data
types, as they do in other programming languages.  It is therefore up to
the individual function to test whether each actual argument belongs to
a type that the function can use.

   All built-in functions do check the types of their actual arguments
when appropriate, and signal a `wrong-type-argument' error if an
argument is of the wrong type.  For example, here is what happens if you
pass an argument to `+' that it cannot handle:

     (+ 2 'a)
          error--> Wrong type argument: number-or-marker-p, a

   If you want your program to handle different types differently, you
must do explicit type checking.  The most common way to check the type
of an object is to call a "type predicate" function.  Emacs has a type
predicate for each type, as well as some predicates for combinations of
types.

   A type predicate function takes one argument; it returns `t' if the
argument belongs to the appropriate type, and `nil' otherwise.
Following a general Lisp convention for predicate functions, most type
predicates' names end with `p'.

   Here is an example which uses the predicates `listp' to check for a
list and `symbolp' to check for a symbol.

     (defun add-on (x)
       (cond ((symbolp x)
              ;; If X is a symbol, put it on LIST.
              (setq list (cons x list)))
             ((listp x)
              ;; If X is a list, add its elements to LIST.
              (setq list (append x list)))
             (t
              ;; We handle only symbols and lists.
              (error "Invalid argument %s in add-on" x))))

   Here is a table of predefined type predicates, in alphabetical order,
with references to further information.

`atom'
     *Note atom: List-related Predicates.

`arrayp'
     *Note arrayp: Array Functions.

`bool-vector-p'
     *Note bool-vector-p: Bool-Vectors.

`bufferp'
     *Note bufferp: Buffer Basics.

`byte-code-function-p'
     *Note byte-code-function-p: Byte-Code Type.

`case-table-p'
     *Note case-table-p: Case Tables.

`char-or-string-p'
     *Note char-or-string-p: Predicates for Strings.

`char-table-p'
     *Note char-table-p: Char-Tables.

`commandp'
     *Note commandp: Interactive Call.

`consp'
     *Note consp: List-related Predicates.

`display-table-p'
     *Note display-table-p: Display Tables.

`floatp'
     *Note floatp: Predicates on Numbers.

`frame-configuration-p'
     *Note frame-configuration-p: Frame Configurations.

`frame-live-p'
     *Note frame-live-p: Deleting Frames.

`framep'
     *Note framep: Frames.

`functionp'
     *Note functionp: Functions.

`hash-table-p'
     *Note hash-table-p: Other Hash.

`integer-or-marker-p'
     *Note integer-or-marker-p: Predicates on Markers.

`integerp'
     *Note integerp: Predicates on Numbers.

`keymapp'
     *Note keymapp: Creating Keymaps.

`keywordp'
     *Note Constant Variables::.

`listp'
     *Note listp: List-related Predicates.

`markerp'
     *Note markerp: Predicates on Markers.

`wholenump'
     *Note wholenump: Predicates on Numbers.

`nlistp'
     *Note nlistp: List-related Predicates.

`numberp'
     *Note numberp: Predicates on Numbers.

`number-or-marker-p'
     *Note number-or-marker-p: Predicates on Markers.

`overlayp'
     *Note overlayp: Overlays.

`processp'
     *Note processp: Processes.

`sequencep'
     *Note sequencep: Sequence Functions.

`stringp'
     *Note stringp: Predicates for Strings.

`subrp'
     *Note subrp: Function Cells.

`symbolp'
     *Note symbolp: Symbols.

`syntax-table-p'
     *Note syntax-table-p: Syntax Tables.

`user-variable-p'
     *Note user-variable-p: Defining Variables.

`vectorp'
     *Note vectorp: Vectors.

`window-configuration-p'
     *Note window-configuration-p: Window Configurations.

`window-live-p'
     *Note window-live-p: Deleting Windows.

`windowp'
     *Note windowp: Basic Windows.

`booleanp'
     *Note booleanp: nil and t.

`string-or-null-p'
     *Note string-or-null-p: Predicates for Strings.

   The most general way to check the type of an object is to call the
function `type-of'.  Recall that each object belongs to one and only
one primitive type; `type-of' tells you which one (*note Lisp Data
Types::).  But `type-of' knows nothing about non-primitive types.  In
most cases, it is more convenient to use type predicates than `type-of'.

 -- Function: type-of object
     This function returns a symbol naming the primitive type of
     OBJECT.  The value is one of the symbols `symbol', `integer',
     `float', `string', `cons', `vector', `char-table', `bool-vector',
     `hash-table', `subr', `compiled-function', `marker', `overlay',
     `window', `buffer', `frame', `process', or `window-configuration'.

          (type-of 1)
               => integer
          (type-of 'nil)
               => symbol
          (type-of '())    ; `()' is `nil'.
               => symbol
          (type-of '(x))
               => cons


File: elisp,  Node: Equality Predicates,  Prev: Type Predicates,  Up: Lisp Data Types

2.7 Equality Predicates
=======================

Here we describe functions that test for equality between any two
objects.  Other functions test equality between objects of specific
types, e.g., strings.  For these predicates, see the appropriate chapter
describing the data type.

 -- Function: eq object1 object2
     This function returns `t' if OBJECT1 and OBJECT2 are the same
     object, `nil' otherwise.

     `eq' returns `t' if OBJECT1 and OBJECT2 are integers with the same
     value.  Also, since symbol names are normally unique, if the
     arguments are symbols with the same name, they are `eq'.  For
     other types (e.g., lists, vectors, strings), two arguments with
     the same contents or elements are not necessarily `eq' to each
     other: they are `eq' only if they are the same object, meaning
     that a change in the contents of one will be reflected by the same
     change in the contents of the other.

          (eq 'foo 'foo)
               => t

          (eq 456 456)
               => t

          (eq "asdf" "asdf")
               => nil

          (eq '(1 (2 (3))) '(1 (2 (3))))
               => nil

          (setq foo '(1 (2 (3))))
               => (1 (2 (3)))
          (eq foo foo)
               => t
          (eq foo '(1 (2 (3))))
               => nil

          (eq [(1 2) 3] [(1 2) 3])
               => nil

          (eq (point-marker) (point-marker))
               => nil

     The `make-symbol' function returns an uninterned symbol, distinct
     from the symbol that is used if you write the name in a Lisp
     expression.  Distinct symbols with the same name are not `eq'.
     *Note Creating Symbols::.

          (eq (make-symbol "foo") 'foo)
               => nil

 -- Function: equal object1 object2
     This function returns `t' if OBJECT1 and OBJECT2 have equal
     components, `nil' otherwise.  Whereas `eq' tests if its arguments
     are the same object, `equal' looks inside nonidentical arguments
     to see if their elements or contents are the same.  So, if two
     objects are `eq', they are `equal', but the converse is not always
     true.

          (equal 'foo 'foo)
               => t

          (equal 456 456)
               => t

          (equal "asdf" "asdf")
               => t
          (eq "asdf" "asdf")
               => nil

          (equal '(1 (2 (3))) '(1 (2 (3))))
               => t
          (eq '(1 (2 (3))) '(1 (2 (3))))
               => nil

          (equal [(1 2) 3] [(1 2) 3])
               => t
          (eq [(1 2) 3] [(1 2) 3])
               => nil

          (equal (point-marker) (point-marker))
               => t

          (eq (point-marker) (point-marker))
               => nil

     Comparison of strings is case-sensitive, but does not take account
     of text properties--it compares only the characters in the
     strings.  Use `equal-including-properties' to also compare text
     properties.  For technical reasons, a unibyte string and a
     multibyte string are `equal' if and only if they contain the same
     sequence of character codes and all these codes are either in the
     range 0 through 127 (ASCII) or 160 through 255
     (`eight-bit-graphic').  (*note Text Representations::).

          (equal "asdf" "ASDF")
               => nil

     However, two distinct buffers are never considered `equal', even if
     their textual contents are the same.

   The test for equality is implemented recursively; for example, given
two cons cells X and Y, `(equal X Y)' returns `t' if and only if both
the expressions below return `t':

     (equal (car X) (car Y))
     (equal (cdr X) (cdr Y))

   Because of this recursive method, circular lists may therefore cause
infinite recursion (leading to an error).

 -- Function: equal-including-properties object1 object2
     This function behaves like `equal' in all cases but also requires
     that for two strings to be equal, they have the same text
     properties.

          (equal "asdf" (propertize "asdf" '(asdf t)))
               => t
          (equal-including-properties "asdf"
                                      (propertize "asdf" '(asdf t)))
               => nil


File: elisp,  Node: Numbers,  Next: Strings and Characters,  Prev: Lisp Data Types,  Up: Top

3 Numbers
*********

GNU Emacs supports two numeric data types: "integers" and "floating
point numbers".  Integers are whole numbers such as -3, 0, 7, 13, and
511.  Their values are exact.  Floating point numbers are numbers with
fractional parts, such as -4.5, 0.0, or 2.71828.  They can also be
expressed in exponential notation: 1.5e2 equals 150; in this example,
`e2' stands for ten to the second power, and that is multiplied by 1.5.
Floating point values are not exact; they have a fixed, limited amount
of precision.

* Menu:

* Integer Basics::            Representation and range of integers.
* Float Basics::	      Representation and range of floating point.
* Predicates on Numbers::     Testing for numbers.
* Comparison of Numbers::     Equality and inequality predicates.
* Numeric Conversions::	      Converting float to integer and vice versa.
* Arithmetic Operations::     How to add, subtract, multiply and divide.
* Rounding Operations::       Explicitly rounding floating point numbers.
* Bitwise Operations::        Logical and, or, not, shifting.
* Math Functions::            Trig, exponential and logarithmic functions.
* Random Numbers::            Obtaining random integers, predictable or not.


File: elisp,  Node: Integer Basics,  Next: Float Basics,  Up: Numbers

3.1 Integer Basics
==================

The range of values for an integer depends on the machine.  The minimum
range is -268435456 to 268435455 (29 bits; i.e., -2**28 to 2**28 - 1),
but some machines may provide a wider range.  Many examples in this
chapter assume an integer has 29 bits.  

   The Lisp reader reads an integer as a sequence of digits with
optional initial sign and optional final period.

      1               ; The integer 1.
      1.              ; The integer 1.
     +1               ; Also the integer 1.
     -1               ; The integer -1.
      536870913       ; Also the integer 1, due to overflow.
      0               ; The integer 0.
     -0               ; The integer 0.

   The syntax for integers in bases other than 10 uses `#' followed by
a letter that specifies the radix: `b' for binary, `o' for octal, `x'
for hex, or `RADIXr' to specify radix RADIX.  Case is not significant
for the letter that specifies the radix.  Thus, `#bINTEGER' reads
INTEGER in binary, and `#RADIXrINTEGER' reads INTEGER in radix RADIX.
Allowed values of RADIX run from 2 to 36.  For example:

     #b101100 => 44
     #o54 => 44
     #x2c => 44
     #24r1k => 44

   To understand how various functions work on integers, especially the
bitwise operators (*note Bitwise Operations::), it is often helpful to
view the numbers in their binary form.

   In 29-bit binary, the decimal integer 5 looks like this:

     0 0000  0000 0000  0000 0000  0000 0101

(We have inserted spaces between groups of 4 bits, and two spaces
between groups of 8 bits, to make the binary integer easier to read.)

   The integer -1 looks like this:

     1 1111  1111 1111  1111 1111  1111 1111

-1 is represented as 29 ones.  (This is called "two's complement"
notation.)

   The negative integer, -5, is creating by subtracting 4 from -1.  In
binary, the decimal integer 4 is 100.  Consequently, -5 looks like this:

     1 1111  1111 1111  1111 1111  1111 1011

   In this implementation, the largest 29-bit binary integer value is
268,435,455 in decimal.  In binary, it looks like this:

     0 1111  1111 1111  1111 1111  1111 1111

   Since the arithmetic functions do not check whether integers go
outside their range, when you add 1 to 268,435,455, the value is the
negative integer -268,435,456:

     (+ 1 268435455)
          => -268435456
          => 1 0000  0000 0000  0000 0000  0000 0000

   Many of the functions described in this chapter accept markers for
arguments in place of numbers.  (*Note Markers::.)  Since the actual
arguments to such functions may be either numbers or markers, we often
give these arguments the name NUMBER-OR-MARKER.  When the argument
value is a marker, its position value is used and its buffer is ignored.

 -- Variable: most-positive-fixnum
     The value of this variable is the largest integer that Emacs Lisp
     can handle.

 -- Variable: most-negative-fixnum
     The value of this variable is the smallest integer that Emacs Lisp
     can handle.  It is negative.


File: elisp,  Node: Float Basics,  Next: Predicates on Numbers,  Prev: Integer Basics,  Up: Numbers

3.2 Floating Point Basics
=========================

Floating point numbers are useful for representing numbers that are not
integral.  The precise range of floating point numbers is
machine-specific; it is the same as the range of the C data type
`double' on the machine you are using.

   The read-syntax for floating point numbers requires either a decimal
point (with at least one digit following), an exponent, or both.  For
example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4' are five ways
of writing a floating point number whose value is 1500.  They are all
equivalent.  You can also use a minus sign to write negative floating
point numbers, as in `-1.0'.

   Most modern computers support the IEEE floating point standard,
which provides for positive infinity and negative infinity as floating
point values.  It also provides for a class of values called NaN or
"not-a-number"; numerical functions return such values in cases where
there is no correct answer.  For example, `(/ 0.0 0.0)' returns a NaN.
For practical purposes, there's no significant difference between
different NaN values in Emacs Lisp, and there's no rule for precisely
which NaN value should be used in a particular case, so Emacs Lisp
doesn't try to distinguish them (but it does report the sign, if you
print it).  Here are the read syntaxes for these special floating point
values:

positive infinity
     `1.0e+INF'

negative infinity
     `-1.0e+INF'

Not-a-number
     `0.0e+NaN' or `-0.0e+NaN'.

   To test whether a floating point value is a NaN, compare it with
itself using `='.  That returns `nil' for a NaN, and `t' for any other
floating point value.

   The value `-0.0' is distinguishable from ordinary zero in IEEE
floating point, but Emacs Lisp `equal' and `=' consider them equal
values.

   You can use `logb' to extract the binary exponent of a floating
point number (or estimate the logarithm of an integer):

 -- Function: logb number
     This function returns the binary exponent of NUMBER.  More
     precisely, the value is the logarithm of NUMBER base 2, rounded
     down to an integer.

          (logb 10)
               => 3
          (logb 10.0e20)
               => 69


File: elisp,  Node: Predicates on Numbers,  Next: Comparison of Numbers,  Prev: Float Basics,  Up: Numbers

3.3 Type Predicates for Numbers
===============================

The functions in this section test for numbers, or for a specific type
of number.  The functions `integerp' and `floatp' can take any type of
Lisp object as argument (they would not be of much use otherwise), but
the `zerop' predicate requires a number as its argument.  See also
`integer-or-marker-p' and `number-or-marker-p', in *Note Predicates on
Markers::.

 -- Function: floatp object
     This predicate tests whether its argument is a floating point
     number and returns `t' if so, `nil' otherwise.

     `floatp' does not exist in Emacs versions 18 and earlier.

 -- Function: integerp object
     This predicate tests whether its argument is an integer, and
     returns `t' if so, `nil' otherwise.

 -- Function: numberp object
     This predicate tests whether its argument is a number (either
     integer or floating point), and returns `t' if so, `nil' otherwise.

 -- Function: wholenump object
     The `wholenump' predicate (whose name comes from the phrase
     "whole-number-p") tests to see whether its argument is a
     nonnegative integer, and returns `t' if so, `nil' otherwise.  0 is
     considered non-negative.

     `natnump' is an obsolete synonym for `wholenump'.

 -- Function: zerop number
     This predicate tests whether its argument is zero, and returns `t'
     if so, `nil' otherwise.  The argument must be a number.

     `(zerop x)' is equivalent to `(= x 0)'.


File: elisp,  Node: Comparison of Numbers,  Next: Numeric Conversions,  Prev: Predicates on Numbers,  Up: Numbers

3.4 Comparison of Numbers
=========================

To test numbers for numerical equality, you should normally use `=',
not `eq'.  There can be many distinct floating point number objects
with the same numeric value.  If you use `eq' to compare them, then you
test whether two values are the same _object_.  By contrast, `='
compares only the numeric values of the objects.

   At present, each integer value has a unique Lisp object in Emacs
Lisp.  Therefore, `eq' is equivalent to `=' where integers are
concerned.  It is sometimes convenient to use `eq' for comparing an
unknown value with an integer, because `eq' does not report an error if
the unknown value is not a number--it accepts arguments of any type.
By contrast, `=' signals an error if the arguments are not numbers or
markers.  However, it is a good idea to use `=' if you can, even for
comparing integers, just in case we change the representation of
integers in a future Emacs version.

   Sometimes it is useful to compare numbers with `equal'; it treats
two numbers as equal if they have the same data type (both integers, or
both floating point) and the same value.  By contrast, `=' can treat an
integer and a floating point number as equal.  *Note Equality
Predicates::.

   There is another wrinkle: because floating point arithmetic is not
exact, it is often a bad idea to check for equality of two floating
point values.  Usually it is better to test for approximate equality.
Here's a function to do this:

     (defvar fuzz-factor 1.0e-6)
     (defun approx-equal (x y)
       (or (and (= x 0) (= y 0))
           (< (/ (abs (- x y))
                 (max (abs x) (abs y)))
              fuzz-factor)))

     Common Lisp note: Comparing numbers in Common Lisp always requires
     `=' because Common Lisp implements multi-word integers, and two
     distinct integer objects can have the same numeric value.  Emacs
     Lisp can have just one integer object for any given value because
     it has a limited range of integer values.

 -- Function: = number-or-marker1 number-or-marker2
     This function tests whether its arguments are numerically equal,
     and returns `t' if so, `nil' otherwise.

 -- Function: eql value1 value2
     This function acts like `eq' except when both arguments are
     numbers.  It compares numbers by type and numeric value, so that
     `(eql 1.0 1)' returns `nil', but `(eql 1.0 1.0)' and `(eql 1 1)'
     both return `t'.

 -- Function: /= number-or-marker1 number-or-marker2
     This function tests whether its arguments are numerically equal,
     and returns `t' if they are not, and `nil' if they are.

 -- Function: < number-or-marker1 number-or-marker2
     This function tests whether its first argument is strictly less
     than its second argument.  It returns `t' if so, `nil' otherwise.

 -- Function: <= number-or-marker1 number-or-marker2
     This function tests whether its first argument is less than or
     equal to its second argument.  It returns `t' if so, `nil'
     otherwise.

 -- Function: > number-or-marker1 number-or-marker2
     This function tests whether its first argument is strictly greater
     than its second argument.  It returns `t' if so, `nil' otherwise.

 -- Function: >= number-or-marker1 number-or-marker2
     This function tests whether its first argument is greater than or
     equal to its second argument.  It returns `t' if so, `nil'
     otherwise.

 -- Function: max number-or-marker &rest numbers-or-markers
     This function returns the largest of its arguments.  If any of the
     arguments is floating-point, the value is returned as floating
     point, even if it was given as an integer.

          (max 20)
               => 20
          (max 1 2.5)
               => 2.5
          (max 1 3 2.5)
               => 3.0

 -- Function: min number-or-marker &rest numbers-or-markers
     This function returns the smallest of its arguments.  If any of
     the arguments is floating-point, the value is returned as floating
     point, even if it was given as an integer.

          (min -4 1)
               => -4

 -- Function: abs number
     This function returns the absolute value of NUMBER.


File: elisp,  Node: Numeric Conversions,  Next: Arithmetic Operations,  Prev: Comparison of Numbers,  Up: Numbers

3.5 Numeric Conversions
=======================

To convert an integer to floating point, use the function `float'.

 -- Function: float number
     This returns NUMBER converted to floating point.  If NUMBER is
     already a floating point number, `float' returns it unchanged.

   There are four functions to convert floating point numbers to
integers; they differ in how they round.  All accept an argument NUMBER
and an optional argument DIVISOR.  Both arguments may be integers or
floating point numbers.  DIVISOR may also be `nil'.  If DIVISOR is
`nil' or omitted, these functions convert NUMBER to an integer, or
return it unchanged if it already is an integer.  If DIVISOR is
non-`nil', they divide NUMBER by DIVISOR and convert the result to an
integer.  An `arith-error' results if DIVISOR is 0.

 -- Function: truncate number &optional divisor
     This returns NUMBER, converted to an integer by rounding towards
     zero.

          (truncate 1.2)
               => 1
          (truncate 1.7)
               => 1
          (truncate -1.2)
               => -1
          (truncate -1.7)
               => -1

 -- Function: floor number &optional divisor
     This returns NUMBER, converted to an integer by rounding downward
     (towards negative infinity).

     If DIVISOR is specified, this uses the kind of division operation
     that corresponds to `mod', rounding downward.

          (floor 1.2)
               => 1
          (floor 1.7)
               => 1
          (floor -1.2)
               => -2
          (floor -1.7)
               => -2
          (floor 5.99 3)
               => 1

 -- Function: ceiling number &optional divisor
     This returns NUMBER, converted to an integer by rounding upward
     (towards positive infinity).

          (ceiling 1.2)
               => 2
          (ceiling 1.7)
               => 2
          (ceiling -1.2)
               => -1
          (ceiling -1.7)
               => -1

 -- Function: round number &optional divisor
     This returns NUMBER, converted to an integer by rounding towards
     the nearest integer.  Rounding a value equidistant between two
     integers may choose the integer closer to zero, or it may prefer
     an even integer, depending on your machine.

          (round 1.2)
               => 1
          (round 1.7)
               => 2
          (round -1.2)
               => -1
          (round -1.7)
               => -2


File: elisp,  Node: Arithmetic Operations,  Next: Rounding Operations,  Prev: Numeric Conversions,  Up: Numbers

3.6 Arithmetic Operations
=========================

Emacs Lisp provides the traditional four arithmetic operations:
addition, subtraction, multiplication, and division.  Remainder and
modulus functions supplement the division functions.  The functions to
add or subtract 1 are provided because they are traditional in Lisp and
commonly used.

   All of these functions except `%' return a floating point value if
any argument is floating.

   It is important to note that in Emacs Lisp, arithmetic functions do
not check for overflow.  Thus `(1+ 268435455)' may evaluate to
-268435456, depending on your hardware.

 -- Function: 1+ number-or-marker
     This function returns NUMBER-OR-MARKER plus 1.  For example,

          (setq foo 4)
               => 4
          (1+ foo)
               => 5

     This function is not analogous to the C operator `++'--it does not
     increment a variable.  It just computes a sum.  Thus, if we
     continue,

          foo
               => 4

     If you want to increment the variable, you must use `setq', like
     this:

          (setq foo (1+ foo))
               => 5

 -- Function: 1- number-or-marker
     This function returns NUMBER-OR-MARKER minus 1.

 -- Function: + &rest numbers-or-markers
     This function adds its arguments together.  When given no
     arguments, `+' returns 0.

          (+)
               => 0
          (+ 1)
               => 1
          (+ 1 2 3 4)
               => 10

 -- Function: - &optional number-or-marker &rest more-numbers-or-markers
     The `-' function serves two purposes: negation and subtraction.
     When `-' has a single argument, the value is the negative of the
     argument.  When there are multiple arguments, `-' subtracts each of
     the MORE-NUMBERS-OR-MARKERS from NUMBER-OR-MARKER, cumulatively.
     If there are no arguments, the result is 0.

          (- 10 1 2 3 4)
               => 0
          (- 10)
               => -10
          (-)
               => 0

 -- Function: * &rest numbers-or-markers
     This function multiplies its arguments together, and returns the
     product.  When given no arguments, `*' returns 1.

          (*)
               => 1
          (* 1)
               => 1
          (* 1 2 3 4)
               => 24

 -- Function: / dividend divisor &rest divisors
     This function divides DIVIDEND by DIVISOR and returns the
     quotient.  If there are additional arguments DIVISORS, then it
     divides DIVIDEND by each divisor in turn.  Each argument may be a
     number or a marker.

     If all the arguments are integers, then the result is an integer
     too.  This means the result has to be rounded.  On most machines,
     the result is rounded towards zero after each division, but some
     machines may round differently with negative arguments.  This is
     because the Lisp function `/' is implemented using the C division
     operator, which also permits machine-dependent rounding.  As a
     practical matter, all known machines round in the standard fashion.

     If you divide an integer by 0, an `arith-error' error is signaled.
     (*Note Errors::.)  Floating point division by zero returns either
     infinity or a NaN if your machine supports IEEE floating point;
     otherwise, it signals an `arith-error' error.

          (/ 6 2)
               => 3
          (/ 5 2)
               => 2
          (/ 5.0 2)
               => 2.5
          (/ 5 2.0)
               => 2.5
          (/ 5.0 2.0)
               => 2.5
          (/ 25 3 2)
               => 4
          (/ -17 6)
               => -2   (could in theory be -3 on some machines)

 -- Function: % dividend divisor
     This function returns the integer remainder after division of
     DIVIDEND by DIVISOR.  The arguments must be integers or markers.

     For negative arguments, the remainder is in principle
     machine-dependent since the quotient is; but in practice, all
     known machines behave alike.

     An `arith-error' results if DIVISOR is 0.

          (% 9 4)
               => 1
          (% -9 4)
               => -1
          (% 9 -4)
               => 1
          (% -9 -4)
               => -1

     For any two integers DIVIDEND and DIVISOR,

          (+ (% DIVIDEND DIVISOR)
             (* (/ DIVIDEND DIVISOR) DIVISOR))

     always equals DIVIDEND.

 -- Function: mod dividend divisor
     This function returns the value of DIVIDEND modulo DIVISOR; in
     other words, the remainder after division of DIVIDEND by DIVISOR,
     but with the same sign as DIVISOR.  The arguments must be numbers
     or markers.

     Unlike `%', `mod' returns a well-defined result for negative
     arguments.  It also permits floating point arguments; it rounds the
     quotient downward (towards minus infinity) to an integer, and uses
     that quotient to compute the remainder.

     An `arith-error' results if DIVISOR is 0.

          (mod 9 4)
               => 1
          (mod -9 4)
               => 3
          (mod 9 -4)
               => -3
          (mod -9 -4)
               => -1
          (mod 5.5 2.5)
               => .5

     For any two numbers DIVIDEND and DIVISOR,

          (+ (mod DIVIDEND DIVISOR)
             (* (floor DIVIDEND DIVISOR) DIVISOR))

     always equals DIVIDEND, subject to rounding error if either
     argument is floating point.  For `floor', see *Note Numeric
     Conversions::.


File: elisp,  Node: Rounding Operations,  Next: Bitwise Operations,  Prev: Arithmetic Operations,  Up: Numbers

3.7 Rounding Operations
=======================

The functions `ffloor', `fceiling', `fround', and `ftruncate' take a
floating point argument and return a floating point result whose value
is a nearby integer.  `ffloor' returns the nearest integer below;
`fceiling', the nearest integer above; `ftruncate', the nearest integer
in the direction towards zero; `fround', the nearest integer.

 -- Function: ffloor float
     This function rounds FLOAT to the next lower integral value, and
     returns that value as a floating point number.

 -- Function: fceiling float
     This function rounds FLOAT to the next higher integral value, and
     returns that value as a floating point number.

 -- Function: ftruncate float
     This function rounds FLOAT towards zero to an integral value, and
     returns that value as a floating point number.

 -- Function: fround float
     This function rounds FLOAT to the nearest integral value, and
     returns that value as a floating point number.


File: elisp,  Node: Bitwise Operations,  Next: Math Functions,  Prev: Rounding Operations,  Up: Numbers

3.8 Bitwise Operations on Integers
==================================

In a computer, an integer is represented as a binary number, a sequence
of "bits" (digits which are either zero or one).  A bitwise operation
acts on the individual bits of such a sequence.  For example,
"shifting" moves the whole sequence left or right one or more places,
reproducing the same pattern "moved over."

   The bitwise operations in Emacs Lisp apply only to integers.

 -- Function: lsh integer1 count
     `lsh', which is an abbreviation for "logical shift", shifts the
     bits in INTEGER1 to the left COUNT places, or to the right if
     COUNT is negative, bringing zeros into the vacated bits.  If COUNT
     is negative, `lsh' shifts zeros into the leftmost
     (most-significant) bit, producing a positive result even if
     INTEGER1 is negative.  Contrast this with `ash', below.

     Here are two examples of `lsh', shifting a pattern of bits one
     place to the left.  We show only the low-order eight bits of the
     binary pattern; the rest are all zero.

          (lsh 5 1)
               => 10
          ;; Decimal 5 becomes decimal 10.
          00000101 => 00001010

          (lsh 7 1)
               => 14
          ;; Decimal 7 becomes decimal 14.
          00000111 => 00001110

     As the examples illustrate, shifting the pattern of bits one place
     to the left produces a number that is twice the value of the
     previous number.

     Shifting a pattern of bits two places to the left produces results
     like this (with 8-bit binary numbers):

          (lsh 3 2)
               => 12
          ;; Decimal 3 becomes decimal 12.
          00000011 => 00001100

     On the other hand, shifting one place to the right looks like this:

          (lsh 6 -1)
               => 3
          ;; Decimal 6 becomes decimal 3.
          00000110 => 00000011

          (lsh 5 -1)
               => 2
          ;; Decimal 5 becomes decimal 2.
          00000101 => 00000010

     As the example illustrates, shifting one place to the right
     divides the value of a positive integer by two, rounding downward.

     The function `lsh', like all Emacs Lisp arithmetic functions, does
     not check for overflow, so shifting left can discard significant
     bits and change the sign of the number.  For example, left shifting
     268,435,455 produces -2 on a 29-bit machine:

          (lsh 268435455 1)          ; left shift
               => -2

     In binary, in the 29-bit implementation, the argument looks like
     this:

          ;; Decimal 268,435,455
          0 1111  1111 1111  1111 1111  1111 1111

     which becomes the following when left shifted:

          ;; Decimal -2
          1 1111  1111 1111  1111 1111  1111 1110

 -- Function: ash integer1 count
     `ash' ("arithmetic shift") shifts the bits in INTEGER1 to the left
     COUNT places, or to the right if COUNT is negative.

     `ash' gives the same results as `lsh' except when INTEGER1 and
     COUNT are both negative.  In that case, `ash' puts ones in the
     empty bit positions on the left, while `lsh' puts zeros in those
     bit positions.

     Thus, with `ash', shifting the pattern of bits one place to the
     right looks like this:

          (ash -6 -1) => -3
          ;; Decimal -6 becomes decimal -3.
          1 1111  1111 1111  1111 1111  1111 1010
               =>
          1 1111  1111 1111  1111 1111  1111 1101

     In contrast, shifting the pattern of bits one place to the right
     with `lsh' looks like this:

          (lsh -6 -1) => 268435453
          ;; Decimal -6 becomes decimal 268,435,453.
          1 1111  1111 1111  1111 1111  1111 1010
               =>
          0 1111  1111 1111  1111 1111  1111 1101

     Here are other examples:

                             ;               29-bit binary values

          (lsh 5 2)          ;   5  =  0 0000  0000 0000  0000 0000  0000 0101
               => 20         ;      =  0 0000  0000 0000  0000 0000  0001 0100
          (ash 5 2)
               => 20
          (lsh -5 2)         ;  -5  =  1 1111  1111 1111  1111 1111  1111 1011
               => -20        ;      =  1 1111  1111 1111  1111 1111  1110 1100
          (ash -5 2)
               => -20
          (lsh 5 -2)         ;   5  =  0 0000  0000 0000  0000 0000  0000 0101
               => 1          ;      =  0 0000  0000 0000  0000 0000  0000 0001
          (ash 5 -2)
               => 1
          (lsh -5 -2)        ;  -5  =  1 1111  1111 1111  1111 1111  1111 1011
               => 134217726  ;      =  0 0111  1111 1111  1111 1111  1111 1110
          (ash -5 -2)        ;  -5  =  1 1111  1111 1111  1111 1111  1111 1011
               => -2         ;      =  1 1111  1111 1111  1111 1111  1111 1110

 -- Function: logand &rest ints-or-markers
     This function returns the "logical and" of the arguments: the Nth
     bit is set in the result if, and only if, the Nth bit is set in
     all the arguments.  ("Set" means that the value of the bit is 1
     rather than 0.)

     For example, using 4-bit binary numbers, the "logical and" of 13
     and 12 is 12: 1101 combined with 1100 produces 1100.  In both the
     binary numbers, the leftmost two bits are set (i.e., they are
     1's), so the leftmost two bits of the returned value are set.
     However, for the rightmost two bits, each is zero in at least one
     of the arguments, so the rightmost two bits of the returned value
     are 0's.

     Therefore,

          (logand 13 12)
               => 12

     If `logand' is not passed any argument, it returns a value of -1.
     This number is an identity element for `logand' because its binary
     representation consists entirely of ones.  If `logand' is passed
     just one argument, it returns that argument.

                             ;                29-bit binary values

          (logand 14 13)     ; 14  =  0 0000  0000 0000  0000 0000  0000 1110
                             ; 13  =  0 0000  0000 0000  0000 0000  0000 1101
               => 12         ; 12  =  0 0000  0000 0000  0000 0000  0000 1100

          (logand 14 13 4)   ; 14  =  0 0000  0000 0000  0000 0000  0000 1110
                             ; 13  =  0 0000  0000 0000  0000 0000  0000 1101
                             ;  4  =  0 0000  0000 0000  0000 0000  0000 0100
               => 4          ;  4  =  0 0000  0000 0000  0000 0000  0000 0100

          (logand)
               => -1         ; -1  =  1 1111  1111 1111  1111 1111  1111 1111

 -- Function: logior &rest ints-or-markers
     This function returns the "inclusive or" of its arguments: the Nth
     bit is set in the result if, and only if, the Nth bit is set in at
     least one of the arguments.  If there are no arguments, the result
     is zero, which is an identity element for this operation.  If
     `logior' is passed just one argument, it returns that argument.

                             ;               29-bit binary values

          (logior 12 5)      ; 12  =  0 0000  0000 0000  0000 0000  0000 1100
                             ;  5  =  0 0000  0000 0000  0000 0000  0000 0101
               => 13         ; 13  =  0 0000  0000 0000  0000 0000  0000 1101

          (logior 12 5 7)    ; 12  =  0 0000  0000 0000  0000 0000  0000 1100
                             ;  5  =  0 0000  0000 0000  0000 0000  0000 0101
                             ;  7  =  0 0000  0000 0000  0000 0000  0000 0111
               => 15         ; 15  =  0 0000  0000 0000  0000 0000  0000 1111

 -- Function: logxor &rest ints-or-markers
     This function returns the "exclusive or" of its arguments: the Nth
     bit is set in the result if, and only if, the Nth bit is set in an
     odd number of the arguments.  If there are no arguments, the
     result is 0, which is an identity element for this operation.  If
     `logxor' is passed just one argument, it returns that argument.

                             ;               29-bit binary values

          (logxor 12 5)      ; 12  =  0 0000  0000 0000  0000 0000  0000 1100
                             ;  5  =  0 0000  0000 0000  0000 0000  0000 0101
               => 9          ;  9  =  0 0000  0000 0000  0000 0000  0000 1001

          (logxor 12 5 7)    ; 12  =  0 0000  0000 0000  0000 0000  0000 1100
                             ;  5  =  0 0000  0000 0000  0000 0000  0000 0101
                             ;  7  =  0 0000  0000 0000  0000 0000  0000 0111
               => 14         ; 14  =  0 0000  0000 0000  0000 0000  0000 1110

 -- Function: lognot integer
     This function returns the logical complement of its argument: the
     Nth bit is one in the result if, and only if, the Nth bit is zero
     in INTEGER, and vice-versa.

          (lognot 5)
               => -6
          ;;  5  =  0 0000  0000 0000  0000 0000  0000 0101
          ;; becomes
          ;; -6  =  1 1111  1111 1111  1111 1111  1111 1010


File: elisp,  Node: Math Functions,  Next: Random Numbers,  Prev: Bitwise Operations,  Up: Numbers

3.9 Standard Mathematical Functions
===================================

These mathematical functions allow integers as well as floating point
numbers as arguments.

 -- Function: sin arg
 -- Function: cos arg
 -- Function: tan arg
     These are the ordinary trigonometric functions, with argument
     measured in radians.

 -- Function: asin arg
     The value of `(asin ARG)' is a number between -pi/2 and pi/2
     (inclusive) whose sine is ARG; if, however, ARG is out of range
     (outside [-1, 1]), it signals a `domain-error' error.

 -- Function: acos arg
     The value of `(acos ARG)' is a number between 0 and pi (inclusive)
     whose cosine is ARG; if, however, ARG is out of range (outside
     [-1, 1]), it signals a `domain-error' error.

 -- Function: atan y &optional x
     The value of `(atan Y)' is a number between -pi/2 and pi/2
     (exclusive) whose tangent is Y.  If the optional second argument X
     is given, the value of `(atan y x)' is the angle in radians
     between the vector `[X, Y]' and the `X' axis.

 -- Function: exp arg
     This is the exponential function; it returns e to the power ARG.  e
     is a fundamental mathematical constant also called the base of
     natural logarithms.

 -- Function: log arg &optional base
     This function returns the logarithm of ARG, with base BASE.  If
     you don't specify BASE, the base e is used.  If ARG is negative,
     it signals a `domain-error' error.

 -- Function: log10 arg
     This function returns the logarithm of ARG, with base 10.  If ARG
     is negative, it signals a `domain-error' error.  `(log10 X)' ==
     `(log X 10)', at least approximately.

 -- Function: expt x y
     This function returns X raised to power Y.  If both arguments are
     integers and Y is positive, the result is an integer; in this
     case, overflow causes truncation, so watch out.

 -- Function: sqrt arg
     This returns the square root of ARG.  If ARG is negative, it
     signals a `domain-error' error.


File: elisp,  Node: Random Numbers,  Prev: Math Functions,  Up: Numbers

3.10 Random Numbers
===================

A deterministic computer program cannot generate true random numbers.
For most purposes, "pseudo-random numbers" suffice.  A series of
pseudo-random numbers is generated in a deterministic fashion.  The
numbers are not truly random, but they have certain properties that
mimic a random series.  For example, all possible values occur equally
often in a pseudo-random series.

   In Emacs, pseudo-random numbers are generated from a "seed" number.
Starting from any given seed, the `random' function always generates
the same sequence of numbers.  Emacs always starts with the same seed
value, so the sequence of values of `random' is actually the same in
each Emacs run!  For example, in one operating system, the first call
to `(random)' after you start Emacs always returns -1457731, and the
second one always returns -7692030.  This repeatability is helpful for
debugging.

   If you want random numbers that don't always come out the same,
execute `(random t)'.  This chooses a new seed based on the current
time of day and on Emacs's process ID number.

 -- Function: random &optional limit
     This function returns a pseudo-random integer.  Repeated calls
     return a series of pseudo-random integers.

     If LIMIT is a positive integer, the value is chosen to be
     nonnegative and less than LIMIT.

     If LIMIT is `t', it means to choose a new seed based on the
     current time of day and on Emacs's process ID number.

     On some machines, any integer representable in Lisp may be the
     result of `random'.  On other machines, the result can never be
     larger than a certain maximum or less than a certain (negative)
     minimum.


File: elisp,  Node: Strings and Characters,  Next: Lists,  Prev: Numbers,  Up: Top

4 Strings and Characters
************************

A string in Emacs Lisp is an array that contains an ordered sequence of
characters.  Strings are used as names of symbols, buffers, and files;
to send messages to users; to hold text being copied between buffers;
and for many other purposes.  Because strings are so important, Emacs
Lisp has many functions expressly for manipulating them.  Emacs Lisp
programs use strings more often than individual characters.

   *Note Strings of Events::, for special considerations for strings of
keyboard character events.

* Menu:

* Basics: String Basics.      Basic properties of strings and characters.
* Predicates for Strings::    Testing whether an object is a string or char.
* Creating Strings::          Functions to allocate new strings.
* Modifying Strings::         Altering the contents of an existing string.
* Text Comparison::           Comparing characters or strings.
* String Conversion::         Converting to and from characters and strings.
* Formatting Strings::        `format': Emacs's analogue of `printf'.
* Case Conversion::           Case conversion functions.
* Case Tables::		      Customizing case conversion.


File: elisp,  Node: String Basics,  Next: Predicates for Strings,  Up: Strings and Characters

4.1 String and Character Basics
===============================

Characters are represented in Emacs Lisp as integers; whether an
integer is a character or not is determined only by how it is used.
Thus, strings really contain integers.

   The length of a string (like any array) is fixed, and cannot be
altered once the string exists.  Strings in Lisp are _not_ terminated
by a distinguished character code.  (By contrast, strings in C are
terminated by a character with ASCII code 0.)

   Since strings are arrays, and therefore sequences as well, you can
operate on them with the general array and sequence functions.  (*Note
Sequences Arrays Vectors::.)  For example, you can access or change
individual characters in a string using the functions `aref' and `aset'
(*note Array Functions::).

   There are two text representations for non-ASCII characters in Emacs
strings (and in buffers): unibyte and multibyte (*note Text
Representations::).  An ASCII character always occupies one byte in a
string; in fact, when a string is all ASCII, there is no real
difference between the unibyte and multibyte representations.  For most
Lisp programming, you don't need to be concerned with these two
representations.

   Sometimes key sequences are represented as strings.  When a string is
a key sequence, string elements in the range 128 to 255 represent meta
characters (which are large integers) rather than character codes in
the range 128 to 255.

   Strings cannot hold characters that have the hyper, super or alt
modifiers; they can hold ASCII control characters, but no other control
characters.  They do not distinguish case in ASCII control characters.
If you want to store such characters in a sequence, such as a key
sequence, you must use a vector instead of a string.  *Note Character
Type::, for more information about the representation of meta and other
modifiers for keyboard input characters.

   Strings are useful for holding regular expressions.  You can also
match regular expressions against strings with `string-match' (*note
Regexp Search::).  The functions `match-string' (*note Simple Match
Data::) and `replace-match' (*note Replacing Match::) are useful for
decomposing and modifying strings after matching regular expressions
against them.

   Like a buffer, a string can contain text properties for the
characters in it, as well as the characters themselves.  *Note Text
Properties::.  All the Lisp primitives that copy text from strings to
buffers or other strings also copy the properties of the characters
being copied.

   *Note Text::, for information about functions that display strings or
copy them into buffers.  *Note Character Type::, and *Note String
Type::, for information about the syntax of characters and strings.
*Note Non-ASCII Characters::, for functions to convert between text
representations and to encode and decode character codes.


File: elisp,  Node: Predicates for Strings,  Next: Creating Strings,  Prev: String Basics,  Up: Strings and Characters

4.2 The Predicates for Strings
==============================

For more information about general sequence and array predicates, see
*Note Sequences Arrays Vectors::, and *Note Arrays::.

 -- Function: stringp object
     This function returns `t' if OBJECT is a string, `nil' otherwise.

 -- Function: string-or-null-p object
     This function returns `t' if OBJECT is a string or nil, `nil'
     otherwise.

 -- Function: char-or-string-p object
     This function returns `t' if OBJECT is a string or a character
     (i.e., an integer), `nil' otherwise.


File: elisp,  Node: Creating Strings,  Next: Modifying Strings,  Prev: Predicates for Strings,  Up: Strings and Characters

4.3 Creating Strings
====================

The following functions create strings, either from scratch, or by
putting strings together, or by taking them apart.

 -- Function: make-string count character
     This function returns a string made up of COUNT repetitions of
     CHARACTER.  If COUNT is negative, an error is signaled.

          (make-string 5 ?x)
               => "xxxxx"
          (make-string 0 ?x)
               => ""

     Other functions to compare with this one include `char-to-string'
     (*note String Conversion::), `make-vector' (*note Vectors::), and
     `make-list' (*note Building Lists::).

 -- Function: string &rest characters
     This returns a string containing the characters CHARACTERS.

          (string ?a ?b ?c)
               => "abc"

 -- Function: substring string start &optional end
     This function returns a new string which consists of those
     characters from STRING in the range from (and including) the
     character at the index START up to (but excluding) the character
     at the index END.  The first character is at index zero.

          (substring "abcdefg" 0 3)
               => "abc"

     Here the index for `a' is 0, the index for `b' is 1, and the index
     for `c' is 2.  Thus, three letters, `abc', are copied from the
     string `"abcdefg"'.  The index 3 marks the character position up
     to which the substring is copied.  The character whose index is 3
     is actually the fourth character in the string.

     A negative number counts from the end of the string, so that -1
     signifies the index of the last character of the string.  For
     example:

          (substring "abcdefg" -3 -1)
               => "ef"

     In this example, the index for `e' is -3, the index for `f' is -2,
     and the index for `g' is -1.  Therefore, `e' and `f' are included,
     and `g' is excluded.

     When `nil' is used for END, it stands for the length of the
     string.  Thus,

          (substring "abcdefg" -3 nil)
               => "efg"

     Omitting the argument END is equivalent to specifying `nil'.  It
     follows that `(substring STRING 0)' returns a copy of all of
     STRING.

          (substring "abcdefg" 0)
               => "abcdefg"

     But we recommend `copy-sequence' for this purpose (*note Sequence
     Functions::).

     If the characters copied from STRING have text properties, the
     properties are copied into the new string also.  *Note Text
     Properties::.

     `substring' also accepts a vector for the first argument.  For
     example:

          (substring [a b (c) "d"] 1 3)
               => [b (c)]

     A `wrong-type-argument' error is signaled if START is not an
     integer or if END is neither an integer nor `nil'.  An
     `args-out-of-range' error is signaled if START indicates a
     character following END, or if either integer is out of range for
     STRING.

     Contrast this function with `buffer-substring' (*note Buffer
     Contents::), which returns a string containing a portion of the
     text in the current buffer.  The beginning of a string is at index
     0, but the beginning of a buffer is at index 1.

 -- Function: substring-no-properties string &optional start end
     This works like `substring' but discards all text properties from
     the value.  Also, START may be omitted or `nil', which is
     equivalent to 0.  Thus, `(substring-no-properties STRING)' returns
     a copy of STRING, with all text properties removed.

 -- Function: concat &rest sequences
     This function returns a new string consisting of the characters in
     the arguments passed to it (along with their text properties, if
     any).  The arguments may be strings, lists of numbers, or vectors
     of numbers; they are not themselves changed.  If `concat' receives
     no arguments, it returns an empty string.

          (concat "abc" "-def")
               => "abc-def"
          (concat "abc" (list 120 121) [122])
               => "abcxyz"
          ;; `nil' is an empty sequence.
          (concat "abc" nil "-def")
               => "abc-def"
          (concat "The " "quick brown " "fox.")
               => "The quick brown fox."
          (concat)
               => ""

     The `concat' function always constructs a new string that is not
     `eq' to any existing string.

     In Emacs versions before 21, when an argument was an integer (not a
     sequence of integers), it was converted to a string of digits
     making up the decimal printed representation of the integer.  This
     obsolete usage no longer works.  The proper way to convert an
     integer to its decimal printed form is with `format' (*note
     Formatting Strings::) or `number-to-string' (*note String
     Conversion::).

     For information about other concatenation functions, see the
     description of `mapconcat' in *Note Mapping Functions::, `vconcat'
     in *Note Vector Functions::, and `append' in *Note Building
     Lists::.

 -- Function: split-string string &optional separators omit-nulls
     This function splits STRING into substrings at matches for the
     regular expression SEPARATORS.  Each match for SEPARATORS defines
     a splitting point; the substrings between the splitting points are
     made into a list, which is the value returned by `split-string'.

     If OMIT-NULLS is `nil', the result contains null strings whenever
     there are two consecutive matches for SEPARATORS, or a match is
     adjacent to the beginning or end of STRING.  If OMIT-NULLS is `t',
     these null strings are omitted from the result.

     If SEPARATORS is `nil' (or omitted), the default is the value of
     `split-string-default-separators'.

     As a special case, when SEPARATORS is `nil' (or omitted), null
     strings are always omitted from the result.  Thus:

          (split-string "  two words ")
               => ("two" "words")

     The result is not `("" "two" "words" "")', which would rarely be
     useful.  If you need such a result, use an explicit value for
     SEPARATORS:

          (split-string "  two words "
                        split-string-default-separators)
               => ("" "two" "words" "")

     More examples:

          (split-string "Soup is good food" "o")
               => ("S" "up is g" "" "d f" "" "d")
          (split-string "Soup is good food" "o" t)
               => ("S" "up is g" "d f" "d")
          (split-string "Soup is good food" "o+")
               => ("S" "up is g" "d f" "d")

     Empty matches do count, except that `split-string' will not look
     for a final empty match when it already reached the end of the
     string using a non-empty match or when STRING is empty:

          (split-string "aooob" "o*")
               => ("" "a" "" "b" "")
          (split-string "ooaboo" "o*")
               => ("" "" "a" "b" "")
          (split-string "" "")
               => ("")

     However, when SEPARATORS can match the empty string, OMIT-NULLS is
     usually `t', so that the subtleties in the three previous examples
     are rarely relevant:

          (split-string "Soup is good food" "o*" t)
               => ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
          (split-string "Nice doggy!" "" t)
               => ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
          (split-string "" "" t)
               => nil

     Somewhat odd, but predictable, behavior can occur for certain
     "non-greedy" values of SEPARATORS that can prefer empty matches
     over non-empty matches.  Again, such values rarely occur in
     practice:

          (split-string "ooo" "o*" t)
               => nil
          (split-string "ooo" "\\|o+" t)
               => ("o" "o" "o")

 -- Variable: split-string-default-separators
     The default value of SEPARATORS for `split-string'.  Its usual
     value is `"[ \f\t\n\r\v]+"'.


File: elisp,  Node: Modifying Strings,  Next: Text Comparison,  Prev: Creating Strings,  Up: Strings and Characters

4.4 Modifying Strings
=====================

The most basic way to alter the contents of an existing string is with
`aset' (*note Array Functions::).  `(aset STRING IDX CHAR)' stores CHAR
into STRING at index IDX.  Each character occupies one or more bytes,
and if CHAR needs a different number of bytes from the character
already present at that index, `aset' signals an error.

   A more powerful function is `store-substring':

 -- Function: store-substring string idx obj
     This function alters part of the contents of the string STRING, by
     storing OBJ starting at index IDX.  The argument OBJ may be either
     a character or a (smaller) string.

     Since it is impossible to change the length of an existing string,
     it is an error if OBJ doesn't fit within STRING's actual length,
     or if any new character requires a different number of bytes from
     the character currently present at that point in STRING.

   To clear out a string that contained a password, use `clear-string':

 -- Function: clear-string string
     This makes STRING a unibyte string and clears its contents to
     zeros.  It may also change STRING's length.


File: elisp,  Node: Text Comparison,  Next: String Conversion,  Prev: Modifying Strings,  Up: Strings and Characters

4.5 Comparison of Characters and Strings
========================================

 -- Function: char-equal character1 character2
     This function returns `t' if the arguments represent the same
     character, `nil' otherwise.  This function ignores differences in
     case if `case-fold-search' is non-`nil'.

          (char-equal ?x ?x)
               => t
          (let ((case-fold-search nil))
            (char-equal ?x ?X))
               => nil

 -- Function: string= string1 string2
     This function returns `t' if the characters of the two strings
     match exactly.  Symbols are also allowed as arguments, in which
     case their print names are used.  Case is always significant,
     regardless of `case-fold-search'.

          (string= "abc" "abc")
               => t
          (string= "abc" "ABC")
               => nil
          (string= "ab" "ABC")
               => nil

     The function `string=' ignores the text properties of the two
     strings.  When `equal' (*note Equality Predicates::) compares two
     strings, it uses `string='.

     For technical reasons, a unibyte and a multibyte string are
     `equal' if and only if they contain the same sequence of character
     codes and all these codes are either in the range 0 through 127
     (ASCII) or 160 through 255 (`eight-bit-graphic').  However, when a
     unibyte string gets converted to a multibyte string, all
     characters with codes in the range 160 through 255 get converted
     to characters with higher codes, whereas ASCII characters remain
     unchanged.  Thus, a unibyte string and its conversion to multibyte
     are only `equal' if the string is all ASCII.  Character codes 160
     through 255 are not entirely proper in multibyte text, even though
     they can occur.  As a consequence, the situation where a unibyte
     and a multibyte string are `equal' without both being all ASCII is
     a technical oddity that very few Emacs Lisp programmers ever get
     confronted with.  *Note Text Representations::.

 -- Function: string-equal string1 string2
     `string-equal' is another name for `string='.

 -- Function: string< string1 string2
     This function compares two strings a character at a time.  It
     scans both the strings at the same time to find the first pair of
     corresponding characters that do not match.  If the lesser
     character of these two is the character from STRING1, then STRING1
     is less, and this function returns `t'.  If the lesser character
     is the one from STRING2, then STRING1 is greater, and this
     function returns `nil'.  If the two strings match entirely, the
     value is `nil'.

     Pairs of characters are compared according to their character
     codes.  Keep in mind that lower case letters have higher numeric
     values in the ASCII character set than their upper case
     counterparts; digits and many punctuation characters have a lower
     numeric value than upper case letters.  An ASCII character is less
     than any non-ASCII character; a unibyte non-ASCII character is
     always less than any multibyte non-ASCII character (*note Text
     Representations::).

          (string< "abc" "abd")
               => t
          (string< "abd" "abc")
               => nil
          (string< "123" "abc")
               => t

     When the strings have different lengths, and they match up to the
     length of STRING1, then the result is `t'.  If they match up to
     the length of STRING2, the result is `nil'.  A string of no
     characters is less than any other string.

          (string< "" "abc")
               => t
          (string< "ab" "abc")
               => t
          (string< "abc" "")
               => nil
          (string< "abc" "ab")
               => nil
          (string< "" "")
               => nil

     Symbols are also allowed as arguments, in which case their print
     names are used.

 -- Function: string-lessp string1 string2
     `string-lessp' is another name for `string<'.

 -- Function: compare-strings string1 start1 end1 string2 start2 end2
          &optional ignore-case
     This function compares the specified part of STRING1 with the
     specified part of STRING2.  The specified part of STRING1 runs
     from index START1 up to index END1 (`nil' means the end of the
     string).  The specified part of STRING2 runs from index START2 up
     to index END2 (`nil' means the end of the string).

     The strings are both converted to multibyte for the comparison
     (*note Text Representations::) so that a unibyte string and its
     conversion to multibyte are always regarded as equal.  If
     IGNORE-CASE is non-`nil', then case is ignored, so that upper case
     letters can be equal to lower case letters.

     If the specified portions of the two strings match, the value is
     `t'.  Otherwise, the value is an integer which indicates how many
     leading characters agree, and which string is less.  Its absolute
     value is one plus the number of characters that agree at the
     beginning of the two strings.  The sign is negative if STRING1 (or
     its specified portion) is less.

 -- Function: assoc-string key alist &optional case-fold
     This function works like `assoc', except that KEY must be a string
     or symbol, and comparison is done using `compare-strings'.
     Symbols are converted to strings before testing.  If CASE-FOLD is
     non-`nil', it ignores case differences.  Unlike `assoc', this
     function can also match elements of the alist that are strings or
     symbols rather than conses.  In particular, ALIST can be a list of
     strings or symbols rather than an actual alist.  *Note Association
     Lists::.

   See also the `compare-buffer-substrings' function in *Note Comparing
Text::, for a way to compare text in buffers.  The function
`string-match', which matches a regular expression against a string,
can be used for a kind of string comparison; see *Note Regexp Search::.


File: elisp,  Node: String Conversion,  Next: Formatting Strings,  Prev: Text Comparison,  Up: Strings and Characters

4.6 Conversion of Characters and Strings
========================================

This section describes functions for conversions between characters,
strings and integers.  `format' (*note Formatting Strings::) and
`prin1-to-string' (*note Output Functions::) can also convert Lisp
objects into strings.  `read-from-string' (*note Input Functions::) can
"convert" a string representation of a Lisp object into an object.  The
functions `string-make-multibyte' and `string-make-unibyte' convert the
text representation of a string (*note Converting Representations::).

   *Note Documentation::, for functions that produce textual
descriptions of text characters and general input events
(`single-key-description' and `text-char-description').  These are used
primarily for making help messages.

 -- Function: char-to-string character
     This function returns a new string containing one character,
     CHARACTER.  This function is semi-obsolete because the function
     `string' is more general.  *Note Creating Strings::.

 -- Function: string-to-char string
     This function returns the first character in STRING.  If the
     string is empty, the function returns 0.  The value is also 0 when
     the first character of STRING is the null character, ASCII code 0.

          (string-to-char "ABC")
               => 65

          (string-to-char "xyz")
               => 120
          (string-to-char "")
               => 0
          (string-to-char "\000")
               => 0

     This function may be eliminated in the future if it does not seem
     useful enough to retain.

 -- Function: number-to-string number
     This function returns a string consisting of the printed base-ten
     representation of NUMBER, which may be an integer or a floating
     point number.  The returned value starts with a minus sign if the
     argument is negative.

          (number-to-string 256)
               => "256"
          (number-to-string -23)
               => "-23"
          (number-to-string -23.5)
               => "-23.5"

     `int-to-string' is a semi-obsolete alias for this function.

     See also the function `format' in *Note Formatting Strings::.

 -- Function: string-to-number string &optional base
     This function returns the numeric value of the characters in
     STRING.  If BASE is non-`nil', it must be an integer between 2 and
     16 (inclusive), and integers are converted in that base.  If BASE
     is `nil', then base ten is used.  Floating point conversion only
     works in base ten; we have not implemented other radices for
     floating point numbers, because that would be much more work and
     does not seem useful.  If STRING looks like an integer but its
     value is too large to fit into a Lisp integer, `string-to-number'
     returns a floating point result.

     The parsing skips spaces and tabs at the beginning of STRING, then
     reads as much of STRING as it can interpret as a number in the
     given base.  (On some systems it ignores other whitespace at the
     beginning, not just spaces and tabs.)  If the first character after
     the ignored whitespace is neither a digit in the given base, nor a
     plus or minus sign, nor the leading dot of a floating point number,
     this function returns 0.

          (string-to-number "256")
               => 256
          (string-to-number "25 is a perfect square.")
               => 25
          (string-to-number "X256")
               => 0
          (string-to-number "-4.5")
               => -4.5
          (string-to-number "1e5")
               => 100000.0

     `string-to-int' is an obsolete alias for this function.

   Here are some other functions that can convert to or from a string:

`concat'
     `concat' can convert a vector or a list into a string.  *Note
     Creating Strings::.

`vconcat'
     `vconcat' can convert a string into a vector.  *Note Vector
     Functions::.

`append'
     `append' can convert a string into a list.  *Note Building Lists::.


File: elisp,  Node: Formatting Strings,  Next: Case Conversion,  Prev: String Conversion,  Up: Strings and Characters

4.7 Formatting Strings
======================

"Formatting" means constructing a string by substitution of computed
values at various places in a constant string.  This constant string
controls how the other values are printed, as well as where they appear;
it is called a "format string".

   Formatting is often useful for computing messages to be displayed.
In fact, the functions `message' and `error' provide the same
formatting feature described here; they differ from `format' only in
how they use the result of formatting.

 -- Function: format string &rest objects
     This function returns a new string that is made by copying STRING
     and then replacing any format specification in the copy with
     encodings of the corresponding OBJECTS.  The arguments OBJECTS are
     the computed values to be formatted.

     The characters in STRING, other than the format specifications,
     are copied directly into the output, including their text
     properties, if any.

   A format specification is a sequence of characters beginning with a
`%'.  Thus, if there is a `%d' in STRING, the `format' function
replaces it with the printed representation of one of the values to be
formatted (one of the arguments OBJECTS).  For example:

     (format "The value of fill-column is %d." fill-column)
          => "The value of fill-column is 72."

   Since `format' interprets `%' characters as format specifications,
you should _never_ pass an arbitrary string as the first argument.
This is particularly true when the string is generated by some Lisp
code.  Unless the string is _known_ to never include any `%'
characters, pass `"%s"', described below, as the first argument, and
the string as the second, like this:

       (format "%s" ARBITRARY-STRING)

   If STRING contains more than one format specification, the format
specifications correspond to successive values from OBJECTS.  Thus, the
first format specification in STRING uses the first such value, the
second format specification uses the second such value, and so on.  Any
extra format specifications (those for which there are no corresponding
values) cause an error.  Any extra values to be formatted are ignored.

   Certain format specifications require values of particular types.  If
you supply a value that doesn't fit the requirements, an error is
signaled.

   Here is a table of valid format specifications:

`%s'
     Replace the specification with the printed representation of the
     object, made without quoting (that is, using `princ', not
     `prin1'--*note Output Functions::).  Thus, strings are represented
     by their contents alone, with no `"' characters, and symbols appear
     without `\' characters.

     If the object is a string, its text properties are copied into the
     output.  The text properties of the `%s' itself are also copied,
     but those of the object take priority.

`%S'
     Replace the specification with the printed representation of the
     object, made with quoting (that is, using `prin1'--*note Output
     Functions::).  Thus, strings are enclosed in `"' characters, and
     `\' characters appear where necessary before special characters.

`%o'
     Replace the specification with the base-eight representation of an
     integer.

`%d'
     Replace the specification with the base-ten representation of an
     integer.

`%x'
`%X'
     Replace the specification with the base-sixteen representation of
     an integer.  `%x' uses lower case and `%X' uses upper case.

`%c'
     Replace the specification with the character which is the value
     given.

`%e'
     Replace the specification with the exponential notation for a
     floating point number.

`%f'
     Replace the specification with the decimal-point notation for a
     floating point number.

`%g'
     Replace the specification with notation for a floating point
     number, using either exponential notation or decimal-point
     notation, whichever is shorter.

`%%'
     Replace the specification with a single `%'.  This format
     specification is unusual in that it does not use a value.  For
     example, `(format "%% %d" 30)' returns `"% 30"'.

   Any other format character results in an `Invalid format operation'
error.

   Here are several examples:

     (format "The name of this buffer is %s." (buffer-name))
          => "The name of this buffer is strings.texi."

     (format "The buffer object prints as %s." (current-buffer))
          => "The buffer object prints as strings.texi."

     (format "The octal value of %d is %o,
              and the hex value is %x." 18 18 18)
          => "The octal value of 18 is 22,
              and the hex value is 12."

   A specification can have a "width", which is a decimal number
between the `%' and the specification character.  If the printed
representation of the object contains fewer characters than this width,
`format' extends it with padding.  The width specifier is ignored for
the `%%' specification.  Any padding introduced by the width specifier
normally consists of spaces inserted on the left:

     (format "%5d is padded on the left with spaces" 123)
          => "  123 is padded on the left with spaces"

If the width is too small, `format' does not truncate the object's
printed representation.  Thus, you can use a width to specify a minimum
spacing between columns with no risk of losing information.  In the
following three examples, `%7s' specifies a minimum width of 7.  In the
first case, the string inserted in place of `%7s' has only 3 letters,
and needs 4 blank spaces as padding.  In the second case, the string
`"specification"' is 13 letters wide but is not truncated.

     (format "The word `%7s' actually has %d letters in it."
             "foo" (length "foo"))
          => "The word `    foo' actually has 3 letters in it."
     (format "The word `%7s' actually has %d letters in it."
             "specification" (length "specification"))
          => "The word `specification' actually has 13 letters in it."

   Immediately after the `%' and before the optional width specifier,
you can also put certain "flag characters".

   The flag `+' inserts a plus sign before a positive number, so that
it always has a sign.  A space character as flag inserts a space before
a positive number.  (Otherwise, positive numbers start with the first
digit.)  These flags are useful for ensuring that positive numbers and
negative numbers use the same number of columns.  They are ignored
except for `%d', `%e', `%f', `%g', and if both flags are used, `+'
takes precedence.

   The flag `#' specifies an "alternate form" which depends on the
format in use.  For `%o', it ensures that the result begins with a `0'.
For `%x' and `%X', it prefixes the result with `0x' or `0X'.  For
`%e', `%f', and `%g', the `#' flag means include a decimal point even
if the precision is zero.

   The flag `-' causes the padding inserted by the width specifier, if
any, to be inserted on the right rather than the left.  The flag `0'
ensures that the padding consists of `0' characters instead of spaces,
inserted on the left.  These flags are ignored for specification
characters for which they do not make sense: `%s', `%S' and `%c' accept
the `0' flag, but still pad with _spaces_ on the left.  If both `-' and
`0' are present and valid, `-' takes precedence.

     (format "%06d is padded on the left with zeros" 123)
          => "000123 is padded on the left with zeros"

     (format "%-6d is padded on the right" 123)
          => "123    is padded on the right"

     (format "The word `%-7s' actually has %d letters in it."
             "foo" (length "foo"))
          => "The word `foo    ' actually has 3 letters in it."

   All the specification characters allow an optional "precision"
before the character (after the width, if present).  The precision is a
decimal-point `.' followed by a digit-string.  For the floating-point
specifications (`%e', `%f', `%g'), the precision specifies how many
decimal places to show; if zero, the decimal-point itself is also
omitted.  For `%s' and `%S', the precision truncates the string to the
given width, so `%.3s' shows only the first three characters of the
representation for OBJECT.  Precision has no effect for other
specification characters.


File: elisp,  Node: Case Conversion,  Next: Case Tables,  Prev: Formatting Strings,  Up: Strings and Characters

4.8 Case Conversion in Lisp
===========================

The character case functions change the case of single characters or of
the contents of strings.  The functions normally convert only
alphabetic characters (the letters `A' through `Z' and `a' through `z',
as well as non-ASCII letters); other characters are not altered.  You
can specify a different case conversion mapping by specifying a case
table (*note Case Tables::).

   These functions do not modify the strings that are passed to them as
arguments.

   The examples below use the characters `X' and `x' which have ASCII
codes 88 and 120 respectively.

 -- Function: downcase string-or-char
     This function converts a character or a string to lower case.

     When the argument to `downcase' is a string, the function creates
     and returns a new string in which each letter in the argument that
     is upper case is converted to lower case.  When the argument to
     `downcase' is a character, `downcase' returns the corresponding
     lower case character.  This value is an integer.  If the original
     character is lower case, or is not a letter, then the value equals
     the original character.

          (downcase "The cat in the hat")
               => "the cat in the hat"

          (downcase ?X)
               => 120

 -- Function: upcase string-or-char
     This function converts a character or a string to upper case.

     When the argument to `upcase' is a string, the function creates
     and returns a new string in which each letter in the argument that
     is lower case is converted to upper case.

     When the argument to `upcase' is a character, `upcase' returns the
     corresponding upper case character.  This value is an integer.  If
     the original character is upper case, or is not a letter, then the
     value returned equals the original character.

          (upcase "The cat in the hat")
               => "THE CAT IN THE HAT"

          (upcase ?x)
               => 88

 -- Function: capitalize string-or-char
     This function capitalizes strings or characters.  If
     STRING-OR-CHAR is a string, the function creates and returns a new
     string, whose contents are a copy of STRING-OR-CHAR in which each
     word has been capitalized.  This means that the first character of
     each word is converted to upper case, and the rest are converted
     to lower case.

     The definition of a word is any sequence of consecutive characters
     that are assigned to the word constituent syntax class in the
     current syntax table (*note Syntax Class Table::).

     When the argument to `capitalize' is a character, `capitalize' has
     the same result as `upcase'.

          (capitalize "The cat in the hat")
               => "The Cat In The Hat"

          (capitalize "THE 77TH-HATTED CAT")
               => "The 77th-Hatted Cat"

          (capitalize ?x)
               => 88

 -- Function: upcase-initials string-or-char
     If STRING-OR-CHAR is a string, this function capitalizes the
     initials of the words in STRING-OR-CHAR, without altering any
     letters other than the initials.  It returns a new string whose
     contents are a copy of STRING-OR-CHAR, in which each word has had
     its initial letter converted to upper case.

     The definition of a word is any sequence of consecutive characters
     that are assigned to the word constituent syntax class in the
     current syntax table (*note Syntax Class Table::).

     When the argument to `upcase-initials' is a character,
     `upcase-initials' has the same result as `upcase'.

          (upcase-initials "The CAT in the hAt")
               => "The CAT In The HAt"

   *Note Text Comparison::, for functions that compare strings; some of
them ignore case differences, or can optionally ignore case differences.


File: elisp,  Node: Case Tables,  Prev: Case Conversion,  Up: Strings and Characters

4.9 The Case Table
==================

You can customize case conversion by installing a special "case table".
A case table specifies the mapping between upper case and lower case
letters.  It affects both the case conversion functions for Lisp
objects (see the previous section) and those that apply to text in the
buffer (*note Case Changes::).  Each buffer has a case table; there is
also a standard case table which is used to initialize the case table
of new buffers.

   A case table is a char-table (*note Char-Tables::) whose subtype is
`case-table'.  This char-table maps each character into the
corresponding lower case character.  It has three extra slots, which
hold related tables:

UPCASE
     The upcase table maps each character into the corresponding upper
     case character.

CANONICALIZE
     The canonicalize table maps all of a set of case-related characters
     into a particular member of that set.

EQUIVALENCES
     The equivalences table maps each one of a set of case-related
     characters into the next character in that set.

   In simple cases, all you need to specify is the mapping to
lower-case; the three related tables will be calculated automatically
from that one.

   For some languages, upper and lower case letters are not in
one-to-one correspondence.  There may be two different lower case
letters with the same upper case equivalent.  In these cases, you need
to specify the maps for both lower case and upper case.

   The extra table CANONICALIZE maps each character to a canonical
equivalent; any two characters that are related by case-conversion have
the same canonical equivalent character.  For example, since `a' and
`A' are related by case-conversion, they should have the same canonical
equivalent character (which should be either `a' for both of them, or
`A' for both of them).

   The extra table EQUIVALENCES is a map that cyclically permutes each
equivalence class (of characters with the same canonical equivalent).
(For ordinary ASCII, this would map `a' into `A' and `A' into `a', and
likewise for each set of equivalent characters.)

   When you construct a case table, you can provide `nil' for
CANONICALIZE; then Emacs fills in this slot from the lower case and
upper case mappings.  You can also provide `nil' for EQUIVALENCES; then
Emacs fills in this slot from CANONICALIZE.  In a case table that is
actually in use, those components are non-`nil'.  Do not try to specify
EQUIVALENCES without also specifying CANONICALIZE.

   Here are the functions for working with case tables:

 -- Function: case-table-p object
     This predicate returns non-`nil' if OBJECT is a valid case table.

 -- Function: set-standard-case-table table
     This function makes TABLE the standard case table, so that it will
     be used in any buffers created subsequently.

 -- Function: standard-case-table
     This returns the standard case table.

 -- Function: current-case-table
     This function returns the current buffer's case table.

 -- Function: set-case-table table
     This sets the current buffer's case table to TABLE.

 -- Macro: with-case-table table body...
     The `with-case-table' macro saves the current case table, makes
     TABLE the current case table, evaluates the BODY forms, and
     finally restores the case table.  The return value is the value of
     the last form in BODY.  The case table is restored even in case of
     an abnormal exit via `throw' or error (*note Nonlocal Exits::).

   Some language environments may modify the case conversions of ASCII
characters; for example, in the Turkish language environment, the ASCII
character `I' is downcased into a Turkish "dotless i".  This can
interfere with code that requires ordinary ASCII case conversion, such
as implementations of ASCII-based network protocols.  In that case, use
the `with-case-table' macro with the variable ASCII-CASE-TABLE, which
stores the unmodified case table for the ASCII character set.

 -- Variable: ascii-case-table
     The case table for the ASCII character set.  This should not be
     modified by any language environment settings.

   The following three functions are convenient subroutines for packages
that define non-ASCII character sets.  They modify the specified case
table CASE-TABLE; they also modify the standard syntax table.  *Note
Syntax Tables::.  Normally you would use these functions to change the
standard case table.

 -- Function: set-case-syntax-pair uc lc case-table
     This function specifies a pair of corresponding letters, one upper
     case and one lower case.

 -- Function: set-case-syntax-delims l r case-table
     This function makes characters L and R a matching pair of
     case-invariant delimiters.

 -- Function: set-case-syntax char syntax case-table
     This function makes CHAR case-invariant, with syntax SYNTAX.

 -- Command: describe-buffer-case-table
     This command displays a description of the contents of the current
     buffer's case table.


File: elisp,  Node: Lists,  Next: Sequences Arrays Vectors,  Prev: Strings and Characters,  Up: Top

5 Lists
*******

A "list" represents a sequence of zero or more elements (which may be
any Lisp objects).  The important difference between lists and vectors
is that two or more lists can share part of their structure; in
addition, you can insert or delete elements in a list without copying
the whole list.

* Menu:

* Cons Cells::          How lists are made out of cons cells.
* List-related Predicates::        Is this object a list?  Comparing two lists.
* List Elements::       Extracting the pieces of a list.
* Building Lists::      Creating list structure.
* List Variables::      Modifying lists stored in variables.
* Modifying Lists::     Storing new pieces into an existing list.
* Sets And Lists::      A list can represent a finite mathematical set.
* Association Lists::   A list can represent a finite relation or mapping.
* Rings::               Managing a fixed-size ring of objects.


File: elisp,  Node: Cons Cells,  Next: List-related Predicates,  Up: Lists

5.1 Lists and Cons Cells
========================

Lists in Lisp are not a primitive data type; they are built up from
"cons cells".  A cons cell is a data object that represents an ordered
pair.  That is, it has two slots, and each slot "holds", or "refers
to", some Lisp object.  One slot is known as the CAR, and the other is
known as the CDR.  (These names are traditional; see *Note Cons Cell
Type::.)  CDR is pronounced "could-er."

   We say that "the CAR of this cons cell is" whatever object its CAR
slot currently holds, and likewise for the CDR.

   A list is a series of cons cells "chained together," so that each
cell refers to the next one.  There is one cons cell for each element of
the list.  By convention, the CARs of the cons cells hold the elements
of the list, and the CDRs are used to chain the list: the CDR slot of
each cons cell refers to the following cons cell.  The CDR of the last
cons cell is `nil'.  This asymmetry between the CAR and the CDR is
entirely a matter of convention; at the level of cons cells, the CAR
and CDR slots have the same characteristics.

   Since `nil' is the conventional value to put in the CDR of the last
cons cell in the list, we call that case a "true list".

   In Lisp, we consider the symbol `nil' a list as well as a symbol; it
is the list with no elements.  For convenience, the symbol `nil' is
considered to have `nil' as its CDR (and also as its CAR).  Therefore,
the CDR of a true list is always a true list.

   If the CDR of a list's last cons cell is some other value, neither
`nil' nor another cons cell, we call the structure a "dotted list",
since its printed representation would use `.'.  There is one other
possibility: some cons cell's CDR could point to one of the previous
cons cells in the list.  We call that structure a "circular list".

   For some purposes, it does not matter whether a list is true,
circular or dotted.  If the program doesn't look far enough down the
list to see the CDR of the final cons cell, it won't care.  However,
some functions that operate on lists demand true lists and signal
errors if given a dotted list.  Most functions that try to find the end
of a list enter infinite loops if given a circular list.

   Because most cons cells are used as part of lists, the phrase "list
structure" has come to mean any structure made out of cons cells.

   The CDR of any nonempty true list L is a list containing all the
elements of L except the first.

   *Note Cons Cell Type::, for the read and print syntax of cons cells
and lists, and for "box and arrow" illustrations of lists.


File: elisp,  Node: List-related Predicates,  Next: List Elements,  Prev: Cons Cells,  Up: Lists

5.2 Predicates on Lists
=======================

The following predicates test whether a Lisp object is an atom, whether
it is a cons cell or is a list, or whether it is the distinguished
object `nil'.  (Many of these predicates can be defined in terms of the
others, but they are used so often that it is worth having all of them.)

 -- Function: consp object
     This function returns `t' if OBJECT is a cons cell, `nil'
     otherwise.  `nil' is not a cons cell, although it _is_ a list.

 -- Function: atom object
     This function returns `t' if OBJECT is an atom, `nil' otherwise.
     All objects except cons cells are atoms.  The symbol `nil' is an
     atom and is also a list; it is the only Lisp object that is both.

          (atom OBJECT) == (not (consp OBJECT))

 -- Function: listp object
     This function returns `t' if OBJECT is a cons cell or `nil'.
     Otherwise, it returns `nil'.

          (listp '(1))
               => t
          (listp '())
               => t

 -- Function: nlistp object
     This function is the opposite of `listp': it returns `t' if OBJECT
     is not a list.  Otherwise, it returns `nil'.

          (listp OBJECT) == (not (nlistp OBJECT))

 -- Function: null object
     This function returns `t' if OBJECT is `nil', and returns `nil'
     otherwise.  This function is identical to `not', but as a matter
     of clarity we use `null' when OBJECT is considered a list and
     `not' when it is considered a truth value (see `not' in *Note
     Combining Conditions::).

          (null '(1))
               => nil
          (null '())
               => t


File: elisp,  Node: List Elements,  Next: Building Lists,  Prev: List-related Predicates,  Up: Lists

5.3 Accessing Elements of Lists
===============================

 -- Function: car cons-cell
     This function returns the value referred to by the first slot of
     the cons cell CONS-CELL.  Expressed another way, this function
     returns the CAR of CONS-CELL.

     As a special case, if CONS-CELL is `nil', then `car' is defined to
     return `nil'; therefore, any list is a valid argument for `car'.
     An error is signaled if the argument is not a cons cell or `nil'.

          (car '(a b c))
               => a
          (car '())
               => nil

 -- Function: cdr cons-cell
     This function returns the value referred to by the second slot of
     the cons cell CONS-CELL.  Expressed another way, this function
     returns the CDR of CONS-CELL.

     As a special case, if CONS-CELL is `nil', then `cdr' is defined to
     return `nil'; therefore, any list is a valid argument for `cdr'.
     An error is signaled if the argument is not a cons cell or `nil'.

          (cdr '(a b c))
               => (b c)
          (cdr '())
               => nil

 -- Function: car-safe object
     This function lets you take the CAR of a cons cell while avoiding
     errors for other data types.  It returns the CAR of OBJECT if
     OBJECT is a cons cell, `nil' otherwise.  This is in contrast to
     `car', which signals an error if OBJECT is not a list.

          (car-safe OBJECT)
          ==
          (let ((x OBJECT))
            (if (consp x)
                (car x)
              nil))

 -- Function: cdr-safe object
     This function lets you take the CDR of a cons cell while avoiding
     errors for other data types.  It returns the CDR of OBJECT if
     OBJECT is a cons cell, `nil' otherwise.  This is in contrast to
     `cdr', which signals an error if OBJECT is not a list.

          (cdr-safe OBJECT)
          ==
          (let ((x OBJECT))
            (if (consp x)
                (cdr x)
              nil))

 -- Macro: pop listname
     This macro is a way of examining the CAR of a list, and taking it
     off the list, all at once.

     It operates on the list which is stored in the symbol LISTNAME.
     It removes this element from the list by setting LISTNAME to the
     CDR of its old value--but it also returns the CAR of that list,
     which is the element being removed.

          x
               => (a b c)
          (pop x)
               => a
          x
               => (b c)

 -- Function: nth n list
     This function returns the Nth element of LIST.  Elements are
     numbered starting with zero, so the CAR of LIST is element number
     zero.  If the length of LIST is N or less, the value is `nil'.

     If N is negative, `nth' returns the first element of LIST.

          (nth 2 '(1 2 3 4))
               => 3
          (nth 10 '(1 2 3 4))
               => nil
          (nth -3 '(1 2 3 4))
               => 1

          (nth n x) == (car (nthcdr n x))

     The function `elt' is similar, but applies to any kind of sequence.
     For historical reasons, it takes its arguments in the opposite
     order.  *Note Sequence Functions::.

 -- Function: nthcdr n list
     This function returns the Nth CDR of LIST.  In other words, it
     skips past the first N links of LIST and returns what follows.

     If N is zero or negative, `nthcdr' returns all of LIST.  If the
     length of LIST is N or less, `nthcdr' returns `nil'.

          (nthcdr 1 '(1 2 3 4))
               => (2 3 4)
          (nthcdr 10 '(1 2 3 4))
               => nil
          (nthcdr -3 '(1 2 3 4))
               => (1 2 3 4)

 -- Function: last list &optional n
     This function returns the last link of LIST.  The `car' of this
     link is the list's last element.  If LIST is null, `nil' is
     returned.  If N is non-`nil', the Nth-to-last link is returned
     instead, or the whole of LIST if N is bigger than LIST's length.

 -- Function: safe-length list
     This function returns the length of LIST, with no risk of either
     an error or an infinite loop.  It generally returns the number of
     distinct cons cells in the list.  However, for circular lists, the
     value is just an upper bound; it is often too large.

     If LIST is not `nil' or a cons cell, `safe-length' returns 0.

   The most common way to compute the length of a list, when you are not
worried that it may be circular, is with `length'.  *Note Sequence
Functions::.

 -- Function: caar cons-cell
     This is the same as `(car (car CONS-CELL))'.

 -- Function: cadr cons-cell
     This is the same as `(car (cdr CONS-CELL))' or `(nth 1 CONS-CELL)'.

 -- Function: cdar cons-cell
     This is the same as `(cdr (car CONS-CELL))'.

 -- Function: cddr cons-cell
     This is the same as `(cdr (cdr CONS-CELL))' or `(nthcdr 2
     CONS-CELL)'.

 -- Function: butlast x &optional n
     This function returns the list X with the last element, or the
     last N elements, removed.  If N is greater than zero it makes a
     copy of the list so as not to damage the original list.  In
     general, `(append (butlast X N) (last X N))' will return a list
     equal to X.

 -- Function: nbutlast x &optional n
     This is a version of `butlast' that works by destructively
     modifying the `cdr' of the appropriate element, rather than making
     a copy of the list.


File: elisp,  Node: Building Lists,  Next: List Variables,  Prev: List Elements,  Up: Lists

5.4 Building Cons Cells and Lists
=================================

Many functions build lists, as lists reside at the very heart of Lisp.
`cons' is the fundamental list-building function; however, it is
interesting to note that `list' is used more times in the source code
for Emacs than `cons'.

 -- Function: cons object1 object2
     This function is the most basic function for building new list
     structure.  It creates a new cons cell, making OBJECT1 the CAR,
     and OBJECT2 the CDR.  It then returns the new cons cell.  The
     arguments OBJECT1 and OBJECT2 may be any Lisp objects, but most
     often OBJECT2 is a list.

          (cons 1 '(2))
               => (1 2)
          (cons 1 '())
               => (1)
          (cons 1 2)
               => (1 . 2)

     `cons' is often used to add a single element to the front of a
     list.  This is called "consing the element onto the list".  (1)
     For example:

          (setq list (cons newelt list))

     Note that there is no conflict between the variable named `list'
     used in this example and the function named `list' described below;
     any symbol can serve both purposes.

 -- Function: list &rest objects
     This function creates a list with OBJECTS as its elements.  The
     resulting list is always `nil'-terminated.  If no OBJECTS are
     given, the empty list is returned.

          (list 1 2 3 4 5)
               => (1 2 3 4 5)
          (list 1 2 '(3 4 5) 'foo)
               => (1 2 (3 4 5) foo)
          (list)
               => nil

 -- Function: make-list length object
     This function creates a list of LENGTH elements, in which each
     element is OBJECT.  Compare `make-list' with `make-string' (*note
     Creating Strings::).

          (make-list 3 'pigs)
               => (pigs pigs pigs)
          (make-list 0 'pigs)
               => nil
          (setq l (make-list 3 '(a b))
               => ((a b) (a b) (a b))
          (eq (car l) (cadr l))
               => t

 -- Function: append &rest sequences
     This function returns a list containing all the elements of
     SEQUENCES.  The SEQUENCES may be lists, vectors, bool-vectors, or
     strings, but the last one should usually be a list.  All arguments
     except the last one are copied, so none of the arguments is
     altered.  (See `nconc' in *Note Rearrangement::, for a way to join
     lists with no copying.)

     More generally, the final argument to `append' may be any Lisp
     object.  The final argument is not copied or converted; it becomes
     the CDR of the last cons cell in the new list.  If the final
     argument is itself a list, then its elements become in effect
     elements of the result list.  If the final element is not a list,
     the result is a dotted list since its final CDR is not `nil' as
     required in a true list.

     In Emacs 20 and before, the `append' function also allowed
     integers as (non last) arguments.  It converted them to strings of
     digits, making up the decimal print representation of the integer,
     and then used the strings instead of the original integers.  This
     obsolete usage no longer works.  The proper way to convert an
     integer to a decimal number in this way is with `format' (*note
     Formatting Strings::) or `number-to-string' (*note String
     Conversion::).

   Here is an example of using `append':

     (setq trees '(pine oak))
          => (pine oak)
     (setq more-trees (append '(maple birch) trees))
          => (maple birch pine oak)

     trees
          => (pine oak)
     more-trees
          => (maple birch pine oak)
     (eq trees (cdr (cdr more-trees)))
          => t

   You can see how `append' works by looking at a box diagram.  The
variable `trees' is set to the list `(pine oak)' and then the variable
`more-trees' is set to the list `(maple birch pine oak)'.  However, the
variable `trees' continues to refer to the original list:

     more-trees                trees
     |                           |
     |     --- ---      --- ---   -> --- ---      --- ---
      --> |   |   |--> |   |   |--> |   |   |--> |   |   |--> nil
           --- ---      --- ---      --- ---      --- ---
            |            |            |            |
            |            |            |            |
             --> maple    -->birch     --> pine     --> oak

   An empty sequence contributes nothing to the value returned by
`append'.  As a consequence of this, a final `nil' argument forces a
copy of the previous argument:

     trees
          => (pine oak)
     (setq wood (append trees nil))
          => (pine oak)
     wood
          => (pine oak)
     (eq wood trees)
          => nil

This once was the usual way to copy a list, before the function
`copy-sequence' was invented.  *Note Sequences Arrays Vectors::.

   Here we show the use of vectors and strings as arguments to `append':

     (append [a b] "cd" nil)
          => (a b 99 100)

   With the help of `apply' (*note Calling Functions::), we can append
all the lists in a list of lists:

     (apply 'append '((a b c) nil (x y z) nil))
          => (a b c x y z)

   If no SEQUENCES are given, `nil' is returned:

     (append)
          => nil

   Here are some examples where the final argument is not a list:

     (append '(x y) 'z)
          => (x y . z)
     (append '(x y) [z])
          => (x y . [z])

The second example shows that when the final argument is a sequence but
not a list, the sequence's elements do not become elements of the
resulting list.  Instead, the sequence becomes the final CDR, like any
other non-list final argument.

 -- Function: reverse list
     This function creates a new list whose elements are the elements of
     LIST, but in reverse order.  The original argument LIST is _not_
     altered.

          (setq x '(1 2 3 4))
               => (1 2 3 4)
          (reverse x)
               => (4 3 2 1)
          x
               => (1 2 3 4)

 -- Function: copy-tree tree &optional vecp
     This function returns a copy of the tree `tree'.  If TREE is a
     cons cell, this makes a new cons cell with the same CAR and CDR,
     then recursively copies the CAR and CDR in the same way.

     Normally, when TREE is anything other than a cons cell,
     `copy-tree' simply returns TREE.  However, if VECP is non-`nil',
     it copies vectors too (and operates recursively on their elements).

 -- Function: number-sequence from &optional to separation
     This returns a list of numbers starting with FROM and incrementing
     by SEPARATION, and ending at or just before TO.  SEPARATION can be
     positive or negative and defaults to 1.  If TO is `nil' or
     numerically equal to FROM, the value is the one-element list
     `(FROM)'.  If TO is less than FROM with a positive SEPARATION, or
     greater than FROM with a negative SEPARATION, the value is `nil'
     because those arguments specify an empty sequence.

     If SEPARATION is 0 and TO is neither `nil' nor numerically equal
     to FROM, `number-sequence' signals an error, since those arguments
     specify an infinite sequence.

     All arguments can be integers or floating point numbers.  However,
     floating point arguments can be tricky, because floating point
     arithmetic is inexact.  For instance, depending on the machine, it
     may quite well happen that `(number-sequence 0.4 0.6 0.2)' returns
     the one element list `(0.4)', whereas `(number-sequence 0.4 0.8
     0.2)' returns a list with three elements.  The Nth element of the
     list is computed by the exact formula `(+ FROM (* N SEPARATION))'.
     Thus, if one wants to make sure that TO is included in the list,
     one can pass an expression of this exact type for TO.
     Alternatively, one can replace TO with a slightly larger value (or
     a slightly more negative value if SEPARATION is negative).

     Some examples:

          (number-sequence 4 9)
               => (4 5 6 7 8 9)
          (number-sequence 9 4 -1)
               => (9 8 7 6 5 4)
          (number-sequence 9 4 -2)
               => (9 7 5)
          (number-sequence 8)
               => (8)
          (number-sequence 8 5)
               => nil
          (number-sequence 5 8 -1)
               => nil
          (number-sequence 1.5 6 2)
               => (1.5 3.5 5.5)

   ---------- Footnotes ----------

   (1) There is no strictly equivalent way to add an element to the end
of a list.  You can use `(append LISTNAME (list NEWELT))', which
creates a whole new list by copying LISTNAME and adding NEWELT to its
end.  Or you can use `(nconc LISTNAME (list NEWELT))', which modifies
LISTNAME by following all the CDRs and then replacing the terminating
`nil'.  Compare this to adding an element to the beginning of a list
with `cons', which neither copies nor modifies the list.


File: elisp,  Node: List Variables,  Next: Modifying Lists,  Prev: Building Lists,  Up: Lists

5.5 Modifying List Variables
============================

These functions, and one macro, provide convenient ways to modify a
list which is stored in a variable.

 -- Macro: push newelt listname
     This macro provides an alternative way to write `(setq LISTNAME
     (cons NEWELT LISTNAME))'.

          (setq l '(a b))
               => (a b)
          (push 'c l)
               => (c a b)
          l
               => (c a b)

   Two functions modify lists that are the values of variables.

 -- Function: add-to-list symbol element &optional append compare-fn
     This function sets the variable SYMBOL by consing ELEMENT onto the
     old value, if ELEMENT is not already a member of that value.  It
     returns the resulting list, whether updated or not.  The value of
     SYMBOL had better be a list already before the call.
     `add-to-list' uses COMPARE-FN to compare ELEMENT against existing
     list members; if COMPARE-FN is `nil', it uses `equal'.

     Normally, if ELEMENT is added, it is added to the front of SYMBOL,
     but if the optional argument APPEND is non-`nil', it is added at
     the end.

     The argument SYMBOL is not implicitly quoted; `add-to-list' is an
     ordinary function, like `set' and unlike `setq'.  Quote the
     argument yourself if that is what you want.

   Here's a scenario showing how to use `add-to-list':

     (setq foo '(a b))
          => (a b)

     (add-to-list 'foo 'c)     ;; Add `c'.
          => (c a b)

     (add-to-list 'foo 'b)     ;; No effect.
          => (c a b)

     foo                       ;; `foo' was changed.
          => (c a b)

   An equivalent expression for `(add-to-list 'VAR VALUE)' is this:

     (or (member VALUE VAR)
         (setq VAR (cons VALUE VAR)))

 -- Function: add-to-ordered-list symbol element &optional order
     This function sets the variable SYMBOL by inserting ELEMENT into
     the old value, which must be a list, at the position specified by
     ORDER.  If ELEMENT is already a member of the list, its position
     in the list is adjusted according to ORDER.  Membership is tested
     using `eq'.  This function returns the resulting list, whether
     updated or not.

     The ORDER is typically a number (integer or float), and the
     elements of the list are sorted in non-decreasing numerical order.

     ORDER may also be omitted or `nil'.  Then the numeric order of
     ELEMENT stays unchanged if it already has one; otherwise, ELEMENT
     has no numeric order.  Elements without a numeric list order are
     placed at the end of the list, in no particular order.

     Any other value for ORDER removes the numeric order of ELEMENT if
     it already has one; otherwise, it is equivalent to `nil'.

     The argument SYMBOL is not implicitly quoted;
     `add-to-ordered-list' is an ordinary function, like `set' and
     unlike `setq'.  Quote the argument yourself if that is what you
     want.

     The ordering information is stored in a hash table on SYMBOL's
     `list-order' property.

   Here's a scenario showing how to use `add-to-ordered-list':

     (setq foo '())
          => nil

     (add-to-ordered-list 'foo 'a 1)     ;; Add `a'.
          => (a)

     (add-to-ordered-list 'foo 'c 3)     ;; Add `c'.
          => (a c)

     (add-to-ordered-list 'foo 'b 2)     ;; Add `b'.
          => (a b c)

     (add-to-ordered-list 'foo 'b 4)     ;; Move `b'.
          => (a c b)

     (add-to-ordered-list 'foo 'd)       ;; Append `d'.
          => (a c b d)

     (add-to-ordered-list 'foo 'e)       ;; Add `e'.
          => (a c b e d)

     foo                       ;; `foo' was changed.
          => (a c b e d)


File: elisp,  Node: Modifying Lists,  Next: Sets And Lists,  Prev: List Variables,  Up: Lists

5.6 Modifying Existing List Structure
=====================================

You can modify the CAR and CDR contents of a cons cell with the
primitives `setcar' and `setcdr'.  We call these "destructive"
operations because they change existing list structure.

     Common Lisp note: Common Lisp uses functions `rplaca' and `rplacd'
     to alter list structure; they change structure the same way as
     `setcar' and `setcdr', but the Common Lisp functions return the
     cons cell while `setcar' and `setcdr' return the new CAR or CDR.

* Menu:

* Setcar::          Replacing an element in a list.
* Setcdr::          Replacing part of the list backbone.
                      This can be used to remove or add elements.
* Rearrangement::   Reordering the elements in a list; combining lists.


File: elisp,  Node: Setcar,  Next: Setcdr,  Up: Modifying Lists

5.6.1 Altering List Elements with `setcar'
------------------------------------------

Changing the CAR of a cons cell is done with `setcar'.  When used on a
list, `setcar' replaces one element of a list with a different element.

 -- Function: setcar cons object
     This function stores OBJECT as the new CAR of CONS, replacing its
     previous CAR.  In other words, it changes the CAR slot of CONS to
     refer to OBJECT.  It returns the value OBJECT.  For example:

          (setq x '(1 2))
               => (1 2)
          (setcar x 4)
               => 4
          x
               => (4 2)

   When a cons cell is part of the shared structure of several lists,
storing a new CAR into the cons changes one element of each of these
lists.  Here is an example:

     ;; Create two lists that are partly shared.
     (setq x1 '(a b c))
          => (a b c)
     (setq x2 (cons 'z (cdr x1)))
          => (z b c)

     ;; Replace the CAR of a shared link.
     (setcar (cdr x1) 'foo)
          => foo
     x1                           ; Both lists are changed.
          => (a foo c)
     x2
          => (z foo c)

     ;; Replace the CAR of a link that is not shared.
     (setcar x1 'baz)
          => baz
     x1                           ; Only one list is changed.
          => (baz foo c)
     x2
          => (z foo c)

   Here is a graphical depiction of the shared structure of the two
lists in the variables `x1' and `x2', showing why replacing `b' changes
them both:

             --- ---        --- ---      --- ---
     x1---> |   |   |----> |   |   |--> |   |   |--> nil
             --- ---        --- ---      --- ---
              |        -->   |            |
              |       |      |            |
               --> a  |       --> b        --> c
                      |
            --- ---   |
     x2--> |   |   |--
            --- ---
             |
             |
              --> z

   Here is an alternative form of box diagram, showing the same
relationship:

     x1:
      --------------       --------------       --------------
     | car   | cdr  |     | car   | cdr  |     | car   | cdr  |
     |   a   |   o------->|   b   |   o------->|   c   |  nil |
     |       |      |  -->|       |      |     |       |      |
      --------------  |    --------------       --------------
                      |
     x2:              |
      --------------  |
     | car   | cdr  | |
     |   z   |   o----
     |       |      |
      --------------


File: elisp,  Node: Setcdr,  Next: Rearrangement,  Prev: Setcar,  Up: Modifying Lists

5.6.2 Altering the CDR of a List
--------------------------------

The lowest-level primitive for modifying a CDR is `setcdr':

 -- Function: setcdr cons object
     This function stores OBJECT as the new CDR of CONS, replacing its
     previous CDR.  In other words, it changes the CDR slot of CONS to
     refer to OBJECT.  It returns the value OBJECT.

   Here is an example of replacing the CDR of a list with a different
list.  All but the first element of the list are removed in favor of a
different sequence of elements.  The first element is unchanged,
because it resides in the CAR of the list, and is not reached via the
CDR.

     (setq x '(1 2 3))
          => (1 2 3)
     (setcdr x '(4))
          => (4)
     x
          => (1 4)

   You can delete elements from the middle of a list by altering the
CDRs of the cons cells in the list.  For example, here we delete the
second element, `b', from the list `(a b c)', by changing the CDR of
the first cons cell:

     (setq x1 '(a b c))
          => (a b c)
     (setcdr x1 (cdr (cdr x1)))
          => (c)
     x1
          => (a c)

   Here is the result in box notation:

                        --------------------
                       |                    |
      --------------   |   --------------   |    --------------
     | car   | cdr  |  |  | car   | cdr  |   -->| car   | cdr  |
     |   a   |   o-----   |   b   |   o-------->|   c   |  nil |
     |       |      |     |       |      |      |       |      |
      --------------       --------------        --------------

The second cons cell, which previously held the element `b', still
exists and its CAR is still `b', but it no longer forms part of this
list.

   It is equally easy to insert a new element by changing CDRs:

     (setq x1 '(a b c))
          => (a b c)
     (setcdr x1 (cons 'd (cdr x1)))
          => (d b c)
     x1
          => (a d b c)

   Here is this result in box notation:

      --------------        -------------       -------------
     | car  | cdr   |      | car  | cdr  |     | car  | cdr  |
     |   a  |   o   |   -->|   b  |   o------->|   c  |  nil |
     |      |   |   |  |   |      |      |     |      |      |
      --------- | --   |    -------------       -------------
                |      |
          -----         --------
         |                      |
         |    ---------------   |
         |   | car   | cdr   |  |
          -->|   d   |   o------
             |       |       |
              ---------------


File: elisp,  Node: Rearrangement,  Prev: Setcdr,  Up: Modifying Lists

5.6.3 Functions that Rearrange Lists
------------------------------------

Here are some functions that rearrange lists "destructively" by
modifying the CDRs of their component cons cells.  We call these
functions "destructive" because they chew up the original lists passed
to them as arguments, relinking their cons cells to form a new list that
is the returned value.

   See `delq', in *Note Sets And Lists::, for another function that
modifies cons cells.

 -- Function: nconc &rest lists
     This function returns a list containing all the elements of LISTS.
     Unlike `append' (*note Building Lists::), the LISTS are _not_
     copied.  Instead, the last CDR of each of the LISTS is changed to
     refer to the following list.  The last of the LISTS is not
     altered.  For example:

          (setq x '(1 2 3))
               => (1 2 3)
          (nconc x '(4 5))
               => (1 2 3 4 5)
          x
               => (1 2 3 4 5)

     Since the last argument of `nconc' is not itself modified, it is
     reasonable to use a constant list, such as `'(4 5)', as in the
     above example.  For the same reason, the last argument need not be
     a list:

          (setq x '(1 2 3))
               => (1 2 3)
          (nconc x 'z)
               => (1 2 3 . z)
          x
               => (1 2 3 . z)

     However, the other arguments (all but the last) must be lists.

     A common pitfall is to use a quoted constant list as a non-last
     argument to `nconc'.  If you do this, your program will change
     each time you run it!  Here is what happens:

          (defun add-foo (x)            ; We want this function to add
            (nconc '(foo) x))           ;   `foo' to the front of its arg.

          (symbol-function 'add-foo)
               => (lambda (x) (nconc (quote (foo)) x))

          (setq xx (add-foo '(1 2)))    ; It seems to work.
               => (foo 1 2)
          (setq xy (add-foo '(3 4)))    ; What happened?
               => (foo 1 2 3 4)
          (eq xx xy)
               => t

          (symbol-function 'add-foo)
               => (lambda (x) (nconc (quote (foo 1 2 3 4) x)))

 -- Function: nreverse list
     This function reverses the order of the elements of LIST.  Unlike
     `reverse', `nreverse' alters its argument by reversing the CDRs in
     the cons cells forming the list.  The cons cell that used to be
     the last one in LIST becomes the first cons cell of the value.

     For example:

          (setq x '(a b c))
               => (a b c)
          x
               => (a b c)
          (nreverse x)
               => (c b a)
          ;; The cons cell that was first is now last.
          x
               => (a)

     To avoid confusion, we usually store the result of `nreverse' back
     in the same variable which held the original list:

          (setq x (nreverse x))

     Here is the `nreverse' of our favorite example, `(a b c)',
     presented graphically:

          Original list head:                       Reversed list:
           -------------        -------------        ------------
          | car  | cdr  |      | car  | cdr  |      | car | cdr  |
          |   a  |  nil |<--   |   b  |   o  |<--   |   c |   o  |
          |      |      |   |  |      |   |  |   |  |     |   |  |
           -------------    |   --------- | -    |   -------- | -
                            |             |      |            |
                             -------------        ------------

 -- Function: sort list predicate
     This function sorts LIST stably, though destructively, and returns
     the sorted list.  It compares elements using PREDICATE.  A stable
     sort is one in which elements with equal sort keys maintain their
     relative order before and after the sort.  Stability is important
     when successive sorts are used to order elements according to
     different criteria.

     The argument PREDICATE must be a function that accepts two
     arguments.  It is called with two elements of LIST.  To get an
     increasing order sort, the PREDICATE should return non-`nil' if the
     first element is "less than" the second, or `nil' if not.

     The comparison function PREDICATE must give reliable results for
     any given pair of arguments, at least within a single call to
     `sort'.  It must be "antisymmetric"; that is, if A is less than B,
     B must not be less than A.  It must be "transitive"--that is, if A
     is less than B, and B is less than C, then A must be less than C.
     If you use a comparison function which does not meet these
     requirements, the result of `sort' is unpredictable.

     The destructive aspect of `sort' is that it rearranges the cons
     cells forming LIST by changing CDRs.  A nondestructive sort
     function would create new cons cells to store the elements in their
     sorted order.  If you wish to make a sorted copy without
     destroying the original, copy it first with `copy-sequence' and
     then sort.

     Sorting does not change the CARs of the cons cells in LIST; the
     cons cell that originally contained the element `a' in LIST still
     has `a' in its CAR after sorting, but it now appears in a
     different position in the list due to the change of CDRs.  For
     example:

          (setq nums '(1 3 2 6 5 4 0))
               => (1 3 2 6 5 4 0)
          (sort nums '<)
               => (0 1 2 3 4 5 6)
          nums
               => (1 2 3 4 5 6)

     *Warning*: Note that the list in `nums' no longer contains 0; this
     is the same cons cell that it was before, but it is no longer the
     first one in the list.  Don't assume a variable that formerly held
     the argument now holds the entire sorted list!  Instead, save the
     result of `sort' and use that.  Most often we store the result
     back into the variable that held the original list:

          (setq nums (sort nums '<))

     *Note Sorting::, for more functions that perform sorting.  See
     `documentation' in *Note Accessing Documentation::, for a useful
     example of `sort'.


File: elisp,  Node: Sets And Lists,  Next: Association Lists,  Prev: Modifying Lists,  Up: Lists

5.7 Using Lists as Sets
=======================

A list can represent an unordered mathematical set--simply consider a
value an element of a set if it appears in the list, and ignore the
order of the list.  To form the union of two sets, use `append' (as
long as you don't mind having duplicate elements).  You can remove
`equal' duplicates using `delete-dups'.  Other useful functions for
sets include `memq' and `delq', and their `equal' versions, `member'
and `delete'.

     Common Lisp note: Common Lisp has functions `union' (which avoids
     duplicate elements) and `intersection' for set operations, but GNU
     Emacs Lisp does not have them.  You can write them in Lisp if you
     wish.

 -- Function: memq object list
     This function tests to see whether OBJECT is a member of LIST.  If
     it is, `memq' returns a list starting with the first occurrence of
     OBJECT.  Otherwise, it returns `nil'.  The letter `q' in `memq'
     says that it uses `eq' to compare OBJECT against the elements of
     the list.  For example:

          (memq 'b '(a b c b a))
               => (b c b a)
          (memq '(2) '((1) (2)))    ; `(2)' and `(2)' are not `eq'.
               => nil

 -- Function: delq object list
     This function destructively removes all elements `eq' to OBJECT
     from LIST.  The letter `q' in `delq' says that it uses `eq' to
     compare OBJECT against the elements of the list, like `memq' and
     `remq'.

   When `delq' deletes elements from the front of the list, it does so
simply by advancing down the list and returning a sublist that starts
after those elements:

     (delq 'a '(a b c)) == (cdr '(a b c))

   When an element to be deleted appears in the middle of the list,
removing it involves changing the CDRs (*note Setcdr::).

     (setq sample-list '(a b c (4)))
          => (a b c (4))
     (delq 'a sample-list)
          => (b c (4))
     sample-list
          => (a b c (4))
     (delq 'c sample-list)
          => (a b (4))
     sample-list
          => (a b (4))

   Note that `(delq 'c sample-list)' modifies `sample-list' to splice
out the third element, but `(delq 'a sample-list)' does not splice
anything--it just returns a shorter list.  Don't assume that a variable
which formerly held the argument LIST now has fewer elements, or that
it still holds the original list!  Instead, save the result of `delq'
and use that.  Most often we store the result back into the variable
that held the original list:

     (setq flowers (delq 'rose flowers))

   In the following example, the `(4)' that `delq' attempts to match
and the `(4)' in the `sample-list' are not `eq':

     (delq '(4) sample-list)
          => (a c (4))

     If you want to delete elements that are `equal' to a given value,
     use `delete' (see below).

 -- Function: remq object list
     This function returns a copy of LIST, with all elements removed
     which are `eq' to OBJECT.  The letter `q' in `remq' says that it
     uses `eq' to compare OBJECT against the elements of `list'.

          (setq sample-list '(a b c a b c))
               => (a b c a b c)
          (remq 'a sample-list)
               => (b c b c)
          sample-list
               => (a b c a b c)

 -- Function: memql object list
     The function `memql' tests to see whether OBJECT is a member of
     LIST, comparing members with OBJECT using `eql', so floating point
     elements are compared by value.  If OBJECT is a member, `memql'
     returns a list starting with its first occurrence in LIST.
     Otherwise, it returns `nil'.

     Compare this with `memq':

          (memql 1.2 '(1.1 1.2 1.3))  ; `1.2' and `1.2' are `eql'.
               => (1.2 1.3)
          (memq 1.2 '(1.1 1.2 1.3))  ; `1.2' and `1.2' are not `eq'.
               => nil

   The following three functions are like `memq', `delq' and `remq',
but use `equal' rather than `eq' to compare elements.  *Note Equality
Predicates::.

 -- Function: member object list
     The function `member' tests to see whether OBJECT is a member of
     LIST, comparing members with OBJECT using `equal'.  If OBJECT is a
     member, `member' returns a list starting with its first occurrence
     in LIST.  Otherwise, it returns `nil'.

     Compare this with `memq':

          (member '(2) '((1) (2)))  ; `(2)' and `(2)' are `equal'.
               => ((2))
          (memq '(2) '((1) (2)))    ; `(2)' and `(2)' are not `eq'.
               => nil
          ;; Two strings with the same contents are `equal'.
          (member "foo" '("foo" "bar"))
               => ("foo" "bar")

 -- Function: delete object sequence
     If `sequence' is a list, this function destructively removes all
     elements `equal' to OBJECT from SEQUENCE.  For lists, `delete' is
     to `delq' as `member' is to `memq': it uses `equal' to compare
     elements with OBJECT, like `member'; when it finds an element that
     matches, it cuts the element out just as `delq' would.

     If `sequence' is a vector or string, `delete' returns a copy of
     `sequence' with all elements `equal' to `object' removed.

     For example:

          (setq l '((2) (1) (2)))
          (delete '(2) l)
               => ((1))
          l
               => ((2) (1))
          ;; If you want to change `l' reliably,
          ;; write `(setq l (delete elt l))'.
          (setq l '((2) (1) (2)))
          (delete '(1) l)
               => ((2) (2))
          l
               => ((2) (2))
          ;; In this case, it makes no difference whether you set `l',
          ;; but you should do so for the sake of the other case.
          (delete '(2) [(2) (1) (2)])
               => [(1)]

 -- Function: remove object sequence
     This function is the non-destructive counterpart of `delete'.  It
     returns a copy of `sequence', a list, vector, or string, with
     elements `equal' to `object' removed.  For example:

          (remove '(2) '((2) (1) (2)))
               => ((1))
          (remove '(2) [(2) (1) (2)])
               => [(1)]

     Common Lisp note: The functions `member', `delete' and `remove' in
     GNU Emacs Lisp are derived from Maclisp, not Common Lisp.  The
     Common Lisp versions do not use `equal' to compare elements.

 -- Function: member-ignore-case object list
     This function is like `member', except that OBJECT should be a
     string and that it ignores differences in letter-case and text
     representation: upper-case and lower-case letters are treated as
     equal, and unibyte strings are converted to multibyte prior to
     comparison.

 -- Function: delete-dups list
     This function destructively removes all `equal' duplicates from
     LIST, stores the result in LIST and returns it.  Of several
     `equal' occurrences of an element in LIST, `delete-dups' keeps the
     first one.

   See also the function `add-to-list', in *Note List Variables::, for
a way to add an element to a list stored in a variable and used as a
set.


File: elisp,  Node: Association Lists,  Next: Rings,  Prev: Sets And Lists,  Up: Lists

5.8 Association Lists
=====================

An "association list", or "alist" for short, records a mapping from
keys to values.  It is a list of cons cells called "associations": the
CAR of each cons cell is the "key", and the CDR is the "associated
value".(1)

   Here is an example of an alist.  The key `pine' is associated with
the value `cones'; the key `oak' is associated with `acorns'; and the
key `maple' is associated with `seeds'.

     ((pine . cones)
      (oak . acorns)
      (maple . seeds))

   Both the values and the keys in an alist may be any Lisp objects.
For example, in the following alist, the symbol `a' is associated with
the number `1', and the string `"b"' is associated with the _list_ `(2
3)', which is the CDR of the alist element:

     ((a . 1) ("b" 2 3))

   Sometimes it is better to design an alist to store the associated
value in the CAR of the CDR of the element.  Here is an example of such
an alist:

     ((rose red) (lily white) (buttercup yellow))

Here we regard `red' as the value associated with `rose'.  One
advantage of this kind of alist is that you can store other related
information--even a list of other items--in the CDR of the CDR.  One
disadvantage is that you cannot use `rassq' (see below) to find the
element containing a given value.  When neither of these considerations
is important, the choice is a matter of taste, as long as you are
consistent about it for any given alist.

   The same alist shown above could be regarded as having the
associated value in the CDR of the element; the value associated with
`rose' would be the list `(red)'.

   Association lists are often used to record information that you might
otherwise keep on a stack, since new associations may be added easily to
the front of the list.  When searching an association list for an
association with a given key, the first one found is returned, if there
is more than one.

   In Emacs Lisp, it is _not_ an error if an element of an association
list is not a cons cell.  The alist search functions simply ignore such
elements.  Many other versions of Lisp signal errors in such cases.

   Note that property lists are similar to association lists in several
respects.  A property list behaves like an association list in which
each key can occur only once.  *Note Property Lists::, for a comparison
of property lists and association lists.

 -- Function: assoc key alist
     This function returns the first association for KEY in ALIST,
     comparing KEY against the alist elements using `equal' (*note
     Equality Predicates::).  It returns `nil' if no association in
     ALIST has a CAR `equal' to KEY.  For example:

          (setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
               => ((pine . cones) (oak . acorns) (maple . seeds))
          (assoc 'oak trees)
               => (oak . acorns)
          (cdr (assoc 'oak trees))
               => acorns
          (assoc 'birch trees)
               => nil

     Here is another example, in which the keys and values are not
     symbols:

          (setq needles-per-cluster
                '((2 "Austrian Pine" "Red Pine")
                  (3 "Pitch Pine")
                  (5 "White Pine")))

          (cdr (assoc 3 needles-per-cluster))
               => ("Pitch Pine")
          (cdr (assoc 2 needles-per-cluster))
               => ("Austrian Pine" "Red Pine")

   The function `assoc-string' is much like `assoc' except that it
ignores certain differences between strings.  *Note Text Comparison::.

 -- Function: rassoc value alist
     This function returns the first association with value VALUE in
     ALIST.  It returns `nil' if no association in ALIST has a CDR
     `equal' to VALUE.

     `rassoc' is like `assoc' except that it compares the CDR of each
     ALIST association instead of the CAR.  You can think of this as
     "reverse `assoc'," finding the key for a given value.

 -- Function: assq key alist
     This function is like `assoc' in that it returns the first
     association for KEY in ALIST, but it makes the comparison using
     `eq' instead of `equal'.  `assq' returns `nil' if no association
     in ALIST has a CAR `eq' to KEY.  This function is used more often
     than `assoc', since `eq' is faster than `equal' and most alists
     use symbols as keys.  *Note Equality Predicates::.

          (setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
               => ((pine . cones) (oak . acorns) (maple . seeds))
          (assq 'pine trees)
               => (pine . cones)

     On the other hand, `assq' is not usually useful in alists where the
     keys may not be symbols:

          (setq leaves
                '(("simple leaves" . oak)
                  ("compound leaves" . horsechestnut)))

          (assq "simple leaves" leaves)
               => nil
          (assoc "simple leaves" leaves)
               => ("simple leaves" . oak)

 -- Function: rassq value alist
     This function returns the first association with value VALUE in
     ALIST.  It returns `nil' if no association in ALIST has a CDR `eq'
     to VALUE.

     `rassq' is like `assq' except that it compares the CDR of each
     ALIST association instead of the CAR.  You can think of this as
     "reverse `assq'," finding the key for a given value.

     For example:

          (setq trees '((pine . cones) (oak . acorns) (maple . seeds)))

          (rassq 'acorns trees)
               => (oak . acorns)
          (rassq 'spores trees)
               => nil

     `rassq' cannot search for a value stored in the CAR of the CDR of
     an element:

          (setq colors '((rose red) (lily white) (buttercup yellow)))

          (rassq 'white colors)
               => nil

     In this case, the CDR of the association `(lily white)' is not the
     symbol `white', but rather the list `(white)'.  This becomes
     clearer if the association is written in dotted pair notation:

          (lily white) == (lily . (white))

 -- Function: assoc-default key alist &optional test default
     This function searches ALIST for a match for KEY.  For each
     element of ALIST, it compares the element (if it is an atom) or
     the element's CAR (if it is a cons) against KEY, by calling TEST
     with two arguments: the element or its CAR, and KEY.  The
     arguments are passed in that order so that you can get useful
     results using `string-match' with an alist that contains regular
     expressions (*note Regexp Search::).  If TEST is omitted or `nil',
     `equal' is used for comparison.

     If an alist element matches KEY by this criterion, then
     `assoc-default' returns a value based on this element.  If the
     element is a cons, then the value is the element's CDR.
     Otherwise, the return value is DEFAULT.

     If no alist element matches KEY, `assoc-default' returns `nil'.

 -- Function: copy-alist alist
     This function returns a two-level deep copy of ALIST: it creates a
     new copy of each association, so that you can alter the
     associations of the new alist without changing the old one.

          (setq needles-per-cluster
                '((2 . ("Austrian Pine" "Red Pine"))
                  (3 . ("Pitch Pine"))
                  (5 . ("White Pine"))))
          =>
          ((2 "Austrian Pine" "Red Pine")
           (3 "Pitch Pine")
           (5 "White Pine"))

          (setq copy (copy-alist needles-per-cluster))
          =>
          ((2 "Austrian Pine" "Red Pine")
           (3 "Pitch Pine")
           (5 "White Pine"))

          (eq needles-per-cluster copy)
               => nil
          (equal needles-per-cluster copy)
               => t
          (eq (car needles-per-cluster) (car copy))
               => nil
          (cdr (car (cdr needles-per-cluster)))
               => ("Pitch Pine")
          (eq (cdr (car (cdr needles-per-cluster)))
              (cdr (car (cdr copy))))
               => t

     This example shows how `copy-alist' makes it possible to change
     the associations of one copy without affecting the other:

          (setcdr (assq 3 copy) '("Martian Vacuum Pine"))
          (cdr (assq 3 needles-per-cluster))
               => ("Pitch Pine")

 -- Function: assq-delete-all key alist
     This function deletes from ALIST all the elements whose CAR is
     `eq' to KEY, much as if you used `delq' to delete each such
     element one by one.  It returns the shortened alist, and often
     modifies the original list structure of ALIST.  For correct
     results, use the return value of `assq-delete-all' rather than
     looking at the saved value of ALIST.

          (setq alist '((foo 1) (bar 2) (foo 3) (lose 4)))
               => ((foo 1) (bar 2) (foo 3) (lose 4))
          (assq-delete-all 'foo alist)
               => ((bar 2) (lose 4))
          alist
               => ((foo 1) (bar 2) (lose 4))

 -- Function: rassq-delete-all value alist
     This function deletes from ALIST all the elements whose CDR is
     `eq' to VALUE.  It returns the shortened alist, and often modifies
     the original list structure of ALIST.  `rassq-delete-all' is like
     `assq-delete-all' except that it compares the CDR of each ALIST
     association instead of the CAR.

   ---------- Footnotes ----------

   (1) This usage of "key" is not related to the term "key sequence";
it means a value used to look up an item in a table.  In this case, the
table is the alist, and the alist associations are the items.


File: elisp,  Node: Rings,  Prev: Association Lists,  Up: Lists

5.9 Managing a Fixed-Size Ring of Objects
=========================================

This section describes functions for operating on rings.  A "ring" is a
fixed-size data structure that supports insertion, deletion, rotation,
and modulo-indexed reference and traversal.

 -- Function: make-ring size
     This returns a new ring capable of holding SIZE objects.  SIZE
     should be an integer.

 -- Function: ring-p object
     This returns `t' if OBJECT is a ring, `nil' otherwise.

 -- Function: ring-size ring
     This returns the maximum capacity of the RING.

 -- Function: ring-length ring
     This returns the number of objects that RING currently contains.
     The value will never exceed that returned by `ring-size'.

 -- Function: ring-elements ring
     This returns a list of the objects in RING, in order, newest first.

 -- Function: ring-copy ring
     This returns a new ring which is a copy of RING.  The new ring
     contains the same (`eq') objects as RING.

 -- Function: ring-empty-p ring
     This returns `t' if RING is empty, `nil' otherwise.

   The newest element in the ring always has index 0.  Higher indices
correspond to older elements.  Indices are computed modulo the ring
length.  Index -1 corresponds to the oldest element, -2 to the
next-oldest, and so forth.

 -- Function: ring-ref ring index
     This returns the object in RING found at index INDEX.  INDEX may
     be negative or greater than the ring length.  If RING is empty,
     `ring-ref' signals an error.

 -- Function: ring-insert ring object
     This inserts OBJECT into RING, making it the newest element, and
     returns OBJECT.

     If the ring is full, insertion removes the oldest element to make
     room for the new element.

 -- Function: ring-remove ring &optional index
     Remove an object from RING, and return that object.  The argument
     INDEX specifies which item to remove; if it is `nil', that means
     to remove the oldest item.  If RING is empty, `ring-remove'
     signals an error.

 -- Function: ring-insert-at-beginning ring object
     This inserts OBJECT into RING, treating it as the oldest element.
     The return value is not significant.

     If the ring is full, this function removes the newest element to
     make room for the inserted element.

   If you are careful not to exceed the ring size, you can use the ring
as a first-in-first-out queue.  For example:

     (let ((fifo (make-ring 5)))
       (mapc (lambda (obj) (ring-insert fifo obj))
             '(0 one "two"))
       (list (ring-remove fifo) t
             (ring-remove fifo) t
             (ring-remove fifo)))
          => (0 t one t "two")


File: elisp,  Node: Sequences Arrays Vectors,  Next: Hash Tables,  Prev: Lists,  Up: Top

6 Sequences, Arrays, and Vectors
********************************

Recall that the "sequence" type is the union of two other Lisp types:
lists and arrays.  In other words, any list is a sequence, and any
array is a sequence.  The common property that all sequences have is
that each is an ordered collection of elements.

   An "array" is a single primitive object that has a slot for each of
its elements.  All the elements are accessible in constant time, but
the length of an existing array cannot be changed.  Strings, vectors,
char-tables and bool-vectors are the four types of arrays.

   A list is a sequence of elements, but it is not a single primitive
object; it is made of cons cells, one cell per element.  Finding the
Nth element requires looking through N cons cells, so elements farther
from the beginning of the list take longer to access.  But it is
possible to add elements to the list, or remove elements.

   The following diagram shows the relationship between these types:

               _____________________________________________
              |                                             |
              |          Sequence                           |
              |  ______   ________________________________  |
              | |      | |                                | |
              | | List | |             Array              | |
              | |      | |    ________       ________     | |
              | |______| |   |        |     |        |    | |
              |          |   | Vector |     | String |    | |
              |          |   |________|     |________|    | |
              |          |  ____________   _____________  | |
              |          | |            | |             | | |
              |          | | Char-table | | Bool-vector | | |
              |          | |____________| |_____________| | |
              |          |________________________________| |
              |_____________________________________________|

   The elements of vectors and lists may be any Lisp objects.  The
elements of strings are all characters.

* Menu:

* Sequence Functions::    Functions that accept any kind of sequence.
* Arrays::                Characteristics of arrays in Emacs Lisp.
* Array Functions::       Functions specifically for arrays.
* Vectors::               Special characteristics of Emacs Lisp vectors.
* Vector Functions::      Functions specifically for vectors.
* Char-Tables::           How to work with char-tables.
* Bool-Vectors::          How to work with bool-vectors.


File: elisp,  Node: Sequence Functions,  Next: Arrays,  Up: Sequences Arrays Vectors

6.1 Sequences
=============

In Emacs Lisp, a "sequence" is either a list or an array.  The common
property of all sequences is that they are ordered collections of
elements.  This section describes functions that accept any kind of
sequence.

 -- Function: sequencep object
     Returns `t' if OBJECT is a list, vector, string, bool-vector, or
     char-table, `nil' otherwise.

 -- Function: length sequence
     This function returns the number of elements in SEQUENCE.  If
     SEQUENCE is a dotted list, a `wrong-type-argument' error is
     signaled.  Circular lists may cause an infinite loop.  For a
     char-table, the value returned is always one more than the maximum
     Emacs character code.

     *Note Definition of safe-length::, for the related function
     `safe-length'.

          (length '(1 2 3))
              => 3
          (length ())
              => 0
          (length "foobar")
              => 6
          (length [1 2 3])
              => 3
          (length (make-bool-vector 5 nil))
              => 5

See also `string-bytes', in *Note Text Representations::.

 -- Function: elt sequence index
     This function returns the element of SEQUENCE indexed by INDEX.
     Legitimate values of INDEX are integers ranging from 0 up to one
     less than the length of SEQUENCE.  If SEQUENCE is a list,
     out-of-range values behave as for `nth'.  *Note Definition of
     nth::.  Otherwise, out-of-range values trigger an
     `args-out-of-range' error.

          (elt [1 2 3 4] 2)
               => 3
          (elt '(1 2 3 4) 2)
               => 3
          ;; We use `string' to show clearly which character `elt' returns.
          (string (elt "1234" 2))
               => "3"
          (elt [1 2 3 4] 4)
               error--> Args out of range: [1 2 3 4], 4
          (elt [1 2 3 4] -1)
               error--> Args out of range: [1 2 3 4], -1

     This function generalizes `aref' (*note Array Functions::) and
     `nth' (*note Definition of nth::).

 -- Function: copy-sequence sequence
     Returns a copy of SEQUENCE.  The copy is the same type of object
     as the original sequence, and it has the same elements in the same
     order.

     Storing a new element into the copy does not affect the original
     SEQUENCE, and vice versa.  However, the elements of the new
     sequence are not copies; they are identical (`eq') to the elements
     of the original.  Therefore, changes made within these elements, as
     found via the copied sequence, are also visible in the original
     sequence.

     If the sequence is a string with text properties, the property
     list in the copy is itself a copy, not shared with the original's
     property list.  However, the actual values of the properties are
     shared.  *Note Text Properties::.

     This function does not work for dotted lists.  Trying to copy a
     circular list may cause an infinite loop.

     See also `append' in *Note Building Lists::, `concat' in *Note
     Creating Strings::, and `vconcat' in *Note Vector Functions::, for
     other ways to copy sequences.

          (setq bar '(1 2))
               => (1 2)
          (setq x (vector 'foo bar))
               => [foo (1 2)]
          (setq y (copy-sequence x))
               => [foo (1 2)]

          (eq x y)
               => nil
          (equal x y)
               => t
          (eq (elt x 1) (elt y 1))
               => t

          ;; Replacing an element of one sequence.
          (aset x 0 'quux)
          x => [quux (1 2)]
          y => [foo (1 2)]

          ;; Modifying the inside of a shared element.
          (setcar (aref x 1) 69)
          x => [quux (69 2)]
          y => [foo (69 2)]


File: elisp,  Node: Arrays,  Next: Array Functions,  Prev: Sequence Functions,  Up: Sequences Arrays Vectors

6.2 Arrays
==========

An "array" object has slots that hold a number of other Lisp objects,
called the elements of the array.  Any element of an array may be
accessed in constant time.  In contrast, an element of a list requires
access time that is proportional to the position of the element in the
list.

   Emacs defines four types of array, all one-dimensional: "strings",
"vectors", "bool-vectors" and "char-tables".  A vector is a general
array; its elements can be any Lisp objects.  A string is a specialized
array; its elements must be characters.  Each type of array has its own
read syntax.  *Note String Type::, and *Note Vector Type::.

   All four kinds of array share these characteristics:

   * The first element of an array has index zero, the second element
     has index 1, and so on.  This is called "zero-origin" indexing.
     For example, an array of four elements has indices 0, 1, 2, and 3.

   * The length of the array is fixed once you create it; you cannot
     change the length of an existing array.

   * For purposes of evaluation, the array is a constant--in other
     words, it evaluates to itself.

   * The elements of an array may be referenced or changed with the
     functions `aref' and `aset', respectively (*note Array
     Functions::).

   When you create an array, other than a char-table, you must specify
its length.  You cannot specify the length of a char-table, because that
is determined by the range of character codes.

   In principle, if you want an array of text characters, you could use
either a string or a vector.  In practice, we always choose strings for
such applications, for four reasons:

   * They occupy one-fourth the space of a vector of the same elements.

   * Strings are printed in a way that shows the contents more clearly
     as text.

   * Strings can hold text properties.  *Note Text Properties::.

   * Many of the specialized editing and I/O facilities of Emacs accept
     only strings.  For example, you cannot insert a vector of
     characters into a buffer the way you can insert a string.  *Note
     Strings and Characters::.

   By contrast, for an array of keyboard input characters (such as a key
sequence), a vector may be necessary, because many keyboard input
characters are outside the range that will fit in a string.  *Note Key
Sequence Input::.


File: elisp,  Node: Array Functions,  Next: Vectors,  Prev: Arrays,  Up: Sequences Arrays Vectors

6.3 Functions that Operate on Arrays
====================================

In this section, we describe the functions that accept all types of
arrays.

 -- Function: arrayp object
     This function returns `t' if OBJECT is an array (i.e., a vector, a
     string, a bool-vector or a char-table).

          (arrayp [a])
               => t
          (arrayp "asdf")
               => t
          (arrayp (syntax-table))    ;; A char-table.
               => t

 -- Function: aref array index
     This function returns the INDEXth element of ARRAY.  The first
     element is at index zero.

          (setq primes [2 3 5 7 11 13])
               => [2 3 5 7 11 13]
          (aref primes 4)
               => 11
          (aref "abcdefg" 1)
               => 98           ; `b' is ASCII code 98.

     See also the function `elt', in *Note Sequence Functions::.

 -- Function: aset array index object
     This function sets the INDEXth element of ARRAY to be OBJECT.  It
     returns OBJECT.

          (setq w [foo bar baz])
               => [foo bar baz]
          (aset w 0 'fu)
               => fu
          w
               => [fu bar baz]

          (setq x "asdfasfd")
               => "asdfasfd"
          (aset x 3 ?Z)
               => 90
          x
               => "asdZasfd"

     If ARRAY is a string and OBJECT is not a character, a
     `wrong-type-argument' error results.  The function converts a
     unibyte string to multibyte if necessary to insert a character.

 -- Function: fillarray array object
     This function fills the array ARRAY with OBJECT, so that each
     element of ARRAY is OBJECT.  It returns ARRAY.

          (setq a [a b c d e f g])
               => [a b c d e f g]
          (fillarray a 0)
               => [0 0 0 0 0 0 0]
          a
               => [0 0 0 0 0 0 0]
          (setq s "When in the course")
               => "When in the course"
          (fillarray s ?-)
               => "------------------"

     If ARRAY is a string and OBJECT is not a character, a
     `wrong-type-argument' error results.

   The general sequence functions `copy-sequence' and `length' are
often useful for objects known to be arrays.  *Note Sequence
Functions::.


File: elisp,  Node: Vectors,  Next: Vector Functions,  Prev: Array Functions,  Up: Sequences Arrays Vectors

6.4 Vectors
===========

Arrays in Lisp, like arrays in most languages, are blocks of memory
whose elements can be accessed in constant time.  A "vector" is a
general-purpose array of specified length; its elements can be any Lisp
objects.  (By contrast, a string can hold only characters as elements.)
Vectors in Emacs are used for obarrays (vectors of symbols), and as part
of keymaps (vectors of commands).  They are also used internally as part
of the representation of a byte-compiled function; if you print such a
function, you will see a vector in it.

   In Emacs Lisp, the indices of the elements of a vector start from
zero and count up from there.

   Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols `a', `b' and `a' is
printed as `[a b a]'.  You can write vectors in the same way in Lisp
input.

   A vector, like a string or a number, is considered a constant for
evaluation: the result of evaluating it is the same vector.  This does
not evaluate or even examine the elements of the vector.  *Note
Self-Evaluating Forms::.

   Here are examples illustrating these principles:

     (setq avector [1 two '(three) "four" [five]])
          => [1 two (quote (three)) "four" [five]]
     (eval avector)
          => [1 two (quote (three)) "four" [five]]
     (eq avector (eval avector))
          => t


File: elisp,  Node: Vector Functions,  Next: Char-Tables,  Prev: Vectors,  Up: Sequences Arrays Vectors

6.5 Functions for Vectors
=========================

Here are some functions that relate to vectors:

 -- Function: vectorp object
     This function returns `t' if OBJECT is a vector.

          (vectorp [a])
               => t
          (vectorp "asdf")
               => nil

 -- Function: vector &rest objects
     This function creates and returns a vector whose elements are the
     arguments, OBJECTS.

          (vector 'foo 23 [bar baz] "rats")
               => [foo 23 [bar baz] "rats"]
          (vector)
               => []

 -- Function: make-vector length object
     This function returns a new vector consisting of LENGTH elements,
     each initialized to OBJECT.

          (setq sleepy (make-vector 9 'Z))
               => [Z Z Z Z Z Z Z Z Z]

 -- Function: vconcat &rest sequences
     This function returns a new vector containing all the elements of
     the SEQUENCES.  The arguments SEQUENCES may be true lists,
     vectors, strings or bool-vectors.  If no SEQUENCES are given, an
     empty vector is returned.

     The value is a newly constructed vector that is not `eq' to any
     existing vector.

          (setq a (vconcat '(A B C) '(D E F)))
               => [A B C D E F]
          (eq a (vconcat a))
               => nil
          (vconcat)
               => []
          (vconcat [A B C] "aa" '(foo (6 7)))
               => [A B C 97 97 foo (6 7)]

     The `vconcat' function also allows byte-code function objects as
     arguments.  This is a special feature to make it easy to access
     the entire contents of a byte-code function object.  *Note
     Byte-Code Objects::.

     In Emacs versions before 21, the `vconcat' function allowed
     integers as arguments, converting them to strings of digits, but
     that feature has been eliminated.  The proper way to convert an
     integer to a decimal number in this way is with `format' (*note
     Formatting Strings::) or `number-to-string' (*note String
     Conversion::).

     For other concatenation functions, see `mapconcat' in *Note
     Mapping Functions::, `concat' in *Note Creating Strings::, and
     `append' in *Note Building Lists::.

   The `append' function also provides a way to convert a vector into a
list with the same elements:

     (setq avector [1 two (quote (three)) "four" [five]])
          => [1 two (quote (three)) "four" [five]]
     (append avector nil)
          => (1 two (quote (three)) "four" [five])


File: elisp,  Node: Char-Tables,  Next: Bool-Vectors,  Prev: Vector Functions,  Up: Sequences Arrays Vectors

6.6 Char-Tables
===============

A char-table is much like a vector, except that it is indexed by
character codes.  Any valid character code, without modifiers, can be
used as an index in a char-table.  You can access a char-table's
elements with `aref' and `aset', as with any array.  In addition, a
char-table can have "extra slots" to hold additional data not
associated with particular character codes.  Char-tables are constants
when evaluated.

   Each char-table has a "subtype" which is a symbol.  The subtype has
two purposes: to distinguish char-tables meant for different uses, and
to control the number of extra slots.  For example, display tables are
char-tables with `display-table' as the subtype, and syntax tables are
char-tables with `syntax-table' as the subtype.  A valid subtype must
have a `char-table-extra-slots' property which is an integer between 0
and 10.  This integer specifies the number of "extra slots" in the
char-table.

   A char-table can have a "parent", which is another char-table.  If
it does, then whenever the char-table specifies `nil' for a particular
character C, it inherits the value specified in the parent.  In other
words, `(aref CHAR-TABLE C)' returns the value from the parent of
CHAR-TABLE if CHAR-TABLE itself specifies `nil'.

   A char-table can also have a "default value".  If so, then `(aref
CHAR-TABLE C)' returns the default value whenever the char-table does
not specify any other non-`nil' value.

 -- Function: make-char-table subtype &optional init
     Return a newly created char-table, with subtype SUBTYPE.  Each
     element is initialized to INIT, which defaults to `nil'.  You
     cannot alter the subtype of a char-table after the char-table is
     created.

     There is no argument to specify the length of the char-table,
     because all char-tables have room for any valid character code as
     an index.

 -- Function: char-table-p object
     This function returns `t' if OBJECT is a char-table, otherwise
     `nil'.

 -- Function: char-table-subtype char-table
     This function returns the subtype symbol of CHAR-TABLE.

 -- Function: set-char-table-default char-table char new-default
     This function sets the default value of generic character CHAR in
     CHAR-TABLE to NEW-DEFAULT.

     There is no special function to access default values in a
     char-table.  To do that, use `char-table-range' (see below).

 -- Function: char-table-parent char-table
     This function returns the parent of CHAR-TABLE.  The parent is
     always either `nil' or another char-table.

 -- Function: set-char-table-parent char-table new-parent
     This function sets the parent of CHAR-TABLE to NEW-PARENT.

 -- Function: char-table-extra-slot char-table n
     This function returns the contents of extra slot N of CHAR-TABLE.
     The number of extra slots in a char-table is determined by its
     subtype.

 -- Function: set-char-table-extra-slot char-table n value
     This function stores VALUE in extra slot N of CHAR-TABLE.

   A char-table can specify an element value for a single character
code; it can also specify a value for an entire character set.

 -- Function: char-table-range char-table range
     This returns the value specified in CHAR-TABLE for a range of
     characters RANGE.  Here are the possibilities for RANGE:

    `nil'
          Refers to the default value.

    CHAR
          Refers to the element for character CHAR (supposing CHAR is a
          valid character code).

    CHARSET
          Refers to the value specified for the whole character set
          CHARSET (*note Character Sets::).

    GENERIC-CHAR
          A generic character stands for a character set, or a row of a
          character set; specifying the generic character as argument is
          equivalent to specifying the character set name.  *Note
          Splitting Characters::, for a description of generic
          characters.

 -- Function: set-char-table-range char-table range value
     This function sets the value in CHAR-TABLE for a range of
     characters RANGE.  Here are the possibilities for RANGE:

    `nil'
          Refers to the default value.

    `t'
          Refers to the whole range of character codes.

    CHAR
          Refers to the element for character CHAR (supposing CHAR is a
          valid character code).

    CHARSET
          Refers to the value specified for the whole character set
          CHARSET (*note Character Sets::).

    GENERIC-CHAR
          A generic character stands for a character set; specifying
          the generic character as argument is equivalent to specifying
          the character set name.  *Note Splitting Characters::, for a
          description of generic characters.

 -- Function: map-char-table function char-table
     This function calls FUNCTION for each element of CHAR-TABLE.
     FUNCTION is called with two arguments, a key and a value.  The key
     is a possible RANGE argument for `char-table-range'--either a
     valid character or a generic character--and the value is
     `(char-table-range CHAR-TABLE KEY)'.

     Overall, the key-value pairs passed to FUNCTION describe all the
     values stored in CHAR-TABLE.

     The return value is always `nil'; to make this function useful,
     FUNCTION should have side effects.  For example, here is how to
     examine each element of the syntax table:

          (let (accumulator)
            (map-char-table
             #'(lambda (key value)
                 (setq accumulator
                       (cons (list key value) accumulator)))
             (syntax-table))
            accumulator)
          =>
          ((475008 nil) (474880 nil) (474752 nil) (474624 nil)
           ... (5 (3)) (4 (3)) (3 (3)) (2 (3)) (1 (3)) (0 (3)))


File: elisp,  Node: Bool-Vectors,  Prev: Char-Tables,  Up: Sequences Arrays Vectors

6.7 Bool-vectors
================

A bool-vector is much like a vector, except that it stores only the
values `t' and `nil'.  If you try to store any non-`nil' value into an
element of the bool-vector, the effect is to store `t' there.  As with
all arrays, bool-vector indices start from 0, and the length cannot be
changed once the bool-vector is created.  Bool-vectors are constants
when evaluated.

   There are two special functions for working with bool-vectors; aside
from that, you manipulate them with same functions used for other kinds
of arrays.

 -- Function: make-bool-vector length initial
     Return a new bool-vector of LENGTH elements, each one initialized
     to INITIAL.

 -- Function: bool-vector-p object
     This returns `t' if OBJECT is a bool-vector, and `nil' otherwise.

   Here is an example of creating, examining, and updating a
bool-vector.  Note that the printed form represents up to 8 boolean
values as a single character.

     (setq bv (make-bool-vector 5 t))
          => #&5"^_"
     (aref bv 1)
          => t
     (aset bv 3 nil)
          => nil
     bv
          => #&5"^W"

These results make sense because the binary codes for control-_ and
control-W are 11111 and 10111, respectively.


File: elisp,  Node: Hash Tables,  Next: Symbols,  Prev: Sequences Arrays Vectors,  Up: Top

7 Hash Tables
*************

A hash table is a very fast kind of lookup table, somewhat like an
alist (*note Association Lists::) in that it maps keys to corresponding
values.  It differs from an alist in these ways:

   * Lookup in a hash table is extremely fast for large tables--in
     fact, the time required is essentially _independent_ of how many
     elements are stored in the table.  For smaller tables (a few tens
     of elements) alists may still be faster because hash tables have a
     more-or-less constant overhead.

   * The correspondences in a hash table are in no particular order.

   * There is no way to share structure between two hash tables, the
     way two alists can share a common tail.

   Emacs Lisp provides a general-purpose hash table data type, along
with a series of functions for operating on them.  Hash tables have no
read syntax, and print in hash notation, like this:

     (make-hash-table)
          => #<hash-table 'eql nil 0/65 0x83af980>

(The term "hash notation" refers to the initial `#' character--*note
Printed Representation::--and has nothing to do with the term "hash
table.")

   Obarrays are also a kind of hash table, but they are a different type
of object and are used only for recording interned symbols (*note
Creating Symbols::).

* Menu:

* Creating Hash::       Functions to create hash tables.
* Hash Access::         Reading and writing the hash table contents.
* Defining Hash::       Defining new comparison methods
* Other Hash::          Miscellaneous.


File: elisp,  Node: Creating Hash,  Next: Hash Access,  Up: Hash Tables

7.1 Creating Hash Tables
========================

The principal function for creating a hash table is `make-hash-table'.

 -- Function: make-hash-table &rest keyword-args
     This function creates a new hash table according to the specified
     arguments.  The arguments should consist of alternating keywords
     (particular symbols recognized specially) and values corresponding
     to them.

     Several keywords make sense in `make-hash-table', but the only two
     that you really need to know about are `:test' and `:weakness'.

    `:test TEST'
          This specifies the method of key lookup for this hash table.
          The default is `eql'; `eq' and `equal' are other alternatives:

         `eql'
               Keys which are numbers are "the same" if they are
               `equal', that is, if they are equal in value and either
               both are integers or both are floating point numbers;
               otherwise, two distinct objects are never "the same."

         `eq'
               Any two distinct Lisp objects are "different" as keys.

         `equal'
               Two Lisp objects are "the same," as keys, if they are
               equal according to `equal'.

          You can use `define-hash-table-test' (*note Defining Hash::)
          to define additional possibilities for TEST.

    `:weakness WEAK'
          The weakness of a hash table specifies whether the presence
          of a key or value in the hash table preserves it from garbage
          collection.

          The value, WEAK, must be one of `nil', `key', `value',
          `key-or-value', `key-and-value', or `t' which is an alias for
          `key-and-value'.  If WEAK is `key' then the hash table does
          not prevent its keys from being collected as garbage (if they
          are not referenced anywhere else); if a particular key does
          get collected, the corresponding association is removed from
          the hash table.

          If WEAK is `value', then the hash table does not prevent
          values from being collected as garbage (if they are not
          referenced anywhere else); if a particular value does get
          collected, the corresponding association is removed from the
          hash table.

          If WEAK is `key-and-value' or `t', both the key and the value
          must be live in order to preserve the association.  Thus, the
          hash table does not protect either keys or values from garbage
          collection; if either one is collected as garbage, that
          removes the association.

          If WEAK is `key-or-value', either the key or the value can
          preserve the association.  Thus, associations are removed
          from the hash table when both their key and value would be
          collected as garbage (if not for references from weak hash
          tables).

          The default for WEAK is `nil', so that all keys and values
          referenced in the hash table are preserved from garbage
          collection.

    `:size SIZE'
          This specifies a hint for how many associations you plan to
          store in the hash table.  If you know the approximate number,
          you can make things a little more efficient by specifying it
          this way.  If you specify too small a size, the hash table
          will grow automatically when necessary, but doing that takes
          some extra time.

          The default size is 65.

    `:rehash-size REHASH-SIZE'
          When you add an association to a hash table and the table is
          "full," it grows automatically.  This value specifies how to
          make the hash table larger, at that time.

          If REHASH-SIZE is an integer, it should be positive, and the
          hash table grows by adding that much to the nominal size.  If
          REHASH-SIZE is a floating point number, it had better be
          greater than 1, and the hash table grows by multiplying the
          old size by that number.

          The default value is 1.5.

    `:rehash-threshold THRESHOLD'
          This specifies the criterion for when the hash table is
          "full" (so it should be made larger).  The value, THRESHOLD,
          should be a positive floating point number, no greater than
          1.  The hash table is "full" whenever the actual number of
          entries exceeds this fraction of the nominal size.  The
          default for THRESHOLD is 0.8.

 -- Function: makehash &optional test
     This is equivalent to `make-hash-table', but with a different style
     argument list.  The argument TEST specifies the method of key
     lookup.

     This function is obsolete. Use `make-hash-table' instead.


File: elisp,  Node: Hash Access,  Next: Defining Hash,  Prev: Creating Hash,  Up: Hash Tables

7.2 Hash Table Access
=====================

This section describes the functions for accessing and storing
associations in a hash table.  In general, any Lisp object can be used
as a hash key, unless the comparison method imposes limits.  Any Lisp
object can also be used as the value.

 -- Function: gethash key table &optional default
     This function looks up KEY in TABLE, and returns its associated
     VALUE--or DEFAULT, if KEY has no association in TABLE.

 -- Function: puthash key value table
     This function enters an association for KEY in TABLE, with value
     VALUE.  If KEY already has an association in TABLE, VALUE replaces
     the old associated value.

 -- Function: remhash key table
     This function removes the association for KEY from TABLE, if there
     is one.  If KEY has no association, `remhash' does nothing.

     Common Lisp note: In Common Lisp, `remhash' returns non-`nil' if
     it actually removed an association and `nil' otherwise.  In Emacs
     Lisp, `remhash' always returns `nil'.

 -- Function: clrhash table
     This function removes all the associations from hash table TABLE,
     so that it becomes empty.  This is also called "clearing" the hash
     table.

     Common Lisp note: In Common Lisp, `clrhash' returns the empty
     TABLE.  In Emacs Lisp, it returns `nil'.

 -- Function: maphash function table
     This function calls FUNCTION once for each of the associations in
     TABLE.  The function FUNCTION should accept two arguments--a KEY
     listed in TABLE, and its associated VALUE.  `maphash' returns
     `nil'.


File: elisp,  Node: Defining Hash,  Next: Other Hash,  Prev: Hash Access,  Up: Hash Tables

7.3 Defining Hash Comparisons
=============================

You can define new methods of key lookup by means of
`define-hash-table-test'.  In order to use this feature, you need to
understand how hash tables work, and what a "hash code" means.

   You can think of a hash table conceptually as a large array of many
slots, each capable of holding one association.  To look up a key,
`gethash' first computes an integer, the hash code, from the key.  It
reduces this integer modulo the length of the array, to produce an
index in the array.  Then it looks in that slot, and if necessary in
other nearby slots, to see if it has found the key being sought.

   Thus, to define a new method of key lookup, you need to specify both
a function to compute the hash code from a key, and a function to
compare two keys directly.

 -- Function: define-hash-table-test name test-fn hash-fn
     This function defines a new hash table test, named NAME.

     After defining NAME in this way, you can use it as the TEST
     argument in `make-hash-table'.  When you do that, the hash table
     will use TEST-FN to compare key values, and HASH-FN to compute a
     "hash code" from a key value.

     The function TEST-FN should accept two arguments, two keys, and
     return non-`nil' if they are considered "the same."

     The function HASH-FN should accept one argument, a key, and return
     an integer that is the "hash code" of that key.  For good results,
     the function should use the whole range of integer values for hash
     codes, including negative integers.

     The specified functions are stored in the property list of NAME
     under the property `hash-table-test'; the property value's form is
     `(TEST-FN HASH-FN)'.

 -- Function: sxhash obj
     This function returns a hash code for Lisp object OBJ.  This is an
     integer which reflects the contents of OBJ and the other Lisp
     objects it points to.

     If two objects OBJ1 and OBJ2 are equal, then `(sxhash OBJ1)' and
     `(sxhash OBJ2)' are the same integer.

     If the two objects are not equal, the values returned by `sxhash'
     are usually different, but not always; once in a rare while, by
     luck, you will encounter two distinct-looking objects that give
     the same result from `sxhash'.

   This example creates a hash table whose keys are strings that are
compared case-insensitively.

     (defun case-fold-string= (a b)
       (compare-strings a nil nil b nil nil t))
     (defun case-fold-string-hash (a)
       (sxhash (upcase a)))

     (define-hash-table-test 'case-fold
       'case-fold-string= 'case-fold-string-hash)

     (make-hash-table :test 'case-fold)

   Here is how you could define a hash table test equivalent to the
predefined test value `equal'.  The keys can be any Lisp object, and
equal-looking objects are considered the same key.

     (define-hash-table-test 'contents-hash 'equal 'sxhash)

     (make-hash-table :test 'contents-hash)


File: elisp,  Node: Other Hash,  Prev: Defining Hash,  Up: Hash Tables

7.4 Other Hash Table Functions
==============================

Here are some other functions for working with hash tables.

 -- Function: hash-table-p table
     This returns non-`nil' if TABLE is a hash table object.

 -- Function: copy-hash-table table
     This function creates and returns a copy of TABLE.  Only the table
     itself is copied--the keys and values are shared.

 -- Function: hash-table-count table
     This function returns the actual number of entries in TABLE.

 -- Function: hash-table-test table
     This returns the TEST value that was given when TABLE was created,
     to specify how to hash and compare keys.  See `make-hash-table'
     (*note Creating Hash::).

 -- Function: hash-table-weakness table
     This function returns the WEAK value that was specified for hash
     table TABLE.

 -- Function: hash-table-rehash-size table
     This returns the rehash size of TABLE.

 -- Function: hash-table-rehash-threshold table
     This returns the rehash threshold of TABLE.

 -- Function: hash-table-size table
     This returns the current nominal size of TABLE.


File: elisp,  Node: Symbols,  Next: Evaluation,  Prev: Hash Tables,  Up: Top

8 Symbols
*********

A "symbol" is an object with a unique name.  This chapter describes
symbols, their components, their property lists, and how they are
created and interned.  Separate chapters describe the use of symbols as
variables and as function names; see *Note Variables::, and *Note
Functions::.  For the precise read syntax for symbols, see *Note Symbol
Type::.

   You can test whether an arbitrary Lisp object is a symbol with
`symbolp':

 -- Function: symbolp object
     This function returns `t' if OBJECT is a symbol, `nil' otherwise.

* Menu:

* Symbol Components::        Symbols have names, values, function definitions
                               and property lists.
* Definitions::              A definition says how a symbol will be used.
* Creating Symbols::         How symbols are kept unique.
* Property Lists::           Each symbol has a property list
                               for recording miscellaneous information.


File: elisp,  Node: Symbol Components,  Next: Definitions,  Prev: Symbols,  Up: Symbols

8.1 Symbol Components
=====================

Each symbol has four components (or "cells"), each of which references
another object:

Print name
     The "print name cell" holds a string that names the symbol for
     reading and printing.  See `symbol-name' in *Note Creating
     Symbols::.

Value
     The "value cell" holds the current value of the symbol as a
     variable.  When a symbol is used as a form, the value of the form
     is the contents of the symbol's value cell.  See `symbol-value' in
     *Note Accessing Variables::.

Function
     The "function cell" holds the function definition of the symbol.
     When a symbol is used as a function, its function definition is
     used in its place.  This cell is also used to make a symbol stand
     for a keymap or a keyboard macro, for editor command execution.
     Because each symbol has separate value and function cells,
     variables names and function names do not conflict.  See
     `symbol-function' in *Note Function Cells::.

Property list
     The "property list cell" holds the property list of the symbol.
     See `symbol-plist' in *Note Property Lists::.

   The print name cell always holds a string, and cannot be changed.
The other three cells can be set individually to any specified Lisp
object.

   The print name cell holds the string that is the name of the symbol.
Since symbols are represented textually by their names, it is important
not to have two symbols with the same name.  The Lisp reader ensures
this: every time it reads a symbol, it looks for an existing symbol with
the specified name before it creates a new one.  (In GNU Emacs Lisp,
this lookup uses a hashing algorithm and an obarray; see *Note Creating
Symbols::.)

   The value cell holds the symbol's value as a variable (*note
Variables::).  That is what you get if you evaluate the symbol as a
Lisp expression (*note Evaluation::).  Any Lisp object is a legitimate
value.  Certain symbols have values that cannot be changed; these
include `nil' and `t', and any symbol whose name starts with `:' (those
are called "keywords").  *Note Constant Variables::.

   We often refer to "the function `foo'" when we really mean the
function stored in the function cell of the symbol `foo'.  We make the
distinction explicit only when necessary.  In normal usage, the
function cell usually contains a function (*note Functions::) or a
macro (*note Macros::), as that is what the Lisp interpreter expects to
see there (*note Evaluation::).  Keyboard macros (*note Keyboard
Macros::), keymaps (*note Keymaps::) and autoload objects (*note
Autoloading::) are also sometimes stored in the function cells of
symbols.

   The property list cell normally should hold a correctly formatted
property list (*note Property Lists::), as a number of functions expect
to see a property list there.

   The function cell or the value cell may be "void", which means that
the cell does not reference any object.  (This is not the same thing as
holding the symbol `void', nor the same as holding the symbol `nil'.)
Examining a function or value cell that is void results in an error,
such as `Symbol's value as variable is void'.

   The four functions `symbol-name', `symbol-value', `symbol-plist',
and `symbol-function' return the contents of the four cells of a
symbol.  Here as an example we show the contents of the four cells of
the symbol `buffer-file-name':

     (symbol-name 'buffer-file-name)
          => "buffer-file-name"
     (symbol-value 'buffer-file-name)
          => "/gnu/elisp/symbols.texi"
     (symbol-function 'buffer-file-name)
          => #<subr buffer-file-name>
     (symbol-plist 'buffer-file-name)
          => (variable-documentation 29529)

Because this symbol is the variable which holds the name of the file
being visited in the current buffer, the value cell contents we see are
the name of the source file of this chapter of the Emacs Lisp Manual.
The property list cell contains the list `(variable-documentation
29529)' which tells the documentation functions where to find the
documentation string for the variable `buffer-file-name' in the
`DOC-VERSION' file.  (29529 is the offset from the beginning of the
`DOC-VERSION' file to where that documentation string begins--see *Note
Documentation Basics::.)  The function cell contains the function for
returning the name of the file.  `buffer-file-name' names a primitive
function, which has no read syntax and prints in hash notation (*note
Primitive Function Type::).  A symbol naming a function written in Lisp
would have a lambda expression (or a byte-code object) in this cell.


File: elisp,  Node: Definitions,  Next: Creating Symbols,  Prev: Symbol Components,  Up: Symbols

8.2 Defining Symbols
====================

A "definition" in Lisp is a special form that announces your intention
to use a certain symbol in a particular way.  In Emacs Lisp, you can
define a symbol as a variable, or define it as a function (or macro),
or both independently.

   A definition construct typically specifies a value or meaning for the
symbol for one kind of use, plus documentation for its meaning when used
in this way.  Thus, when you define a symbol as a variable, you can
supply an initial value for the variable, plus documentation for the
variable.

   `defvar' and `defconst' are special forms that define a symbol as a
global variable.  They are documented in detail in *Note Defining
Variables::.  For defining user option variables that can be
customized, use `defcustom' (*note Customization::).

   `defun' defines a symbol as a function, creating a lambda expression
and storing it in the function cell of the symbol.  This lambda
expression thus becomes the function definition of the symbol.  (The
term "function definition," meaning the contents of the function cell,
is derived from the idea that `defun' gives the symbol its definition
as a function.)  `defsubst' and `defalias' are two other ways of
defining a function.  *Note Functions::.

   `defmacro' defines a symbol as a macro.  It creates a macro object
and stores it in the function cell of the symbol.  Note that a given
symbol can be a macro or a function, but not both at once, because both
macro and function definitions are kept in the function cell, and that
cell can hold only one Lisp object at any given time.  *Note Macros::.

   In Emacs Lisp, a definition is not required in order to use a symbol
as a variable or function.  Thus, you can make a symbol a global
variable with `setq', whether you define it first or not.  The real
purpose of definitions is to guide programmers and programming tools.
They inform programmers who read the code that certain symbols are
_intended_ to be used as variables, or as functions.  In addition,
utilities such as `etags' and `make-docfile' recognize definitions, and
add appropriate information to tag tables and the `DOC-VERSION' file.
*Note Accessing Documentation::.


File: elisp,  Node: Creating Symbols,  Next: Property Lists,  Prev: Definitions,  Up: Symbols

8.3 Creating and Interning Symbols
==================================

To understand how symbols are created in GNU Emacs Lisp, you must know
how Lisp reads them.  Lisp must ensure that it finds the same symbol
every time it reads the same set of characters.  Failure to do so would
cause complete confusion.

   When the Lisp reader encounters a symbol, it reads all the characters
of the name.  Then it "hashes" those characters to find an index in a
table called an "obarray".  Hashing is an efficient method of looking
something up.  For example, instead of searching a telephone book cover
to cover when looking up Jan Jones, you start with the J's and go from
there.  That is a simple version of hashing.  Each element of the
obarray is a "bucket" which holds all the symbols with a given hash
code; to look for a given name, it is sufficient to look through all
the symbols in the bucket for that name's hash code.  (The same idea is
used for general Emacs hash tables, but they are a different data type;
see *Note Hash Tables::.)

   If a symbol with the desired name is found, the reader uses that
symbol.  If the obarray does not contain a symbol with that name, the
reader makes a new symbol and adds it to the obarray.  Finding or adding
a symbol with a certain name is called "interning" it, and the symbol
is then called an "interned symbol".

   Interning ensures that each obarray has just one symbol with any
particular name.  Other like-named symbols may exist, but not in the
same obarray.  Thus, the reader gets the same symbols for the same
names, as long as you keep reading with the same obarray.

   Interning usually happens automatically in the reader, but sometimes
other programs need to do it.  For example, after the `M-x' command
obtains the command name as a string using the minibuffer, it then
interns the string, to get the interned symbol with that name.

   No obarray contains all symbols; in fact, some symbols are not in any
obarray.  They are called "uninterned symbols".  An uninterned symbol
has the same four cells as other symbols; however, the only way to gain
access to it is by finding it in some other object or as the value of a
variable.

   Creating an uninterned symbol is useful in generating Lisp code,
because an uninterned symbol used as a variable in the code you generate
cannot clash with any variables used in other Lisp programs.

   In Emacs Lisp, an obarray is actually a vector.  Each element of the
vector is a bucket; its value is either an interned symbol whose name
hashes to that bucket, or 0 if the bucket is empty.  Each interned
symbol has an internal link (invisible to the user) to the next symbol
in the bucket.  Because these links are invisible, there is no way to
find all the symbols in an obarray except using `mapatoms' (below).
The order of symbols in a bucket is not significant.

   In an empty obarray, every element is 0, so you can create an obarray
with `(make-vector LENGTH 0)'.  *This is the only valid way to create
an obarray.*  Prime numbers as lengths tend to result in good hashing;
lengths one less than a power of two are also good.

   *Do not try to put symbols in an obarray yourself.*  This does not
work--only `intern' can enter a symbol in an obarray properly.

     Common Lisp note: In Common Lisp, a single symbol may be interned
     in several obarrays.

   Most of the functions below take a name and sometimes an obarray as
arguments.  A `wrong-type-argument' error is signaled if the name is
not a string, or if the obarray is not a vector.

 -- Function: symbol-name symbol
     This function returns the string that is SYMBOL's name.  For
     example:

          (symbol-name 'foo)
               => "foo"

     *Warning:* Changing the string by substituting characters does
     change the name of the symbol, but fails to update the obarray, so
     don't do it!

 -- Function: make-symbol name
     This function returns a newly-allocated, uninterned symbol whose
     name is NAME (which must be a string).  Its value and function
     definition are void, and its property list is `nil'.  In the
     example below, the value of `sym' is not `eq' to `foo' because it
     is a distinct uninterned symbol whose name is also `foo'.

          (setq sym (make-symbol "foo"))
               => foo
          (eq sym 'foo)
               => nil

 -- Function: intern name &optional obarray
     This function returns the interned symbol whose name is NAME.  If
     there is no such symbol in the obarray OBARRAY, `intern' creates a
     new one, adds it to the obarray, and returns it.  If OBARRAY is
     omitted, the value of the global variable `obarray' is used.

          (setq sym (intern "foo"))
               => foo
          (eq sym 'foo)
               => t

          (setq sym1 (intern "foo" other-obarray))
               => foo
          (eq sym1 'foo)
               => nil

     Common Lisp note: In Common Lisp, you can intern an existing symbol
     in an obarray.  In Emacs Lisp, you cannot do this, because the
     argument to `intern' must be a string, not a symbol.

 -- Function: intern-soft name &optional obarray
     This function returns the symbol in OBARRAY whose name is NAME, or
     `nil' if OBARRAY has no symbol with that name.  Therefore, you can
     use `intern-soft' to test whether a symbol with a given name is
     already interned.  If OBARRAY is omitted, the value of the global
     variable `obarray' is used.

     The argument NAME may also be a symbol; in that case, the function
     returns NAME if NAME is interned in the specified obarray, and
     otherwise `nil'.

          (intern-soft "frazzle")        ; No such symbol exists.
               => nil
          (make-symbol "frazzle")        ; Create an uninterned one.
               => frazzle
          (intern-soft "frazzle")        ; That one cannot be found.
               => nil
          (setq sym (intern "frazzle"))  ; Create an interned one.
               => frazzle
          (intern-soft "frazzle")        ; That one can be found!
               => frazzle
          (eq sym 'frazzle)              ; And it is the same one.
               => t

 -- Variable: obarray
     This variable is the standard obarray for use by `intern' and
     `read'.

 -- Function: mapatoms function &optional obarray
     This function calls FUNCTION once with each symbol in the obarray
     OBARRAY.  Then it returns `nil'.  If OBARRAY is omitted, it
     defaults to the value of `obarray', the standard obarray for
     ordinary symbols.

          (setq count 0)
               => 0
          (defun count-syms (s)
            (setq count (1+ count)))
               => count-syms
          (mapatoms 'count-syms)
               => nil
          count
               => 1871

     See `documentation' in *Note Accessing Documentation::, for another
     example using `mapatoms'.

 -- Function: unintern symbol &optional obarray
     This function deletes SYMBOL from the obarray OBARRAY.  If
     `symbol' is not actually in the obarray, `unintern' does nothing.
     If OBARRAY is `nil', the current obarray is used.

     If you provide a string instead of a symbol as SYMBOL, it stands
     for a symbol name.  Then `unintern' deletes the symbol (if any) in
     the obarray which has that name.  If there is no such symbol,
     `unintern' does nothing.

     If `unintern' does delete a symbol, it returns `t'.  Otherwise it
     returns `nil'.


File: elisp,  Node: Property Lists,  Prev: Creating Symbols,  Up: Symbols

8.4 Property Lists
==================

A "property list" ("plist" for short) is a list of paired elements
stored in the property list cell of a symbol.  Each of the pairs
associates a property name (usually a symbol) with a property or value.
Property lists are generally used to record information about a
symbol, such as its documentation as a variable, the name of the file
where it was defined, or perhaps even the grammatical class of the
symbol (representing a word) in a language-understanding system.

   Character positions in a string or buffer can also have property
lists.  *Note Text Properties::.

   The property names and values in a property list can be any Lisp
objects, but the names are usually symbols.  Property list functions
compare the property names using `eq'.  Here is an example of a
property list, found on the symbol `progn' when the compiler is loaded:

     (lisp-indent-function 0 byte-compile byte-compile-progn)

Here `lisp-indent-function' and `byte-compile' are property names, and
the other two elements are the corresponding values.

* Menu:

* Plists and Alists::           Comparison of the advantages of property
                                  lists and association lists.
* Symbol Plists::               Functions to access symbols' property lists.
* Other Plists::                Accessing property lists stored elsewhere.


File: elisp,  Node: Plists and Alists,  Next: Symbol Plists,  Up: Property Lists

8.4.1 Property Lists and Association Lists
------------------------------------------

Association lists (*note Association Lists::) are very similar to
property lists.  In contrast to association lists, the order of the
pairs in the property list is not significant since the property names
must be distinct.

   Property lists are better than association lists for attaching
information to various Lisp function names or variables.  If your
program keeps all of its associations in one association list, it will
typically need to search that entire list each time it checks for an
association.  This could be slow.  By contrast, if you keep the same
information in the property lists of the function names or variables
themselves, each search will scan only the length of one property list,
which is usually short.  This is why the documentation for a variable is
recorded in a property named `variable-documentation'.  The byte
compiler likewise uses properties to record those functions needing
special treatment.

   However, association lists have their own advantages.  Depending on
your application, it may be faster to add an association to the front of
an association list than to update a property.  All properties for a
symbol are stored in the same property list, so there is a possibility
of a conflict between different uses of a property name.  (For this
reason, it is a good idea to choose property names that are probably
unique, such as by beginning the property name with the program's usual
name-prefix for variables and functions.)  An association list may be
used like a stack where associations are pushed on the front of the list
and later discarded; this is not possible with a property list.


File: elisp,  Node: Symbol Plists,  Next: Other Plists,  Prev: Plists and Alists,  Up: Property Lists

8.4.2 Property List Functions for Symbols
-----------------------------------------

 -- Function: symbol-plist symbol
     This function returns the property list of SYMBOL.

 -- Function: setplist symbol plist
     This function sets SYMBOL's property list to PLIST.  Normally,
     PLIST should be a well-formed property list, but this is not
     enforced.  The return value is PLIST.

          (setplist 'foo '(a 1 b (2 3) c nil))
               => (a 1 b (2 3) c nil)
          (symbol-plist 'foo)
               => (a 1 b (2 3) c nil)

     For symbols in special obarrays, which are not used for ordinary
     purposes, it may make sense to use the property list cell in a
     nonstandard fashion; in fact, the abbrev mechanism does so (*note
     Abbrevs::).

 -- Function: get symbol property
     This function finds the value of the property named PROPERTY in
     SYMBOL's property list.  If there is no such property, `nil' is
     returned.  Thus, there is no distinction between a value of `nil'
     and the absence of the property.

     The name PROPERTY is compared with the existing property names
     using `eq', so any object is a legitimate property.

     See `put' for an example.

 -- Function: put symbol property value
     This function puts VALUE onto SYMBOL's property list under the
     property name PROPERTY, replacing any previous property value.
     The `put' function returns VALUE.

          (put 'fly 'verb 'transitive)
               =>'transitive
          (put 'fly 'noun '(a buzzing little bug))
               => (a buzzing little bug)
          (get 'fly 'verb)
               => transitive
          (symbol-plist 'fly)
               => (verb transitive noun (a buzzing little bug))


File: elisp,  Node: Other Plists,  Prev: Symbol Plists,  Up: Property Lists

8.4.3 Property Lists Outside Symbols
------------------------------------

These functions are useful for manipulating property lists that are
stored in places other than symbols:

 -- Function: plist-get plist property
     This returns the value of the PROPERTY property stored in the
     property list PLIST.  For example,

          (plist-get '(foo 4) 'foo)
               => 4
          (plist-get '(foo 4 bad) 'foo)
               => 4
          (plist-get '(foo 4 bad) 'bad)
               => `nil'

     It accepts a malformed PLIST argument and always returns `nil' if
     PROPERTY is not found in the PLIST.  For example,

          (plist-get '(foo 4 bad) 'bar)
               => nil

 -- Function: plist-put plist property value
     This stores VALUE as the value of the PROPERTY property in the
     property list PLIST.  It may modify PLIST destructively, or it may
     construct a new list structure without altering the old.  The
     function returns the modified property list, so you can store that
     back in the place where you got PLIST.  For example,

          (setq my-plist '(bar t foo 4))
               => (bar t foo 4)
          (setq my-plist (plist-put my-plist 'foo 69))
               => (bar t foo 69)
          (setq my-plist (plist-put my-plist 'quux '(a)))
               => (bar t foo 69 quux (a))

   You could define `put' in terms of `plist-put' as follows:

     (defun put (symbol prop value)
       (setplist symbol
                 (plist-put (symbol-plist symbol) prop value)))

 -- Function: lax-plist-get plist property
     Like `plist-get' except that it compares properties using `equal'
     instead of `eq'.

 -- Function: lax-plist-put plist property value
     Like `plist-put' except that it compares properties using `equal'
     instead of `eq'.

 -- Function: plist-member plist property
     This returns non-`nil' if PLIST contains the given PROPERTY.
     Unlike `plist-get', this allows you to distinguish between a
     missing property and a property with the value `nil'.  The value
     is actually the tail of PLIST whose `car' is PROPERTY.


File: elisp,  Node: Evaluation,  Next: Control Structures,  Prev: Symbols,  Up: Top

9 Evaluation
************

The "evaluation" of expressions in Emacs Lisp is performed by the "Lisp
interpreter"--a program that receives a Lisp object as input and
computes its "value as an expression".  How it does this depends on the
data type of the object, according to rules described in this chapter.
The interpreter runs automatically to evaluate portions of your
program, but can also be called explicitly via the Lisp primitive
function `eval'.

* Menu:

* Intro Eval::  Evaluation in the scheme of things.
* Forms::       How various sorts of objects are evaluated.
* Quoting::     Avoiding evaluation (to put constants in the program).
* Eval::        How to invoke the Lisp interpreter explicitly.


File: elisp,  Node: Intro Eval,  Next: Forms,  Up: Evaluation

9.1 Introduction to Evaluation
==============================

The Lisp interpreter, or evaluator, is the program that computes the
value of an expression that is given to it.  When a function written in
Lisp is called, the evaluator computes the value of the function by
evaluating the expressions in the function body.  Thus, running any
Lisp program really means running the Lisp interpreter.

   How the evaluator handles an object depends primarily on the data
type of the object.

   A Lisp object that is intended for evaluation is called an
"expression" or a "form".  The fact that expressions are data objects
and not merely text is one of the fundamental differences between
Lisp-like languages and typical programming languages.  Any object can
be evaluated, but in practice only numbers, symbols, lists and strings
are evaluated very often.

   It is very common to read a Lisp expression and then evaluate the
expression, but reading and evaluation are separate activities, and
either can be performed alone.  Reading per se does not evaluate
anything; it converts the printed representation of a Lisp object to the
object itself.  It is up to the caller of `read' whether this object is
a form to be evaluated, or serves some entirely different purpose.
*Note Input Functions::.

   Do not confuse evaluation with command key interpretation.  The
editor command loop translates keyboard input into a command (an
interactively callable function) using the active keymaps, and then
uses `call-interactively' to invoke the command.  The execution of the
command itself involves evaluation if the command is written in Lisp,
but that is not a part of command key interpretation itself.  *Note
Command Loop::.

   Evaluation is a recursive process.  That is, evaluation of a form may
call `eval' to evaluate parts of the form.  For example, evaluation of
a function call first evaluates each argument of the function call, and
then evaluates each form in the function body.  Consider evaluation of
the form `(car x)': the subform `x' must first be evaluated
recursively, so that its value can be passed as an argument to the
function `car'.

   Evaluation of a function call ultimately calls the function specified
in it.  *Note Functions::.  The execution of the function may itself
work by evaluating the function definition; or the function may be a
Lisp primitive implemented in C, or it may be a byte-compiled function
(*note Byte Compilation::).

   The evaluation of forms takes place in a context called the
"environment", which consists of the current values and bindings of all
Lisp variables.(1)  Whenever a form refers to a variable without
creating a new binding for it, the value of the variable's binding in
the current environment is used.  *Note Variables::.

   Evaluation of a form may create new environments for recursive
evaluation by binding variables (*note Local Variables::).  These
environments are temporary and vanish by the time evaluation of the form
is complete.  The form may also make changes that persist; these changes
are called "side effects".  An example of a form that produces side
effects is `(setq foo 1)'.

   The details of what evaluation means for each kind of form are
described below (*note Forms::).

   ---------- Footnotes ----------

   (1) This definition of "environment" is specifically not intended to
include all the data that can affect the result of a program.


File: elisp,  Node: Forms,  Next: Quoting,  Prev: Intro Eval,  Up: Evaluation

9.2 Kinds of Forms
==================

A Lisp object that is intended to be evaluated is called a "form".  How
Emacs evaluates a form depends on its data type.  Emacs has three
different kinds of form that are evaluated differently: symbols, lists,
and "all other types."  This section describes all three kinds, one by
one, starting with the "all other types" which are self-evaluating
forms.

* Menu:

* Self-Evaluating Forms::   Forms that evaluate to themselves.
* Symbol Forms::            Symbols evaluate as variables.
* Classifying Lists::       How to distinguish various sorts of list forms.
* Function Indirection::    When a symbol appears as the car of a list,
			      we find the real function via the symbol.
* Function Forms::          Forms that call functions.
* Macro Forms::             Forms that call macros.
* Special Forms::           "Special forms" are idiosyncratic primitives,
                              most of them extremely important.
* Autoloading::             Functions set up to load files
                              containing their real definitions.


File: elisp,  Node: Self-Evaluating Forms,  Next: Symbol Forms,  Up: Forms

9.2.1 Self-Evaluating Forms
---------------------------

A "self-evaluating form" is any form that is not a list or symbol.
Self-evaluating forms evaluate to themselves: the result of evaluation
is the same object that was evaluated.  Thus, the number 25 evaluates to
25, and the string `"foo"' evaluates to the string `"foo"'.  Likewise,
evaluation of a vector does not cause evaluation of the elements of the
vector--it returns the same vector with its contents unchanged.

     '123               ; A number, shown without evaluation.
          => 123
     123                ; Evaluated as usual--result is the same.
          => 123
     (eval '123)        ; Evaluated "by hand"--result is the same.
          => 123
     (eval (eval '123)) ; Evaluating twice changes nothing.
          => 123

   It is common to write numbers, characters, strings, and even vectors
in Lisp code, taking advantage of the fact that they self-evaluate.
However, it is quite unusual to do this for types that lack a read
syntax, because there's no way to write them textually.  It is possible
to construct Lisp expressions containing these types by means of a Lisp
program.  Here is an example:

     ;; Build an expression containing a buffer object.
     (setq print-exp (list 'print (current-buffer)))
          => (print #<buffer eval.texi>)
     ;; Evaluate it.
     (eval print-exp)
          -| #<buffer eval.texi>
          => #<buffer eval.texi>


File: elisp,  Node: Symbol Forms,  Next: Classifying Lists,  Prev: Self-Evaluating Forms,  Up: Forms

9.2.2 Symbol Forms
------------------

When a symbol is evaluated, it is treated as a variable.  The result is
the variable's value, if it has one.  If it has none (if its value cell
is void), an error is signaled.  For more information on the use of
variables, see *Note Variables::.

   In the following example, we set the value of a symbol with `setq'.
Then we evaluate the symbol, and get back the value that `setq' stored.

     (setq a 123)
          => 123
     (eval 'a)
          => 123
     a
          => 123

   The symbols `nil' and `t' are treated specially, so that the value
of `nil' is always `nil', and the value of `t' is always `t'; you
cannot set or bind them to any other values.  Thus, these two symbols
act like self-evaluating forms, even though `eval' treats them like any
other symbol.  A symbol whose name starts with `:' also self-evaluates
in the same way; likewise, its value ordinarily cannot be changed.
*Note Constant Variables::.


File: elisp,  Node: Classifying Lists,  Next: Function Indirection,  Prev: Symbol Forms,  Up: Forms

9.2.3 Classification of List Forms
----------------------------------

A form that is a nonempty list is either a function call, a macro call,
or a special form, according to its first element.  These three kinds
of forms are evaluated in different ways, described below.  The
remaining list elements constitute the "arguments" for the function,
macro, or special form.

   The first step in evaluating a nonempty list is to examine its first
element.  This element alone determines what kind of form the list is
and how the rest of the list is to be processed.  The first element is
_not_ evaluated, as it would be in some Lisp dialects such as Scheme.


File: elisp,  Node: Function Indirection,  Next: Function Forms,  Prev: Classifying Lists,  Up: Forms

9.2.4 Symbol Function Indirection
---------------------------------

If the first element of the list is a symbol then evaluation examines
the symbol's function cell, and uses its contents instead of the
original symbol.  If the contents are another symbol, this process,
called "symbol function indirection", is repeated until it obtains a
non-symbol.  *Note Function Names::, for more information about using a
symbol as a name for a function stored in the function cell of the
symbol.

   One possible consequence of this process is an infinite loop, in the
event that a symbol's function cell refers to the same symbol.  Or a
symbol may have a void function cell, in which case the subroutine
`symbol-function' signals a `void-function' error.  But if neither of
these things happens, we eventually obtain a non-symbol, which ought to
be a function or other suitable object.

   More precisely, we should now have a Lisp function (a lambda
expression), a byte-code function, a primitive function, a Lisp macro, a
special form, or an autoload object.  Each of these types is a case
described in one of the following sections.  If the object is not one of
these types, the error `invalid-function' is signaled.

   The following example illustrates the symbol indirection process.  We
use `fset' to set the function cell of a symbol and `symbol-function'
to get the function cell contents (*note Function Cells::).
Specifically, we store the symbol `car' into the function cell of
`first', and the symbol `first' into the function cell of `erste'.

     ;; Build this function cell linkage:
     ;;   -------------       -----        -------        -------
     ;;  | #<subr car> | <-- | car |  <-- | first |  <-- | erste |
     ;;   -------------       -----        -------        -------

     (symbol-function 'car)
          => #<subr car>
     (fset 'first 'car)
          => car
     (fset 'erste 'first)
          => first
     (erste '(1 2 3))   ; Call the function referenced by `erste'.
          => 1

   By contrast, the following example calls a function without any
symbol function indirection, because the first element is an anonymous
Lisp function, not a symbol.

     ((lambda (arg) (erste arg))
      '(1 2 3))
          => 1

Executing the function itself evaluates its body; this does involve
symbol function indirection when calling `erste'.

   The built-in function `indirect-function' provides an easy way to
perform symbol function indirection explicitly.

 -- Function: indirect-function function &optional noerror
     This function returns the meaning of FUNCTION as a function.  If
     FUNCTION is a symbol, then it finds FUNCTION's function definition
     and starts over with that value.  If FUNCTION is not a symbol,
     then it returns FUNCTION itself.

     This function signals a `void-function' error if the final symbol
     is unbound and optional argument NOERROR is `nil' or omitted.
     Otherwise, if NOERROR is non-`nil', it returns `nil' if the final
     symbol is unbound.

     It signals a `cyclic-function-indirection' error if there is a
     loop in the chain of symbols.

     Here is how you could define `indirect-function' in Lisp:

          (defun indirect-function (function)
            (if (symbolp function)
                (indirect-function (symbol-function function))
              function))


File: elisp,  Node: Function Forms,  Next: Macro Forms,  Prev: Function Indirection,  Up: Forms

9.2.5 Evaluation of Function Forms
----------------------------------

If the first element of a list being evaluated is a Lisp function
object, byte-code object or primitive function object, then that list is
a "function call".  For example, here is a call to the function `+':

     (+ 1 x)

   The first step in evaluating a function call is to evaluate the
remaining elements of the list from left to right.  The results are the
actual argument values, one value for each list element.  The next step
is to call the function with this list of arguments, effectively using
the function `apply' (*note Calling Functions::).  If the function is
written in Lisp, the arguments are used to bind the argument variables
of the function (*note Lambda Expressions::); then the forms in the
function body are evaluated in order, and the value of the last body
form becomes the value of the function call.


File: elisp,  Node: Macro Forms,  Next: Special Forms,  Prev: Function Forms,  Up: Forms

9.2.6 Lisp Macro Evaluation
---------------------------

If the first element of a list being evaluated is a macro object, then
the list is a "macro call".  When a macro call is evaluated, the
elements of the rest of the list are _not_ initially evaluated.
Instead, these elements themselves are used as the arguments of the
macro.  The macro definition computes a replacement form, called the
"expansion" of the macro, to be evaluated in place of the original
form.  The expansion may be any sort of form: a self-evaluating
constant, a symbol, or a list.  If the expansion is itself a macro call,
this process of expansion repeats until some other sort of form results.

   Ordinary evaluation of a macro call finishes by evaluating the
expansion.  However, the macro expansion is not necessarily evaluated
right away, or at all, because other programs also expand macro calls,
and they may or may not evaluate the expansions.

   Normally, the argument expressions are not evaluated as part of
computing the macro expansion, but instead appear as part of the
expansion, so they are computed when the expansion is evaluated.

   For example, given a macro defined as follows:

     (defmacro cadr (x)
       (list 'car (list 'cdr x)))

an expression such as `(cadr (assq 'handler list))' is a macro call,
and its expansion is:

     (car (cdr (assq 'handler list)))

Note that the argument `(assq 'handler list)' appears in the expansion.

   *Note Macros::, for a complete description of Emacs Lisp macros.


File: elisp,  Node: Special Forms,  Next: Autoloading,  Prev: Macro Forms,  Up: Forms

9.2.7 Special Forms
-------------------

A "special form" is a primitive function specially marked so that its
arguments are not all evaluated.  Most special forms define control
structures or perform variable bindings--things which functions cannot
do.

   Each special form has its own rules for which arguments are evaluated
and which are used without evaluation.  Whether a particular argument is
evaluated may depend on the results of evaluating other arguments.

   Here is a list, in alphabetical order, of all of the special forms in
Emacs Lisp with a reference to where each is described.

`and'
     *note Combining Conditions::

`catch'
     *note Catch and Throw::

`cond'
     *note Conditionals::

`condition-case'
     *note Handling Errors::

`defconst'
     *note Defining Variables::

`defmacro'
     *note Defining Macros::

`defun'
     *note Defining Functions::

`defvar'
     *note Defining Variables::

`function'
     *note Anonymous Functions::

`if'
     *note Conditionals::

`interactive'
     *note Interactive Call::

`let'
`let*'
     *note Local Variables::

`or'
     *note Combining Conditions::

`prog1'
`prog2'
`progn'
     *note Sequencing::

`quote'
     *note Quoting::

`save-current-buffer'
     *note Current Buffer::

`save-excursion'
     *note Excursions::

`save-restriction'
     *note Narrowing::

`save-window-excursion'
     *note Window Configurations::

`setq'
     *note Setting Variables::

`setq-default'
     *note Creating Buffer-Local::

`track-mouse'
     *note Mouse Tracking::

`unwind-protect'
     *note Nonlocal Exits::

`while'
     *note Iteration::

`with-output-to-temp-buffer'
     *note Temporary Displays::

     Common Lisp note: Here are some comparisons of special forms in
     GNU Emacs Lisp and Common Lisp.  `setq', `if', and `catch' are
     special forms in both Emacs Lisp and Common Lisp.  `defun' is a
     special form in Emacs Lisp, but a macro in Common Lisp.
     `save-excursion' is a special form in Emacs Lisp, but doesn't
     exist in Common Lisp.  `throw' is a special form in Common Lisp
     (because it must be able to throw multiple values), but it is a
     function in Emacs Lisp (which doesn't have multiple values).


File: elisp,  Node: Autoloading,  Prev: Special Forms,  Up: Forms

9.2.8 Autoloading
-----------------

The "autoload" feature allows you to call a function or macro whose
function definition has not yet been loaded into Emacs.  It specifies
which file contains the definition.  When an autoload object appears as
a symbol's function definition, calling that symbol as a function
automatically loads the specified file; then it calls the real
definition loaded from that file.  *Note Autoload::.


File: elisp,  Node: Quoting,  Next: Eval,  Prev: Forms,  Up: Evaluation

9.3 Quoting
===========

The special form `quote' returns its single argument, as written,
without evaluating it.  This provides a way to include constant symbols
and lists, which are not self-evaluating objects, in a program.  (It is
not necessary to quote self-evaluating objects such as numbers, strings,
and vectors.)

 -- Special Form: quote object
     This special form returns OBJECT, without evaluating it.

   Because `quote' is used so often in programs, Lisp provides a
convenient read syntax for it.  An apostrophe character (`'') followed
by a Lisp object (in read syntax) expands to a list whose first element
is `quote', and whose second element is the object.  Thus, the read
syntax `'x' is an abbreviation for `(quote x)'.

   Here are some examples of expressions that use `quote':

     (quote (+ 1 2))
          => (+ 1 2)
     (quote foo)
          => foo
     'foo
          => foo
     ''foo
          => (quote foo)
     '(quote foo)
          => (quote foo)
     ['foo]
          => [(quote foo)]

   Other quoting constructs include `function' (*note Anonymous
Functions::), which causes an anonymous lambda expression written in
Lisp to be compiled, and ``' (*note Backquote::), which is used to quote
only part of a list, while computing and substituting other parts.


File: elisp,  Node: Eval,  Prev: Quoting,  Up: Evaluation

9.4 Eval
========

Most often, forms are evaluated automatically, by virtue of their
occurrence in a program being run.  On rare occasions, you may need to
write code that evaluates a form that is computed at run time, such as
after reading a form from text being edited or getting one from a
property list.  On these occasions, use the `eval' function.

   The functions and variables described in this section evaluate forms,
specify limits to the evaluation process, or record recently returned
values.  Loading a file also does evaluation (*note Loading::).

   It is generally cleaner and more flexible to store a function in a
data structure, and call it with `funcall' or `apply', than to store an
expression in the data structure and evaluate it.  Using functions
provides the ability to pass information to them as arguments.

 -- Function: eval form
     This is the basic function evaluating an expression.  It evaluates
     FORM in the current environment and returns the result.  How the
     evaluation proceeds depends on the type of the object (*note
     Forms::).

     Since `eval' is a function, the argument expression that appears
     in a call to `eval' is evaluated twice: once as preparation before
     `eval' is called, and again by the `eval' function itself.  Here
     is an example:

          (setq foo 'bar)
               => bar
          (setq bar 'baz)
               => baz
          ;; Here `eval' receives argument `foo'
          (eval 'foo)
               => bar
          ;; Here `eval' receives argument `bar', which is the value of `foo'
          (eval foo)
               => baz

     The number of currently active calls to `eval' is limited to
     `max-lisp-eval-depth' (see below).

 -- Command: eval-region start end &optional stream read-function
     This function evaluates the forms in the current buffer in the
     region defined by the positions START and END.  It reads forms from
     the region and calls `eval' on them until the end of the region is
     reached, or until an error is signaled and not handled.

     By default, `eval-region' does not produce any output.  However,
     if STREAM is non-`nil', any output produced by output functions
     (*note Output Functions::), as well as the values that result from
     evaluating the expressions in the region are printed using STREAM.
     *Note Output Streams::.

     If READ-FUNCTION is non-`nil', it should be a function, which is
     used instead of `read' to read expressions one by one.  This
     function is called with one argument, the stream for reading
     input.  You can also use the variable `load-read-function' (*note
     How Programs Do Loading: Definition of load-read-function.)  to
     specify this function, but it is more robust to use the
     READ-FUNCTION argument.

     `eval-region' does not move point.  It always returns `nil'.

 -- Command: eval-buffer &optional buffer-or-name stream filename
          unibyte print
     This is similar to `eval-region', but the arguments provide
     different optional features.  `eval-buffer' operates on the entire
     accessible portion of buffer BUFFER-OR-NAME.  BUFFER-OR-NAME can
     be a buffer, a buffer name (a string), or `nil' (or omitted),
     which means to use the current buffer.  STREAM is used as in
     `eval-region', unless STREAM is `nil' and PRINT non-`nil'.  In
     that case, values that result from evaluating the expressions are
     still discarded, but the output of the output functions is printed
     in the echo area.  FILENAME is the file name to use for
     `load-history' (*note Unloading::), and defaults to
     `buffer-file-name' (*note Buffer File Name::).  If UNIBYTE is
     non-`nil', `read' converts strings to unibyte whenever possible.

     `eval-current-buffer' is an alias for this command.

 -- Variable: max-lisp-eval-depth
     This variable defines the maximum depth allowed in calls to `eval',
     `apply', and `funcall' before an error is signaled (with error
     message `"Lisp nesting exceeds max-lisp-eval-depth"').

     This limit, with the associated error when it is exceeded, is one
     way Emacs Lisp avoids infinite recursion on an ill-defined
     function.  If you increase the value of `max-lisp-eval-depth' too
     much, such code can cause stack overflow instead.  

     The depth limit counts internal uses of `eval', `apply', and
     `funcall', such as for calling the functions mentioned in Lisp
     expressions, and recursive evaluation of function call arguments
     and function body forms, as well as explicit calls in Lisp code.

     The default value of this variable is 300.  If you set it to a
     value less than 100, Lisp will reset it to 100 if the given value
     is reached.  Entry to the Lisp debugger increases the value, if
     there is little room left, to make sure the debugger itself has
     room to execute.

     `max-specpdl-size' provides another limit on nesting.  *Note Local
     Variables: Definition of max-specpdl-size.

 -- Variable: values
     The value of this variable is a list of the values returned by all
     the expressions that were read, evaluated, and printed from buffers
     (including the minibuffer) by the standard Emacs commands which do
     this.  (Note that this does _not_ include evaluation in `*ielm*'
     buffers, nor evaluation using `C-j' in `lisp-interaction-mode'.)
     The elements are ordered most recent first.

          (setq x 1)
               => 1
          (list 'A (1+ 2) auto-save-default)
               => (A 3 t)
          values
               => ((A 3 t) 1 ...)

     This variable is useful for referring back to values of forms
     recently evaluated.  It is generally a bad idea to print the value
     of `values' itself, since this may be very long.  Instead, examine
     particular elements, like this:

          ;; Refer to the most recent evaluation result.
          (nth 0 values)
               => (A 3 t)
          ;; That put a new element on,
          ;;   so all elements move back one.
          (nth 1 values)
               => (A 3 t)
          ;; This gets the element that was next-to-most-recent
          ;;   before this example.
          (nth 3 values)
               => 1


File: elisp,  Node: Control Structures,  Next: Variables,  Prev: Evaluation,  Up: Top

10 Control Structures
*********************

A Lisp program consists of expressions or "forms" (*note Forms::).  We
control the order of execution of these forms by enclosing them in
"control structures".  Control structures are special forms which
control when, whether, or how many times to execute the forms they
contain.

   The simplest order of execution is sequential execution: first form
A, then form B, and so on.  This is what happens when you write several
forms in succession in the body of a function, or at top level in a
file of Lisp code--the forms are executed in the order written.  We
call this "textual order".  For example, if a function body consists of
two forms A and B, evaluation of the function evaluates first A and
then B.  The result of evaluating B becomes the value of the function.

   Explicit control structures make possible an order of execution other
than sequential.

   Emacs Lisp provides several kinds of control structure, including
other varieties of sequencing, conditionals, iteration, and (controlled)
jumps--all discussed below.  The built-in control structures are
special forms since their subforms are not necessarily evaluated or not
evaluated sequentially.  You can use macros to define your own control
structure constructs (*note Macros::).

* Menu:

* Sequencing::             Evaluation in textual order.
* Conditionals::           `if', `cond', `when', `unless'.
* Combining Conditions::   `and', `or', `not'.
* Iteration::              `while' loops.
* Nonlocal Exits::         Jumping out of a sequence.


File: elisp,  Node: Sequencing,  Next: Conditionals,  Up: Control Structures

10.1 Sequencing
===============

Evaluating forms in the order they appear is the most common way
control passes from one form to another.  In some contexts, such as in a
function body, this happens automatically.  Elsewhere you must use a
control structure construct to do this: `progn', the simplest control
construct of Lisp.

   A `progn' special form looks like this:

     (progn A B C ...)

and it says to execute the forms A, B, C, and so on, in that order.
These forms are called the "body" of the `progn' form.  The value of
the last form in the body becomes the value of the entire `progn'.
`(progn)' returns `nil'.

   In the early days of Lisp, `progn' was the only way to execute two
or more forms in succession and use the value of the last of them.  But
programmers found they often needed to use a `progn' in the body of a
function, where (at that time) only one form was allowed.  So the body
of a function was made into an "implicit `progn'": several forms are
allowed just as in the body of an actual `progn'.  Many other control
structures likewise contain an implicit `progn'.  As a result, `progn'
is not used as much as it was many years ago.  It is needed now most
often inside an `unwind-protect', `and', `or', or in the THEN-part of
an `if'.

 -- Special Form: progn forms...
     This special form evaluates all of the FORMS, in textual order,
     returning the result of the final form.

          (progn (print "The first form")
                 (print "The second form")
                 (print "The third form"))
               -| "The first form"
               -| "The second form"
               -| "The third form"
          => "The third form"

   Two other control constructs likewise evaluate a series of forms but
return a different value:

 -- Special Form: prog1 form1 forms...
     This special form evaluates FORM1 and all of the FORMS, in textual
     order, returning the result of FORM1.

          (prog1 (print "The first form")
                 (print "The second form")
                 (print "The third form"))
               -| "The first form"
               -| "The second form"
               -| "The third form"
          => "The first form"

     Here is a way to remove the first element from a list in the
     variable `x', then return the value of that former element:

          (prog1 (car x) (setq x (cdr x)))

 -- Special Form: prog2 form1 form2 forms...
     This special form evaluates FORM1, FORM2, and all of the following
     FORMS, in textual order, returning the result of FORM2.

          (prog2 (print "The first form")
                 (print "The second form")
                 (print "The third form"))
               -| "The first form"
               -| "The second form"
               -| "The third form"
          => "The second form"


File: elisp,  Node: Conditionals,  Next: Combining Conditions,  Prev: Sequencing,  Up: Control Structures

10.2 Conditionals
=================

Conditional control structures choose among alternatives.  Emacs Lisp
has four conditional forms: `if', which is much the same as in other
languages; `when' and `unless', which are variants of `if'; and `cond',
which is a generalized case statement.

 -- Special Form: if condition then-form else-forms...
     `if' chooses between the THEN-FORM and the ELSE-FORMS based on the
     value of CONDITION.  If the evaluated CONDITION is non-`nil',
     THEN-FORM is evaluated and the result returned.  Otherwise, the
     ELSE-FORMS are evaluated in textual order, and the value of the
     last one is returned.  (The ELSE part of `if' is an example of an
     implicit `progn'.  *Note Sequencing::.)

     If CONDITION has the value `nil', and no ELSE-FORMS are given,
     `if' returns `nil'.

     `if' is a special form because the branch that is not selected is
     never evaluated--it is ignored.  Thus, in the example below,
     `true' is not printed because `print' is never called.

          (if nil
              (print 'true)
            'very-false)
          => very-false

 -- Macro: when condition then-forms...
     This is a variant of `if' where there are no ELSE-FORMS, and
     possibly several THEN-FORMS.  In particular,

          (when CONDITION A B C)

     is entirely equivalent to

          (if CONDITION (progn A B C) nil)

 -- Macro: unless condition forms...
     This is a variant of `if' where there is no THEN-FORM:

          (unless CONDITION A B C)

     is entirely equivalent to

          (if CONDITION nil
             A B C)

 -- Special Form: cond clause...
     `cond' chooses among an arbitrary number of alternatives.  Each
     CLAUSE in the `cond' must be a list.  The CAR of this list is the
     CONDITION; the remaining elements, if any, the BODY-FORMS.  Thus,
     a clause looks like this:

          (CONDITION BODY-FORMS...)

     `cond' tries the clauses in textual order, by evaluating the
     CONDITION of each clause.  If the value of CONDITION is non-`nil',
     the clause "succeeds"; then `cond' evaluates its BODY-FORMS, and
     the value of the last of BODY-FORMS becomes the value of the
     `cond'.  The remaining clauses are ignored.

     If the value of CONDITION is `nil', the clause "fails," so the
     `cond' moves on to the following clause, trying its CONDITION.

     If every CONDITION evaluates to `nil', so that every clause fails,
     `cond' returns `nil'.

     A clause may also look like this:

          (CONDITION)

     Then, if CONDITION is non-`nil' when tested, the value of
     CONDITION becomes the value of the `cond' form.

     The following example has four clauses, which test for the cases
     where the value of `x' is a number, string, buffer and symbol,
     respectively:

          (cond ((numberp x) x)
                ((stringp x) x)
                ((bufferp x)
                 (setq temporary-hack x) ; multiple body-forms
                 (buffer-name x))        ; in one clause
                ((symbolp x) (symbol-value x)))

     Often we want to execute the last clause whenever none of the
     previous clauses was successful.  To do this, we use `t' as the
     CONDITION of the last clause, like this: `(t BODY-FORMS)'.  The
     form `t' evaluates to `t', which is never `nil', so this clause
     never fails, provided the `cond' gets to it at all.

     For example,

          (setq a 5)
          (cond ((eq a 'hack) 'foo)
                (t "default"))
          => "default"

     This `cond' expression returns `foo' if the value of `a' is
     `hack', and returns the string `"default"' otherwise.

   Any conditional construct can be expressed with `cond' or with `if'.
Therefore, the choice between them is a matter of style.  For example:

     (if A B C)
     ==
     (cond (A B) (t C))


File: elisp,  Node: Combining Conditions,  Next: Iteration,  Prev: Conditionals,  Up: Control Structures

10.3 Constructs for Combining Conditions
========================================

This section describes three constructs that are often used together
with `if' and `cond' to express complicated conditions.  The constructs
`and' and `or' can also be used individually as kinds of multiple
conditional constructs.

 -- Function: not condition
     This function tests for the falsehood of CONDITION.  It returns
     `t' if CONDITION is `nil', and `nil' otherwise.  The function
     `not' is identical to `null', and we recommend using the name
     `null' if you are testing for an empty list.

 -- Special Form: and conditions...
     The `and' special form tests whether all the CONDITIONS are true.
     It works by evaluating the CONDITIONS one by one in the order
     written.

     If any of the CONDITIONS evaluates to `nil', then the result of
     the `and' must be `nil' regardless of the remaining CONDITIONS; so
     `and' returns `nil' right away, ignoring the remaining CONDITIONS.

     If all the CONDITIONS turn out non-`nil', then the value of the
     last of them becomes the value of the `and' form.  Just `(and)',
     with no CONDITIONS, returns `t', appropriate because all the
     CONDITIONS turned out non-`nil'.  (Think about it; which one did
     not?)

     Here is an example.  The first condition returns the integer 1,
     which is not `nil'.  Similarly, the second condition returns the
     integer 2, which is not `nil'.  The third condition is `nil', so
     the remaining condition is never evaluated.

          (and (print 1) (print 2) nil (print 3))
               -| 1
               -| 2
          => nil

     Here is a more realistic example of using `and':

          (if (and (consp foo) (eq (car foo) 'x))
              (message "foo is a list starting with x"))

     Note that `(car foo)' is not executed if `(consp foo)' returns
     `nil', thus avoiding an error.

     `and' expressions can also be written using either `if' or `cond'.
     Here's how:

          (and ARG1 ARG2 ARG3)
          ==
          (if ARG1 (if ARG2 ARG3))
          ==
          (cond (ARG1 (cond (ARG2 ARG3))))

 -- Special Form: or conditions...
     The `or' special form tests whether at least one of the CONDITIONS
     is true.  It works by evaluating all the CONDITIONS one by one in
     the order written.

     If any of the CONDITIONS evaluates to a non-`nil' value, then the
     result of the `or' must be non-`nil'; so `or' returns right away,
     ignoring the remaining CONDITIONS.  The value it returns is the
     non-`nil' value of the condition just evaluated.

     If all the CONDITIONS turn out `nil', then the `or' expression
     returns `nil'.  Just `(or)', with no CONDITIONS, returns `nil',
     appropriate because all the CONDITIONS turned out `nil'.  (Think
     about it; which one did not?)

     For example, this expression tests whether `x' is either `nil' or
     the integer zero:

          (or (eq x nil) (eq x 0))

     Like the `and' construct, `or' can be written in terms of `cond'.
     For example:

          (or ARG1 ARG2 ARG3)
          ==
          (cond (ARG1)
                (ARG2)
                (ARG3))

     You could almost write `or' in terms of `if', but not quite:

          (if ARG1 ARG1
            (if ARG2 ARG2
              ARG3))

     This is not completely equivalent because it can evaluate ARG1 or
     ARG2 twice.  By contrast, `(or ARG1 ARG2 ARG3)' never evaluates
     any argument more than once.


File: elisp,  Node: Iteration,  Next: Nonlocal Exits,  Prev: Combining Conditions,  Up: Control Structures

10.4 Iteration
==============

Iteration means executing part of a program repetitively.  For example,
you might want to repeat some computation once for each element of a
list, or once for each integer from 0 to N.  You can do this in Emacs
Lisp with the special form `while':

 -- Special Form: while condition forms...
     `while' first evaluates CONDITION.  If the result is non-`nil', it
     evaluates FORMS in textual order.  Then it reevaluates CONDITION,
     and if the result is non-`nil', it evaluates FORMS again.  This
     process repeats until CONDITION evaluates to `nil'.

     There is no limit on the number of iterations that may occur.  The
     loop will continue until either CONDITION evaluates to `nil' or
     until an error or `throw' jumps out of it (*note Nonlocal Exits::).

     The value of a `while' form is always `nil'.

          (setq num 0)
               => 0
          (while (< num 4)
            (princ (format "Iteration %d." num))
            (setq num (1+ num)))
               -| Iteration 0.
               -| Iteration 1.
               -| Iteration 2.
               -| Iteration 3.
               => nil

     To write a "repeat...until" loop, which will execute something on
     each iteration and then do the end-test, put the body followed by
     the end-test in a `progn' as the first argument of `while', as
     shown here:

          (while (progn
                   (forward-line 1)
                   (not (looking-at "^$"))))

     This moves forward one line and continues moving by lines until it
     reaches an empty line.  It is peculiar in that the `while' has no
     body, just the end test (which also does the real work of moving
     point).

   The `dolist' and `dotimes' macros provide convenient ways to write
two common kinds of loops.

 -- Macro: dolist (var list [result]) body...
     This construct executes BODY once for each element of LIST,
     binding the variable VAR locally to hold the current element.
     Then it returns the value of evaluating RESULT, or `nil' if RESULT
     is omitted.  For example, here is how you could use `dolist' to
     define the `reverse' function:

          (defun reverse (list)
            (let (value)
              (dolist (elt list value)
                (setq value (cons elt value)))))

 -- Macro: dotimes (var count [result]) body...
     This construct executes BODY once for each integer from 0
     (inclusive) to COUNT (exclusive), binding the variable VAR to the
     integer for the current iteration.  Then it returns the value of
     evaluating RESULT, or `nil' if RESULT is omitted.  Here is an
     example of using `dotimes' to do something 100 times:

          (dotimes (i 100)
            (insert "I will not obey absurd orders\n"))


File: elisp,  Node: Nonlocal Exits,  Prev: Iteration,  Up: Control Structures

10.5 Nonlocal Exits
===================

A "nonlocal exit" is a transfer of control from one point in a program
to another remote point.  Nonlocal exits can occur in Emacs Lisp as a
result of errors; you can also use them under explicit control.
Nonlocal exits unbind all variable bindings made by the constructs being
exited.

* Menu:

* Catch and Throw::     Nonlocal exits for the program's own purposes.
* Examples of Catch::   Showing how such nonlocal exits can be written.
* Errors::              How errors are signaled and handled.
* Cleanups::            Arranging to run a cleanup form if an error happens.


File: elisp,  Node: Catch and Throw,  Next: Examples of Catch,  Up: Nonlocal Exits

10.5.1 Explicit Nonlocal Exits: `catch' and `throw'
---------------------------------------------------

Most control constructs affect only the flow of control within the
construct itself.  The function `throw' is the exception to this rule
of normal program execution: it performs a nonlocal exit on request.
(There are other exceptions, but they are for error handling only.)
`throw' is used inside a `catch', and jumps back to that `catch'.  For
example:

     (defun foo-outer ()
       (catch 'foo
         (foo-inner)))

     (defun foo-inner ()
       ...
       (if x
           (throw 'foo t))
       ...)

The `throw' form, if executed, transfers control straight back to the
corresponding `catch', which returns immediately.  The code following
the `throw' is not executed.  The second argument of `throw' is used as
the return value of the `catch'.

   The function `throw' finds the matching `catch' based on the first
argument: it searches for a `catch' whose first argument is `eq' to the
one specified in the `throw'.  If there is more than one applicable
`catch', the innermost one takes precedence.  Thus, in the above
example, the `throw' specifies `foo', and the `catch' in `foo-outer'
specifies the same symbol, so that `catch' is the applicable one
(assuming there is no other matching `catch' in between).

   Executing `throw' exits all Lisp constructs up to the matching
`catch', including function calls.  When binding constructs such as
`let' or function calls are exited in this way, the bindings are
unbound, just as they are when these constructs exit normally (*note
Local Variables::).  Likewise, `throw' restores the buffer and position
saved by `save-excursion' (*note Excursions::), and the narrowing
status saved by `save-restriction' and the window selection saved by
`save-window-excursion' (*note Window Configurations::).  It also runs
any cleanups established with the `unwind-protect' special form when it
exits that form (*note Cleanups::).

   The `throw' need not appear lexically within the `catch' that it
jumps to.  It can equally well be called from another function called
within the `catch'.  As long as the `throw' takes place chronologically
after entry to the `catch', and chronologically before exit from it, it
has access to that `catch'.  This is why `throw' can be used in
commands such as `exit-recursive-edit' that throw back to the editor
command loop (*note Recursive Editing::).

     Common Lisp note: Most other versions of Lisp, including Common
     Lisp, have several ways of transferring control nonsequentially:
     `return', `return-from', and `go', for example.  Emacs Lisp has
     only `throw'.

 -- Special Form: catch tag body...
     `catch' establishes a return point for the `throw' function.  The
     return point is distinguished from other such return points by
     TAG, which may be any Lisp object except `nil'.  The argument TAG
     is evaluated normally before the return point is established.

     With the return point in effect, `catch' evaluates the forms of the
     BODY in textual order.  If the forms execute normally (without
     error or nonlocal exit) the value of the last body form is
     returned from the `catch'.

     If a `throw' is executed during the execution of BODY, specifying
     the same value TAG, the `catch' form exits immediately; the value
     it returns is whatever was specified as the second argument of
     `throw'.

 -- Function: throw tag value
     The purpose of `throw' is to return from a return point previously
     established with `catch'.  The argument TAG is used to choose
     among the various existing return points; it must be `eq' to the
     value specified in the `catch'.  If multiple return points match
     TAG, the innermost one is used.

     The argument VALUE is used as the value to return from that
     `catch'.

     If no return point is in effect with tag TAG, then a `no-catch'
     error is signaled with data `(TAG VALUE)'.


File: elisp,  Node: Examples of Catch,  Next: Errors,  Prev: Catch and Throw,  Up: Nonlocal Exits

10.5.2 Examples of `catch' and `throw'
--------------------------------------

One way to use `catch' and `throw' is to exit from a doubly nested
loop.  (In most languages, this would be done with a "go to.")  Here we
compute `(foo I J)' for I and J varying from 0 to 9:

     (defun search-foo ()
       (catch 'loop
         (let ((i 0))
           (while (< i 10)
             (let ((j 0))
               (while (< j 10)
                 (if (foo i j)
                     (throw 'loop (list i j)))
                 (setq j (1+ j))))
             (setq i (1+ i))))))

If `foo' ever returns non-`nil', we stop immediately and return a list
of I and J.  If `foo' always returns `nil', the `catch' returns
normally, and the value is `nil', since that is the result of the
`while'.

   Here are two tricky examples, slightly different, showing two return
points at once.  First, two return points with the same tag, `hack':

     (defun catch2 (tag)
       (catch tag
         (throw 'hack 'yes)))
     => catch2

     (catch 'hack
       (print (catch2 'hack))
       'no)
     -| yes
     => no

Since both return points have tags that match the `throw', it goes to
the inner one, the one established in `catch2'.  Therefore, `catch2'
returns normally with value `yes', and this value is printed.  Finally
the second body form in the outer `catch', which is `'no', is evaluated
and returned from the outer `catch'.

   Now let's change the argument given to `catch2':

     (catch 'hack
       (print (catch2 'quux))
       'no)
     => yes

We still have two return points, but this time only the outer one has
the tag `hack'; the inner one has the tag `quux' instead.  Therefore,
`throw' makes the outer `catch' return the value `yes'.  The function
`print' is never called, and the body-form `'no' is never evaluated.


File: elisp,  Node: Errors,  Next: Cleanups,  Prev: Examples of Catch,  Up: Nonlocal Exits

10.5.3 Errors
-------------

When Emacs Lisp attempts to evaluate a form that, for some reason,
cannot be evaluated, it "signals" an "error".

   When an error is signaled, Emacs's default reaction is to print an
error message and terminate execution of the current command.  This is
the right thing to do in most cases, such as if you type `C-f' at the
end of the buffer.

   In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers that should be deleted before
the program is finished.  In such cases, you would use `unwind-protect'
to establish "cleanup expressions" to be evaluated in case of error.
(*Note Cleanups::.)  Occasionally, you may wish the program to continue
execution despite an error in a subroutine.  In these cases, you would
use `condition-case' to establish "error handlers" to recover control
in case of error.

   Resist the temptation to use error handling to transfer control from
one part of the program to another; use `catch' and `throw' instead.
*Note Catch and Throw::.

* Menu:

* Signaling Errors::      How to report an error.
* Processing of Errors::  What Emacs does when you report an error.
* Handling Errors::       How you can trap errors and continue execution.
* Error Symbols::         How errors are classified for trapping them.


File: elisp,  Node: Signaling Errors,  Next: Processing of Errors,  Up: Errors

10.5.3.1 How to Signal an Error
...............................

"Signaling" an error means beginning error processing.  Error
processing normally aborts all or part of the running program and
returns to a point that is set up to handle the error (*note Processing
of Errors::).  Here we describe how to signal an error.

   Most errors are signaled "automatically" within Lisp primitives
which you call for other purposes, such as if you try to take the CAR
of an integer or move forward a character at the end of the buffer.
You can also signal errors explicitly with the functions `error' and
`signal'.

   Quitting, which happens when the user types `C-g', is not considered
an error, but it is handled almost like an error.  *Note Quitting::.

   Every error specifies an error message, one way or another.  The
message should state what is wrong ("File does not exist"), not how
things ought to be ("File must exist").  The convention in Emacs Lisp
is that error messages should start with a capital letter, but should
not end with any sort of punctuation.

 -- Function: error format-string &rest args
     This function signals an error with an error message constructed by
     applying `format' (*note Formatting Strings::) to FORMAT-STRING
     and ARGS.

     These examples show typical uses of `error':

          (error "That is an error -- try something else")
               error--> That is an error -- try something else

          (error "You have committed %d errors" 10)
               error--> You have committed 10 errors

     `error' works by calling `signal' with two arguments: the error
     symbol `error', and a list containing the string returned by
     `format'.

     *Warning:* If you want to use your own string as an error message
     verbatim, don't just write `(error STRING)'.  If STRING contains
     `%', it will be interpreted as a format specifier, with
     undesirable results.  Instead, use `(error "%s" STRING)'.

 -- Function: signal error-symbol data
     This function signals an error named by ERROR-SYMBOL.  The
     argument DATA is a list of additional Lisp objects relevant to the
     circumstances of the error.

     The argument ERROR-SYMBOL must be an "error symbol"--a symbol
     bearing a property `error-conditions' whose value is a list of
     condition names.  This is how Emacs Lisp classifies different
     sorts of errors. *Note Error Symbols::, for a description of error
     symbols, error conditions and condition names.

     If the error is not handled, the two arguments are used in printing
     the error message.  Normally, this error message is provided by the
     `error-message' property of ERROR-SYMBOL.  If DATA is non-`nil',
     this is followed by a colon and a comma separated list of the
     unevaluated elements of DATA.  For `error', the error message is
     the CAR of DATA (that must be a string).  Subcategories of
     `file-error' are handled specially.

     The number and significance of the objects in DATA depends on
     ERROR-SYMBOL.  For example, with a `wrong-type-arg' error, there
     should be two objects in the list: a predicate that describes the
     type that was expected, and the object that failed to fit that
     type.

     Both ERROR-SYMBOL and DATA are available to any error handlers
     that handle the error: `condition-case' binds a local variable to
     a list of the form `(ERROR-SYMBOL .  DATA)' (*note Handling
     Errors::).

     The function `signal' never returns (though in older Emacs versions
     it could sometimes return).

          (signal 'wrong-number-of-arguments '(x y))
               error--> Wrong number of arguments: x, y

          (signal 'no-such-error '("My unknown error condition"))
               error--> peculiar error: "My unknown error condition"

     Common Lisp note: Emacs Lisp has nothing like the Common Lisp
     concept of continuable errors.


File: elisp,  Node: Processing of Errors,  Next: Handling Errors,  Prev: Signaling Errors,  Up: Errors

10.5.3.2 How Emacs Processes Errors
...................................

When an error is signaled, `signal' searches for an active "handler"
for the error.  A handler is a sequence of Lisp expressions designated
to be executed if an error happens in part of the Lisp program.  If the
error has an applicable handler, the handler is executed, and control
resumes following the handler.  The handler executes in the environment
of the `condition-case' that established it; all functions called
within that `condition-case' have already been exited, and the handler
cannot return to them.

   If there is no applicable handler for the error, it terminates the
current command and returns control to the editor command loop.  (The
command loop has an implicit handler for all kinds of errors.)  The
command loop's handler uses the error symbol and associated data to
print an error message.  You can use the variable
`command-error-function' to control how this is done:

 -- Variable: command-error-function
     This variable, if non-`nil', specifies a function to use to handle
     errors that return control to the Emacs command loop.  The
     function should take three arguments: DATA, a list of the same
     form that `condition-case' would bind to its variable; CONTEXT, a
     string describing the situation in which the error occurred, or
     (more often) `nil'; and CALLER, the Lisp function which called the
     primitive that signaled the error.

   An error that has no explicit handler may call the Lisp debugger.
The debugger is enabled if the variable `debug-on-error' (*note Error
Debugging::) is non-`nil'.  Unlike error handlers, the debugger runs in
the environment of the error, so that you can examine values of
variables precisely as they were at the time of the error.


File: elisp,  Node: Handling Errors,  Next: Error Symbols,  Prev: Processing of Errors,  Up: Errors

10.5.3.3 Writing Code to Handle Errors
......................................

The usual effect of signaling an error is to terminate the command that
is running and return immediately to the Emacs editor command loop.
You can arrange to trap errors occurring in a part of your program by
establishing an error handler, with the special form `condition-case'.
A simple example looks like this:

     (condition-case nil
         (delete-file filename)
       (error nil))

This deletes the file named FILENAME, catching any error and returning
`nil' if an error occurs.

   The second argument of `condition-case' is called the "protected
form".  (In the example above, the protected form is a call to
`delete-file'.)  The error handlers go into effect when this form
begins execution and are deactivated when this form returns.  They
remain in effect for all the intervening time.  In particular, they are
in effect during the execution of functions called by this form, in
their subroutines, and so on.  This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including
`signal' and `error') called by the protected form, not by the
protected form itself.

   The arguments after the protected form are handlers.  Each handler
lists one or more "condition names" (which are symbols) to specify
which errors it will handle.  The error symbol specified when an error
is signaled also defines a list of condition names.  A handler applies
to an error if they have any condition names in common.  In the example
above, there is one handler, and it specifies one condition name,
`error', which covers all errors.

   The search for an applicable handler checks all the established
handlers starting with the most recently established one.  Thus, if two
nested `condition-case' forms offer to handle the same error, the inner
of the two gets to handle it.

   If an error is handled by some `condition-case' form, this
ordinarily prevents the debugger from being run, even if
`debug-on-error' says this error should invoke the debugger.  *Note
Error Debugging::.  If you want to be able to debug errors that are
caught by a `condition-case', set the variable `debug-on-signal' to a
non-`nil' value.

   When an error is handled, control returns to the handler.  Before
this happens, Emacs unbinds all variable bindings made by binding
constructs that are being exited and executes the cleanups of all
`unwind-protect' forms that are exited.  Once control arrives at the
handler, the body of the handler is executed.

   After execution of the handler body, execution returns from the
`condition-case' form.  Because the protected form is exited completely
before execution of the handler, the handler cannot resume execution at
the point of the error, nor can it examine variable bindings that were
made within the protected form.  All it can do is clean up and proceed.

   The `condition-case' construct is often used to trap errors that are
predictable, such as failure to open a file in a call to
`insert-file-contents'.  It is also used to trap errors that are
totally unpredictable, such as when the program evaluates an expression
read from the user.

   Error signaling and handling have some resemblance to `throw' and
`catch' (*note Catch and Throw::), but they are entirely separate
facilities.  An error cannot be caught by a `catch', and a `throw'
cannot be handled by an error handler (though using `throw' when there
is no suitable `catch' signals an error that can be handled).

 -- Special Form: condition-case var protected-form handlers...
     This special form establishes the error handlers HANDLERS around
     the execution of PROTECTED-FORM.  If PROTECTED-FORM executes
     without error, the value it returns becomes the value of the
     `condition-case' form; in this case, the `condition-case' has no
     effect.  The `condition-case' form makes a difference when an
     error occurs during PROTECTED-FORM.

     Each of the HANDLERS is a list of the form `(CONDITIONS BODY...)'.
     Here CONDITIONS is an error condition name to be handled, or a
     list of condition names; BODY is one or more Lisp expressions to
     be executed when this handler handles an error.  Here are examples
     of handlers:

          (error nil)

          (arith-error (message "Division by zero"))

          ((arith-error file-error)
           (message
            "Either division by zero or failure to open a file"))

     Each error that occurs has an "error symbol" that describes what
     kind of error it is.  The `error-conditions' property of this
     symbol is a list of condition names (*note Error Symbols::).  Emacs
     searches all the active `condition-case' forms for a handler that
     specifies one or more of these condition names; the innermost
     matching `condition-case' handles the error.  Within this
     `condition-case', the first applicable handler handles the error.

     After executing the body of the handler, the `condition-case'
     returns normally, using the value of the last form in the handler
     body as the overall value.

     The argument VAR is a variable.  `condition-case' does not bind
     this variable when executing the PROTECTED-FORM, only when it
     handles an error.  At that time, it binds VAR locally to an "error
     description", which is a list giving the particulars of the error.
     The error description has the form `(ERROR-SYMBOL . DATA)'.  The
     handler can refer to this list to decide what to do.  For example,
     if the error is for failure opening a file, the file name is the
     second element of DATA--the third element of the error description.

     If VAR is `nil', that means no variable is bound.  Then the error
     symbol and associated data are not available to the handler.

 -- Function: error-message-string error-description
     This function returns the error message string for a given error
     descriptor.  It is useful if you want to handle an error by
     printing the usual error message for that error.  *Note Definition
     of signal::.

   Here is an example of using `condition-case' to handle the error
that results from dividing by zero.  The handler displays the error
message (but without a beep), then returns a very large number.

     (defun safe-divide (dividend divisor)
       (condition-case err
           ;; Protected form.
           (/ dividend divisor)
         ;; The handler.
         (arith-error                        ; Condition.
          ;; Display the usual message for this error.
          (message "%s" (error-message-string err))
          1000000)))
     => safe-divide

     (safe-divide 5 0)
          -| Arithmetic error: (arith-error)
     => 1000000

The handler specifies condition name `arith-error' so that it will
handle only division-by-zero errors.  Other kinds of errors will not be
handled, at least not by this `condition-case'.  Thus,

     (safe-divide nil 3)
          error--> Wrong type argument: number-or-marker-p, nil

   Here is a `condition-case' that catches all kinds of errors,
including those signaled with `error':

     (setq baz 34)
          => 34

     (condition-case err
         (if (eq baz 35)
             t
           ;; This is a call to the function `error'.
           (error "Rats!  The variable %s was %s, not 35" 'baz baz))
       ;; This is the handler; it is not a form.
       (error (princ (format "The error was: %s" err))
              2))
     -| The error was: (error "Rats!  The variable baz was 34, not 35")
     => 2


File: elisp,  Node: Error Symbols,  Prev: Handling Errors,  Up: Errors

10.5.3.4 Error Symbols and Condition Names
..........................................

When you signal an error, you specify an "error symbol" to specify the
kind of error you have in mind.  Each error has one and only one error
symbol to categorize it.  This is the finest classification of errors
defined by the Emacs Lisp language.

   These narrow classifications are grouped into a hierarchy of wider
classes called "error conditions", identified by "condition names".
The narrowest such classes belong to the error symbols themselves: each
error symbol is also a condition name.  There are also condition names
for more extensive classes, up to the condition name `error' which
takes in all kinds of errors (but not `quit').  Thus, each error has
one or more condition names: `error', the error symbol if that is
distinct from `error', and perhaps some intermediate classifications.

   In order for a symbol to be an error symbol, it must have an
`error-conditions' property which gives a list of condition names.
This list defines the conditions that this kind of error belongs to.
(The error symbol itself, and the symbol `error', should always be
members of this list.)  Thus, the hierarchy of condition names is
defined by the `error-conditions' properties of the error symbols.
Because quitting is not considered an error, the value of the
`error-conditions' property of `quit' is just `(quit)'.

   In addition to the `error-conditions' list, the error symbol should
have an `error-message' property whose value is a string to be printed
when that error is signaled but not handled.  If the error symbol has
no `error-message' property or if the `error-message' property exists,
but is not a string, the error message `peculiar error' is used.  *Note
Definition of signal::.

   Here is how we define a new error symbol, `new-error':

     (put 'new-error
          'error-conditions
          '(error my-own-errors new-error))
     => (error my-own-errors new-error)
     (put 'new-error 'error-message "A new error")
     => "A new error"

This error has three condition names: `new-error', the narrowest
classification; `my-own-errors', which we imagine is a wider
classification; and `error', which is the widest of all.

   The error string should start with a capital letter but it should
not end with a period.  This is for consistency with the rest of Emacs.

   Naturally, Emacs will never signal `new-error' on its own; only an
explicit call to `signal' (*note Definition of signal::) in your code
can do this:

     (signal 'new-error '(x y))
          error--> A new error: x, y

   This error can be handled through any of the three condition names.
This example handles `new-error' and any other errors in the class
`my-own-errors':

     (condition-case foo
         (bar nil t)
       (my-own-errors nil))

   The significant way that errors are classified is by their condition
names--the names used to match errors with handlers.  An error symbol
serves only as a convenient way to specify the intended error message
and list of condition names.  It would be cumbersome to give `signal' a
list of condition names rather than one error symbol.

   By contrast, using only error symbols without condition names would
seriously decrease the power of `condition-case'.  Condition names make
it possible to categorize errors at various levels of generality when
you write an error handler.  Using error symbols alone would eliminate
all but the narrowest level of classification.

   *Note Standard Errors::, for a list of all the standard error symbols
and their conditions.


File: elisp,  Node: Cleanups,  Prev: Errors,  Up: Nonlocal Exits

10.5.4 Cleaning Up from Nonlocal Exits
--------------------------------------

The `unwind-protect' construct is essential whenever you temporarily
put a data structure in an inconsistent state; it permits you to make
the data consistent again in the event of an error or throw.  (Another
more specific cleanup construct that is used only for changes in buffer
contents is the atomic change group; *Note Atomic Changes::.)

 -- Special Form: unwind-protect body-form cleanup-forms...
     `unwind-protect' executes BODY-FORM with a guarantee that the
     CLEANUP-FORMS will be evaluated if control leaves BODY-FORM, no
     matter how that happens.  BODY-FORM may complete normally, or
     execute a `throw' out of the `unwind-protect', or cause an error;
     in all cases, the CLEANUP-FORMS will be evaluated.

     If BODY-FORM finishes normally, `unwind-protect' returns the value
     of BODY-FORM, after it evaluates the CLEANUP-FORMS.  If BODY-FORM
     does not finish, `unwind-protect' does not return any value in the
     normal sense.

     Only BODY-FORM is protected by the `unwind-protect'.  If any of
     the CLEANUP-FORMS themselves exits nonlocally (via a `throw' or an
     error), `unwind-protect' is _not_ guaranteed to evaluate the rest
     of them.  If the failure of one of the CLEANUP-FORMS has the
     potential to cause trouble, then protect it with another
     `unwind-protect' around that form.

     The number of currently active `unwind-protect' forms counts,
     together with the number of local variable bindings, against the
     limit `max-specpdl-size' (*note Local Variables: Definition of
     max-specpdl-size.).

   For example, here we make an invisible buffer for temporary use, and
make sure to kill it before finishing:

     (save-excursion
       (let ((buffer (get-buffer-create " *temp*")))
         (set-buffer buffer)
         (unwind-protect
             BODY-FORM
           (kill-buffer buffer))))

You might think that we could just as well write `(kill-buffer
(current-buffer))' and dispense with the variable `buffer'.  However,
the way shown above is safer, if BODY-FORM happens to get an error
after switching to a different buffer!  (Alternatively, you could write
another `save-excursion' around BODY-FORM, to ensure that the temporary
buffer becomes current again in time to kill it.)

   Emacs includes a standard macro called `with-temp-buffer' which
expands into more or less the code shown above (*note Current Buffer:
Definition of with-temp-buffer.).  Several of the macros defined in
this manual use `unwind-protect' in this way.

   Here is an actual example derived from an FTP package.  It creates a
process (*note Processes::) to try to establish a connection to a remote
machine.  As the function `ftp-login' is highly susceptible to numerous
problems that the writer of the function cannot anticipate, it is
protected with a form that guarantees deletion of the process in the
event of failure.  Otherwise, Emacs might fill up with useless
subprocesses.

     (let ((win nil))
       (unwind-protect
           (progn
             (setq process (ftp-setup-buffer host file))
             (if (setq win (ftp-login process host user password))
                 (message "Logged in")
               (error "Ftp login failed")))
         (or win (and process (delete-process process)))))

   This example has a small bug: if the user types `C-g' to quit, and
the quit happens immediately after the function `ftp-setup-buffer'
returns but before the variable `process' is set, the process will not
be killed.  There is no easy way to fix this bug, but at least it is
very unlikely.


File: elisp,  Node: Variables,  Next: Functions,  Prev: Control Structures,  Up: Top

11 Variables
************

A "variable" is a name used in a program to stand for a value.  Nearly
all programming languages have variables of some sort.  In the text of
a Lisp program, variables are written using the syntax for symbols.

   In Lisp, unlike most programming languages, programs are represented
primarily as Lisp objects and only secondarily as text.  The Lisp
objects used for variables are symbols: the symbol name is the variable
name, and the variable's value is stored in the value cell of the
symbol.  The use of a symbol as a variable is independent of its use as
a function name.  *Note Symbol Components::.

   The Lisp objects that constitute a Lisp program determine the textual
form of the program--it is simply the read syntax for those Lisp
objects.  This is why, for example, a variable in a textual Lisp program
is written using the read syntax for the symbol that represents the
variable.

* Menu:

* Global Variables::      Variable values that exist permanently, everywhere.
* Constant Variables::    Certain "variables" have values that never change.
* Local Variables::       Variable values that exist only temporarily.
* Void Variables::        Symbols that lack values.
* Defining Variables::    A definition says a symbol is used as a variable.
* Tips for Defining::     Things you should think about when you
                            define a variable.
* Accessing Variables::   Examining values of variables whose names
                            are known only at run time.
* Setting Variables::     Storing new values in variables.
* Variable Scoping::      How Lisp chooses among local and global values.
* Buffer-Local Variables::  Variable values in effect only in one buffer.
* Future Local Variables::  New kinds of local values we might add some day.
* File Local Variables::  Handling local variable lists in files.
* Variable Aliases::      Variables that are aliases for other variables.
* Variables with Restricted Values::  Non-constant variables whose value can
                                        _not_ be an arbitrary Lisp object.


File: elisp,  Node: Global Variables,  Next: Constant Variables,  Up: Variables

11.1 Global Variables
=====================

The simplest way to use a variable is "globally".  This means that the
variable has just one value at a time, and this value is in effect (at
least for the moment) throughout the Lisp system.  The value remains in
effect until you specify a new one.  When a new value replaces the old
one, no trace of the old value remains in the variable.

   You specify a value for a symbol with `setq'.  For example,

     (setq x '(a b))

gives the variable `x' the value `(a b)'.  Note that `setq' does not
evaluate its first argument, the name of the variable, but it does
evaluate the second argument, the new value.

   Once the variable has a value, you can refer to it by using the
symbol by itself as an expression.  Thus,

     x => (a b)

assuming the `setq' form shown above has already been executed.

   If you do set the same variable again, the new value replaces the old
one:

     x
          => (a b)
     (setq x 4)
          => 4
     x
          => 4


File: elisp,  Node: Constant Variables,  Next: Local Variables,  Prev: Global Variables,  Up: Variables

11.2 Variables that Never Change
================================

In Emacs Lisp, certain symbols normally evaluate to themselves.  These
include `nil' and `t', as well as any symbol whose name starts with `:'
(these are called "keywords").  These symbols cannot be rebound, nor
can their values be changed.  Any attempt to set or bind `nil' or `t'
signals a `setting-constant' error.  The same is true for a keyword (a
symbol whose name starts with `:'), if it is interned in the standard
obarray, except that setting such a symbol to itself is not an error.

     nil == 'nil
          => nil
     (setq nil 500)
     error--> Attempt to set constant symbol: nil

 -- Function: keywordp object
     function returns `t' if OBJECT is a symbol whose name starts with
     `:', interned in the standard obarray, and returns `nil' otherwise.


File: elisp,  Node: Local Variables,  Next: Void Variables,  Prev: Constant Variables,  Up: Variables

11.3 Local Variables
====================

Global variables have values that last until explicitly superseded with
new values.  Sometimes it is useful to create variable values that
exist temporarily--only until a certain part of the program finishes.
These values are called "local", and the variables so used are called
"local variables".

   For example, when a function is called, its argument variables
receive new local values that last until the function exits.  The `let'
special form explicitly establishes new local values for specified
variables; these last until exit from the `let' form.

   Establishing a local value saves away the previous value (or lack of
one) of the variable.  When the life span of the local value is over,
the previous value is restored.  In the mean time, we say that the
previous value is "shadowed" and "not visible".  Both global and local
values may be shadowed (*note Scope::).

   If you set a variable (such as with `setq') while it is local, this
replaces the local value; it does not alter the global value, or
previous local values, that are shadowed.  To model this behavior, we
speak of a "local binding" of the variable as well as a local value.

   The local binding is a conceptual place that holds a local value.
Entry to a function, or a special form such as `let', creates the local
binding; exit from the function or from the `let' removes the local
binding.  As long as the local binding lasts, the variable's value is
stored within it.  Use of `setq' or `set' while there is a local
binding stores a different value into the local binding; it does not
create a new binding.

   We also speak of the "global binding", which is where (conceptually)
the global value is kept.

   A variable can have more than one local binding at a time (for
example, if there are nested `let' forms that bind it).  In such a
case, the most recently created local binding that still exists is the
"current binding" of the variable.  (This rule is called "dynamic
scoping"; see *Note Variable Scoping::.)  If there are no local
bindings, the variable's global binding is its current binding.  We
sometimes call the current binding the "most-local existing binding",
for emphasis.  Ordinary evaluation of a symbol always returns the value
of its current binding.

   The special forms `let' and `let*' exist to create local bindings.

 -- Special Form: let (bindings...) forms...
     This special form binds variables according to BINDINGS and then
     evaluates all of the FORMS in textual order.  The `let'-form
     returns the value of the last form in FORMS.

     Each of the BINDINGS is either (i) a symbol, in which case that
     symbol is bound to `nil'; or (ii) a list of the form `(SYMBOL
     VALUE-FORM)', in which case SYMBOL is bound to the result of
     evaluating VALUE-FORM.  If VALUE-FORM is omitted, `nil' is used.

     All of the VALUE-FORMs in BINDINGS are evaluated in the order they
     appear and _before_ binding any of the symbols to them.  Here is
     an example of this: `z' is bound to the old value of `y', which is
     2, not the new value of `y', which is 1.

          (setq y 2)
               => 2
          (let ((y 1)
                (z y))
            (list y z))
               => (1 2)

 -- Special Form: let* (bindings...) forms...
     This special form is like `let', but it binds each variable right
     after computing its local value, before computing the local value
     for the next variable.  Therefore, an expression in BINDINGS can
     reasonably refer to the preceding symbols bound in this `let*'
     form.  Compare the following example with the example above for
     `let'.

          (setq y 2)
               => 2
          (let* ((y 1)
                 (z y))    ; Use the just-established value of `y'.
            (list y z))
               => (1 1)

   Here is a complete list of the other facilities that create local
bindings:

   * Function calls (*note Functions::).

   * Macro calls (*note Macros::).

   * `condition-case' (*note Errors::).

   Variables can also have buffer-local bindings (*note Buffer-Local
Variables::); a few variables have terminal-local bindings (*note
Multiple Displays::).  These kinds of bindings work somewhat like
ordinary local bindings, but they are localized depending on "where"
you are in Emacs, rather than localized in time.

 -- Variable: max-specpdl-size
     This variable defines the limit on the total number of local
     variable bindings and `unwind-protect' cleanups (*note Cleaning Up
     from Nonlocal Exits: Cleanups.) that are allowed before signaling
     an error (with data `"Variable binding depth exceeds
     max-specpdl-size"').

     This limit, with the associated error when it is exceeded, is one
     way that Lisp avoids infinite recursion on an ill-defined function.
     `max-lisp-eval-depth' provides another limit on depth of nesting.
     *Note Eval: Definition of max-lisp-eval-depth.

     The default value is 1000.  Entry to the Lisp debugger increases
     the value, if there is little room left, to make sure the debugger
     itself has room to execute.


File: elisp,  Node: Void Variables,  Next: Defining Variables,  Prev: Local Variables,  Up: Variables

11.4 When a Variable is "Void"
==============================

If you have never given a symbol any value as a global variable, we say
that that symbol's global value is "void".  In other words, the
symbol's value cell does not have any Lisp object in it.  If you try to
evaluate the symbol, you get a `void-variable' error rather than a
value.

   Note that a value of `nil' is not the same as void.  The symbol
`nil' is a Lisp object and can be the value of a variable just as any
other object can be; but it is _a value_.  A void variable does not
have any value.

   After you have given a variable a value, you can make it void once
more using `makunbound'.

 -- Function: makunbound symbol
     This function makes the current variable binding of SYMBOL void.
     Subsequent attempts to use this symbol's value as a variable will
     signal the error `void-variable', unless and until you set it
     again.

     `makunbound' returns SYMBOL.

          (makunbound 'x)      ; Make the global value of `x' void.
               => x
          x
          error--> Symbol's value as variable is void: x

     If SYMBOL is locally bound, `makunbound' affects the most local
     existing binding.  This is the only way a symbol can have a void
     local binding, since all the constructs that create local bindings
     create them with values.  In this case, the voidness lasts at most
     as long as the binding does; when the binding is removed due to
     exit from the construct that made it, the previous local or global
     binding is reexposed as usual, and the variable is no longer void
     unless the newly reexposed binding was void all along.

          (setq x 1)               ; Put a value in the global binding.
               => 1
          (let ((x 2))             ; Locally bind it.
            (makunbound 'x)        ; Void the local binding.
            x)
          error--> Symbol's value as variable is void: x
          x                        ; The global binding is unchanged.
               => 1

          (let ((x 2))             ; Locally bind it.
            (let ((x 3))           ; And again.
              (makunbound 'x)      ; Void the innermost-local binding.
              x))                  ; And refer: it's void.
          error--> Symbol's value as variable is void: x

          (let ((x 2))
            (let ((x 3))
              (makunbound 'x))     ; Void inner binding, then remove it.
            x)                     ; Now outer `let' binding is visible.
               => 2

   A variable that has been made void with `makunbound' is
indistinguishable from one that has never received a value and has
always been void.

   You can use the function `boundp' to test whether a variable is
currently void.

 -- Function: boundp variable
     `boundp' returns `t' if VARIABLE (a symbol) is not void; more
     precisely, if its current binding is not void.  It returns `nil'
     otherwise.

          (boundp 'abracadabra)          ; Starts out void.
               => nil
          (let ((abracadabra 5))         ; Locally bind it.
            (boundp 'abracadabra))
               => t
          (boundp 'abracadabra)          ; Still globally void.
               => nil
          (setq abracadabra 5)           ; Make it globally nonvoid.
               => 5
          (boundp 'abracadabra)
               => t


File: elisp,  Node: Defining Variables,  Next: Tips for Defining,  Prev: Void Variables,  Up: Variables

11.5 Defining Global Variables
==============================

You may announce your intention to use a symbol as a global variable
with a "variable definition": a special form, either `defconst' or
`defvar'.

   In Emacs Lisp, definitions serve three purposes.  First, they inform
people who read the code that certain symbols are _intended_ to be used
a certain way (as variables).  Second, they inform the Lisp system of
these things, supplying a value and documentation.  Third, they provide
information to utilities such as `etags' and `make-docfile', which
create data bases of the functions and variables in a program.

   The difference between `defconst' and `defvar' is primarily a matter
of intent, serving to inform human readers of whether the value should
ever change.  Emacs Lisp does not restrict the ways in which a variable
can be used based on `defconst' or `defvar' declarations.  However, it
does make a difference for initialization: `defconst' unconditionally
initializes the variable, while `defvar' initializes it only if it is
void.

 -- Special Form: defvar symbol [value [doc-string]]
     This special form defines SYMBOL as a variable and can also
     initialize and document it.  The definition informs a person
     reading your code that SYMBOL is used as a variable that might be
     set or changed.  Note that SYMBOL is not evaluated; the symbol to
     be defined must appear explicitly in the `defvar'.

     If SYMBOL is void and VALUE is specified, `defvar' evaluates it
     and sets SYMBOL to the result.  But if SYMBOL already has a value
     (i.e., it is not void), VALUE is not even evaluated, and SYMBOL's
     value remains unchanged.  If VALUE is omitted, the value of SYMBOL
     is not changed in any case.

     If SYMBOL has a buffer-local binding in the current buffer,
     `defvar' operates on the default value, which is
     buffer-independent, not the current (buffer-local) binding.  It
     sets the default value if the default value is void.  *Note
     Buffer-Local Variables::.

     When you evaluate a top-level `defvar' form with `C-M-x' in Emacs
     Lisp mode (`eval-defun'), a special feature of `eval-defun'
     arranges to set the variable unconditionally, without testing
     whether its value is void.

     If the DOC-STRING argument appears, it specifies the documentation
     for the variable.  (This opportunity to specify documentation is
     one of the main benefits of defining the variable.)  The
     documentation is stored in the symbol's `variable-documentation'
     property.  The Emacs help functions (*note Documentation::) look
     for this property.

     If the variable is a user option that users would want to set
     interactively, you should use `*' as the first character of
     DOC-STRING.  This lets users set the variable conveniently using
     the `set-variable' command.  Note that you should nearly always
     use `defcustom' instead of `defvar' to define these variables, so
     that users can use `M-x customize' and related commands to set
     them.  *Note Customization::.

     Here are some examples.  This form defines `foo' but does not
     initialize it:

          (defvar foo)
               => foo

     This example initializes the value of `bar' to `23', and gives it
     a documentation string:

          (defvar bar 23
            "The normal weight of a bar.")
               => bar

     The following form changes the documentation string for `bar',
     making it a user option, but does not change the value, since `bar'
     already has a value.  (The addition `(1+ nil)' would get an error
     if it were evaluated, but since it is not evaluated, there is no
     error.)

          (defvar bar (1+ nil)
            "*The normal weight of a bar.")
               => bar
          bar
               => 23

     Here is an equivalent expression for the `defvar' special form:

          (defvar SYMBOL VALUE DOC-STRING)
          ==
          (progn
            (if (not (boundp 'SYMBOL))
                (setq SYMBOL VALUE))
            (if 'DOC-STRING
              (put 'SYMBOL 'variable-documentation 'DOC-STRING))
            'SYMBOL)

     The `defvar' form returns SYMBOL, but it is normally used at top
     level in a file where its value does not matter.

 -- Special Form: defconst symbol value [doc-string]
     This special form defines SYMBOL as a value and initializes it.
     It informs a person reading your code that SYMBOL has a standard
     global value, established here, that should not be changed by the
     user or by other programs.  Note that SYMBOL is not evaluated; the
     symbol to be defined must appear explicitly in the `defconst'.

     `defconst' always evaluates VALUE, and sets the value of SYMBOL to
     the result.  If SYMBOL does have a buffer-local binding in the
     current buffer, `defconst' sets the default value, not the
     buffer-local value.  (But you should not be making buffer-local
     bindings for a symbol that is defined with `defconst'.)

     Here, `pi' is a constant that presumably ought not to be changed
     by anyone (attempts by the Indiana State Legislature
     notwithstanding).  As the second form illustrates, however, this
     is only advisory.

          (defconst pi 3.1415 "Pi to five places.")
               => pi
          (setq pi 3)
               => pi
          pi
               => 3

 -- Function: user-variable-p variable
     This function returns `t' if VARIABLE is a user option--a variable
     intended to be set by the user for customization--and `nil'
     otherwise.  (Variables other than user options exist for the
     internal purposes of Lisp programs, and users need not know about
     them.)

     User option variables are distinguished from other variables either
     though being declared using `defcustom'(1) or by the first
     character of their `variable-documentation' property.  If the
     property exists and is a string, and its first character is `*',
     then the variable is a user option.  Aliases of user options are
     also user options.

   If a user option variable has a `variable-interactive' property, the
`set-variable' command uses that value to control reading the new value
for the variable.  The property's value is used as if it were specified
in `interactive' (*note Using Interactive::).  However, this feature is
largely obsoleted by `defcustom' (*note Customization::).

   *Warning:* If the `defconst' and `defvar' special forms are used
while the variable has a local binding (made with `let', or a function
argument), they set the local-binding's value; the top-level binding is
not changed.  This is not what you usually want.  To prevent it, use
these special forms at top level in a file, where normally no local
binding is in effect, and make sure to load the file before making a
local binding for the variable.

   ---------- Footnotes ----------

   (1) They may also be declared equivalently in `cus-start.el'.


File: elisp,  Node: Tips for Defining,  Next: Accessing Variables,  Prev: Defining Variables,  Up: Variables

11.6 Tips for Defining Variables Robustly
=========================================

When you define a variable whose value is a function, or a list of
functions, use a name that ends in `-function' or `-functions',
respectively.

   There are several other variable name conventions; here is a
complete list:

`...-hook'
     The variable is a normal hook (*note Hooks::).

`...-function'
     The value is a function.

`...-functions'
     The value is a list of functions.

`...-form'
     The value is a form (an expression).

`...-forms'
     The value is a list of forms (expressions).

`...-predicate'
     The value is a predicate--a function of one argument that returns
     non-`nil' for "good" arguments and `nil' for "bad" arguments.

`...-flag'
     The value is significant only as to whether it is `nil' or not.

`...-program'
     The value is a program name.

`...-command'
     The value is a whole shell command.

`...-switches'
     The value specifies options for a command.

   When you define a variable, always consider whether you should mark
it as "risky"; see *Note File Local Variables::.

   When defining and initializing a variable that holds a complicated
value (such as a keymap with bindings in it), it's best to put the
entire computation of the value into the `defvar', like this:

     (defvar my-mode-map
       (let ((map (make-sparse-keymap)))
         (define-key map "\C-c\C-a" 'my-command)
         ...
         map)
       DOCSTRING)

This method has several benefits.  First, if the user quits while
loading the file, the variable is either still uninitialized or
initialized properly, never in-between.  If it is still uninitialized,
reloading the file will initialize it properly.  Second, reloading the
file once the variable is initialized will not alter it; that is
important if the user has run hooks to alter part of the contents (such
as, to rebind keys).  Third, evaluating the `defvar' form with `C-M-x'
_will_ reinitialize the map completely.

   Putting so much code in the `defvar' form has one disadvantage: it
puts the documentation string far away from the line which names the
variable.  Here's a safe way to avoid that:

     (defvar my-mode-map nil
       DOCSTRING)
     (unless my-mode-map
       (let ((map (make-sparse-keymap)))
         (define-key map "\C-c\C-a" 'my-command)
         ...
         (setq my-mode-map map)))

This has all the same advantages as putting the initialization inside
the `defvar', except that you must type `C-M-x' twice, once on each
form, if you do want to reinitialize the variable.

   But be careful not to write the code like this:

     (defvar my-mode-map nil
       DOCSTRING)
     (unless my-mode-map
       (setq my-mode-map (make-sparse-keymap))
       (define-key my-mode-map "\C-c\C-a" 'my-command)
       ...)

This code sets the variable, then alters it, but it does so in more than
one step.  If the user quits just after the `setq', that leaves the
variable neither correctly initialized nor void nor `nil'.  Once that
happens, reloading the file will not initialize the variable; it will
remain incomplete.


File: elisp,  Node: Accessing Variables,  Next: Setting Variables,  Prev: Tips for Defining,  Up: Variables

11.7 Accessing Variable Values
==============================

The usual way to reference a variable is to write the symbol which
names it (*note Symbol Forms::).  This requires you to specify the
variable name when you write the program.  Usually that is exactly what
you want to do.  Occasionally you need to choose at run time which
variable to reference; then you can use `symbol-value'.

 -- Function: symbol-value symbol
     This function returns the value of SYMBOL.  This is the value in
     the innermost local binding of the symbol, or its global value if
     it has no local bindings.

          (setq abracadabra 5)
               => 5
          (setq foo 9)
               => 9

          ;; Here the symbol `abracadabra'
          ;;   is the symbol whose value is examined.
          (let ((abracadabra 'foo))
            (symbol-value 'abracadabra))
               => foo

          ;; Here, the value of `abracadabra',
          ;;   which is `foo',
          ;;   is the symbol whose value is examined.
          (let ((abracadabra 'foo))
            (symbol-value abracadabra))
               => 9

          (symbol-value 'abracadabra)
               => 5

     A `void-variable' error is signaled if the current binding of
     SYMBOL is void.


File: elisp,  Node: Setting Variables,  Next: Variable Scoping,  Prev: Accessing Variables,  Up: Variables

11.8 How to Alter a Variable Value
==================================

The usual way to change the value of a variable is with the special
form `setq'.  When you need to compute the choice of variable at run
time, use the function `set'.

 -- Special Form: setq [symbol form]...
     This special form is the most common method of changing a
     variable's value.  Each SYMBOL is given a new value, which is the
     result of evaluating the corresponding FORM.  The most-local
     existing binding of the symbol is changed.

     `setq' does not evaluate SYMBOL; it sets the symbol that you
     write.  We say that this argument is "automatically quoted".  The
     `q' in `setq' stands for "quoted."

     The value of the `setq' form is the value of the last FORM.

          (setq x (1+ 2))
               => 3
          x                   ; `x' now has a global value.
               => 3
          (let ((x 5))
            (setq x 6)        ; The local binding of `x' is set.
            x)
               => 6
          x                   ; The global value is unchanged.
               => 3

     Note that the first FORM is evaluated, then the first SYMBOL is
     set, then the second FORM is evaluated, then the second SYMBOL is
     set, and so on:

          (setq x 10          ; Notice that `x' is set before
                y (1+ x))     ;   the value of `y' is computed.
               => 11

 -- Function: set symbol value
     This function sets SYMBOL's value to VALUE, then returns VALUE.
     Since `set' is a function, the expression written for SYMBOL is
     evaluated to obtain the symbol to set.

     The most-local existing binding of the variable is the binding
     that is set; shadowed bindings are not affected.

          (set one 1)
          error--> Symbol's value as variable is void: one
          (set 'one 1)
               => 1
          (set 'two 'one)
               => one
          (set two 2)         ; `two' evaluates to symbol `one'.
               => 2
          one                 ; So it is `one' that was set.
               => 2
          (let ((one 1))      ; This binding of `one' is set,
            (set 'one 3)      ;   not the global value.
            one)
               => 3
          one
               => 2

     If SYMBOL is not actually a symbol, a `wrong-type-argument' error
     is signaled.

          (set '(x y) 'z)
          error--> Wrong type argument: symbolp, (x y)

     Logically speaking, `set' is a more fundamental primitive than
     `setq'.  Any use of `setq' can be trivially rewritten to use
     `set'; `setq' could even be defined as a macro, given the
     availability of `set'.  However, `set' itself is rarely used;
     beginners hardly need to know about it.  It is useful only for
     choosing at run time which variable to set.  For example, the
     command `set-variable', which reads a variable name from the user
     and then sets the variable, needs to use `set'.

          Common Lisp note: In Common Lisp, `set' always changes the
          symbol's "special" or dynamic value, ignoring any lexical
          bindings.  In Emacs Lisp, all variables and all bindings are
          dynamic, so `set' always affects the most local existing
          binding.


File: elisp,  Node: Variable Scoping,  Next: Buffer-Local Variables,  Prev: Setting Variables,  Up: Variables

11.9 Scoping Rules for Variable Bindings
========================================

A given symbol `foo' can have several local variable bindings,
established at different places in the Lisp program, as well as a global
binding.  The most recently established binding takes precedence over
the others.

   Local bindings in Emacs Lisp have "indefinite scope" and "dynamic
extent".  "Scope" refers to _where_ textually in the source code the
binding can be accessed.  "Indefinite scope" means that any part of the
program can potentially access the variable binding.  "Extent" refers
to _when_, as the program is executing, the binding exists.  "Dynamic
extent" means that the binding lasts as long as the activation of the
construct that established it.

   The combination of dynamic extent and indefinite scope is called
"dynamic scoping".  By contrast, most programming languages use
"lexical scoping", in which references to a local variable must be
located textually within the function or block that binds the variable.

     Common Lisp note: Variables declared "special" in Common Lisp are
     dynamically scoped, like all variables in Emacs Lisp.

* Menu:

* Scope::          Scope means where in the program a value is visible.
                     Comparison with other languages.
* Extent::         Extent means how long in time a value exists.
* Impl of Scope::  Two ways to implement dynamic scoping.
* Using Scoping::  How to use dynamic scoping carefully and avoid problems.


File: elisp,  Node: Scope,  Next: Extent,  Up: Variable Scoping

11.9.1 Scope
------------

Emacs Lisp uses "indefinite scope" for local variable bindings.  This
means that any function anywhere in the program text might access a
given binding of a variable.  Consider the following function
definitions:

     (defun binder (x)   ; `x' is bound in `binder'.
        (foo 5))         ; `foo' is some other function.

     (defun user ()      ; `x' is used "free" in `user'.
       (list x))

   In a lexically scoped language, the binding of `x' in `binder' would
never be accessible in `user', because `user' is not textually
contained within the function `binder'.  However, in dynamically-scoped
Emacs Lisp, `user' may or may not refer to the binding of `x'
established in `binder', depending on the circumstances:

   * If we call `user' directly without calling `binder' at all, then
     whatever binding of `x' is found, it cannot come from `binder'.

   * If we define `foo' as follows and then call `binder', then the
     binding made in `binder' will be seen in `user':

          (defun foo (lose)
            (user))

   * However, if we define `foo' as follows and then call `binder',
     then the binding made in `binder' _will not_ be seen in `user':

          (defun foo (x)
            (user))

     Here, when `foo' is called by `binder', it binds `x'.  (The
     binding in `foo' is said to "shadow" the one made in `binder'.)
     Therefore, `user' will access the `x' bound by `foo' instead of
     the one bound by `binder'.

   Emacs Lisp uses dynamic scoping because simple implementations of
lexical scoping are slow.  In addition, every Lisp system needs to offer
dynamic scoping at least as an option; if lexical scoping is the norm,
there must be a way to specify dynamic scoping instead for a particular
variable.  It might not be a bad thing for Emacs to offer both, but
implementing it with dynamic scoping only was much easier.


File: elisp,  Node: Extent,  Next: Impl of Scope,  Prev: Scope,  Up: Variable Scoping

11.9.2 Extent
-------------

"Extent" refers to the time during program execution that a variable
name is valid.  In Emacs Lisp, a variable is valid only while the form
that bound it is executing.  This is called "dynamic extent".  "Local"
or "automatic" variables in most languages, including C and Pascal,
have dynamic extent.

   One alternative to dynamic extent is "indefinite extent".  This
means that a variable binding can live on past the exit from the form
that made the binding.  Common Lisp and Scheme, for example, support
this, but Emacs Lisp does not.

   To illustrate this, the function below, `make-add', returns a
function that purports to add N to its own argument M.  This would work
in Common Lisp, but it does not do the job in Emacs Lisp, because after
the call to `make-add' exits, the variable `n' is no longer bound to
the actual argument 2.

     (defun make-add (n)
         (function (lambda (m) (+ n m))))  ; Return a function.
          => make-add
     (fset 'add2 (make-add 2))  ; Define function `add2'
                                ;   with `(make-add 2)'.
          => (lambda (m) (+ n m))
     (add2 4)                   ; Try to add 2 to 4.
     error--> Symbol's value as variable is void: n

   Some Lisp dialects have "closures," objects that are like functions
but record additional variable bindings.  Emacs Lisp does not have
closures.


File: elisp,  Node: Impl of Scope,  Next: Using Scoping,  Prev: Extent,  Up: Variable Scoping

11.9.3 Implementation of Dynamic Scoping
----------------------------------------

A simple sample implementation (which is not how Emacs Lisp actually
works) may help you understand dynamic binding.  This technique is
called "deep binding" and was used in early Lisp systems.

   Suppose there is a stack of bindings, which are variable-value pairs.
At entry to a function or to a `let' form, we can push bindings onto
the stack for the arguments or local variables created there.  We can
pop those bindings from the stack at exit from the binding construct.

   We can find the value of a variable by searching the stack from top
to bottom for a binding for that variable; the value from that binding
is the value of the variable.  To set the variable, we search for the
current binding, then store the new value into that binding.

   As you can see, a function's bindings remain in effect as long as it
continues execution, even during its calls to other functions.  That is
why we say the extent of the binding is dynamic.  And any other function
can refer to the bindings, if it uses the same variables while the
bindings are in effect.  That is why we say the scope is indefinite.

   The actual implementation of variable scoping in GNU Emacs Lisp uses
a technique called "shallow binding".  Each variable has a standard
place in which its current value is always found--the value cell of the
symbol.

   In shallow binding, setting the variable works by storing a value in
the value cell.  Creating a new binding works by pushing the old value
(belonging to a previous binding) onto a stack, and storing the new
local value in the value cell.  Eliminating a binding works by popping
the old value off the stack, into the value cell.

   We use shallow binding because it has the same results as deep
binding, but runs faster, since there is never a need to search for a
binding.


File: elisp,  Node: Using Scoping,  Prev: Impl of Scope,  Up: Variable Scoping

11.9.4 Proper Use of Dynamic Scoping
------------------------------------

Binding a variable in one function and using it in another is a
powerful technique, but if used without restraint, it can make programs
hard to understand.  There are two clean ways to use this technique:

   * Use or bind the variable only in a few related functions, written
     close together in one file.  Such a variable is used for
     communication within one program.

     You should write comments to inform other programmers that they
     can see all uses of the variable before them, and to advise them
     not to add uses elsewhere.

   * Give the variable a well-defined, documented meaning, and make all
     appropriate functions refer to it (but not bind it or set it)
     wherever that meaning is relevant.  For example, the variable
     `case-fold-search' is defined as "non-`nil' means ignore case when
     searching"; various search and replace functions refer to it
     directly or through their subroutines, but do not bind or set it.

     Then you can bind the variable in other programs, knowing reliably
     what the effect will be.

   In either case, you should define the variable with `defvar'.  This
helps other people understand your program by telling them to look for
inter-function usage.  It also avoids a warning from the byte compiler.
Choose the variable's name to avoid name conflicts--don't use short
names like `x'.


File: elisp,  Node: Buffer-Local Variables,  Next: Future Local Variables,  Prev: Variable Scoping,  Up: Variables

11.10 Buffer-Local Variables
============================

Global and local variable bindings are found in most programming
languages in one form or another.  Emacs, however, also supports
additional, unusual kinds of variable binding, such as "buffer-local"
bindings, which apply only in one buffer.  Having different values for
a variable in different buffers is an important customization method.
(A few variables have bindings that are local to each terminal; see
*Note Multiple Displays::.)

* Menu:

* Intro to Buffer-Local::      Introduction and concepts.
* Creating Buffer-Local::      Creating and destroying buffer-local bindings.
* Default Value::              The default value is seen in buffers
                                 that don't have their own buffer-local values.


File: elisp,  Node: Intro to Buffer-Local,  Next: Creating Buffer-Local,  Up: Buffer-Local Variables

11.10.1 Introduction to Buffer-Local Variables
----------------------------------------------

A buffer-local variable has a buffer-local binding associated with a
particular buffer.  The binding is in effect when that buffer is
current; otherwise, it is not in effect.  If you set the variable while
a buffer-local binding is in effect, the new value goes in that binding,
so its other bindings are unchanged.  This means that the change is
visible only in the buffer where you made it.

   The variable's ordinary binding, which is not associated with any
specific buffer, is called the "default binding".  In most cases, this
is the global binding.

   A variable can have buffer-local bindings in some buffers but not in
other buffers.  The default binding is shared by all the buffers that
don't have their own bindings for the variable.  (This includes all
newly-created buffers.)  If you set the variable in a buffer that does
not have a buffer-local binding for it, this sets the default binding,
so the new value is visible in all the buffers that see the default
binding.

   The most common use of buffer-local bindings is for major modes to
change variables that control the behavior of commands.  For example, C
mode and Lisp mode both set the variable `paragraph-start' to specify
that only blank lines separate paragraphs.  They do this by making the
variable buffer-local in the buffer that is being put into C mode or
Lisp mode, and then setting it to the new value for that mode.  *Note
Major Modes::.

   The usual way to make a buffer-local binding is with
`make-local-variable', which is what major mode commands typically use.
This affects just the current buffer; all other buffers (including
those yet to be created) will continue to share the default value unless
they are explicitly given their own buffer-local bindings.

   A more powerful operation is to mark the variable as "automatically
buffer-local" by calling `make-variable-buffer-local'.  You can think
of this as making the variable local in all buffers, even those yet to
be created.  More precisely, the effect is that setting the variable
automatically makes the variable local to the current buffer if it is
not already so.  All buffers start out by sharing the default value of
the variable as usual, but setting the variable creates a buffer-local
binding for the current buffer.  The new value is stored in the
buffer-local binding, leaving the default binding untouched.  This
means that the default value cannot be changed with `setq' in any
buffer; the only way to change it is with `setq-default'.

   *Warning:* When a variable has buffer-local bindings in one or more
buffers, `let' rebinds the binding that's currently in effect.  For
instance, if the current buffer has a buffer-local value, `let'
temporarily rebinds that.  If no buffer-local bindings are in effect,
`let' rebinds the default value.  If inside the `let' you then change
to a different current buffer in which a different binding is in effect,
you won't see the `let' binding any more.  And if you exit the `let'
while still in the other buffer, you won't see the unbinding occur
(though it will occur properly).  Here is an example to illustrate:

     (setq foo 'g)
     (set-buffer "a")
     (make-local-variable 'foo)
     (setq foo 'a)
     (let ((foo 'temp))
       ;; foo => 'temp  ; let binding in buffer `a'
       (set-buffer "b")
       ;; foo => 'g     ; the global value since foo is not local in `b'
       BODY...)
     foo => 'g        ; exiting restored the local value in buffer `a',
                      ; but we don't see that in buffer `b'
     (set-buffer "a") ; verify the local value was restored
     foo => 'a

   Note that references to `foo' in BODY access the buffer-local
binding of buffer `b'.

   When a file specifies local variable values, these become
buffer-local values when you visit the file.  *Note File Variables:
(emacs)File Variables.


File: elisp,  Node: Creating Buffer-Local,  Next: Default Value,  Prev: Intro to Buffer-Local,  Up: Buffer-Local Variables

11.10.2 Creating and Deleting Buffer-Local Bindings
---------------------------------------------------

 -- Command: make-local-variable variable
     This function creates a buffer-local binding in the current buffer
     for VARIABLE (a symbol).  Other buffers are not affected.  The
     value returned is VARIABLE.

     The buffer-local value of VARIABLE starts out as the same value
     VARIABLE previously had.  If VARIABLE was void, it remains void.

          ;; In buffer `b1':
          (setq foo 5)                ; Affects all buffers.
               => 5
          (make-local-variable 'foo)  ; Now it is local in `b1'.
               => foo
          foo                         ; That did not change
               => 5                   ;   the value.
          (setq foo 6)                ; Change the value
               => 6                   ;   in `b1'.
          foo
               => 6

          ;; In buffer `b2', the value hasn't changed.
          (save-excursion
            (set-buffer "b2")
            foo)
               => 5

     Making a variable buffer-local within a `let'-binding for that
     variable does not work reliably, unless the buffer in which you do
     this is not current either on entry to or exit from the `let'.
     This is because `let' does not distinguish between different kinds
     of bindings; it knows only which variable the binding was made for.

     If the variable is terminal-local, this function signals an error.
     Such variables cannot have buffer-local bindings as well.  *Note
     Multiple Displays::.

     *Warning:* do not use `make-local-variable' for a hook variable.
     The hook variables are automatically made buffer-local as needed
     if you use the LOCAL argument to `add-hook' or `remove-hook'.

 -- Command: make-variable-buffer-local variable
     This function marks VARIABLE (a symbol) automatically
     buffer-local, so that any subsequent attempt to set it will make it
     local to the current buffer at the time.

     A peculiar wrinkle of this feature is that binding the variable
     (with `let' or other binding constructs) does not create a
     buffer-local binding for it.  Only setting the variable (with
     `set' or `setq'), while the variable does not have a `let'-style
     binding that was made in the current buffer, does so.

     If VARIABLE does not have a default value, then calling this
     command will give it a default value of `nil'.  If VARIABLE
     already has a default value, that value remains unchanged.
     Subsequently calling `makunbound' on VARIABLE will result in a
     void buffer-local value and leave the default value unaffected.

     The value returned is VARIABLE.

     *Warning:* Don't assume that you should use
     `make-variable-buffer-local' for user-option variables, simply
     because users _might_ want to customize them differently in
     different buffers.  Users can make any variable local, when they
     wish to.  It is better to leave the choice to them.

     The time to use `make-variable-buffer-local' is when it is crucial
     that no two buffers ever share the same binding.  For example,
     when a variable is used for internal purposes in a Lisp program
     which depends on having separate values in separate buffers, then
     using `make-variable-buffer-local' can be the best solution.

 -- Function: local-variable-p variable &optional buffer
     This returns `t' if VARIABLE is buffer-local in buffer BUFFER
     (which defaults to the current buffer); otherwise, `nil'.

 -- Function: local-variable-if-set-p variable &optional buffer
     This returns `t' if VARIABLE will become buffer-local in buffer
     BUFFER (which defaults to the current buffer) if it is set there.

 -- Function: buffer-local-value variable buffer
     This function returns the buffer-local binding of VARIABLE (a
     symbol) in buffer BUFFER.  If VARIABLE does not have a
     buffer-local binding in buffer BUFFER, it returns the default
     value (*note Default Value::) of VARIABLE instead.

 -- Function: buffer-local-variables &optional buffer
     This function returns a list describing the buffer-local variables
     in buffer BUFFER.  (If BUFFER is omitted, the current buffer is
     used.)  It returns an association list (*note Association Lists::)
     in which each element contains one buffer-local variable and its
     value.  However, when a variable's buffer-local binding in BUFFER
     is void, then the variable appears directly in the resulting list.

          (make-local-variable 'foobar)
          (makunbound 'foobar)
          (make-local-variable 'bind-me)
          (setq bind-me 69)
          (setq lcl (buffer-local-variables))
              ;; First, built-in variables local in all buffers:
          => ((mark-active . nil)
              (buffer-undo-list . nil)
              (mode-name . "Fundamental")
              ...
              ;; Next, non-built-in buffer-local variables.
              ;; This one is buffer-local and void:
              foobar
              ;; This one is buffer-local and nonvoid:
              (bind-me . 69))

     Note that storing new values into the CDRs of cons cells in this
     list does _not_ change the buffer-local values of the variables.

 -- Command: kill-local-variable variable
     This function deletes the buffer-local binding (if any) for
     VARIABLE (a symbol) in the current buffer.  As a result, the
     default binding of VARIABLE becomes visible in this buffer.  This
     typically results in a change in the value of VARIABLE, since the
     default value is usually different from the buffer-local value just
     eliminated.

     If you kill the buffer-local binding of a variable that
     automatically becomes buffer-local when set, this makes the
     default value visible in the current buffer.  However, if you set
     the variable again, that will once again create a buffer-local
     binding for it.

     `kill-local-variable' returns VARIABLE.

     This function is a command because it is sometimes useful to kill
     one buffer-local variable interactively, just as it is useful to
     create buffer-local variables interactively.

 -- Function: kill-all-local-variables
     This function eliminates all the buffer-local variable bindings of
     the current buffer except for variables marked as "permanent."  As
     a result, the buffer will see the default values of most variables.

     This function also resets certain other information pertaining to
     the buffer: it sets the local keymap to `nil', the syntax table to
     the value of `(standard-syntax-table)', the case table to
     `(standard-case-table)', and the abbrev table to the value of
     `fundamental-mode-abbrev-table'.

     The very first thing this function does is run the normal hook
     `change-major-mode-hook' (see below).

     Every major mode command begins by calling this function, which
     has the effect of switching to Fundamental mode and erasing most
     of the effects of the previous major mode.  To ensure that this
     does its job, the variables that major modes set should not be
     marked permanent.

     `kill-all-local-variables' returns `nil'.

 -- Variable: change-major-mode-hook
     The function `kill-all-local-variables' runs this normal hook
     before it does anything else.  This gives major modes a way to
     arrange for something special to be done if the user switches to a
     different major mode.  It is also useful for buffer-specific minor
     modes that should be forgotten if the user changes the major mode.

     For best results, make this variable buffer-local, so that it will
     disappear after doing its job and will not interfere with the
     subsequent major mode.  *Note Hooks::.

   A buffer-local variable is "permanent" if the variable name (a
symbol) has a `permanent-local' property that is non-`nil'.  Permanent
locals are appropriate for data pertaining to where the file came from
or how to save it, rather than with how to edit the contents.


File: elisp,  Node: Default Value,  Prev: Creating Buffer-Local,  Up: Buffer-Local Variables

11.10.3 The Default Value of a Buffer-Local Variable
----------------------------------------------------

The global value of a variable with buffer-local bindings is also
called the "default" value, because it is the value that is in effect
whenever neither the current buffer nor the selected frame has its own
binding for the variable.

   The functions `default-value' and `setq-default' access and change a
variable's default value regardless of whether the current buffer has a
buffer-local binding.  For example, you could use `setq-default' to
change the default setting of `paragraph-start' for most buffers; and
this would work even when you are in a C or Lisp mode buffer that has a
buffer-local value for this variable.

   The special forms `defvar' and `defconst' also set the default value
(if they set the variable at all), rather than any buffer-local value.

 -- Function: default-value symbol
     This function returns SYMBOL's default value.  This is the value
     that is seen in buffers and frames that do not have their own
     values for this variable.  If SYMBOL is not buffer-local, this is
     equivalent to `symbol-value' (*note Accessing Variables::).

 -- Function: default-boundp symbol
     The function `default-boundp' tells you whether SYMBOL's default
     value is nonvoid.  If `(default-boundp 'foo)' returns `nil', then
     `(default-value 'foo)' would get an error.

     `default-boundp' is to `default-value' as `boundp' is to
     `symbol-value'.

 -- Special Form: setq-default [symbol form]...
     This special form gives each SYMBOL a new default value, which is
     the result of evaluating the corresponding FORM.  It does not
     evaluate SYMBOL, but does evaluate FORM.  The value of the
     `setq-default' form is the value of the last FORM.

     If a SYMBOL is not buffer-local for the current buffer, and is not
     marked automatically buffer-local, `setq-default' has the same
     effect as `setq'.  If SYMBOL is buffer-local for the current
     buffer, then this changes the value that other buffers will see
     (as long as they don't have a buffer-local value), but not the
     value that the current buffer sees.

          ;; In buffer `foo':
          (make-local-variable 'buffer-local)
               => buffer-local
          (setq buffer-local 'value-in-foo)
               => value-in-foo
          (setq-default buffer-local 'new-default)
               => new-default
          buffer-local
               => value-in-foo
          (default-value 'buffer-local)
               => new-default

          ;; In (the new) buffer `bar':
          buffer-local
               => new-default
          (default-value 'buffer-local)
               => new-default
          (setq buffer-local 'another-default)
               => another-default
          (default-value 'buffer-local)
               => another-default

          ;; Back in buffer `foo':
          buffer-local
               => value-in-foo
          (default-value 'buffer-local)
               => another-default

 -- Function: set-default symbol value
     This function is like `setq-default', except that SYMBOL is an
     ordinary evaluated argument.

          (set-default (car '(a b c)) 23)
               => 23
          (default-value 'a)
               => 23


File: elisp,  Node: Future Local Variables,  Next: File Local Variables,  Prev: Buffer-Local Variables,  Up: Variables

11.11 Possible Future Local Variables
=====================================

We have considered the idea of bindings that are local to a category of
frames--for example, all color frames, or all frames with dark
backgrounds.  We have not implemented them because it is not clear that
this feature is really useful.  You can get more or less the same
results by adding a function to `after-make-frame-functions', set up to
define a particular frame parameter according to the appropriate
conditions for each frame.

   It would also be possible to implement window-local bindings.  We
don't know of many situations where they would be useful, and it seems
that indirect buffers (*note Indirect Buffers::) with buffer-local
bindings offer a way to handle these situations more robustly.

   If sufficient application is found for either of these two kinds of
local bindings, we will provide it in a subsequent Emacs version.


File: elisp,  Node: File Local Variables,  Next: Variable Aliases,  Prev: Future Local Variables,  Up: Variables

11.12 File Local Variables
==========================

A file can specify local variable values; Emacs uses these to create
buffer-local bindings for those variables in the buffer visiting that
file.  *Note Local Variables in Files: (emacs)File variables, for basic
information about file local variables.  This section describes the
functions and variables that affect processing of file local variables.

 -- User Option: enable-local-variables
     This variable controls whether to process file local variables.
     The possible values are:

    `t' (the default)
          Set the safe variables, and query (once) about any unsafe
          variables.

    `:safe'
          Set only the safe variables and do not query.

    `:all'
          Set all the variables and do not query.

    `nil'
          Don't set any variables.

    anything else
          Query (once) about all the variables.

 -- Function: hack-local-variables &optional mode-only
     This function parses, and binds or evaluates as appropriate, any
     local variables specified by the contents of the current buffer.
     The variable `enable-local-variables' has its effect here.
     However, this function does not look for the `mode:' local
     variable in the `-*-' line.  `set-auto-mode' does that, also taking
     `enable-local-variables' into account (*note Auto Major Mode::).

     If the optional argument MODE-ONLY is non-`nil', then all this
     function does is return `t' if the `-*-' line or the local
     variables list specifies a mode and `nil' otherwise.  It does not
     set the mode nor any other file local variable.

   If a file local variable could specify a function that would be
called later, or an expression that would be executed later, simply
visiting a file could take over your Emacs.  Emacs takes several
measures to prevent this.

   You can specify safe values for a variable with a
`safe-local-variable' property.  The property has to be a function of
one argument; any value is safe if the function returns non-`nil' given
that value.  Many commonly encountered file variables standardly have
`safe-local-variable' properties, including `fill-column',
`fill-prefix', and `indent-tabs-mode'.  For boolean-valued variables
that are safe, use `booleanp' as the property value.  Lambda
expressions should be quoted so that `describe-variable' can display
the predicate.

 -- User Option: safe-local-variable-values
     This variable provides another way to mark some variable values as
     safe.  It is a list of cons cells `(VAR . VAL)', where VAR is a
     variable name and VAL is a value which is safe for that variable.

     When Emacs asks the user whether or not to obey a set of file local
     variable specifications, the user can choose to mark them as safe.
     Doing so adds those variable/value pairs to
     `safe-local-variable-values', and saves it to the user's custom
     file.

 -- Function: safe-local-variable-p sym val
     This function returns non-`nil' if it is safe to give SYM the
     value VAL, based on the above criteria.

   Some variables are considered "risky".  A variable whose name ends
in any of `-command', `-frame-alist', `-function', `-functions',
`-hook', `-hooks', `-form', `-forms', `-map', `-map-alist',
`-mode-alist', `-program', or `-predicate' is considered risky.  The
variables `font-lock-keywords', `font-lock-keywords' followed by a
digit, and `font-lock-syntactic-keywords' are also considered risky.
Finally, any variable whose name has a non-`nil' `risky-local-variable'
property is considered risky.

 -- Function: risky-local-variable-p sym
     This function returns non-`nil' if SYM is a risky variable, based
     on the above criteria.

   If a variable is risky, it will not be entered automatically into
`safe-local-variable-values' as described above.  Therefore, Emacs will
always query before setting a risky variable, unless the user
explicitly allows the setting by customizing
`safe-local-variable-values' directly.

 -- Variable: ignored-local-variables
     This variable holds a list of variables that should not be given
     local values by files.  Any value specified for one of these
     variables is completely ignored.

   The `Eval:' "variable" is also a potential loophole, so Emacs
normally asks for confirmation before handling it.

 -- User Option: enable-local-eval
     This variable controls processing of `Eval:' in `-*-' lines or
     local variables lists in files being visited.  A value of `t'
     means process them unconditionally; `nil' means ignore them;
     anything else means ask the user what to do for each file.  The
     default value is `maybe'.

 -- User Option: safe-local-eval-forms
     This variable holds a list of expressions that are safe to
     evaluate when found in the `Eval:' "variable" in a file local
     variables list.

   If the expression is a function call and the function has a
`safe-local-eval-function' property, the property value determines
whether the expression is safe to evaluate.  The property value can be
a predicate to call to test the expression, a list of such predicates
(it's safe if any predicate succeeds), or `t' (always safe provided the
arguments are constant).

   Text properties are also potential loopholes, since their values
could include functions to call.  So Emacs discards all text properties
from string values specified for file local variables.


File: elisp,  Node: Variable Aliases,  Next: Variables with Restricted Values,  Prev: File Local Variables,  Up: Variables

11.13 Variable Aliases
======================

It is sometimes useful to make two variables synonyms, so that both
variables always have the same value, and changing either one also
changes the other.  Whenever you change the name of a variable--either
because you realize its old name was not well chosen, or because its
meaning has partly changed--it can be useful to keep the old name as an
_alias_ of the new one for compatibility.  You can do this with
`defvaralias'.

 -- Function: defvaralias new-alias base-variable &optional docstring
     This function defines the symbol NEW-ALIAS as a variable alias for
     symbol BASE-VARIABLE. This means that retrieving the value of
     NEW-ALIAS returns the value of BASE-VARIABLE, and changing the
     value of NEW-ALIAS changes the value of BASE-VARIABLE.  The two
     aliased variable names always share the same value and the same
     bindings.

     If the DOCSTRING argument is non-`nil', it specifies the
     documentation for NEW-ALIAS; otherwise, the alias gets the same
     documentation as BASE-VARIABLE has, if any, unless BASE-VARIABLE
     is itself an alias, in which case NEW-ALIAS gets the documentation
     of the variable at the end of the chain of aliases.

     This function returns BASE-VARIABLE.

   Variable aliases are convenient for replacing an old name for a
variable with a new name.  `make-obsolete-variable' declares that the
old name is obsolete and therefore that it may be removed at some stage
in the future.

 -- Function: make-obsolete-variable obsolete-name current-name
          &optional when
     This function makes the byte-compiler warn that the variable
     OBSOLETE-NAME is obsolete.  If CURRENT-NAME is a symbol, it is the
     variable's new name; then the warning message says to use
     CURRENT-NAME instead of OBSOLETE-NAME.  If CURRENT-NAME is a
     string, this is the message and there is no replacement variable.

     If provided, WHEN should be a string indicating when the variable
     was first made obsolete--for example, a date or a release number.

   You can make two variables synonyms and declare one obsolete at the
same time using the macro `define-obsolete-variable-alias'.

 -- Macro: define-obsolete-variable-alias obsolete-name current-name
          &optional when docstring
     This macro marks the variable OBSOLETE-NAME as obsolete and also
     makes it an alias for the variable CURRENT-NAME.  It is equivalent
     to the following:

          (defvaralias OBSOLETE-NAME CURRENT-NAME DOCSTRING)
          (make-obsolete-variable OBSOLETE-NAME CURRENT-NAME WHEN)

 -- Function: indirect-variable variable
     This function returns the variable at the end of the chain of
     aliases of VARIABLE.  If VARIABLE is not a symbol, or if VARIABLE
     is not defined as an alias, the function returns VARIABLE.

     This function signals a `cyclic-variable-indirection' error if
     there is a loop in the chain of symbols.

     (defvaralias 'foo 'bar)
     (indirect-variable 'foo)
          => bar
     (indirect-variable 'bar)
          => bar
     (setq bar 2)
     bar
          => 2
     foo
          => 2
     (setq foo 0)
     bar
          => 0
     foo
          => 0


File: elisp,  Node: Variables with Restricted Values,  Prev: Variable Aliases,  Up: Variables

11.14 Variables with Restricted Values
======================================

Ordinary Lisp variables can be assigned any value that is a valid Lisp
object.  However, certain Lisp variables are not defined in Lisp, but
in C.  Most of these variables are defined in the C code using
`DEFVAR_LISP'.  Like variables defined in Lisp, these can take on any
value.  However, some variables are defined using `DEFVAR_INT' or
`DEFVAR_BOOL'.  *Note Writing Emacs Primitives: Defining Lisp variables
in C, in particular the description of functions of the type
`syms_of_FILENAME', for a brief discussion of the C implementation.

   Variables of type `DEFVAR_BOOL' can only take on the values `nil' or
`t'.  Attempting to assign them any other value will set them to `t':

     (let ((display-hourglass 5))
       display-hourglass)
          => t

 -- Variable: byte-boolean-vars
     This variable holds a list of all variables of type `DEFVAR_BOOL'.

   Variables of type `DEFVAR_INT' can only take on integer values.
Attempting to assign them any other value will result in an error:

     (setq window-min-height 5.0)
     error--> Wrong type argument: integerp, 5.0


File: elisp,  Node: Functions,  Next: Macros,  Prev: Variables,  Up: Top

12 Functions
************

A Lisp program is composed mainly of Lisp functions.  This chapter
explains what functions are, how they accept arguments, and how to
define them.

* Menu:

* What Is a Function::    Lisp functions vs. primitives; terminology.
* Lambda Expressions::    How functions are expressed as Lisp objects.
* Function Names::        A symbol can serve as the name of a function.
* Defining Functions::    Lisp expressions for defining functions.
* Calling Functions::     How to use an existing function.
* Mapping Functions::     Applying a function to each element of a list, etc.
* Anonymous Functions::   Lambda expressions are functions with no names.
* Function Cells::        Accessing or setting the function definition
                            of a symbol.
* Obsolete Functions::    Declaring functions obsolete.
* Inline Functions::	  Defining functions that the compiler will open code.
* Function Safety::       Determining whether a function is safe to call.
* Related Topics::        Cross-references to specific Lisp primitives
                            that have a special bearing on how functions work.


File: elisp,  Node: What Is a Function,  Next: Lambda Expressions,  Up: Functions

12.1 What Is a Function?
========================

In a general sense, a function is a rule for carrying on a computation
given several values called "arguments".  The result of the computation
is called the value of the function.  The computation can also have
side effects: lasting changes in the values of variables or the
contents of data structures.

   Here are important terms for functions in Emacs Lisp and for other
function-like objects.

"function"
     In Emacs Lisp, a "function" is anything that can be applied to
     arguments in a Lisp program.  In some cases, we use it more
     specifically to mean a function written in Lisp.  Special forms and
     macros are not functions.

"primitive"
     A "primitive" is a function callable from Lisp that is written in
     C, such as `car' or `append'.  These functions are also called
     "built-in functions", or "subrs".  (Special forms are also
     considered primitives.)

     Usually the reason we implement a function as a primitive is either
     because it is fundamental, because it provides a low-level
     interface to operating system services, or because it needs to run
     fast.  Primitives can be modified or added only by changing the C
     sources and recompiling the editor.  See *Note Writing Emacs
     Primitives::.

"lambda expression"
     A "lambda expression" is a function written in Lisp.  These are
     described in the following section.  *Note Lambda Expressions::.

"special form"
     A "special form" is a primitive that is like a function but does
     not evaluate all of its arguments in the usual way.  It may
     evaluate only some of the arguments, or may evaluate them in an
     unusual order, or several times.  Many special forms are described
     in *Note Control Structures::.

"macro"
     A "macro" is a construct defined in Lisp by the programmer.  It
     differs from a function in that it translates a Lisp expression
     that you write into an equivalent expression to be evaluated
     instead of the original expression.  Macros enable Lisp
     programmers to do the sorts of things that special forms can do.
     *Note Macros::, for how to define and use macros.

"command"
     A "command" is an object that `command-execute' can invoke; it is
     a possible definition for a key sequence.  Some functions are
     commands; a function written in Lisp is a command if it contains an
     interactive declaration (*note Defining Commands::).  Such a
     function can be called from Lisp expressions like other functions;
     in this case, the fact that the function is a command makes no
     difference.

     Keyboard macros (strings and vectors) are commands also, even
     though they are not functions.  A symbol is a command if its
     function definition is a command; such symbols can be invoked with
     `M-x'.  The symbol is a function as well if the definition is a
     function.  *Note Interactive Call::.

"keystroke command"
     A "keystroke command" is a command that is bound to a key sequence
     (typically one to three keystrokes).  The distinction is made here
     merely to avoid confusion with the meaning of "command" in
     non-Emacs editors; for Lisp programs, the distinction is normally
     unimportant.

"byte-code function"
     A "byte-code function" is a function that has been compiled by the
     byte compiler.  *Note Byte-Code Type::.

 -- Function: functionp object
     This function returns `t' if OBJECT is any kind of function, or a
     special form, or, recursively, a symbol whose function definition
     is a function or special form.  (This does not include macros.)

   Unlike `functionp', the next three functions do _not_ treat a symbol
as its function definition.

 -- Function: subrp object
     This function returns `t' if OBJECT is a built-in function (i.e.,
     a Lisp primitive).

          (subrp 'message)            ; `message' is a symbol,
               => nil                 ;   not a subr object.
          (subrp (symbol-function 'message))
               => t

 -- Function: byte-code-function-p object
     This function returns `t' if OBJECT is a byte-code function.  For
     example:

          (byte-code-function-p (symbol-function 'next-line))
               => t

 -- Function: subr-arity subr
     This function provides information about the argument list of a
     primitive, SUBR.  The returned value is a pair `(MIN . MAX)'.  MIN
     is the minimum number of args.  MAX is the maximum number or the
     symbol `many', for a function with `&rest' arguments, or the
     symbol `unevalled' if SUBR is a special form.


File: elisp,  Node: Lambda Expressions,  Next: Function Names,  Prev: What Is a Function,  Up: Functions

12.2 Lambda Expressions
=======================

A function written in Lisp is a list that looks like this:

     (lambda (ARG-VARIABLES...)
       [DOCUMENTATION-STRING]
       [INTERACTIVE-DECLARATION]
       BODY-FORMS...)

Such a list is called a "lambda expression".  In Emacs Lisp, it
actually is valid as an expression--it evaluates to itself.  In some
other Lisp dialects, a lambda expression is not a valid expression at
all.  In either case, its main use is not to be evaluated as an
expression, but to be called as a function.

* Menu:

* Lambda Components::       The parts of a lambda expression.
* Simple Lambda::           A simple example.
* Argument List::           Details and special features of argument lists.
* Function Documentation::  How to put documentation in a function.


File: elisp,  Node: Lambda Components,  Next: Simple Lambda,  Up: Lambda Expressions

12.2.1 Components of a Lambda Expression
----------------------------------------

A function written in Lisp (a "lambda expression") is a list that looks
like this:

     (lambda (ARG-VARIABLES...)
       [DOCUMENTATION-STRING]
       [INTERACTIVE-DECLARATION]
       BODY-FORMS...)

The first element of a lambda expression is always the symbol `lambda'.
This indicates that the list represents a function.  The reason
functions are defined to start with `lambda' is so that other lists,
intended for other uses, will not accidentally be valid as functions.

   The second element is a list of symbols--the argument variable names.
This is called the "lambda list".  When a Lisp function is called, the
argument values are matched up against the variables in the lambda
list, which are given local bindings with the values provided.  *Note
Local Variables::.

   The documentation string is a Lisp string object placed within the
function definition to describe the function for the Emacs help
facilities.  *Note Function Documentation::.

   The interactive declaration is a list of the form `(interactive
CODE-STRING)'.  This declares how to provide arguments if the function
is used interactively.  Functions with this declaration are called
"commands"; they can be called using `M-x' or bound to a key.
Functions not intended to be called in this way should not have
interactive declarations.  *Note Defining Commands::, for how to write
an interactive declaration.

   The rest of the elements are the "body" of the function: the Lisp
code to do the work of the function (or, as a Lisp programmer would say,
"a list of Lisp forms to evaluate").  The value returned by the
function is the value returned by the last element of the body.


File: elisp,  Node: Simple Lambda,  Next: Argument List,  Prev: Lambda Components,  Up: Lambda Expressions

12.2.2 A Simple Lambda-Expression Example
-----------------------------------------

Consider for example the following function:

     (lambda (a b c) (+ a b c))

We can call this function by writing it as the CAR of an expression,
like this:

     ((lambda (a b c) (+ a b c))
      1 2 3)

This call evaluates the body of the lambda expression  with the variable
`a' bound to 1, `b' bound to 2, and `c' bound to 3.  Evaluation of the
body adds these three numbers, producing the result 6; therefore, this
call to the function returns the value 6.

   Note that the arguments can be the results of other function calls,
as in this example:

     ((lambda (a b c) (+ a b c))
      1 (* 2 3) (- 5 4))

This evaluates the arguments `1', `(* 2 3)', and `(- 5 4)' from left to
right.  Then it applies the lambda expression to the argument values 1,
6 and 1 to produce the value 8.

   It is not often useful to write a lambda expression as the CAR of a
form in this way.  You can get the same result, of making local
variables and giving them values, using the special form `let' (*note
Local Variables::).  And `let' is clearer and easier to use.  In
practice, lambda expressions are either stored as the function
definitions of symbols, to produce named functions, or passed as
arguments to other functions (*note Anonymous Functions::).

   However, calls to explicit lambda expressions were very useful in the
old days of Lisp, before the special form `let' was invented.  At that
time, they were the only way to bind and initialize local variables.


File: elisp,  Node: Argument List,  Next: Function Documentation,  Prev: Simple Lambda,  Up: Lambda Expressions

12.2.3 Other Features of Argument Lists
---------------------------------------

Our simple sample function, `(lambda (a b c) (+ a b c))', specifies
three argument variables, so it must be called with three arguments: if
you try to call it with only two arguments or four arguments, you get a
`wrong-number-of-arguments' error.

   It is often convenient to write a function that allows certain
arguments to be omitted.  For example, the function `substring' accepts
three arguments--a string, the start index and the end index--but the
third argument defaults to the LENGTH of the string if you omit it.  It
is also convenient for certain functions to accept an indefinite number
of arguments, as the functions `list' and `+' do.

   To specify optional arguments that may be omitted when a function is
called, simply include the keyword `&optional' before the optional
arguments.  To specify a list of zero or more extra arguments, include
the keyword `&rest' before one final argument.

   Thus, the complete syntax for an argument list is as follows:

     (REQUIRED-VARS...
      [&optional OPTIONAL-VARS...]
      [&rest REST-VAR])

The square brackets indicate that the `&optional' and `&rest' clauses,
and the variables that follow them, are optional.

   A call to the function requires one actual argument for each of the
REQUIRED-VARS.  There may be actual arguments for zero or more of the
OPTIONAL-VARS, and there cannot be any actual arguments beyond that
unless the lambda list uses `&rest'.  In that case, there may be any
number of extra actual arguments.

   If actual arguments for the optional and rest variables are omitted,
then they always default to `nil'.  There is no way for the function to
distinguish between an explicit argument of `nil' and an omitted
argument.  However, the body of the function is free to consider `nil'
an abbreviation for some other meaningful value.  This is what
`substring' does; `nil' as the third argument to `substring' means to
use the length of the string supplied.

     Common Lisp note: Common Lisp allows the function to specify what
     default value to use when an optional argument is omitted; Emacs
     Lisp always uses `nil'.  Emacs Lisp does not support "supplied-p"
     variables that tell you whether an argument was explicitly passed.

   For example, an argument list that looks like this:

     (a b &optional c d &rest e)

binds `a' and `b' to the first two actual arguments, which are
required.  If one or two more arguments are provided, `c' and `d' are
bound to them respectively; any arguments after the first four are
collected into a list and `e' is bound to that list.  If there are only
two arguments, `c' is `nil'; if two or three arguments, `d' is `nil';
if four arguments or fewer, `e' is `nil'.

   There is no way to have required arguments following optional
ones--it would not make sense.  To see why this must be so, suppose
that `c' in the example were optional and `d' were required.  Suppose
three actual arguments are given; which variable would the third
argument be for?  Would it be used for the C, or for D?  One can argue
for both possibilities.  Similarly, it makes no sense to have any more
arguments (either required or optional) after a `&rest' argument.

   Here are some examples of argument lists and proper calls:

     ((lambda (n) (1+ n))                ; One required:
      1)                                 ; requires exactly one argument.
          => 2
     ((lambda (n &optional n1)           ; One required and one optional:
              (if n1 (+ n n1) (1+ n)))   ; 1 or 2 arguments.
      1 2)
          => 3
     ((lambda (n &rest ns)               ; One required and one rest:
              (+ n (apply '+ ns)))       ; 1 or more arguments.
      1 2 3 4 5)
          => 15


File: elisp,  Node: Function Documentation,  Prev: Argument List,  Up: Lambda Expressions

12.2.4 Documentation Strings of Functions
-----------------------------------------

A lambda expression may optionally have a "documentation string" just
after the lambda list.  This string does not affect execution of the
function; it is a kind of comment, but a systematized comment which
actually appears inside the Lisp world and can be used by the Emacs help
facilities.  *Note Documentation::, for how the DOCUMENTATION-STRING is
accessed.

   It is a good idea to provide documentation strings for all the
functions in your program, even those that are called only from within
your program.  Documentation strings are like comments, except that they
are easier to access.

   The first line of the documentation string should stand on its own,
because `apropos' displays just this first line.  It should consist of
one or two complete sentences that summarize the function's purpose.

   The start of the documentation string is usually indented in the
source file, but since these spaces come before the starting
double-quote, they are not part of the string.  Some people make a
practice of indenting any additional lines of the string so that the
text lines up in the program source.  _That is a mistake._  The
indentation of the following lines is inside the string; what looks
nice in the source code will look ugly when displayed by the help
commands.

   You may wonder how the documentation string could be optional, since
there are required components of the function that follow it (the body).
Since evaluation of a string returns that string, without any side
effects, it has no effect if it is not the last form in the body.
Thus, in practice, there is no confusion between the first form of the
body and the documentation string; if the only body form is a string
then it serves both as the return value and as the documentation.

   The last line of the documentation string can specify calling
conventions different from the actual function arguments.  Write text
like this:

     \(fn ARGLIST)

following a blank line, at the beginning of the line, with no newline
following it inside the documentation string.  (The `\' is used to
avoid confusing the Emacs motion commands.)  The calling convention
specified in this way appears in help messages in place of the one
derived from the actual arguments of the function.

   This feature is particularly useful for macro definitions, since the
arguments written in a macro definition often do not correspond to the
way users think of the parts of the macro call.


File: elisp,  Node: Function Names,  Next: Defining Functions,  Prev: Lambda Expressions,  Up: Functions

12.3 Naming a Function
======================

In most computer languages, every function has a name; the idea of a
function without a name is nonsensical.  In Lisp, a function in the
strictest sense has no name.  It is simply a list whose first element is
`lambda', a byte-code function object, or a primitive subr-object.

   However, a symbol can serve as the name of a function.  This happens
when you put the function in the symbol's "function cell" (*note Symbol
Components::).  Then the symbol itself becomes a valid, callable
function, equivalent to the list or subr-object that its function cell
refers to.  The contents of the function cell are also called the
symbol's "function definition".  The procedure of using a symbol's
function definition in place of the symbol is called "symbol function
indirection"; see *Note Function Indirection::.

   In practice, nearly all functions are given names in this way and
referred to through their names.  For example, the symbol `car' works
as a function and does what it does because the primitive subr-object
`#<subr car>' is stored in its function cell.

   We give functions names because it is convenient to refer to them by
their names in Lisp expressions.  For primitive subr-objects such as
`#<subr car>', names are the only way you can refer to them: there is
no read syntax for such objects.  For functions written in Lisp, the
name is more convenient to use in a call than an explicit lambda
expression.  Also, a function with a name can refer to itself--it can
be recursive.  Writing the function's name in its own definition is much
more convenient than making the function definition point to itself
(something that is not impossible but that has various disadvantages in
practice).

   We often identify functions with the symbols used to name them.  For
example, we often speak of "the function `car'," not distinguishing
between the symbol `car' and the primitive subr-object that is its
function definition.  For most purposes, the distinction is not
important.

   Even so, keep in mind that a function need not have a unique name.
While a given function object _usually_ appears in the function cell of
only one symbol, this is just a matter of convenience.  It is easy to
store it in several symbols using `fset'; then each of the symbols is
equally well a name for the same function.

   A symbol used as a function name may also be used as a variable;
these two uses of a symbol are independent and do not conflict.  (Some
Lisp dialects, such as Scheme, do not distinguish between a symbol's
value and its function definition; a symbol's value as a variable is
also its function definition.)  If you have not given a symbol a
function definition, you cannot use it as a function; whether the
symbol has a value as a variable makes no difference to this.


File: elisp,  Node: Defining Functions,  Next: Calling Functions,  Prev: Function Names,  Up: Functions

12.4 Defining Functions
=======================

We usually give a name to a function when it is first created.  This is
called "defining a function", and it is done with the `defun' special
form.

 -- Special Form: defun name argument-list body-forms
     `defun' is the usual way to define new Lisp functions.  It defines
     the symbol NAME as a function that looks like this:

          (lambda ARGUMENT-LIST . BODY-FORMS)

     `defun' stores this lambda expression in the function cell of
     NAME.  It returns the value NAME, but usually we ignore this value.

     As described previously, ARGUMENT-LIST is a list of argument names
     and may include the keywords `&optional' and `&rest' (*note Lambda
     Expressions::).  Also, the first two of the BODY-FORMS may be a
     documentation string and an interactive declaration.

     There is no conflict if the same symbol NAME is also used as a
     variable, since the symbol's value cell is independent of the
     function cell.  *Note Symbol Components::.

     Here are some examples:

          (defun foo () 5)
               => foo
          (foo)
               => 5

          (defun bar (a &optional b &rest c)
              (list a b c))
               => bar
          (bar 1 2 3 4 5)
               => (1 2 (3 4 5))
          (bar 1)
               => (1 nil nil)
          (bar)
          error--> Wrong number of arguments.

          (defun capitalize-backwards ()
            "Upcase the last letter of a word."
            (interactive)
            (backward-word 1)
            (forward-word 1)
            (backward-char 1)
            (capitalize-word 1))
               => capitalize-backwards

     Be careful not to redefine existing functions unintentionally.
     `defun' redefines even primitive functions such as `car' without
     any hesitation or notification.  Redefining a function already
     defined is often done deliberately, and there is no way to
     distinguish deliberate redefinition from unintentional
     redefinition.

 -- Function: defalias name definition &optional docstring
     This special form defines the symbol NAME as a function, with
     definition DEFINITION (which can be any valid Lisp function).  It
     returns DEFINITION.

     If DOCSTRING is non-`nil', it becomes the function documentation
     of NAME.  Otherwise, any documentation provided by DEFINITION is
     used.

     The proper place to use `defalias' is where a specific function
     name is being defined--especially where that name appears
     explicitly in the source file being loaded.  This is because
     `defalias' records which file defined the function, just like
     `defun' (*note Unloading::).

     By contrast, in programs that manipulate function definitions for
     other purposes, it is better to use `fset', which does not keep
     such records.  *Note Function Cells::.

   You cannot create a new primitive function with `defun' or
`defalias', but you can use them to change the function definition of
any symbol, even one such as `car' or `x-popup-menu' whose normal
definition is a primitive.  However, this is risky: for instance, it is
next to impossible to redefine `car' without breaking Lisp completely.
Redefining an obscure function such as `x-popup-menu' is less
dangerous, but it still may not work as you expect.  If there are calls
to the primitive from C code, they call the primitive's C definition
directly, so changing the symbol's definition will have no effect on
them.

   See also `defsubst', which defines a function like `defun' and tells
the Lisp compiler to open-code it.  *Note Inline Functions::.


File: elisp,  Node: Calling Functions,  Next: Mapping Functions,  Prev: Defining Functions,  Up: Functions

12.5 Calling Functions
======================

Defining functions is only half the battle.  Functions don't do
anything until you "call" them, i.e., tell them to run.  Calling a
function is also known as "invocation".

   The most common way of invoking a function is by evaluating a list.
For example, evaluating the list `(concat "a" "b")' calls the function
`concat' with arguments `"a"' and `"b"'.  *Note Evaluation::, for a
description of evaluation.

   When you write a list as an expression in your program, you specify
which function to call, and how many arguments to give it, in the text
of the program.  Usually that's just what you want.  Occasionally you
need to compute at run time which function to call.  To do that, use
the function `funcall'.  When you also need to determine at run time
how many arguments to pass, use `apply'.

 -- Function: funcall function &rest arguments
     `funcall' calls FUNCTION with ARGUMENTS, and returns whatever
     FUNCTION returns.

     Since `funcall' is a function, all of its arguments, including
     FUNCTION, are evaluated before `funcall' is called.  This means
     that you can use any expression to obtain the function to be
     called.  It also means that `funcall' does not see the expressions
     you write for the ARGUMENTS, only their values.  These values are
     _not_ evaluated a second time in the act of calling FUNCTION; the
     operation of `funcall' is like the normal procedure for calling a
     function, once its arguments have already been evaluated.

     The argument FUNCTION must be either a Lisp function or a
     primitive function.  Special forms and macros are not allowed,
     because they make sense only when given the "unevaluated" argument
     expressions.  `funcall' cannot provide these because, as we saw
     above, it never knows them in the first place.

          (setq f 'list)
               => list
          (funcall f 'x 'y 'z)
               => (x y z)
          (funcall f 'x 'y '(z))
               => (x y (z))
          (funcall 'and t nil)
          error--> Invalid function: #<subr and>

     Compare these examples with the examples of `apply'.

 -- Function: apply function &rest arguments
     `apply' calls FUNCTION with ARGUMENTS, just like `funcall' but
     with one difference: the last of ARGUMENTS is a list of objects,
     which are passed to FUNCTION as separate arguments, rather than a
     single list.  We say that `apply' "spreads" this list so that each
     individual element becomes an argument.

     `apply' returns the result of calling FUNCTION.  As with
     `funcall', FUNCTION must either be a Lisp function or a primitive
     function; special forms and macros do not make sense in `apply'.

          (setq f 'list)
               => list
          (apply f 'x 'y 'z)
          error--> Wrong type argument: listp, z
          (apply '+ 1 2 '(3 4))
               => 10
          (apply '+ '(1 2 3 4))
               => 10

          (apply 'append '((a b c) nil (x y z) nil))
               => (a b c x y z)

     For an interesting example of using `apply', see *Note Definition
     of mapcar::.

   It is common for Lisp functions to accept functions as arguments or
find them in data structures (especially in hook variables and property
lists) and call them using `funcall' or `apply'.  Functions that accept
function arguments are often called "functionals".

   Sometimes, when you call a functional, it is useful to supply a no-op
function as the argument.  Here are two different kinds of no-op
function:

 -- Function: identity arg
     This function returns ARG and has no side effects.

 -- Function: ignore &rest args
     This function ignores any arguments and returns `nil'.


File: elisp,  Node: Mapping Functions,  Next: Anonymous Functions,  Prev: Calling Functions,  Up: Functions

12.6 Mapping Functions
======================

A "mapping function" applies a given function (_not_ a special form or
macro) to each element of a list or other collection.  Emacs Lisp has
several such functions; `mapcar' and `mapconcat', which scan a list,
are described here.  *Note Definition of mapatoms::, for the function
`mapatoms' which maps over the symbols in an obarray.  *Note Definition
of maphash::, for the function `maphash' which maps over key/value
associations in a hash table.

   These mapping functions do not allow char-tables because a char-table
is a sparse array whose nominal range of indices is very large.  To map
over a char-table in a way that deals properly with its sparse nature,
use the function `map-char-table' (*note Char-Tables::).

 -- Function: mapcar function sequence
     `mapcar' applies FUNCTION to each element of SEQUENCE in turn, and
     returns a list of the results.

     The argument SEQUENCE can be any kind of sequence except a
     char-table; that is, a list, a vector, a bool-vector, or a string.
     The result is always a list.  The length of the result is the
     same as the length of SEQUENCE.  For example:

          (mapcar 'car '((a b) (c d) (e f)))
               => (a c e)
          (mapcar '1+ [1 2 3])
               => (2 3 4)
          (mapcar 'char-to-string "abc")
               => ("a" "b" "c")

          ;; Call each function in `my-hooks'.
          (mapcar 'funcall my-hooks)

          (defun mapcar* (function &rest args)
            "Apply FUNCTION to successive cars of all ARGS.
          Return the list of results."
            ;; If no list is exhausted,
            (if (not (memq nil args))
                ;; apply function to CARs.
                (cons (apply function (mapcar 'car args))
                      (apply 'mapcar* function
                             ;; Recurse for rest of elements.
                             (mapcar 'cdr args)))))

          (mapcar* 'cons '(a b c) '(1 2 3 4))
               => ((a . 1) (b . 2) (c . 3))

 -- Function: mapc function sequence
     `mapc' is like `mapcar' except that FUNCTION is used for
     side-effects only--the values it returns are ignored, not collected
     into a list.  `mapc' always returns SEQUENCE.

 -- Function: mapconcat function sequence separator
     `mapconcat' applies FUNCTION to each element of SEQUENCE: the
     results, which must be strings, are concatenated.  Between each
     pair of result strings, `mapconcat' inserts the string SEPARATOR.
     Usually SEPARATOR contains a space or comma or other suitable
     punctuation.

     The argument FUNCTION must be a function that can take one
     argument and return a string.  The argument SEQUENCE can be any
     kind of sequence except a char-table; that is, a list, a vector, a
     bool-vector, or a string.

          (mapconcat 'symbol-name
                     '(The cat in the hat)
                     " ")
               => "The cat in the hat"

          (mapconcat (function (lambda (x) (format "%c" (1+ x))))
                     "HAL-8000"
                     "")
               => "IBM.9111"


File: elisp,  Node: Anonymous Functions,  Next: Function Cells,  Prev: Mapping Functions,  Up: Functions

12.7 Anonymous Functions
========================

In Lisp, a function is a list that starts with `lambda', a byte-code
function compiled from such a list, or alternatively a primitive
subr-object; names are "extra."  Although usually functions are defined
with `defun' and given names at the same time, it is occasionally more
concise to use an explicit lambda expression--an anonymous function.
Such a list is valid wherever a function name is.

   Any method of creating such a list makes a valid function.  Even
this:

     (setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x))))
     => (lambda (x) (+ 12 x))

This computes a list that looks like `(lambda (x) (+ 12 x))' and makes
it the value (_not_ the function definition!) of `silly'.

   Here is how we might call this function:

     (funcall silly 1)
     => 13

(It does _not_ work to write `(silly 1)', because this function is not
the _function definition_ of `silly'.  We have not given `silly' any
function definition, just a value as a variable.)

   Most of the time, anonymous functions are constants that appear in
your program.  For example, you might want to pass one as an argument to
the function `mapcar', which applies any given function to each element
of a list.

   Here we define a function `change-property' which uses a function as
its third argument:

     (defun change-property (symbol prop function)
       (let ((value (get symbol prop)))
         (put symbol prop (funcall function value))))

Here we define a function that uses `change-property', passing it a
function to double a number:

     (defun double-property (symbol prop)
       (change-property symbol prop '(lambda (x) (* 2 x))))

In such cases, we usually use the special form `function' instead of
simple quotation to quote the anonymous function, like this:

     (defun double-property (symbol prop)
       (change-property symbol prop
                        (function (lambda (x) (* 2 x)))))

   Using `function' instead of `quote' makes a difference if you
compile the function `double-property'.  For example, if you compile
the second definition of `double-property', the anonymous function is
compiled as well.  By contrast, if you compile the first definition
which uses ordinary `quote', the argument passed to `change-property'
is the precise list shown:

     (lambda (x) (* x 2))

The Lisp compiler cannot assume this list is a function, even though it
looks like one, since it does not know what `change-property' will do
with the list.  Perhaps it will check whether the CAR of the third
element is the symbol `*'!  Using `function' tells the compiler it is
safe to go ahead and compile the constant function.

   Nowadays it is possible to omit `function' entirely, like this:

     (defun double-property (symbol prop)
       (change-property symbol prop (lambda (x) (* 2 x))))

This is because `lambda' itself implies `function'.

   We sometimes write `function' instead of `quote' when quoting the
name of a function, but this usage is just a sort of comment:

     (function SYMBOL) == (quote SYMBOL) == 'SYMBOL

   The read syntax `#'' is a short-hand for using `function'.  For
example,

     #'(lambda (x) (* x x))

is equivalent to

     (function (lambda (x) (* x x)))

 -- Special Form: function function-object
     This special form returns FUNCTION-OBJECT without evaluating it.
     In this, it is equivalent to `quote'.  However, it serves as a
     note to the Emacs Lisp compiler that FUNCTION-OBJECT is intended
     to be used only as a function, and therefore can safely be
     compiled.  Contrast this with `quote', in *Note Quoting::.

   *Note describe-symbols example::, for a realistic example using
`function' and an anonymous function.


File: elisp,  Node: Function Cells,  Next: Obsolete Functions,  Prev: Anonymous Functions,  Up: Functions

12.8 Accessing Function Cell Contents
=====================================

The "function definition" of a symbol is the object stored in the
function cell of the symbol.  The functions described here access, test,
and set the function cell of symbols.

   See also the function `indirect-function'.  *Note Definition of
indirect-function::.

 -- Function: symbol-function symbol
     This returns the object in the function cell of SYMBOL.  If the
     symbol's function cell is void, a `void-function' error is
     signaled.

     This function does not check that the returned object is a
     legitimate function.

          (defun bar (n) (+ n 2))
               => bar
          (symbol-function 'bar)
               => (lambda (n) (+ n 2))
          (fset 'baz 'bar)
               => bar
          (symbol-function 'baz)
               => bar

   If you have never given a symbol any function definition, we say that
that symbol's function cell is "void".  In other words, the function
cell does not have any Lisp object in it.  If you try to call such a
symbol as a function, it signals a `void-function' error.

   Note that void is not the same as `nil' or the symbol `void'.  The
symbols `nil' and `void' are Lisp objects, and can be stored into a
function cell just as any other object can be (and they can be valid
functions if you define them in turn with `defun').  A void function
cell contains no object whatsoever.

   You can test the voidness of a symbol's function definition with
`fboundp'.  After you have given a symbol a function definition, you
can make it void once more using `fmakunbound'.

 -- Function: fboundp symbol
     This function returns `t' if the symbol has an object in its
     function cell, `nil' otherwise.  It does not check that the object
     is a legitimate function.

 -- Function: fmakunbound symbol
     This function makes SYMBOL's function cell void, so that a
     subsequent attempt to access this cell will cause a
     `void-function' error.  It returns SYMBOL.  (See also
     `makunbound', in *Note Void Variables::.)

          (defun foo (x) x)
               => foo
          (foo 1)
               =>1
          (fmakunbound 'foo)
               => foo
          (foo 1)
          error--> Symbol's function definition is void: foo

 -- Function: fset symbol definition
     This function stores DEFINITION in the function cell of SYMBOL.
     The result is DEFINITION.  Normally DEFINITION should be a
     function or the name of a function, but this is not checked.  The
     argument SYMBOL is an ordinary evaluated argument.

     There are three normal uses of this function:

        * Copying one symbol's function definition to another--in other
          words, making an alternate name for a function.  (If you
          think of this as the definition of the new name, you should
          use `defalias' instead of `fset'; see *Note Definition of
          defalias::.)

        * Giving a symbol a function definition that is not a list and
          therefore cannot be made with `defun'.  For example, you can
          use `fset' to give a symbol `s1' a function definition which
          is another symbol `s2'; then `s1' serves as an alias for
          whatever definition `s2' presently has.  (Once again use
          `defalias' instead of `fset' if you think of this as the
          definition of `s1'.)

        * In constructs for defining or altering functions.  If `defun'
          were not a primitive, it could be written in Lisp (as a
          macro) using `fset'.

     Here are examples of these uses:

          ;; Save `foo''s definition in `old-foo'.
          (fset 'old-foo (symbol-function 'foo))

          ;; Make the symbol `car' the function definition of `xfirst'.
          ;; (Most likely, `defalias' would be better than `fset' here.)
          (fset 'xfirst 'car)
               => car
          (xfirst '(1 2 3))
               => 1
          (symbol-function 'xfirst)
               => car
          (symbol-function (symbol-function 'xfirst))
               => #<subr car>

          ;; Define a named keyboard macro.
          (fset 'kill-two-lines "\^u2\^k")
               => "\^u2\^k"

          ;; Here is a function that alters other functions.
          (defun copy-function-definition (new old)
            "Define NEW with the same function definition as OLD."
            (fset new (symbol-function old)))

   `fset' is sometimes used to save the old definition of a function
before redefining it.  That permits the new definition to invoke the
old definition.  But it is unmodular and unclean for a Lisp file to
redefine a function defined elsewhere.  If you want to modify a
function defined by another package, it is cleaner to use `defadvice'
(*note Advising Functions::).


File: elisp,  Node: Obsolete Functions,  Next: Inline Functions,  Prev: Function Cells,  Up: Functions

12.9 Declaring Functions Obsolete
=================================

You can use `make-obsolete' to declare a function obsolete.  This
indicates that the function may be removed at some stage in the future.

 -- Function: make-obsolete obsolete-name current-name &optional when
     This function makes the byte compiler warn that the function
     OBSOLETE-NAME is obsolete.  If CURRENT-NAME is a symbol, the
     warning message says to use CURRENT-NAME instead of OBSOLETE-NAME.
     CURRENT-NAME does not need to be an alias for OBSOLETE-NAME; it
     can be a different function with similar functionality.  If
     CURRENT-NAME is a string, it is the warning message.

     If provided, WHEN should be a string indicating when the function
     was first made obsolete--for example, a date or a release number.

   You can define a function as an alias and declare it obsolete at the
same time using the macro `define-obsolete-function-alias'.

 -- Macro: define-obsolete-function-alias obsolete-name current-name
          &optional when docstring
     This macro marks the function OBSOLETE-NAME obsolete and also
     defines it as an alias for the function CURRENT-NAME.  It is
     equivalent to the following:

          (defalias OBSOLETE-NAME CURRENT-NAME DOCSTRING)
          (make-obsolete OBSOLETE-NAME CURRENT-NAME WHEN)


File: elisp,  Node: Inline Functions,  Next: Function Safety,  Prev: Obsolete Functions,  Up: Functions

12.10 Inline Functions
======================

You can define an "inline function" by using `defsubst' instead of
`defun'.  An inline function works just like an ordinary function
except for one thing: when you compile a call to the function, the
function's definition is open-coded into the caller.

   Making a function inline makes explicit calls run faster.  But it
also has disadvantages.  For one thing, it reduces flexibility; if you
change the definition of the function, calls already inlined still use
the old definition until you recompile them.

   Another disadvantage is that making a large function inline can
increase the size of compiled code both in files and in memory.  Since
the speed advantage of inline functions is greatest for small
functions, you generally should not make large functions inline.

   Also, inline functions do not behave well with respect to debugging,
tracing, and advising (*note Advising Functions::).  Since ease of
debugging and the flexibility of redefining functions are important
features of Emacs, you should not make a function inline, even if it's
small, unless its speed is really crucial, and you've timed the code to
verify that using `defun' actually has performance problems.

   It's possible to define a macro to expand into the same code that an
inline function would execute.  (*Note Macros::.)  But the macro would
be limited to direct use in expressions--a macro cannot be called with
`apply', `mapcar' and so on.  Also, it takes some work to convert an
ordinary function into a macro.  To convert it into an inline function
is very easy; simply replace `defun' with `defsubst'.  Since each
argument of an inline function is evaluated exactly once, you needn't
worry about how many times the body uses the arguments, as you do for
macros.  (*Note Argument Evaluation::.)

   Inline functions can be used and open-coded later on in the same
file, following the definition, just like macros.


File: elisp,  Node: Function Safety,  Next: Related Topics,  Prev: Inline Functions,  Up: Functions

12.11 Determining whether a Function is Safe to Call
====================================================

Some major modes such as SES call functions that are stored in user
files.  (*note (ses)Top::, for more information on SES.)  User files
sometimes have poor pedigrees--you can get a spreadsheet from someone
you've just met, or you can get one through email from someone you've
never met.  So it is risky to call a function whose source code is
stored in a user file until you have determined that it is safe.

 -- Function: unsafep form &optional unsafep-vars
     Returns `nil' if FORM is a "safe" Lisp expression, or returns a
     list that describes why it might be unsafe.  The argument
     UNSAFEP-VARS is a list of symbols known to have temporary bindings
     at this point; it is mainly used for internal recursive calls.
     The current buffer is an implicit argument, which provides a list
     of buffer-local bindings.

   Being quick and simple, `unsafep' does a very light analysis and
rejects many Lisp expressions that are actually safe.  There are no
known cases where `unsafep' returns `nil' for an unsafe expression.
However, a "safe" Lisp expression can return a string with a `display'
property, containing an associated Lisp expression to be executed after
the string is inserted into a buffer.  This associated expression can
be a virus.  In order to be safe, you must delete properties from all
strings calculated by user code before inserting them into buffers.


File: elisp,  Node: Related Topics,  Prev: Function Safety,  Up: Functions

12.12 Other Topics Related to Functions
=======================================

Here is a table of several functions that do things related to function
calling and function definitions.  They are documented elsewhere, but
we provide cross references here.

`apply'
     See *Note Calling Functions::.

`autoload'
     See *Note Autoload::.

`call-interactively'
     See *Note Interactive Call::.

`called-interactively-p'
     See *Note Distinguish Interactive::.

`commandp'
     See *Note Interactive Call::.

`documentation'
     See *Note Accessing Documentation::.

`eval'
     See *Note Eval::.

`funcall'
     See *Note Calling Functions::.

`function'
     See *Note Anonymous Functions::.

`ignore'
     See *Note Calling Functions::.

`indirect-function'
     See *Note Function Indirection::.

`interactive'
     See *Note Using Interactive::.

`interactive-p'
     See *Note Distinguish Interactive::.

`mapatoms'
     See *Note Creating Symbols::.

`mapcar'
     See *Note Mapping Functions::.

`map-char-table'
     See *Note Char-Tables::.

`mapconcat'
     See *Note Mapping Functions::.

`undefined'
     See *Note Functions for Key Lookup::.


File: elisp,  Node: Macros,  Next: Customization,  Prev: Functions,  Up: Top

13 Macros
*********

"Macros" enable you to define new control constructs and other language
features.  A macro is defined much like a function, but instead of
telling how to compute a value, it tells how to compute another Lisp
expression which will in turn compute the value.  We call this
expression the "expansion" of the macro.

   Macros can do this because they operate on the unevaluated
expressions for the arguments, not on the argument values as functions
do.  They can therefore construct an expansion containing these
argument expressions or parts of them.

   If you are using a macro to do something an ordinary function could
do, just for the sake of speed, consider using an inline function
instead.  *Note Inline Functions::.

* Menu:

* Simple Macro::            A basic example.
* Expansion::               How, when and why macros are expanded.
* Compiling Macros::        How macros are expanded by the compiler.
* Defining Macros::         How to write a macro definition.
* Backquote::               Easier construction of list structure.
* Problems with Macros::    Don't evaluate the macro arguments too many times.
                              Don't hide the user's variables.
* Indenting Macros::        Specifying how to indent macro calls.


File: elisp,  Node: Simple Macro,  Next: Expansion,  Up: Macros

13.1 A Simple Example of a Macro
================================

Suppose we would like to define a Lisp construct to increment a
variable value, much like the `++' operator in C.  We would like to
write `(inc x)' and have the effect of `(setq x (1+ x))'.  Here's a
macro definition that does the job:

     (defmacro inc (var)
        (list 'setq var (list '1+ var)))

   When this is called with `(inc x)', the argument VAR is the symbol
`x'--_not_ the _value_ of `x', as it would be in a function.  The body
of the macro uses this to construct the expansion, which is `(setq x
(1+ x))'.  Once the macro definition returns this expansion, Lisp
proceeds to evaluate it, thus incrementing `x'.


File: elisp,  Node: Expansion,  Next: Compiling Macros,  Prev: Simple Macro,  Up: Macros

13.2 Expansion of a Macro Call
==============================

A macro call looks just like a function call in that it is a list which
starts with the name of the macro.  The rest of the elements of the list
are the arguments of the macro.

   Evaluation of the macro call begins like evaluation of a function
call except for one crucial difference: the macro arguments are the
actual expressions appearing in the macro call.  They are not evaluated
before they are given to the macro definition.  By contrast, the
arguments of a function are results of evaluating the elements of the
function call list.

   Having obtained the arguments, Lisp invokes the macro definition just
as a function is invoked.  The argument variables of the macro are bound
to the argument values from the macro call, or to a list of them in the
case of a `&rest' argument.  And the macro body executes and returns
its value just as a function body does.

   The second crucial difference between macros and functions is that
the value returned by the macro body is not the value of the macro call.
Instead, it is an alternate expression for computing that value, also
known as the "expansion" of the macro.  The Lisp interpreter proceeds
to evaluate the expansion as soon as it comes back from the macro.

   Since the expansion is evaluated in the normal manner, it may contain
calls to other macros.  It may even be a call to the same macro, though
this is unusual.

   You can see the expansion of a given macro call by calling
`macroexpand'.

 -- Function: macroexpand form &optional environment
     This function expands FORM, if it is a macro call.  If the result
     is another macro call, it is expanded in turn, until something
     which is not a macro call results.  That is the value returned by
     `macroexpand'.  If FORM is not a macro call to begin with, it is
     returned as given.

     Note that `macroexpand' does not look at the subexpressions of
     FORM (although some macro definitions may do so).  Even if they
     are macro calls themselves, `macroexpand' does not expand them.

     The function `macroexpand' does not expand calls to inline
     functions.  Normally there is no need for that, since a call to an
     inline function is no harder to understand than a call to an
     ordinary function.

     If ENVIRONMENT is provided, it specifies an alist of macro
     definitions that shadow the currently defined macros.  Byte
     compilation uses this feature.

          (defmacro inc (var)
              (list 'setq var (list '1+ var)))
               => inc

          (macroexpand '(inc r))
               => (setq r (1+ r))

          (defmacro inc2 (var1 var2)
              (list 'progn (list 'inc var1) (list 'inc var2)))
               => inc2

          (macroexpand '(inc2 r s))
               => (progn (inc r) (inc s))  ; `inc' not expanded here.

 -- Function: macroexpand-all form &optional environment
     `macroexpand-all' expands macros like `macroexpand', but will look
     for and expand all macros in FORM, not just at the top-level.  If
     no macros are expanded, the return value is `eq' to FORM.

     Repeating the example used for `macroexpand' above with
     `macroexpand-all', we see that `macroexpand-all' _does_ expand the
     embedded calls to `inc':

          (macroexpand-all '(inc2 r s))
               => (progn (setq r (1+ r)) (setq s (1+ s)))



File: elisp,  Node: Compiling Macros,  Next: Defining Macros,  Prev: Expansion,  Up: Macros

13.3 Macros and Byte Compilation
================================

You might ask why we take the trouble to compute an expansion for a
macro and then evaluate the expansion.  Why not have the macro body
produce the desired results directly?  The reason has to do with
compilation.

   When a macro call appears in a Lisp program being compiled, the Lisp
compiler calls the macro definition just as the interpreter would, and
receives an expansion.  But instead of evaluating this expansion, it
compiles the expansion as if it had appeared directly in the program.
As a result, the compiled code produces the value and side effects
intended for the macro, but executes at full compiled speed.  This would
not work if the macro body computed the value and side effects
itself--they would be computed at compile time, which is not useful.

   In order for compilation of macro calls to work, the macros must
already be defined in Lisp when the calls to them are compiled.  The
compiler has a special feature to help you do this: if a file being
compiled contains a `defmacro' form, the macro is defined temporarily
for the rest of the compilation of that file.  To make this feature
work, you must put the `defmacro' in the same file where it is used,
and before its first use.

   Byte-compiling a file executes any `require' calls at top-level in
the file.  This is in case the file needs the required packages for
proper compilation.  One way to ensure that necessary macro definitions
are available during compilation is to require the files that define
them (*note Named Features::).  To avoid loading the macro definition
files when someone _runs_ the compiled program, write
`eval-when-compile' around the `require' calls (*note Eval During
Compile::).


File: elisp,  Node: Defining Macros,  Next: Backquote,  Prev: Compiling Macros,  Up: Macros

13.4 Defining Macros
====================

A Lisp macro is a list whose CAR is `macro'.  Its CDR should be a
function; expansion of the macro works by applying the function (with
`apply') to the list of unevaluated argument-expressions from the macro
call.

   It is possible to use an anonymous Lisp macro just like an anonymous
function, but this is never done, because it does not make sense to pass
an anonymous macro to functionals such as `mapcar'.  In practice, all
Lisp macros have names, and they are usually defined with the special
form `defmacro'.

 -- Special Form: defmacro name argument-list body-forms...
     `defmacro' defines the symbol NAME as a macro that looks like this:

          (macro lambda ARGUMENT-LIST . BODY-FORMS)

     (Note that the CDR of this list is a function--a lambda
     expression.)  This macro object is stored in the function cell of
     NAME.  The value returned by evaluating the `defmacro' form is
     NAME, but usually we ignore this value.

     The shape and meaning of ARGUMENT-LIST is the same as in a
     function, and the keywords `&rest' and `&optional' may be used
     (*note Argument List::).  Macros may have a documentation string,
     but any `interactive' declaration is ignored since macros cannot be
     called interactively.

   The body of the macro definition can include a `declare' form, which
can specify how <TAB> should indent macro calls, and how to step
through them for Edebug.

 -- Macro: declare SPECS...
     A `declare' form is used in a macro definition to specify various
     additional information about it.  Two kinds of specification are
     currently supported:

    `(debug EDEBUG-FORM-SPEC)'
          Specify how to step through macro calls for Edebug.  *Note
          Instrumenting Macro Calls::.

    `(indent INDENT-SPEC)'
          Specify how to indent calls to this macro.  *Note Indenting
          Macros::, for more details.

     A `declare' form only has its special effect in the body of a
     `defmacro' form if it immediately follows the documentation
     string, if present, or the argument list otherwise.  (Strictly
     speaking, _several_ `declare' forms can follow the documentation
     string or argument list, but since a `declare' form can have
     several SPECS, they can always be combined into a single form.)
     When used at other places in a `defmacro' form, or outside a
     `defmacro' form, `declare' just returns `nil' without evaluating
     any SPECS.

   No macro absolutely needs a `declare' form, because that form has no
effect on how the macro expands, on what the macro means in the
program.  It only affects secondary features: indentation and Edebug.


File: elisp,  Node: Backquote,  Next: Problems with Macros,  Prev: Defining Macros,  Up: Macros

13.5 Backquote
==============

Macros often need to construct large list structures from a mixture of
constants and nonconstant parts.  To make this easier, use the ``'
syntax (usually called "backquote").

   Backquote allows you to quote a list, but selectively evaluate
elements of that list.  In the simplest case, it is identical to the
special form `quote' (*note Quoting::).  For example, these two forms
yield identical results:

     `(a list of (+ 2 3) elements)
          => (a list of (+ 2 3) elements)
     '(a list of (+ 2 3) elements)
          => (a list of (+ 2 3) elements)

   The special marker `,' inside of the argument to backquote indicates
a value that isn't constant.  Backquote evaluates the argument of `,'
and puts the value in the list structure:

     (list 'a 'list 'of (+ 2 3) 'elements)
          => (a list of 5 elements)
     `(a list of ,(+ 2 3) elements)
          => (a list of 5 elements)

   Substitution with `,' is allowed at deeper levels of the list
structure also.  For example:

     (defmacro t-becomes-nil (variable)
       `(if (eq ,variable t)
            (setq ,variable nil)))

     (t-becomes-nil foo)
          == (if (eq foo t) (setq foo nil))

   You can also "splice" an evaluated value into the resulting list,
using the special marker `,@'.  The elements of the spliced list become
elements at the same level as the other elements of the resulting list.
The equivalent code without using ``' is often unreadable.  Here are
some examples:

     (setq some-list '(2 3))
          => (2 3)
     (cons 1 (append some-list '(4) some-list))
          => (1 2 3 4 2 3)
     `(1 ,@some-list 4 ,@some-list)
          => (1 2 3 4 2 3)

     (setq list '(hack foo bar))
          => (hack foo bar)
     (cons 'use
       (cons 'the
         (cons 'words (append (cdr list) '(as elements)))))
          => (use the words foo bar as elements)
     `(use the words ,@(cdr list) as elements)
          => (use the words foo bar as elements)

   In old Emacs versions, before version 19.29, ``' used a different
syntax which required an extra level of parentheses around the entire
backquote construct.  Likewise, each `,' or `,@' substitution required
an extra level of parentheses surrounding both the `,' or `,@' and the
following expression.  The old syntax required whitespace between the
``', `,' or `,@' and the following expression.

   This syntax is still accepted, for compatibility with old Emacs
versions, but support for it will soon disappear.


File: elisp,  Node: Problems with Macros,  Next: Indenting Macros,  Prev: Backquote,  Up: Macros

13.6 Common Problems Using Macros
=================================

The basic facts of macro expansion have counterintuitive consequences.
This section describes some important consequences that can lead to
trouble, and rules to follow to avoid trouble.

* Menu:

* Wrong Time::             Do the work in the expansion, not in the macro.
* Argument Evaluation::    The expansion should evaluate each macro arg once.
* Surprising Local Vars::  Local variable bindings in the expansion
                              require special care.
* Eval During Expansion::  Don't evaluate them; put them in the expansion.
* Repeated Expansion::     Avoid depending on how many times expansion is done.


File: elisp,  Node: Wrong Time,  Next: Argument Evaluation,  Up: Problems with Macros

13.6.1 Wrong Time
-----------------

The most common problem in writing macros is doing some of the real
work prematurely--while expanding the macro, rather than in the
expansion itself.  For instance, one real package had this macro
definition:

     (defmacro my-set-buffer-multibyte (arg)
       (if (fboundp 'set-buffer-multibyte)
           (set-buffer-multibyte arg)))

   With this erroneous macro definition, the program worked fine when
interpreted but failed when compiled.  This macro definition called
`set-buffer-multibyte' during compilation, which was wrong, and then
did nothing when the compiled package was run.  The definition that the
programmer really wanted was this:

     (defmacro my-set-buffer-multibyte (arg)
       (if (fboundp 'set-buffer-multibyte)
           `(set-buffer-multibyte ,arg)))

This macro expands, if appropriate, into a call to
`set-buffer-multibyte' that will be executed when the compiled program
is actually run.


File: elisp,  Node: Argument Evaluation,  Next: Surprising Local Vars,  Prev: Wrong Time,  Up: Problems with Macros

13.6.2 Evaluating Macro Arguments Repeatedly
--------------------------------------------

When defining a macro you must pay attention to the number of times the
arguments will be evaluated when the expansion is executed.  The
following macro (used to facilitate iteration) illustrates the problem.
This macro allows us to write a simple "for" loop such as one might
find in Pascal.

     (defmacro for (var from init to final do &rest body)
       "Execute a simple \"for\" loop.
     For example, (for i from 1 to 10 do (print i))."
       (list 'let (list (list var init))
             (cons 'while (cons (list '<= var final)
                                (append body (list (list 'inc var)))))))
     => for

     (for i from 1 to 3 do
        (setq square (* i i))
        (princ (format "\n%d %d" i square)))
     ==>
     (let ((i 1))
       (while (<= i 3)
         (setq square (* i i))
         (princ (format "\n%d %d" i square))
         (inc i)))

          -|1       1
          -|2       4
          -|3       9
     => nil

The arguments `from', `to', and `do' in this macro are "syntactic
sugar"; they are entirely ignored.  The idea is that you will write
noise words (such as `from', `to', and `do') in those positions in the
macro call.

   Here's an equivalent definition simplified through use of backquote:

     (defmacro for (var from init to final do &rest body)
       "Execute a simple \"for\" loop.
     For example, (for i from 1 to 10 do (print i))."
       `(let ((,var ,init))
          (while (<= ,var ,final)
            ,@body
            (inc ,var))))

   Both forms of this definition (with backquote and without) suffer
from the defect that FINAL is evaluated on every iteration.  If FINAL
is a constant, this is not a problem.  If it is a more complex form,
say `(long-complex-calculation x)', this can slow down the execution
significantly.  If FINAL has side effects, executing it more than once
is probably incorrect.

   A well-designed macro definition takes steps to avoid this problem by
producing an expansion that evaluates the argument expressions exactly
once unless repeated evaluation is part of the intended purpose of the
macro.  Here is a correct expansion for the `for' macro:

     (let ((i 1)
           (max 3))
       (while (<= i max)
         (setq square (* i i))
         (princ (format "%d      %d" i square))
         (inc i)))

   Here is a macro definition that creates this expansion:

     (defmacro for (var from init to final do &rest body)
       "Execute a simple for loop: (for i from 1 to 10 do (print i))."
       `(let ((,var ,init)
              (max ,final))
          (while (<= ,var max)
            ,@body
            (inc ,var))))

   Unfortunately, this fix introduces another problem, described in the
following section.


File: elisp,  Node: Surprising Local Vars,  Next: Eval During Expansion,  Prev: Argument Evaluation,  Up: Problems with Macros

13.6.3 Local Variables in Macro Expansions
------------------------------------------

In the previous section, the definition of `for' was fixed as follows
to make the expansion evaluate the macro arguments the proper number of
times:

     (defmacro for (var from init to final do &rest body)
       "Execute a simple for loop: (for i from 1 to 10 do (print i))."
       `(let ((,var ,init)
              (max ,final))
          (while (<= ,var max)
            ,@body
            (inc ,var))))

The new definition of `for' has a new problem: it introduces a local
variable named `max' which the user does not expect.  This causes
trouble in examples such as the following:

     (let ((max 0))
       (for x from 0 to 10 do
         (let ((this (frob x)))
           (if (< max this)
               (setq max this)))))

The references to `max' inside the body of the `for', which are
supposed to refer to the user's binding of `max', really access the
binding made by `for'.

   The way to correct this is to use an uninterned symbol instead of
`max' (*note Creating Symbols::).  The uninterned symbol can be bound
and referred to just like any other symbol, but since it is created by
`for', we know that it cannot already appear in the user's program.
Since it is not interned, there is no way the user can put it into the
program later.  It will never appear anywhere except where put by
`for'.  Here is a definition of `for' that works this way:

     (defmacro for (var from init to final do &rest body)
       "Execute a simple for loop: (for i from 1 to 10 do (print i))."
       (let ((tempvar (make-symbol "max")))
         `(let ((,var ,init)
                (,tempvar ,final))
            (while (<= ,var ,tempvar)
              ,@body
              (inc ,var)))))

This creates an uninterned symbol named `max' and puts it in the
expansion instead of the usual interned symbol `max' that appears in
expressions ordinarily.


File: elisp,  Node: Eval During Expansion,  Next: Repeated Expansion,  Prev: Surprising Local Vars,  Up: Problems with Macros

13.6.4 Evaluating Macro Arguments in Expansion
----------------------------------------------

Another problem can happen if the macro definition itself evaluates any
of the macro argument expressions, such as by calling `eval' (*note
Eval::).  If the argument is supposed to refer to the user's variables,
you may have trouble if the user happens to use a variable with the
same name as one of the macro arguments.  Inside the macro body, the
macro argument binding is the most local binding of this variable, so
any references inside the form being evaluated do refer to it.  Here is
an example:

     (defmacro foo (a)
       (list 'setq (eval a) t))
          => foo
     (setq x 'b)
     (foo x) ==> (setq b t)
          => t                  ; and `b' has been set.
     ;; but
     (setq a 'c)
     (foo a) ==> (setq a t)
          => t                  ; but this set `a', not `c'.

   It makes a difference whether the user's variable is named `a' or
`x', because `a' conflicts with the macro argument variable `a'.

   Another problem with calling `eval' in a macro definition is that it
probably won't do what you intend in a compiled program.  The
byte-compiler runs macro definitions while compiling the program, when
the program's own computations (which you might have wished to access
with `eval') don't occur and its local variable bindings don't exist.

   To avoid these problems, *don't evaluate an argument expression
while computing the macro expansion*.  Instead, substitute the
expression into the macro expansion, so that its value will be computed
as part of executing the expansion.  This is how the other examples in
this chapter work.


File: elisp,  Node: Repeated Expansion,  Prev: Eval During Expansion,  Up: Problems with Macros

13.6.5 How Many Times is the Macro Expanded?
--------------------------------------------

Occasionally problems result from the fact that a macro call is
expanded each time it is evaluated in an interpreted function, but is
expanded only once (during compilation) for a compiled function.  If the
macro definition has side effects, they will work differently depending
on how many times the macro is expanded.

   Therefore, you should avoid side effects in computation of the macro
expansion, unless you really know what you are doing.

   One special kind of side effect can't be avoided: constructing Lisp
objects.  Almost all macro expansions include constructed lists; that is
the whole point of most macros.  This is usually safe; there is just one
case where you must be careful: when the object you construct is part
of a quoted constant in the macro expansion.

   If the macro is expanded just once, in compilation, then the object
is constructed just once, during compilation.  But in interpreted
execution, the macro is expanded each time the macro call runs, and this
means a new object is constructed each time.

   In most clean Lisp code, this difference won't matter.  It can matter
only if you perform side-effects on the objects constructed by the macro
definition.  Thus, to avoid trouble, *avoid side effects on objects
constructed by macro definitions*.  Here is an example of how such side
effects can get you into trouble:

     (defmacro empty-object ()
       (list 'quote (cons nil nil)))

     (defun initialize (condition)
       (let ((object (empty-object)))
         (if condition
             (setcar object condition))
         object))

If `initialize' is interpreted, a new list `(nil)' is constructed each
time `initialize' is called.  Thus, no side effect survives between
calls.  If `initialize' is compiled, then the macro `empty-object' is
expanded during compilation, producing a single "constant" `(nil)' that
is reused and altered each time `initialize' is called.

   One way to avoid pathological cases like this is to think of
`empty-object' as a funny kind of constant, not as a memory allocation
construct.  You wouldn't use `setcar' on a constant such as `'(nil)',
so naturally you won't use it on `(empty-object)' either.


File: elisp,  Node: Indenting Macros,  Prev: Problems with Macros,  Up: Macros

13.7 Indenting Macros
=====================

You can use the `declare' form in the macro definition to specify how
to <TAB> should indent indent calls to the macro.  You write it like
this:

     (declare (indent INDENT-SPEC))

Here are the possibilities for INDENT-SPEC:

`nil'
     This is the same as no property--use the standard indentation
     pattern.

`defun'
     Handle this function like a `def' construct: treat the second line
     as the start of a "body".

an integer, NUMBER
     The first NUMBER arguments of the function are "distinguished"
     arguments; the rest are considered the body of the expression.  A
     line in the expression is indented according to whether the first
     argument on it is distinguished or not.  If the argument is part
     of the body, the line is indented `lisp-body-indent' more columns
     than the open-parenthesis starting the containing expression.  If
     the argument is distinguished and is either the first or second
     argument, it is indented _twice_ that many extra columns.  If the
     argument is distinguished and not the first or second argument,
     the line uses the standard pattern.

a symbol, SYMBOL
     SYMBOL should be a function name; that function is called to
     calculate the indentation of a line within this expression.  The
     function receives two arguments:
    STATE
          The value returned by `parse-partial-sexp' (a Lisp primitive
          for indentation and nesting computation) when it parses up to
          the beginning of this line.

    POS
          The position at which the line being indented begins.
     It should return either a number, which is the number of columns of
     indentation for that line, or a list whose car is such a number.
     The difference between returning a number and returning a list is
     that a number says that all following lines at the same nesting
     level should be indented just like this one; a list says that
     following lines might call for different indentations.  This makes
     a difference when the indentation is being computed by `C-M-q'; if
     the value is a number, `C-M-q' need not recalculate indentation
     for the following lines until the end of the list.


File: elisp,  Node: Customization,  Next: Loading,  Prev: Macros,  Up: Top

14 Writing Customization Definitions
************************************

This chapter describes how to declare user options for customization,
and also customization groups for classifying them.  We use the term
"customization item" to include both kinds of customization
definitions--as well as face definitions (*note Defining Faces::).

* Menu:

* Common Keywords::      Common keyword arguments for all kinds of
                           customization declarations.
* Group Definitions::    Writing customization group definitions.
* Variable Definitions:: Declaring user options.
* Customization Types::  Specifying the type of a user option.


File: elisp,  Node: Common Keywords,  Next: Group Definitions,  Up: Customization

14.1 Common Item Keywords
=========================

All kinds of customization declarations (for variables and groups, and
for faces) accept keyword arguments for specifying various information.
This section describes some keywords that apply to all kinds.

   All of these keywords, except `:tag', can be used more than once in
a given item.  Each use of the keyword has an independent effect.  The
keyword `:tag' is an exception because any given item can only display
one name.

`:tag LABEL'
     Use LABEL, a string, instead of the item's name, to label the item
     in customization menus and buffers.  *Don't use a tag which is
     substantially different from the item's real name; that would
     cause confusion.*  One legitimate case for use of `:tag' is to
     specify a dash where normally a hyphen would be converted to a
     space:

          (defcustom cursor-in-non-selected-windows ...
            :tag "Cursor In Non-selected Windows"

`:group GROUP'
     Put this customization item in group GROUP.  When you use `:group'
     in a `defgroup', it makes the new group a subgroup of GROUP.

     If you use this keyword more than once, you can put a single item
     into more than one group.  Displaying any of those groups will
     show this item.  Please don't overdo this, since the result would
     be annoying.

`:link LINK-DATA'
     Include an external link after the documentation string for this
     item.  This is a sentence containing an active field which
     references some other documentation.

     There are several alternatives you can use for LINK-DATA:

    `(custom-manual INFO-NODE)'
          Link to an Info node; INFO-NODE is a string which specifies
          the node name, as in `"(emacs)Top"'.  The link appears as
          `[Manual]' in the customization buffer and enters the built-in
          Info reader on INFO-NODE.

    `(info-link INFO-NODE)'
          Like `custom-manual' except that the link appears in the
          customization buffer with the Info node name.

    `(url-link URL)'
          Link to a web page; URL is a string which specifies the URL.
          The link appears in the customization buffer as URL and
          invokes the WWW browser specified by
          `browse-url-browser-function'.

    `(emacs-commentary-link LIBRARY)'
          Link to the commentary section of a library; LIBRARY is a
          string which specifies the library name.

    `(emacs-library-link LIBRARY)'
          Link to an Emacs Lisp library file; LIBRARY is a string which
          specifies the library name.

    `(file-link FILE)'
          Link to a file; FILE is a string which specifies the name of
          the file to visit with `find-file' when the user invokes this
          link.

    `(function-link FUNCTION)'
          Link to the documentation of a function; FUNCTION is a string
          which specifies the name of the function to describe with
          `describe-function' when the user invokes this link.

    `(variable-link VARIABLE)'
          Link to the documentation of a variable; VARIABLE is a string
          which specifies the name of the variable to describe with
          `describe-variable' when the user invokes this link.

    `(custom-group-link GROUP)'
          Link to another customization group.  Invoking it creates a
          new customization buffer for GROUP.

     You can specify the text to use in the customization buffer by
     adding `:tag NAME' after the first element of the LINK-DATA; for
     example, `(info-link :tag "foo" "(emacs)Top")' makes a link to the
     Emacs manual which appears in the buffer as `foo'.

     An item can have more than one external link; however, most items
     have none at all.

`:load FILE'
     Load file FILE (a string) before displaying this customization
     item.  Loading is done with `load-library', and only if the file is
     not already loaded.

`:require FEATURE'
     Execute `(require 'FEATURE)' when your saved customizations set
     the value of this item.  FEATURE should be a symbol.

     The most common reason to use `:require' is when a variable enables
     a feature such as a minor mode, and just setting the variable
     won't have any effect unless the code which implements the mode is
     loaded.

`:version VERSION'
     This keyword specifies that the item was first introduced in Emacs
     version VERSION, or that its default value was changed in that
     version.  The value VERSION must be a string.

`:package-version '(PACKAGE . VERSION)'
     This keyword specifies that the item was first introduced in
     PACKAGE version VERSION, or that its meaning or default value was
     changed in that version.  The value of PACKAGE is a symbol and
     VERSION is a string.

     This keyword takes priority over `:version'.

     PACKAGE should be the official name of the package, such as MH-E
     or Gnus.  If the package PACKAGE is released as part of Emacs,
     PACKAGE and VERSION should appear in the value of
     `customize-package-emacs-version-alist'.

   Packages distributed as part of Emacs that use the
`:package-version' keyword must also update the
`customize-package-emacs-version-alist' variable.

 -- Variable: customize-package-emacs-version-alist
     This alist provides a mapping for the versions of Emacs that are
     associated with versions of a package listed in the
     `:package-version' keyword.  Its elements look like this:

          (PACKAGE (PVERSION . EVERSION)...)

     For each PACKAGE, which is a symbol, there are one or more
     elements that contain a package version PVERSION with an
     associated Emacs version EVERSION.  These versions are strings.
     For example, the MH-E package updates this alist with the
     following:

          (add-to-list 'customize-package-emacs-version-alist
                       '(MH-E ("6.0" . "22.1") ("6.1" . "22.1") ("7.0" . "22.1")
                              ("7.1" . "22.1") ("7.2" . "22.1") ("7.3" . "22.1")
                              ("7.4" . "22.1") ("8.0" . "22.1")))

     The value of PACKAGE needs to be unique and it needs to match the
     PACKAGE value appearing in the `:package-version' keyword.  Since
     the user might see the value in a error message, a good choice is
     the official name of the package, such as MH-E or Gnus.


File: elisp,  Node: Group Definitions,  Next: Variable Definitions,  Prev: Common Keywords,  Up: Customization

14.2 Defining Customization Groups
==================================

Each Emacs Lisp package should have one main customization group which
contains all the options, faces and other groups in the package.  If the
package has a small number of options and faces, use just one group and
put everything in it.  When there are more than twelve or so options and
faces, then you should structure them into subgroups, and put the
subgroups under the package's main customization group.  It is OK to
put some of the options and faces in the package's main group alongside
the subgroups.

   The package's main or only group should be a member of one or more of
the standard customization groups.  (To display the full list of them,
use `M-x customize'.)  Choose one or more of them (but not too many),
and add your group to each of them using the `:group' keyword.

   The way to declare new customization groups is with `defgroup'.

 -- Macro: defgroup group members doc [keyword value]...
     Declare GROUP as a customization group containing MEMBERS.  Do not
     quote the symbol GROUP.  The argument DOC specifies the
     documentation string for the group.

     The argument MEMBERS is a list specifying an initial set of
     customization items to be members of the group.  However, most
     often MEMBERS is `nil', and you specify the group's members by
     using the `:group' keyword when defining those members.

     If you want to specify group members through MEMBERS, each element
     should have the form `(NAME WIDGET)'.  Here NAME is a symbol, and
     WIDGET is a widget type for editing that symbol.  Useful widgets
     are `custom-variable' for a variable, `custom-face' for a face,
     and `custom-group' for a group.

     When you introduce a new group into Emacs, use the `:version'
     keyword in the `defgroup'; then you need not use it for the
     individual members of the group.

     In addition to the common keywords (*note Common Keywords::), you
     can also use this keyword in `defgroup':

    `:prefix PREFIX'
          If the name of an item in the group starts with PREFIX, then
          the tag for that item is constructed (by default) by omitting
          PREFIX.

          One group can have any number of prefixes.

   The prefix-discarding feature is currently turned off, which means
that `:prefix' currently has no effect.  We did this because we found
that discarding the specified prefixes often led to confusing names for
options.  This happened because the people who wrote the `defgroup'
definitions for various groups added `:prefix' keywords whenever they
make logical sense--that is, whenever the variables in the library have
a common prefix.

   In order to obtain good results with `:prefix', it would be
necessary to check the specific effects of discarding a particular
prefix, given the specific items in a group and their names and
documentation.  If the resulting text is not clear, then `:prefix'
should not be used in that case.

   It should be possible to recheck all the customization groups, delete
the `:prefix' specifications which give unclear results, and then turn
this feature back on, if someone would like to do the work.


File: elisp,  Node: Variable Definitions,  Next: Customization Types,  Prev: Group Definitions,  Up: Customization

14.3 Defining Customization Variables
=====================================

Use `defcustom' to declare user-customizable variables.

 -- Macro: defcustom option standard doc [keyword value]...
     This construct declares OPTION as a customizable user option
     variable.  You should not quote OPTION.  The argument DOC
     specifies the documentation string for the variable.  There is no
     need to start it with a `*', because `defcustom' automatically
     marks OPTION as a "user option" (*note Defining Variables::).

     The argument STANDARD is an expression that specifies the standard
     value for OPTION.  Evaluating the `defcustom' form evaluates
     STANDARD, but does not necessarily install the standard value.  If
     OPTION already has a default value, `defcustom' does not change
     it.  If the user has saved a customization for OPTION, `defcustom'
     installs the user's customized value as OPTION's default value.
     If neither of those cases applies, `defcustom' installs the result
     of evaluating STANDARD as the default value.

     The expression STANDARD can be evaluated at various other times,
     too--whenever the customization facility needs to know OPTION's
     standard value.  So be sure to use an expression which is harmless
     to evaluate at any time.  We recommend avoiding backquotes in
     STANDARD, because they are not expanded when editing the value, so
     list values will appear to have the wrong structure.

     Every `defcustom' should specify `:group' at least once.

     If you specify the `:set' keyword, to make the variable take other
     special actions when set through the customization buffer, the
     variable's documentation string should tell the user specifically
     how to do the same job in hand-written Lisp code.

     When you evaluate a `defcustom' form with `C-M-x' in Emacs Lisp
     mode (`eval-defun'), a special feature of `eval-defun' arranges to
     set the variable unconditionally, without testing whether its
     value is void.  (The same feature applies to `defvar'.)  *Note
     Defining Variables::.

   `defcustom' accepts the following additional keywords:

`:type TYPE'
     Use TYPE as the data type for this option.  It specifies which
     values are legitimate, and how to display the value.  *Note
     Customization Types::, for more information.

`:options VALUE-LIST'
     Specify the list of reasonable values for use in this option.  The
     user is not restricted to using only these values, but they are
     offered as convenient alternatives.

     This is meaningful only for certain types, currently including
     `hook', `plist' and `alist'.  See the definition of the individual
     types for a description of how to use `:options'.

`:set SETFUNCTION'
     Specify SETFUNCTION as the way to change the value of this option.
     The function SETFUNCTION should take two arguments, a symbol (the
     option name) and the new value, and should do whatever is
     necessary to update the value properly for this option (which may
     not mean simply setting the option as a Lisp variable).  The
     default for SETFUNCTION is `set-default'.

`:get GETFUNCTION'
     Specify GETFUNCTION as the way to extract the value of this
     option.  The function GETFUNCTION should take one argument, a
     symbol, and should return whatever customize should use as the
     "current value" for that symbol (which need not be the symbol's
     Lisp value).  The default is `default-value'.

     You have to really understand the workings of Custom to use `:get'
     correctly.  It is meant for values that are treated in Custom as
     variables but are not actually stored in Lisp variables.  It is
     almost surely a mistake to specify `getfunction' for a value that
     really is stored in a Lisp variable.

`:initialize FUNCTION'
     FUNCTION should be a function used to initialize the variable when
     the `defcustom' is evaluated.  It should take two arguments, the
     option name (a symbol) and the value.  Here are some predefined
     functions meant for use in this way:

    `custom-initialize-set'
          Use the variable's `:set' function to initialize the
          variable, but do not reinitialize it if it is already
          non-void.

    `custom-initialize-default'
          Like `custom-initialize-set', but use the function
          `set-default' to set the variable, instead of the variable's
          `:set' function.  This is the usual choice for a variable
          whose `:set' function enables or disables a minor mode; with
          this choice, defining the variable will not call the minor
          mode function, but customizing the variable will do so.

    `custom-initialize-reset'
          Always use the `:set' function to initialize the variable.  If
          the variable is already non-void, reset it by calling the
          `:set' function using the current value (returned by the
          `:get' method).  This is the default `:initialize' function.

    `custom-initialize-changed'
          Use the `:set' function to initialize the variable, if it is
          already set or has been customized; otherwise, just use
          `set-default'.

    `custom-initialize-safe-set'
    `custom-initialize-safe-default'
          These functions behave like `custom-initialize-set'
          (`custom-initialize-default', respectively), but catch errors.
          If an error occurs during initialization, they set the
          variable to `nil' using `set-default', and throw no error.

          These two functions are only meant for options defined in
          pre-loaded files, where some variables or functions used to
          compute the option's value may not yet be defined.  The
          option normally gets updated in `startup.el', ignoring the
          previously computed value.  Because of this typical usage,
          the value which these two functions compute normally only
          matters when, after startup, one unsets the option's value
          and then reevaluates the defcustom.  By that time, the
          necessary variables and functions will be defined, so there
          will not be an error.

`:set-after VARIABLES'
     When setting variables according to saved customizations, make
     sure to set the variables VARIABLES before this one; in other
     words, delay setting this variable until after those others have
     been handled.  Use `:set-after' if setting this variable won't
     work properly unless those other variables already have their
     intended values.

   The `:require' keyword is useful for an option that turns on the
operation of a certain feature.  Assuming that the package is coded to
check the value of the option, you still need to arrange for the package
to be loaded.  You can do that with `:require'.  *Note Common
Keywords::.  Here is an example, from the library `saveplace.el':

     (defcustom save-place nil
       "Non-nil means automatically save place in each file..."
       :type 'boolean
       :require 'saveplace
       :group 'save-place)

   If a customization item has a type such as `hook' or `alist', which
supports `:options', you can add additional values to the list from
outside the `defcustom' declaration by calling
`custom-add-frequent-value'.  For example, if you define a function
`my-lisp-mode-initialization' intended to be called from
`emacs-lisp-mode-hook', you might want to add that to the list of
reasonable values for `emacs-lisp-mode-hook', but not by editing its
definition.  You can do it thus:

     (custom-add-frequent-value 'emacs-lisp-mode-hook
        'my-lisp-mode-initialization)

 -- Function: custom-add-frequent-value symbol value
     For the customization option SYMBOL, add VALUE to the list of
     reasonable values.

     The precise effect of adding a value depends on the customization
     type of SYMBOL.

   Internally, `defcustom' uses the symbol property `standard-value' to
record the expression for the standard value, and `saved-value' to
record the value saved by the user with the customization buffer.  Both
properties are actually lists whose car is an expression which
evaluates to the value.


File: elisp,  Node: Customization Types,  Prev: Variable Definitions,  Up: Customization

14.4 Customization Types
========================

When you define a user option with `defcustom', you must specify its
"customization type".  That is a Lisp object which describes (1) which
values are legitimate and (2) how to display the value in the
customization buffer for editing.

   You specify the customization type in `defcustom' with the `:type'
keyword.  The argument of `:type' is evaluated, but only once when the
`defcustom' is executed, so it isn't useful for the value to vary.
Normally we use a quoted constant.  For example:

     (defcustom diff-command "diff"
       "The command to use to run diff."
       :type '(string)
       :group 'diff)

   In general, a customization type is a list whose first element is a
symbol, one of the customization type names defined in the following
sections.  After this symbol come a number of arguments, depending on
the symbol.  Between the type symbol and its arguments, you can
optionally write keyword-value pairs (*note Type Keywords::).

   Some of the type symbols do not use any arguments; those are called
"simple types".  For a simple type, if you do not use any keyword-value
pairs, you can omit the parentheses around the type symbol.  For
example just `string' as a customization type is equivalent to
`(string)'.

* Menu:

* Simple Types::
* Composite Types::
* Splicing into Lists::
* Type Keywords::
* Defining New Types::

   All customization types are implemented as widgets; see *Note
Introduction: (widget)Top, for details.


File: elisp,  Node: Simple Types,  Next: Composite Types,  Up: Customization Types

14.4.1 Simple Types
-------------------

This section describes all the simple customization types.

`sexp'
     The value may be any Lisp object that can be printed and read
     back.  You can use `sexp' as a fall-back for any option, if you
     don't want to take the time to work out a more specific type to
     use.

`integer'
     The value must be an integer, and is represented textually in the
     customization buffer.

`number'
     The value must be a number (floating point or integer), and is
     represented textually in the customization buffer.

`float'
     The value must be a floating point number, and is represented
     textually in the customization buffer.

`string'
     The value must be a string, and the customization buffer shows
     just the contents, with no delimiting `"' characters and no
     quoting with `\'.

`regexp'
     Like `string' except that the string must be a valid regular
     expression.

`character'
     The value must be a character code.  A character code is actually
     an integer, but this type shows the value by inserting the
     character in the buffer, rather than by showing the number.

`file'
     The value must be a file name, and you can do completion with
     `M-<TAB>'.

`(file :must-match t)'
     The value must be a file name for an existing file, and you can do
     completion with `M-<TAB>'.

`directory'
     The value must be a directory name, and you can do completion with
     `M-<TAB>'.

`hook'
     The value must be a list of functions (or a single function, but
     that is obsolete usage).  This customization type is used for hook
     variables.  You can use the `:options' keyword in a hook variable's
     `defcustom' to specify a list of functions recommended for use in
     the hook; see *Note Variable Definitions::.

`alist'
     The value must be a list of cons-cells, the CAR of each cell
     representing a key, and the CDR of the same cell representing an
     associated value.  The user can add and delete key/value pairs, and
     edit both the key and the value of each pair.

     You can specify the key and value types like this:

          (alist :key-type KEY-TYPE :value-type VALUE-TYPE)

     where KEY-TYPE and VALUE-TYPE are customization type
     specifications.  The default key type is `sexp', and the default
     value type is `sexp'.

     The user can add any key matching the specified key type, but you
     can give some keys a preferential treatment by specifying them
     with the `:options' (see *Note Variable Definitions::).  The
     specified keys will always be shown in the customize buffer
     (together with a suitable value), with a checkbox to include or
     exclude or disable the key/value pair from the alist.  The user
     will not be able to edit the keys specified by the `:options'
     keyword argument.

     The argument to the `:options' keywords should be a list of
     specifications for reasonable keys in the alist.  Ordinarily, they
     are simply atoms, which stand for themselves as.  For example:

          :options '("foo" "bar" "baz")

     specifies that there are three "known" keys, namely `"foo"',
     `"bar"' and `"baz"', which will always be shown first.

     You may want to restrict the value type for specific keys, for
     example, the value associated with the `"bar"' key can only be an
     integer.  You can specify this by using a list instead of an atom
     in the list.  The first element will specify the key, like before,
     while the second element will specify the value type.  For example:

          :options '("foo" ("bar" integer) "baz")

     Finally, you may want to change how the key is presented.  By
     default, the key is simply shown as a `const', since the user
     cannot change the special keys specified with the `:options'
     keyword.  However, you may want to use a more specialized type for
     presenting the key, like `function-item' if you know it is a
     symbol with a function binding.  This is done by using a
     customization type specification instead of a symbol for the key.

          :options '("foo" ((function-item some-function) integer)
                     "baz")

     Many alists use lists with two elements, instead of cons cells.
     For example,

          (defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
            "Each element is a list of the form (KEY VALUE).")

     instead of

          (defcustom cons-alist '(("foo" . 1) ("bar" . 2) ("baz" . 3))
            "Each element is a cons-cell (KEY . VALUE).")

     Because of the way lists are implemented on top of cons cells, you
     can treat `list-alist' in the example above as a cons cell alist,
     where the value type is a list with a single element containing
     the real value.

          (defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
            "Each element is a list of the form (KEY VALUE)."
            :type '(alist :value-type (group integer)))

     The `group' widget is used here instead of `list' only because the
     formatting is better suited for the purpose.

     Similarly, you can have alists with more values associated with
     each key, using variations of this trick:

          (defcustom person-data '(("brian"  50 t)
                                   ("dorith" 55 nil)
                                   ("ken"    52 t))
            "Alist of basic info about people.
          Each element has the form (NAME AGE MALE-FLAG)."
            :type '(alist :value-type (group integer boolean)))

          (defcustom pets '(("brian")
                            ("dorith" "dog" "guppy")
                            ("ken" "cat"))
            "Alist of people's pets.
          In an element (KEY . VALUE), KEY is the person's name,
          and the VALUE is a list of that person's pets."
            :type '(alist :value-type (repeat string)))

`plist'
     The `plist' custom type is similar to the `alist' (see above),
     except that the information is stored as a property list, i.e. a
     list of this form:

          (KEY VALUE KEY VALUE KEY VALUE ...)

     The default `:key-type' for `plist' is `symbol', rather than
     `sexp'.

`symbol'
     The value must be a symbol.  It appears in the customization
     buffer as the name of the symbol.

`function'
     The value must be either a lambda expression or a function name.
     When it is a function name, you can do completion with `M-<TAB>'.

`variable'
     The value must be a variable name, and you can do completion with
     `M-<TAB>'.

`face'
     The value must be a symbol which is a face name, and you can do
     completion with `M-<TAB>'.

`boolean'
     The value is boolean--either `nil' or `t'.  Note that by using
     `choice' and `const' together (see the next section), you can
     specify that the value must be `nil' or `t', but also specify the
     text to describe each value in a way that fits the specific
     meaning of the alternative.

`coding-system'
     The value must be a coding-system name, and you can do completion
     with `M-<TAB>'.

`color'
     The value must be a valid color name, and you can do completion
     with `M-<TAB>'.  A sample is provided.


File: elisp,  Node: Composite Types,  Next: Splicing into Lists,  Prev: Simple Types,  Up: Customization Types

14.4.2 Composite Types
----------------------

When none of the simple types is appropriate, you can use composite
types, which build new types from other types or from specified data.
The specified types or data are called the "arguments" of the composite
type.  The composite type normally looks like this:

     (CONSTRUCTOR ARGUMENTS...)

but you can also add keyword-value pairs before the arguments, like
this:

     (CONSTRUCTOR {KEYWORD VALUE}... ARGUMENTS...)

   Here is a table of constructors and how to use them to write
composite types:

`(cons CAR-TYPE CDR-TYPE)'
     The value must be a cons cell, its CAR must fit CAR-TYPE, and its
     CDR must fit CDR-TYPE.  For example, `(cons string symbol)' is a
     customization type which matches values such as `("foo" . foo)'.

     In the customization buffer, the CAR and the CDR are displayed and
     edited separately, each according to the type that you specify for
     it.

`(list ELEMENT-TYPES...)'
     The value must be a list with exactly as many elements as the
     ELEMENT-TYPES given; and each element must fit the corresponding
     ELEMENT-TYPE.

     For example, `(list integer string function)' describes a list of
     three elements; the first element must be an integer, the second a
     string, and the third a function.

     In the customization buffer, each element is displayed and edited
     separately, according to the type specified for it.

`(group ELEMENT-TYPES...)'
     This works like `list' except for the formatting of text in the
     Custom buffer.  `list' labels each element value with its tag;
     `group' does not.

`(vector ELEMENT-TYPES...)'
     Like `list' except that the value must be a vector instead of a
     list.  The elements work the same as in `list'.

`(choice ALTERNATIVE-TYPES...)'
     The value must fit at least one of ALTERNATIVE-TYPES.  For
     example, `(choice integer string)' allows either an integer or a
     string.

     In the customization buffer, the user selects an alternative using
     a menu, and can then edit the value in the usual way for that
     alternative.

     Normally the strings in this menu are determined automatically
     from the choices; however, you can specify different strings for
     the menu by including the `:tag' keyword in the alternatives.  For
     example, if an integer stands for a number of spaces, while a
     string is text to use verbatim, you might write the customization
     type this way,

          (choice (integer :tag "Number of spaces")
                  (string :tag "Literal text"))

     so that the menu offers `Number of spaces' and `Literal text'.

     In any alternative for which `nil' is not a valid value, other than
     a `const', you should specify a valid default for that alternative
     using the `:value' keyword.  *Note Type Keywords::.

     If some values are covered by more than one of the alternatives,
     customize will choose the first alternative that the value fits.
     This means you should always list the most specific types first,
     and the most general last.  Here's an example of proper usage:

          (choice (const :tag "Off" nil)
                  symbol (sexp :tag "Other"))

     This way, the special value `nil' is not treated like other
     symbols, and symbols are not treated like other Lisp expressions.

`(radio ELEMENT-TYPES...)'
     This is similar to `choice', except that the choices are displayed
     using `radio buttons' rather than a menu.  This has the advantage
     of displaying documentation for the choices when applicable and so
     is often a good choice for a choice between constant functions
     (`function-item' customization types).

`(const VALUE)'
     The value must be VALUE--nothing else is allowed.

     The main use of `const' is inside of `choice'.  For example,
     `(choice integer (const nil))' allows either an integer or `nil'.

     `:tag' is often used with `const', inside of `choice'.  For
     example,

          (choice (const :tag "Yes" t)
                  (const :tag "No" nil)
                  (const :tag "Ask" foo))

     describes a variable for which `t' means yes, `nil' means no, and
     `foo' means "ask."

`(other VALUE)'
     This alternative can match any Lisp value, but if the user chooses
     this alternative, that selects the value VALUE.

     The main use of `other' is as the last element of `choice'.  For
     example,

          (choice (const :tag "Yes" t)
                  (const :tag "No" nil)
                  (other :tag "Ask" foo))

     describes a variable for which `t' means yes, `nil' means no, and
     anything else means "ask."  If the user chooses `Ask' from the
     menu of alternatives, that specifies the value `foo'; but any
     other value (not `t', `nil' or `foo') displays as `Ask', just like
     `foo'.

`(function-item FUNCTION)'
     Like `const', but used for values which are functions.  This
     displays the documentation string as well as the function name.
     The documentation string is either the one you specify with
     `:doc', or FUNCTION's own documentation string.

`(variable-item VARIABLE)'
     Like `const', but used for values which are variable names.  This
     displays the documentation string as well as the variable name.
     The documentation string is either the one you specify with
     `:doc', or VARIABLE's own documentation string.

`(set TYPES...)'
     The value must be a list, and each element of the list must match
     one of the TYPES specified.

     This appears in the customization buffer as a checklist, so that
     each of TYPES may have either one corresponding element or none.
     It is not possible to specify two different elements that match
     the same one of TYPES.  For example, `(set integer symbol)' allows
     one integer and/or one symbol in the list; it does not allow
     multiple integers or multiple symbols.  As a result, it is rare to
     use nonspecific types such as `integer' in a `set'.

     Most often, the TYPES in a `set' are `const' types, as shown here:

          (set (const :bold) (const :italic))

     Sometimes they describe possible elements in an alist:

          (set (cons :tag "Height" (const height) integer)
               (cons :tag "Width" (const width) integer))

     That lets the user specify a height value optionally and a width
     value optionally.

`(repeat ELEMENT-TYPE)'
     The value must be a list and each element of the list must fit the
     type ELEMENT-TYPE.  This appears in the customization buffer as a
     list of elements, with `[INS]' and `[DEL]' buttons for adding more
     elements or removing elements.

`(restricted-sexp :match-alternatives CRITERIA)'
     This is the most general composite type construct.  The value may
     be any Lisp object that satisfies one of CRITERIA.  CRITERIA
     should be a list, and each element should be one of these
     possibilities:

        * A predicate--that is, a function of one argument that has no
          side effects, and returns either `nil' or non-`nil' according
          to the argument.  Using a predicate in the list says that
          objects for which the predicate returns non-`nil' are
          acceptable.

        * A quoted constant--that is, `'OBJECT'.  This sort of element
          in the list says that OBJECT itself is an acceptable value.

     For example,

          (restricted-sexp :match-alternatives
                           (integerp 't 'nil))

     allows integers, `t' and `nil' as legitimate values.

     The customization buffer shows all legitimate values using their
     read syntax, and the user edits them textually.

   Here is a table of the keywords you can use in keyword-value pairs
in a composite type:

`:tag TAG'
     Use TAG as the name of this alternative, for user communication
     purposes.  This is useful for a type that appears inside of a
     `choice'.

`:match-alternatives CRITERIA'
     Use CRITERIA to match possible values.  This is used only in
     `restricted-sexp'.

`:args ARGUMENT-LIST'
     Use the elements of ARGUMENT-LIST as the arguments of the type
     construct.  For instance, `(const :args (foo))' is equivalent to
     `(const foo)'.  You rarely need to write `:args' explicitly,
     because normally the arguments are recognized automatically as
     whatever follows the last keyword-value pair.


File: elisp,  Node: Splicing into Lists,  Next: Type Keywords,  Prev: Composite Types,  Up: Customization Types

14.4.3 Splicing into Lists
--------------------------

The `:inline' feature lets you splice a variable number of elements
into the middle of a list or vector.  You use it in a `set', `choice'
or `repeat' type which appears among the element-types of a `list' or
`vector'.

   Normally, each of the element-types in a `list' or `vector'
describes one and only one element of the list or vector.  Thus, if an
element-type is a `repeat', that specifies a list of unspecified length
which appears as one element.

   But when the element-type uses `:inline', the value it matches is
merged directly into the containing sequence.  For example, if it
matches a list with three elements, those become three elements of the
overall sequence.  This is analogous to using `,@' in the backquote
construct.

   For example, to specify a list whose first element must be `baz' and
whose remaining arguments should be zero or more of `foo' and `bar',
use this customization type:

     (list (const baz) (set :inline t (const foo) (const bar)))

This matches values such as `(baz)', `(baz foo)', `(baz bar)' and `(baz
foo bar)'.

   When the element-type is a `choice', you use `:inline' not in the
`choice' itself, but in (some of) the alternatives of the `choice'.
For example, to match a list which must start with a file name,
followed either by the symbol `t' or two strings, use this
customization type:

     (list file
           (choice (const t)
                   (list :inline t string string)))

If the user chooses the first alternative in the choice, then the
overall list has two elements and the second element is `t'.  If the
user chooses the second alternative, then the overall list has three
elements and the second and third must be strings.


File: elisp,  Node: Type Keywords,  Next: Defining New Types,  Prev: Splicing into Lists,  Up: Customization Types

14.4.4 Type Keywords
--------------------

You can specify keyword-argument pairs in a customization type after the
type name symbol.  Here are the keywords you can use, and their
meanings:

`:value DEFAULT'
     This is used for a type that appears as an alternative inside of
     `choice'; it specifies the default value to use, at first, if and
     when the user selects this alternative with the menu in the
     customization buffer.

     Of course, if the actual value of the option fits this
     alternative, it will appear showing the actual value, not DEFAULT.

     If `nil' is not a valid value for the alternative, then it is
     essential to specify a valid default with `:value'.

`:format FORMAT-STRING'
     This string will be inserted in the buffer to represent the value
     corresponding to the type.  The following `%' escapes are available
     for use in FORMAT-STRING:

    `%[BUTTON%]'
          Display the text BUTTON marked as a button.  The `:action'
          attribute specifies what the button will do if the user
          invokes it; its value is a function which takes two
          arguments--the widget which the button appears in, and the
          event.

          There is no way to specify two different buttons with
          different actions.

    `%{SAMPLE%}'
          Show SAMPLE in a special face specified by `:sample-face'.

    `%v'
          Substitute the item's value.  How the value is represented
          depends on the kind of item, and (for variables) on the
          customization type.

    `%d'
          Substitute the item's documentation string.

    `%h'
          Like `%d', but if the documentation string is more than one
          line, add an active field to control whether to show all of
          it or just the first line.

    `%t'
          Substitute the tag here.  You specify the tag with the `:tag'
          keyword.

    `%%'
          Display a literal `%'.

`:action ACTION'
     Perform ACTION if the user clicks on a button.

`:button-face FACE'
     Use the face FACE (a face name or a list of face names) for button
     text displayed with `%[...%]'.

`:button-prefix PREFIX'
`:button-suffix SUFFIX'
     These specify the text to display before and after a button.  Each
     can be:

    `nil'
          No text is inserted.

    a string
          The string is inserted literally.

    a symbol
          The symbol's value is used.

`:tag TAG'
     Use TAG (a string) as the tag for the value (or part of the value)
     that corresponds to this type.

`:doc DOC'
     Use DOC as the documentation string for this value (or part of the
     value) that corresponds to this type.  In order for this to work,
     you must specify a value for `:format', and use `%d' or `%h' in
     that value.

     The usual reason to specify a documentation string for a type is to
     provide more information about the meanings of alternatives inside
     a `:choice' type or the parts of some other composite type.

`:help-echo MOTION-DOC'
     When you move to this item with `widget-forward' or
     `widget-backward', it will display the string MOTION-DOC in the
     echo area.  In addition, MOTION-DOC is used as the mouse
     `help-echo' string and may actually be a function or form evaluated
     to yield a help string.  If it is a function, it is called with one
     argument, the widget.

`:match FUNCTION'
     Specify how to decide whether a value matches the type.  The
     corresponding value, FUNCTION, should be a function that accepts
     two arguments, a widget and a value; it should return non-`nil' if
     the value is acceptable.

`:validate FUNCTION'
     Specify a validation function for input.  FUNCTION takes a widget
     as an argument, and should return `nil' if the widget's current
     value is valid for the widget.  Otherwise, it should return the
     widget containing the invalid data, and set that widget's `:error'
     property to a string explaining the error.



File: elisp,  Node: Defining New Types,  Prev: Type Keywords,  Up: Customization Types

14.4.5 Defining New Types
-------------------------

In the previous sections we have described how to construct elaborate
type specifications for `defcustom'.  In some cases you may want to
give such a type specification a name.  The obvious case is when you
are using the same type for many user options: rather than repeat the
specification for each option, you can give the type specification a
name, and use that name each `defcustom'.  The other case is when a
user option's value is a recursive data structure.  To make it possible
for a datatype to refer to itself, it needs to have a name.

   Since custom types are implemented as widgets, the way to define a
new customize type is to define a new widget.  We are not going to
describe the widget interface here in details, see *Note Introduction:
(widget)Top, for that.  Instead we are going to demonstrate the minimal
functionality needed for defining new customize types by a simple
example.

     (define-widget 'binary-tree-of-string 'lazy
       "A binary tree made of cons-cells and strings."
       :offset 4
       :tag "Node"
       :type '(choice (string :tag "Leaf" :value "")
                      (cons :tag "Interior"
                            :value ("" . "")
                            binary-tree-of-string
                            binary-tree-of-string)))

     (defcustom foo-bar ""
       "Sample variable holding a binary tree of strings."
       :type 'binary-tree-of-string)

   The function to define a new widget is called `define-widget'.  The
first argument is the symbol we want to make a new widget type.  The
second argument is a symbol representing an existing widget, the new
widget is going to be defined in terms of difference from the existing
widget.  For the purpose of defining new customization types, the
`lazy' widget is perfect, because it accepts a `:type' keyword argument
with the same syntax as the keyword argument to `defcustom' with the
same name.  The third argument is a documentation string for the new
widget.  You will be able to see that string with the `M-x
widget-browse <RET> binary-tree-of-string <RET>' command.

   After these mandatory arguments follow the keyword arguments.  The
most important is `:type', which describes the data type we want to
match with this widget.  Here a `binary-tree-of-string' is described as
being either a string, or a cons-cell whose car and cdr are themselves
both `binary-tree-of-string'.  Note the reference to the widget type we
are currently in the process of defining.  The `:tag' attribute is a
string to name the widget in the user interface, and the `:offset'
argument is there to ensure that child nodes are indented four spaces
relative to the parent node, making the tree structure apparent in the
customization buffer.

   The `defcustom' shows how the new widget can be used as an ordinary
customization type.

   The reason for the name `lazy' is that the other composite widgets
convert their inferior widgets to internal form when the widget is
instantiated in a buffer.  This conversion is recursive, so the
inferior widgets will convert _their_ inferior widgets.  If the data
structure is itself recursive, this conversion is an infinite
recursion.  The `lazy' widget prevents the recursion: it convert its
`:type' argument only when needed.


File: elisp,  Node: Loading,  Next: Byte Compilation,  Prev: Customization,  Up: Top

15 Loading
**********

Loading a file of Lisp code means bringing its contents into the Lisp
environment in the form of Lisp objects.  Emacs finds and opens the
file, reads the text, evaluates each form, and then closes the file.

   The load functions evaluate all the expressions in a file just as
the `eval-buffer' function evaluates all the expressions in a buffer.
The difference is that the load functions read and evaluate the text in
the file as found on disk, not the text in an Emacs buffer.

   The loaded file must contain Lisp expressions, either as source code
or as byte-compiled code.  Each form in the file is called a "top-level
form".  There is no special format for the forms in a loadable file;
any form in a file may equally well be typed directly into a buffer and
evaluated there.  (Indeed, most code is tested this way.)  Most often,
the forms are function definitions and variable definitions.

   A file containing Lisp code is often called a "library".  Thus, the
"Rmail library" is a file containing code for Rmail mode.  Similarly, a
"Lisp library directory" is a directory of files containing Lisp code.

* Menu:

* How Programs Do Loading:: The `load' function and others.
* Load Suffixes::           Details about the suffixes that `load' tries.
* Library Search::          Finding a library to load.
* Loading Non-ASCII::       Non-ASCII characters in Emacs Lisp files.
* Autoload::                Setting up a function to autoload.
* Repeated Loading::        Precautions about loading a file twice.
* Named Features::          Loading a library if it isn't already loaded.
* Where Defined::           Finding which file defined a certain symbol.
* Unloading::		    How to "unload" a library that was loaded.
* Hooks for Loading::	    Providing code to be run when
			      particular libraries are loaded.


File: elisp,  Node: How Programs Do Loading,  Next: Load Suffixes,  Up: Loading

15.1 How Programs Do Loading
============================

Emacs Lisp has several interfaces for loading.  For example, `autoload'
creates a placeholder object for a function defined in a file; trying
to call the autoloading function loads the file to get the function's
real definition (*note Autoload::).  `require' loads a file if it isn't
already loaded (*note Named Features::).  Ultimately, all these
facilities call the `load' function to do the work.

 -- Function: load filename &optional missing-ok nomessage nosuffix
          must-suffix
     This function finds and opens a file of Lisp code, evaluates all
     the forms in it, and closes the file.

     To find the file, `load' first looks for a file named
     `FILENAME.elc', that is, for a file whose name is FILENAME with
     the extension `.elc' appended.  If such a file exists, it is
     loaded.  If there is no file by that name, then `load' looks for a
     file named `FILENAME.el'.  If that file exists, it is loaded.
     Finally, if neither of those names is found, `load' looks for a
     file named FILENAME with nothing appended, and loads it if it
     exists.  (The `load' function is not clever about looking at
     FILENAME.  In the perverse case of a file named `foo.el.el',
     evaluation of `(load "foo.el")' will indeed find it.)

     If Auto Compression mode is enabled, as it is by default, then if
     `load' can not find a file, it searches for a compressed version
     of the file before trying other file names.  It decompresses and
     loads it if it exists.  It looks for compressed versions by
     appending each of the suffixes in `jka-compr-load-suffixes' to the
     file name.  The value of this variable must be a list of strings.
     Its standard value is `(".gz")'.

     If the optional argument NOSUFFIX is non-`nil', then `load' does
     not try the suffixes `.elc' and `.el'.  In this case, you must
     specify the precise file name you want, except that, if Auto
     Compression mode is enabled, `load' will still use
     `jka-compr-load-suffixes' to find compressed versions.  By
     specifying the precise file name and using `t' for NOSUFFIX, you
     can prevent perverse file names such as `foo.el.el' from being
     tried.

     If the optional argument MUST-SUFFIX is non-`nil', then `load'
     insists that the file name used must end in either `.el' or `.elc'
     (possibly extended with a compression suffix), unless it contains
     an explicit directory name.

     If FILENAME is a relative file name, such as `foo' or
     `baz/foo.bar', `load' searches for the file using the variable
     `load-path'.  It appends FILENAME to each of the directories
     listed in `load-path', and loads the first file it finds whose name
     matches.  The current default directory is tried only if it is
     specified in `load-path', where `nil' stands for the default
     directory.  `load' tries all three possible suffixes in the first
     directory in `load-path', then all three suffixes in the second
     directory, and so on.  *Note Library Search::.

     If you get a warning that `foo.elc' is older than `foo.el', it
     means you should consider recompiling `foo.el'.  *Note Byte
     Compilation::.

     When loading a source file (not compiled), `load' performs
     character set translation just as Emacs would do when visiting the
     file.  *Note Coding Systems::.

     Messages like `Loading foo...' and `Loading foo...done' appear in
     the echo area during loading unless NOMESSAGE is non-`nil'.

     Any unhandled errors while loading a file terminate loading.  If
     the load was done for the sake of `autoload', any function
     definitions made during the loading are undone.

     If `load' can't find the file to load, then normally it signals the
     error `file-error' (with `Cannot open load file FILENAME').  But
     if MISSING-OK is non-`nil', then `load' just returns `nil'.

     You can use the variable `load-read-function' to specify a function
     for `load' to use instead of `read' for reading expressions.  See
     below.

     `load' returns `t' if the file loads successfully.

 -- Command: load-file filename
     This command loads the file FILENAME.  If FILENAME is a relative
     file name, then the current default directory is assumed.  This
     command does not use `load-path', and does not append suffixes.
     However, it does look for compressed versions (if Auto Compression
     Mode is enabled).  Use this command if you wish to specify
     precisely the file name to load.

 -- Command: load-library library
     This command loads the library named LIBRARY.  It is equivalent to
     `load', except in how it reads its argument interactively.

 -- Variable: load-in-progress
     This variable is non-`nil' if Emacs is in the process of loading a
     file, and it is `nil' otherwise.

 -- Variable: load-read-function
     This variable specifies an alternate expression-reading function
     for `load' and `eval-region' to use instead of `read'.  The
     function should accept one argument, just as `read' does.

     Normally, the variable's value is `nil', which means those
     functions should use `read'.

     Instead of using this variable, it is cleaner to use another, newer
     feature: to pass the function as the READ-FUNCTION argument to
     `eval-region'.  *Note Eval: Definition of eval-region.

   For information about how `load' is used in building Emacs, see
*Note Building Emacs::.


File: elisp,  Node: Load Suffixes,  Next: Library Search,  Prev: How Programs Do Loading,  Up: Loading

15.2 Load Suffixes
==================

We now describe some technical details about the exact suffixes that
`load' tries.

 -- Variable: load-suffixes
     This is a list of suffixes indicating (compiled or source) Emacs
     Lisp files.  It should not include the empty string.  `load' uses
     these suffixes in order when it appends Lisp suffixes to the
     specified file name.  The standard value is `(".elc" ".el")' which
     produces the behavior described in the previous section.

 -- Variable: load-file-rep-suffixes
     This is a list of suffixes that indicate representations of the
     same file.  This list should normally start with the empty string.
     When `load' searches for a file it appends the suffixes in this
     list, in order, to the file name, before searching for another
     file.

     Enabling Auto Compression mode appends the suffixes in
     `jka-compr-load-suffixes' to this list and disabling Auto
     Compression mode removes them again.  The standard value of
     `load-file-rep-suffixes' if Auto Compression mode is disabled is
     `("")'.  Given that the standard value of
     `jka-compr-load-suffixes' is `(".gz")', the standard value of
     `load-file-rep-suffixes' if Auto Compression mode is enabled is
     `("" ".gz")'.

 -- Function: get-load-suffixes
     This function returns the list of all suffixes that `load' should
     try, in order, when its MUST-SUFFIX argument is non-`nil'.  This
     takes both `load-suffixes' and `load-file-rep-suffixes' into
     account.  If `load-suffixes', `jka-compr-load-suffixes' and
     `load-file-rep-suffixes' all have their standard values, this
     function returns `(".elc" ".elc.gz" ".el" ".el.gz")' if Auto
     Compression mode is enabled and `(".elc" ".el")' if Auto
     Compression mode is disabled.

   To summarize, `load' normally first tries the suffixes in the value
of `(get-load-suffixes)' and then those in `load-file-rep-suffixes'.
If NOSUFFIX is non-`nil', it skips the former group, and if MUST-SUFFIX
is non-`nil', it skips the latter group.


File: elisp,  Node: Library Search,  Next: Loading Non-ASCII,  Prev: Load Suffixes,  Up: Loading

15.3 Library Search
===================

When Emacs loads a Lisp library, it searches for the library in a list
of directories specified by the variable `load-path'.

 -- User Option: load-path
     The value of this variable is a list of directories to search when
     loading files with `load'.  Each element is a string (which must be
     a directory name) or `nil' (which stands for the current working
     directory).

   The value of `load-path' is initialized from the environment
variable `EMACSLOADPATH', if that exists; otherwise its default value
is specified in `emacs/src/epaths.h' when Emacs is built.  Then the
list is expanded by adding subdirectories of the directories in the
list.

   The syntax of `EMACSLOADPATH' is the same as used for `PATH'; `:'
(or `;', according to the operating system) separates directory names,
and `.' is used for the current default directory.  Here is an example
of how to set your `EMACSLOADPATH' variable from a `csh' `.login' file:

     setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp

   Here is how to set it using `sh':

     export EMACSLOADPATH
     EMACSLOADPATH=.:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp

   Here is an example of code you can place in your init file (*note
Init File::) to add several directories to the front of your default
`load-path':

     (setq load-path
           (append (list nil "/user/bil/emacs"
                         "/usr/local/lisplib"
                         "~/emacs")
                   load-path))

In this example, the path searches the current working directory first,
followed then by the `/user/bil/emacs' directory, the
`/usr/local/lisplib' directory, and the `~/emacs' directory, which are
then followed by the standard directories for Lisp code.

   Dumping Emacs uses a special value of `load-path'.  If the value of
`load-path' at the end of dumping is unchanged (that is, still the same
special value), the dumped Emacs switches to the ordinary `load-path'
value when it starts up, as described above.  But if `load-path' has
any other value at the end of dumping, that value is used for execution
of the dumped Emacs also.

   Therefore, if you want to change `load-path' temporarily for loading
a few libraries in `site-init.el' or `site-load.el', you should bind
`load-path' locally with `let' around the calls to `load'.

   The default value of `load-path', when running an Emacs which has
been installed on the system, includes two special directories (and
their subdirectories as well):

     "/usr/local/share/emacs/VERSION/site-lisp"

and

     "/usr/local/share/emacs/site-lisp"

The first one is for locally installed packages for a particular Emacs
version; the second is for locally installed packages meant for use with
all installed Emacs versions.

   There are several reasons why a Lisp package that works well in one
Emacs version can cause trouble in another.  Sometimes packages need
updating for incompatible changes in Emacs; sometimes they depend on
undocumented internal Emacs data that can change without notice;
sometimes a newer Emacs version incorporates a version of the package,
and should be used only with that version.

   Emacs finds these directories' subdirectories and adds them to
`load-path' when it starts up.  Both immediate subdirectories and
subdirectories multiple levels down are added to `load-path'.

   Not all subdirectories are included, though.  Subdirectories whose
names do not start with a letter or digit are excluded.  Subdirectories
named `RCS' or `CVS' are excluded.  Also, a subdirectory which contains
a file named `.nosearch' is excluded.  You can use these methods to
prevent certain subdirectories of the `site-lisp' directories from
being searched.

   If you run Emacs from the directory where it was built--that is, an
executable that has not been formally installed--then `load-path'
normally contains two additional directories.  These are the `lisp' and
`site-lisp' subdirectories of the main build directory.  (Both are
represented as absolute file names.)

 -- Command: locate-library library &optional nosuffix path
          interactive-call
     This command finds the precise file name for library LIBRARY.  It
     searches for the library in the same way `load' does, and the
     argument NOSUFFIX has the same meaning as in `load': don't add
     suffixes `.elc' or `.el' to the specified name LIBRARY.

     If the PATH is non-`nil', that list of directories is used instead
     of `load-path'.

     When `locate-library' is called from a program, it returns the file
     name as a string.  When the user runs `locate-library'
     interactively, the argument INTERACTIVE-CALL is `t', and this
     tells `locate-library' to display the file name in the echo area.


File: elisp,  Node: Loading Non-ASCII,  Next: Autoload,  Prev: Library Search,  Up: Loading

15.4 Loading Non-ASCII Characters
=================================

When Emacs Lisp programs contain string constants with non-ASCII
characters, these can be represented within Emacs either as unibyte
strings or as multibyte strings (*note Text Representations::).  Which
representation is used depends on how the file is read into Emacs.  If
it is read with decoding into multibyte representation, the text of the
Lisp program will be multibyte text, and its string constants will be
multibyte strings.  If a file containing Latin-1 characters (for
example) is read without decoding, the text of the program will be
unibyte text, and its string constants will be unibyte strings.  *Note
Coding Systems::.

   To make the results more predictable, Emacs always performs decoding
into the multibyte representation when loading Lisp files, even if it
was started with the `--unibyte' option.  This means that string
constants with non-ASCII characters translate into multibyte strings.
The only exception is when a particular file specifies no decoding.

   The reason Emacs is designed this way is so that Lisp programs give
predictable results, regardless of how Emacs was started.  In addition,
this enables programs that depend on using multibyte text to work even
in a unibyte Emacs.  Of course, such programs should be designed to
notice whether the user prefers unibyte or multibyte text, by checking
`default-enable-multibyte-characters', and convert representations
appropriately.

   In most Emacs Lisp programs, the fact that non-ASCII strings are
multibyte strings should not be noticeable, since inserting them in
unibyte buffers converts them to unibyte automatically.  However, if
this does make a difference, you can force a particular Lisp file to be
interpreted as unibyte by writing `-*-unibyte: t;-*-' in a comment on
the file's first line.  With that designator, the file will
unconditionally be interpreted as unibyte, even in an ordinary
multibyte Emacs session.  This can matter when making keybindings to
non-ASCII characters written as `?vLITERAL'.


File: elisp,  Node: Autoload,  Next: Repeated Loading,  Prev: Loading Non-ASCII,  Up: Loading

15.5 Autoload
=============

The "autoload" facility allows you to make a function or macro known in
Lisp, but put off loading the file that defines it.  The first call to
the function automatically reads the proper file to install the real
definition and other associated code, then runs the real definition as
if it had been loaded all along.

   There are two ways to set up an autoloaded function: by calling
`autoload', and by writing a special "magic" comment in the source
before the real definition.  `autoload' is the low-level primitive for
autoloading; any Lisp program can call `autoload' at any time.  Magic
comments are the most convenient way to make a function autoload, for
packages installed along with Emacs.  These comments do nothing on
their own, but they serve as a guide for the command
`update-file-autoloads', which constructs calls to `autoload' and
arranges to execute them when Emacs is built.

 -- Function: autoload function filename &optional docstring
          interactive type
     This function defines the function (or macro) named FUNCTION so as
     to load automatically from FILENAME.  The string FILENAME
     specifies the file to load to get the real definition of FUNCTION.

     If FILENAME does not contain either a directory name, or the
     suffix `.el' or `.elc', then `autoload' insists on adding one of
     these suffixes, and it will not load from a file whose name is
     just FILENAME with no added suffix.  (The variable `load-suffixes'
     specifies the exact required suffixes.)

     The argument DOCSTRING is the documentation string for the
     function.  Specifying the documentation string in the call to
     `autoload' makes it possible to look at the documentation without
     loading the function's real definition.  Normally, this should be
     identical to the documentation string in the function definition
     itself.  If it isn't, the function definition's documentation
     string takes effect when it is loaded.

     If INTERACTIVE is non-`nil', that says FUNCTION can be called
     interactively.  This lets completion in `M-x' work without loading
     FUNCTION's real definition.  The complete interactive
     specification is not given here; it's not needed unless the user
     actually calls FUNCTION, and when that happens, it's time to load
     the real definition.

     You can autoload macros and keymaps as well as ordinary functions.
     Specify TYPE as `macro' if FUNCTION is really a macro.  Specify
     TYPE as `keymap' if FUNCTION is really a keymap.  Various parts of
     Emacs need to know this information without loading the real
     definition.

     An autoloaded keymap loads automatically during key lookup when a
     prefix key's binding is the symbol FUNCTION.  Autoloading does not
     occur for other kinds of access to the keymap.  In particular, it
     does not happen when a Lisp program gets the keymap from the value
     of a variable and calls `define-key'; not even if the variable
     name is the same symbol FUNCTION.

     If FUNCTION already has a non-void function definition that is not
     an autoload object, `autoload' does nothing and returns `nil'.  If
     the function cell of FUNCTION is void, or is already an autoload
     object, then it is defined as an autoload object like this:

          (autoload FILENAME DOCSTRING INTERACTIVE TYPE)

     For example,

          (symbol-function 'run-prolog)
               => (autoload "prolog" 169681 t nil)

     In this case, `"prolog"' is the name of the file to load, 169681
     refers to the documentation string in the `emacs/etc/DOC-VERSION'
     file (*note Documentation Basics::), `t' means the function is
     interactive, and `nil' that it is not a macro or a keymap.

   The autoloaded file usually contains other definitions and may
require or provide one or more features.  If the file is not completely
loaded (due to an error in the evaluation of its contents), any function
definitions or `provide' calls that occurred during the load are
undone.  This is to ensure that the next attempt to call any function
autoloading from this file will try again to load the file.  If not for
this, then some of the functions in the file might be defined by the
aborted load, but fail to work properly for the lack of certain
subroutines not loaded successfully because they come later in the file.

   If the autoloaded file fails to define the desired Lisp function or
macro, then an error is signaled with data `"Autoloading failed to
define function FUNCTION-NAME"'.

   A magic autoload comment (often called an "autoload cookie")
consists of `;;;###autoload', on a line by itself, just before the real
definition of the function in its autoloadable source file.  The
command `M-x update-file-autoloads' writes a corresponding `autoload'
call into `loaddefs.el'.  Building Emacs loads `loaddefs.el' and thus
calls `autoload'.  `M-x update-directory-autoloads' is even more
powerful; it updates autoloads for all files in the current directory.

   The same magic comment can copy any kind of form into `loaddefs.el'.
If the form following the magic comment is not a function-defining
form or a `defcustom' form, it is copied verbatim.  "Function-defining
forms" include `define-skeleton', `define-derived-mode',
`define-generic-mode' and `define-minor-mode' as well as `defun' and
`defmacro'.  To save space, a `defcustom' form is converted to a
`defvar' in `loaddefs.el', with some additional information if it uses
`:require'.

   You can also use a magic comment to execute a form at build time
_without_ executing it when the file itself is loaded.  To do this,
write the form _on the same line_ as the magic comment.  Since it is in
a comment, it does nothing when you load the source file; but `M-x
update-file-autoloads' copies it to `loaddefs.el', where it is executed
while building Emacs.

   The following example shows how `doctor' is prepared for autoloading
with a magic comment:

     ;;;###autoload
     (defun doctor ()
       "Switch to *doctor* buffer and start giving psychotherapy."
       (interactive)
       (switch-to-buffer "*doctor*")
       (doctor-mode))

Here's what that produces in `loaddefs.el':

     (autoload (quote doctor) "doctor" "\
     Switch to *doctor* buffer and start giving psychotherapy.

     \(fn)" t nil)

The backslash and newline immediately following the double-quote are a
convention used only in the preloaded uncompiled Lisp files such as
`loaddefs.el'; they tell `make-docfile' to put the documentation string
in the `etc/DOC' file.  *Note Building Emacs::.  See also the
commentary in `lib-src/make-docfile.c'.  `(fn)' in the usage part of
the documentation string is replaced with the function's name when the
various help functions (*note Help Functions::) display it.

   If you write a function definition with an unusual macro that is not
one of the known and recognized function definition methods, use of an
ordinary magic autoload comment would copy the whole definition into
`loaddefs.el'.  That is not desirable.  You can put the desired
`autoload' call into `loaddefs.el' instead by writing this:

     ;;;###autoload (autoload 'foo "myfile")
     (mydefunmacro foo
       ...)


File: elisp,  Node: Repeated Loading,  Next: Named Features,  Prev: Autoload,  Up: Loading

15.6 Repeated Loading
=====================

You can load a given file more than once in an Emacs session.  For
example, after you have rewritten and reinstalled a function definition
by editing it in a buffer, you may wish to return to the original
version; you can do this by reloading the file it came from.

   When you load or reload files, bear in mind that the `load' and
`load-library' functions automatically load a byte-compiled file rather
than a non-compiled file of similar name.  If you rewrite a file that
you intend to save and reinstall, you need to byte-compile the new
version; otherwise Emacs will load the older, byte-compiled file instead
of your newer, non-compiled file!  If that happens, the message
displayed when loading the file includes, `(compiled; note, source is
newer)', to remind you to recompile it.

   When writing the forms in a Lisp library file, keep in mind that the
file might be loaded more than once.  For example, think about whether
each variable should be reinitialized when you reload the library;
`defvar' does not change the value if the variable is already
initialized.  (*Note Defining Variables::.)

   The simplest way to add an element to an alist is like this:

     (push '(leif-mode " Leif") minor-mode-alist)

But this would add multiple elements if the library is reloaded.  To
avoid the problem, write this:

     (or (assq 'leif-mode minor-mode-alist)
         (push '(leif-mode " Leif") minor-mode-alist))

or this:

     (add-to-list '(leif-mode " Leif") minor-mode-alist)

   Occasionally you will want to test explicitly whether a library has
already been loaded.  Here's one way to test, in a library, whether it
has been loaded before:

     (defvar foo-was-loaded nil)

     (unless foo-was-loaded
       EXECUTE-FIRST-TIME-ONLY
       (setq foo-was-loaded t))

If the library uses `provide' to provide a named feature, you can use
`featurep' earlier in the file to test whether the `provide' call has
been executed before.  *Note Named Features::.


File: elisp,  Node: Named Features,  Next: Where Defined,  Prev: Repeated Loading,  Up: Loading

15.7 Features
=============

`provide' and `require' are an alternative to `autoload' for loading
files automatically.  They work in terms of named "features".
Autoloading is triggered by calling a specific function, but a feature
is loaded the first time another program asks for it by name.

   A feature name is a symbol that stands for a collection of functions,
variables, etc.  The file that defines them should "provide" the
feature.  Another program that uses them may ensure they are defined by
"requiring" the feature.  This loads the file of definitions if it
hasn't been loaded already.

   To require the presence of a feature, call `require' with the
feature name as argument.  `require' looks in the global variable
`features' to see whether the desired feature has been provided
already.  If not, it loads the feature from the appropriate file.  This
file should call `provide' at the top level to add the feature to
`features'; if it fails to do so, `require' signals an error.  

   For example, in `emacs/lisp/prolog.el', the definition for
`run-prolog' includes the following code:

     (defun run-prolog ()
       "Run an inferior Prolog process, with I/O via buffer *prolog*."
       (interactive)
       (require 'comint)
       (switch-to-buffer (make-comint "prolog" prolog-program-name))
       (inferior-prolog-mode))

The expression `(require 'comint)' loads the file `comint.el' if it has
not yet been loaded.  This ensures that `make-comint' is defined.
Features are normally named after the files that provide them, so that
`require' need not be given the file name.

   The `comint.el' file contains the following top-level expression:

     (provide 'comint)

This adds `comint' to the global `features' list, so that `(require
'comint)' will henceforth know that nothing needs to be done.

   When `require' is used at top level in a file, it takes effect when
you byte-compile that file (*note Byte Compilation::) as well as when
you load it.  This is in case the required package contains macros that
the byte compiler must know about.  It also avoids byte-compiler
warnings for functions and variables defined in the file loaded with
`require'.

   Although top-level calls to `require' are evaluated during byte
compilation, `provide' calls are not.  Therefore, you can ensure that a
file of definitions is loaded before it is byte-compiled by including a
`provide' followed by a `require' for the same feature, as in the
following example.

     (provide 'my-feature)  ; Ignored by byte compiler,
                            ;   evaluated by `load'.
     (require 'my-feature)  ; Evaluated by byte compiler.

The compiler ignores the `provide', then processes the `require' by
loading the file in question.  Loading the file does execute the
`provide' call, so the subsequent `require' call does nothing when the
file is loaded.

 -- Function: provide feature &optional subfeatures
     This function announces that FEATURE is now loaded, or being
     loaded, into the current Emacs session.  This means that the
     facilities associated with FEATURE are or will be available for
     other Lisp programs.

     The direct effect of calling `provide' is to add FEATURE to the
     front of the list `features' if it is not already in the list.
     The argument FEATURE must be a symbol.  `provide' returns FEATURE.

     If provided, SUBFEATURES should be a list of symbols indicating a
     set of specific subfeatures provided by this version of FEATURE.
     You can test the presence of a subfeature using `featurep'.  The
     idea of subfeatures is that you use them when a package (which is
     one FEATURE) is complex enough to make it useful to give names to
     various parts or functionalities of the package, which might or
     might not be loaded, or might or might not be present in a given
     version.  *Note Network Feature Testing::, for an example.

          features
               => (bar bish)

          (provide 'foo)
               => foo
          features
               => (foo bar bish)

     When a file is loaded to satisfy an autoload, and it stops due to
     an error in the evaluation of its contents, any function
     definitions or `provide' calls that occurred during the load are
     undone.  *Note Autoload::.

 -- Function: require feature &optional filename noerror
     This function checks whether FEATURE is present in the current
     Emacs session (using `(featurep FEATURE)'; see below).  The
     argument FEATURE must be a symbol.

     If the feature is not present, then `require' loads FILENAME with
     `load'.  If FILENAME is not supplied, then the name of the symbol
     FEATURE is used as the base file name to load.  However, in this
     case, `require' insists on finding FEATURE with an added `.el' or
     `.elc' suffix (possibly extended with a compression suffix); a
     file whose name is just FEATURE won't be used.  (The variable
     `load-suffixes' specifies the exact required Lisp suffixes.)

     If NOERROR is non-`nil', that suppresses errors from actual
     loading of the file.  In that case, `require' returns `nil' if
     loading the file fails.  Normally, `require' returns FEATURE.

     If loading the file succeeds but does not provide FEATURE,
     `require' signals an error, `Required feature FEATURE was not
     provided'.

 -- Function: featurep feature &optional subfeature
     This function returns `t' if FEATURE has been provided in the
     current Emacs session (i.e., if FEATURE is a member of
     `features'.)  If SUBFEATURE is non-`nil', then the function
     returns `t' only if that subfeature is provided as well (i.e. if
     SUBFEATURE is a member of the `subfeature' property of the FEATURE
     symbol.)

 -- Variable: features
     The value of this variable is a list of symbols that are the
     features loaded in the current Emacs session.  Each symbol was put
     in this list with a call to `provide'.  The order of the elements
     in the `features' list is not significant.


File: elisp,  Node: Where Defined,  Next: Unloading,  Prev: Named Features,  Up: Loading

15.8 Which File Defined a Certain Symbol
========================================

 -- Function: symbol-file symbol &optional type
     This function returns the name of the file that defined SYMBOL.
     If TYPE is `nil', then any kind of definition is acceptable.  If
     TYPE is `defun' or `defvar', that specifies function definition
     only or variable definition only.

     The value is normally an absolute file name.  It can also be
     `nil', if the definition is not associated with any file.

   The basis for `symbol-file' is the data in the variable
`load-history'.

 -- Variable: load-history
     This variable's value is an alist connecting library file names
     with the names of functions and variables they define, the
     features they provide, and the features they require.

     Each element is a list and describes one library.  The CAR of the
     list is the absolute file name of the library, as a string.  The
     rest of the list elements have these forms:

    `VAR'
          The symbol VAR was defined as a variable.

    `(defun . FUN)'
          The function FUN was defined.

    `(t . FUN)'
          The function FUN was previously an autoload before this
          library redefined it as a function.  The following element is
          always `(defun . FUN)', which represents defining FUN as a
          function.

    `(autoload . FUN)'
          The function FUN was defined as an autoload.

    `(require . FEATURE)'
          The feature FEATURE was required.

    `(provide . FEATURE)'
          The feature FEATURE was provided.

     The value of `load-history' may have one element whose CAR is
     `nil'.  This element describes definitions made with `eval-buffer'
     on a buffer that is not visiting a file.

   The command `eval-region' updates `load-history', but does so by
adding the symbols defined to the element for the file being visited,
rather than replacing that element.  *Note Eval::.


File: elisp,  Node: Unloading,  Next: Hooks for Loading,  Prev: Where Defined,  Up: Loading

15.9 Unloading
==============

You can discard the functions and variables loaded by a library to
reclaim memory for other Lisp objects.  To do this, use the function
`unload-feature':

 -- Command: unload-feature feature &optional force
     This command unloads the library that provided feature FEATURE.
     It undefines all functions, macros, and variables defined in that
     library with `defun', `defalias', `defsubst', `defmacro',
     `defconst', `defvar', and `defcustom'.  It then restores any
     autoloads formerly associated with those symbols.  (Loading saves
     these in the `autoload' property of the symbol.)

     Before restoring the previous definitions, `unload-feature' runs
     `remove-hook' to remove functions in the library from certain
     hooks.  These hooks include variables whose names end in `hook' or
     `-hooks', plus those listed in `unload-feature-special-hooks', as
     well as `auto-mode-alist'.  This is to prevent Emacs from ceasing
     to function because important hooks refer to functions that are no
     longer defined.

     Standard unloading activities also undoes ELP profiling of
     functions in that library, unprovides any features provided by the
     library, and cancels timers held in variables defined by the
     library.

     If these measures are not sufficient to prevent malfunction, a
     library can define an explicit unloader named
     `FEATURE-unload-function'.  If that symbol is defined as a
     function, `unload-feature' calls it with no arguments before doing
     anything else.  It can do whatever is appropriate to unload the
     library.  If it returns `nil', `unload-feature' proceeds to take
     the normal unload actions.  Otherwise it considers the job to be
     done.

     Ordinarily, `unload-feature' refuses to unload a library on which
     other loaded libraries depend.  (A library A depends on library B
     if A contains a `require' for B.)  If the optional argument FORCE
     is non-`nil', dependencies are ignored and you can unload any
     library.

   The `unload-feature' function is written in Lisp; its actions are
based on the variable `load-history'.

 -- Variable: unload-feature-special-hooks
     This variable holds a list of hooks to be scanned before unloading
     a library, to remove functions defined in the library.


File: elisp,  Node: Hooks for Loading,  Prev: Unloading,  Up: Loading

15.10 Hooks for Loading
=======================

You can ask for code to be executed if and when a particular library is
loaded, by calling `eval-after-load'.

 -- Function: eval-after-load library form
     This function arranges to evaluate FORM at the end of loading the
     file LIBRARY, each time LIBRARY is loaded.  If LIBRARY is already
     loaded, it evaluates FORM right away.  Don't forget to quote FORM!

     You don't need to give a directory or extension in the file name
     LIBRARY--normally you just give a bare file name, like this:

          (eval-after-load "edebug" '(def-edebug-spec c-point t))

     To restrict which files can trigger the evaluation, include a
     directory or an extension or both in LIBRARY.  Only a file whose
     absolute true name (i.e., the name with all symbolic links chased
     out) matches all the given name components will match.  In the
     following example, `my_inst.elc' or `my_inst.elc.gz' in some
     directory `..../foo/bar' will trigger the evaluation, but not
     `my_inst.el':

          (eval-after-load "foo/bar/my_inst.elc" ...)

     LIBRARY can also be a feature (i.e. a symbol), in which case FORM
     is evaluated when `(provide LIBRARY)' is called.

     An error in FORM does not undo the load, but does prevent
     execution of the rest of FORM.

   In general, well-designed Lisp programs should not use this feature.
The clean and modular ways to interact with a Lisp library are (1)
examine and set the library's variables (those which are meant for
outside use), and (2) call the library's functions.  If you wish to do
(1), you can do it immediately--there is no need to wait for when the
library is loaded.  To do (2), you must load the library (preferably
with `require').

   But it is OK to use `eval-after-load' in your personal
customizations if you don't feel they must meet the design standards for
programs meant for wider use.

 -- Variable: after-load-alist
     This variable, an alist built by `eval-after-load', holds the
     expressions to evaluate when particular libraries are loaded.  Each
     element looks like this:

          (REGEXP-OR-FEATURE FORMS...)

     The key REGEXP-OR-FEATURE is either a regular expression or a
     symbol, and the value is a list of forms.  The forms are evaluated
     when the key matches the absolute true name of the file being
     `load'ed or the symbol being `provide'd.


File: elisp,  Node: Byte Compilation,  Next: Advising Functions,  Prev: Loading,  Up: Top

16 Byte Compilation
*******************

Emacs Lisp has a "compiler" that translates functions written in Lisp
into a special representation called "byte-code" that can be executed
more efficiently.  The compiler replaces Lisp function definitions with
byte-code.  When a byte-code function is called, its definition is
evaluated by the "byte-code interpreter".

   Because the byte-compiled code is evaluated by the byte-code
interpreter, instead of being executed directly by the machine's
hardware (as true compiled code is), byte-code is completely
transportable from machine to machine without recompilation.  It is not,
however, as fast as true compiled code.

   Compiling a Lisp file with the Emacs byte compiler always reads the
file as multibyte text, even if Emacs was started with `--unibyte',
unless the file specifies otherwise.  This is so that compilation gives
results compatible with running the same file without compilation.
*Note Loading Non-ASCII::.

   In general, any version of Emacs can run byte-compiled code produced
by recent earlier versions of Emacs, but the reverse is not true.

   If you do not want a Lisp file to be compiled, ever, put a file-local
variable binding for `no-byte-compile' into it, like this:

     ;; -*-no-byte-compile: t; -*-

   *Note Compilation Errors::, for how to investigate errors occurring
in byte compilation.

* Menu:

* Speed of Byte-Code::          An example of speedup from byte compilation.
* Compilation Functions::       Byte compilation functions.
* Docs and Compilation::        Dynamic loading of documentation strings.
* Dynamic Loading::             Dynamic loading of individual functions.
* Eval During Compile::  	Code to be evaluated when you compile.
* Compiler Errors::             Handling compiler error messages.
* Byte-Code Objects::		The data type used for byte-compiled functions.
* Disassembly::                 Disassembling byte-code; how to read byte-code.


File: elisp,  Node: Speed of Byte-Code,  Next: Compilation Functions,  Up: Byte Compilation

16.1 Performance of Byte-Compiled Code
======================================

A byte-compiled function is not as efficient as a primitive function
written in C, but runs much faster than the version written in Lisp.
Here is an example:

     (defun silly-loop (n)
       "Return time before and after N iterations of a loop."
       (let ((t1 (current-time-string)))
         (while (> (setq n (1- n))
                   0))
         (list t1 (current-time-string))))
     => silly-loop

     (silly-loop 100000)
     => ("Fri Mar 18 17:25:57 1994"
         "Fri Mar 18 17:26:28 1994")  ; 31 seconds

     (byte-compile 'silly-loop)
     => [Compiled code not shown]

     (silly-loop 100000)
     => ("Fri Mar 18 17:26:52 1994"
         "Fri Mar 18 17:26:58 1994")  ; 6 seconds

   In this example, the interpreted code required 31 seconds to run,
whereas the byte-compiled code required 6 seconds.  These results are
representative, but actual results will vary greatly.


File: elisp,  Node: Compilation Functions,  Next: Docs and Compilation,  Prev: Speed of Byte-Code,  Up: Byte Compilation

16.2 The Compilation Functions
==============================

You can byte-compile an individual function or macro definition with
the `byte-compile' function.  You can compile a whole file with
`byte-compile-file', or several files with `byte-recompile-directory'
or `batch-byte-compile'.

   The byte compiler produces error messages and warnings about each
file in a buffer called `*Compile-Log*'.  These report things in your
program that suggest a problem but are not necessarily erroneous.

   Be careful when writing macro calls in files that you may someday
byte-compile.  Macro calls are expanded when they are compiled, so the
macros must already be defined for proper compilation.  For more
details, see *Note Compiling Macros::.  If a program does not work the
same way when compiled as it does when interpreted, erroneous macro
definitions are one likely cause (*note Problems with Macros::).
Inline (`defsubst') functions are less troublesome; if you compile a
call to such a function before its definition is known, the call will
still work right, it will just run slower.

   Normally, compiling a file does not evaluate the file's contents or
load the file.  But it does execute any `require' calls at top level in
the file.  One way to ensure that necessary macro definitions are
available during compilation is to require the file that defines them
(*note Named Features::).  To avoid loading the macro definition files
when someone _runs_ the compiled program, write `eval-when-compile'
around the `require' calls (*note Eval During Compile::).

 -- Function: byte-compile symbol
     This function byte-compiles the function definition of SYMBOL,
     replacing the previous definition with the compiled one.  The
     function definition of SYMBOL must be the actual code for the
     function; i.e., the compiler does not follow indirection to
     another symbol.  `byte-compile' returns the new, compiled
     definition of SYMBOL.

     If SYMBOL's definition is a byte-code function object,
     `byte-compile' does nothing and returns `nil'.  Lisp records only
     one function definition for any symbol, and if that is already
     compiled, non-compiled code is not available anywhere.  So there
     is no way to "compile the same definition again."

          (defun factorial (integer)
            "Compute factorial of INTEGER."
            (if (= 1 integer) 1
              (* integer (factorial (1- integer)))))
          => factorial

          (byte-compile 'factorial)
          =>
          #[(integer)
            "^H\301U\203^H^@\301\207\302^H\303^HS!\"\207"
            [integer 1 * factorial]
            4 "Compute factorial of INTEGER."]

     The result is a byte-code function object.  The string it contains
     is the actual byte-code; each character in it is an instruction or
     an operand of an instruction.  The vector contains all the
     constants, variable names and function names used by the function,
     except for certain primitives that are coded as special
     instructions.

     If the argument to `byte-compile' is a `lambda' expression, it
     returns the corresponding compiled code, but does not store it
     anywhere.

 -- Command: compile-defun &optional arg
     This command reads the defun containing point, compiles it, and
     evaluates the result.  If you use this on a defun that is actually
     a function definition, the effect is to install a compiled version
     of that function.

     `compile-defun' normally displays the result of evaluation in the
     echo area, but if ARG is non-`nil', it inserts the result in the
     current buffer after the form it compiled.

 -- Command: byte-compile-file filename &optional load
     This function compiles a file of Lisp code named FILENAME into a
     file of byte-code.  The output file's name is made by changing the
     `.el' suffix into `.elc'; if FILENAME does not end in `.el', it
     adds `.elc' to the end of FILENAME.

     Compilation works by reading the input file one form at a time.
     If it is a definition of a function or macro, the compiled
     function or macro definition is written out.  Other forms are
     batched together, then each batch is compiled, and written so that
     its compiled code will be executed when the file is read.  All
     comments are discarded when the input file is read.

     This command returns `t' if there were no errors and `nil'
     otherwise.  When called interactively, it prompts for the file
     name.

     If LOAD is non-`nil', this command loads the compiled file after
     compiling it.  Interactively, LOAD is the prefix argument.

          % ls -l push*
          -rw-r--r--  1 lewis     791 Oct  5 20:31 push.el

          (byte-compile-file "~/emacs/push.el")
               => t

          % ls -l push*
          -rw-r--r--  1 lewis     791 Oct  5 20:31 push.el
          -rw-rw-rw-  1 lewis     638 Oct  8 20:25 push.elc

 -- Command: byte-recompile-directory directory &optional flag force
     This command recompiles every `.el' file in DIRECTORY (or its
     subdirectories) that needs recompilation.  A file needs
     recompilation if a `.elc' file exists but is older than the `.el'
     file.

     When a `.el' file has no corresponding `.elc' file, FLAG says what
     to do.  If it is `nil', this command ignores these files.  If FLAG
     is 0, it compiles them.  If it is neither `nil' nor 0, it asks the
     user whether to compile each such file, and asks about each
     subdirectory as well.

     Interactively, `byte-recompile-directory' prompts for DIRECTORY
     and FLAG is the prefix argument.

     If FORCE is non-`nil', this command recompiles every `.el' file
     that has a `.elc' file.

     The returned value is unpredictable.

 -- Function: batch-byte-compile &optional noforce
     This function runs `byte-compile-file' on files specified on the
     command line.  This function must be used only in a batch
     execution of Emacs, as it kills Emacs on completion.  An error in
     one file does not prevent processing of subsequent files, but no
     output file will be generated for it, and the Emacs process will
     terminate with a nonzero status code.

     If NOFORCE is non-`nil', this function does not recompile files
     that have an up-to-date `.elc' file.

          % emacs -batch -f batch-byte-compile *.el

 -- Function: byte-code code-string data-vector max-stack
     This function actually interprets byte-code.  A byte-compiled
     function is actually defined with a body that calls `byte-code'.
     Don't call this function yourself--only the byte compiler knows
     how to generate valid calls to this function.

     In Emacs version 18, byte-code was always executed by way of a
     call to the function `byte-code'.  Nowadays, byte-code is usually
     executed as part of a byte-code function object, and only rarely
     through an explicit call to `byte-code'.


File: elisp,  Node: Docs and Compilation,  Next: Dynamic Loading,  Prev: Compilation Functions,  Up: Byte Compilation

16.3 Documentation Strings and Compilation
==========================================

Functions and variables loaded from a byte-compiled file access their
documentation strings dynamically from the file whenever needed.  This
saves space within Emacs, and makes loading faster because the
documentation strings themselves need not be processed while loading the
file.  Actual access to the documentation strings becomes slower as a
result, but this normally is not enough to bother users.

   Dynamic access to documentation strings does have drawbacks:

   * If you delete or move the compiled file after loading it, Emacs
     can no longer access the documentation strings for the functions
     and variables in the file.

   * If you alter the compiled file (such as by compiling a new
     version), then further access to documentation strings in this
     file will probably give nonsense results.

   If your site installs Emacs following the usual procedures, these
problems will never normally occur.  Installing a new version uses a new
directory with a different name; as long as the old version remains
installed, its files will remain unmodified in the places where they are
expected to be.

   However, if you have built Emacs yourself and use it from the
directory where you built it, you will experience this problem
occasionally if you edit and recompile Lisp files.  When it happens, you
can cure the problem by reloading the file after recompiling it.

   You can turn off this feature at compile time by setting
`byte-compile-dynamic-docstrings' to `nil'; this is useful mainly if
you expect to change the file, and you want Emacs processes that have
already loaded it to keep working when the file changes.  You can do
this globally, or for one source file by specifying a file-local
binding for the variable.  One way to do that is by adding this string
to the file's first line:

     -*-byte-compile-dynamic-docstrings: nil;-*-

 -- Variable: byte-compile-dynamic-docstrings
     If this is non-`nil', the byte compiler generates compiled files
     that are set up for dynamic loading of documentation strings.

   The dynamic documentation string feature writes compiled files that
use a special Lisp reader construct, `#@COUNT'.  This construct skips
the next COUNT characters.  It also uses the `#$' construct, which
stands for "the name of this file, as a string."  It is usually best
not to use these constructs in Lisp source files, since they are not
designed to be clear to humans reading the file.


File: elisp,  Node: Dynamic Loading,  Next: Eval During Compile,  Prev: Docs and Compilation,  Up: Byte Compilation

16.4 Dynamic Loading of Individual Functions
============================================

When you compile a file, you can optionally enable the "dynamic
function loading" feature (also known as "lazy loading").  With dynamic
function loading, loading the file doesn't fully read the function
definitions in the file.  Instead, each function definition contains a
place-holder which refers to the file.  The first time each function is
called, it reads the full definition from the file, to replace the
place-holder.

   The advantage of dynamic function loading is that loading the file
becomes much faster.  This is a good thing for a file which contains
many separate user-callable functions, if using one of them does not
imply you will probably also use the rest.  A specialized mode which
provides many keyboard commands often has that usage pattern: a user may
invoke the mode, but use only a few of the commands it provides.

   The dynamic loading feature has certain disadvantages:

   * If you delete or move the compiled file after loading it, Emacs
     can no longer load the remaining function definitions not already
     loaded.

   * If you alter the compiled file (such as by compiling a new
     version), then trying to load any function not already loaded will
     usually yield nonsense results.

   These problems will never happen in normal circumstances with
installed Emacs files.  But they are quite likely to happen with Lisp
files that you are changing.  The easiest way to prevent these problems
is to reload the new compiled file immediately after each recompilation.

   The byte compiler uses the dynamic function loading feature if the
variable `byte-compile-dynamic' is non-`nil' at compilation time.  Do
not set this variable globally, since dynamic loading is desirable only
for certain files.  Instead, enable the feature for specific source
files with file-local variable bindings.  For example, you could do it
by writing this text in the source file's first line:

     -*-byte-compile-dynamic: t;-*-

 -- Variable: byte-compile-dynamic
     If this is non-`nil', the byte compiler generates compiled files
     that are set up for dynamic function loading.

 -- Function: fetch-bytecode function
     If FUNCTION is a byte-code function object, this immediately
     finishes loading the byte code of FUNCTION from its byte-compiled
     file, if it is not fully loaded already.  Otherwise, it does
     nothing.  It always returns FUNCTION.


File: elisp,  Node: Eval During Compile,  Next: Compiler Errors,  Prev: Dynamic Loading,  Up: Byte Compilation

16.5 Evaluation During Compilation
==================================

These features permit you to write code to be evaluated during
compilation of a program.

 -- Special Form: eval-and-compile body...
     This form marks BODY to be evaluated both when you compile the
     containing code and when you run it (whether compiled or not).

     You can get a similar result by putting BODY in a separate file
     and referring to that file with `require'.  That method is
     preferable when BODY is large.  Effectively `require' is
     automatically `eval-and-compile', the package is loaded both when
     compiling and executing.

     `autoload' is also effectively `eval-and-compile' too.  It's
     recognized when compiling, so uses of such a function don't produce
     "not known to be defined" warnings.

     Most uses of `eval-and-compile' are fairly sophisticated.

     If a macro has a helper function to build its result, and that
     macro is used both locally and outside the package, then
     `eval-and-compile' should be used to get the helper both when
     compiling and then later when running.

     If functions are defined programmatically (with `fset' say), then
     `eval-and-compile' can be used to have that done at compile-time
     as well as run-time, so calls to those functions are checked (and
     warnings about "not known to be defined" suppressed).

 -- Special Form: eval-when-compile body...
     This form marks BODY to be evaluated at compile time but not when
     the compiled program is loaded.  The result of evaluation by the
     compiler becomes a constant which appears in the compiled program.
     If you load the source file, rather than compiling it, BODY is
     evaluated normally.

     If you have a constant that needs some calculation to produce,
     `eval-when-compile' can do that at compile-time.  For example,

          (defvar my-regexp
            (eval-when-compile (regexp-opt '("aaa" "aba" "abb"))))

     If you're using another package, but only need macros from it (the
     byte compiler will expand those), then `eval-when-compile' can be
     used to load it for compiling, but not executing.  For example,

          (eval-when-compile
            (require 'my-macro-package))  ;; only macros needed from this

     The same sort of thing goes for macros and `defsubst' functions
     defined locally and only for use within the file.  They are needed
     for compiling the file, but in most cases they are not needed for
     execution of the compiled file.  For example,

          (eval-when-compile
            (unless (fboundp 'some-new-thing)
              (defmacro 'some-new-thing ()
                (compatibility code))))

     This is often good for code that's only a fallback for
     compatibility with other versions of Emacs.

     *Common Lisp Note:* At top level, `eval-when-compile' is analogous
     to the Common Lisp idiom `(eval-when (compile eval) ...)'.
     Elsewhere, the Common Lisp `#.' reader macro (but not when
     interpreting) is closer to what `eval-when-compile' does.


File: elisp,  Node: Compiler Errors,  Next: Byte-Code Objects,  Prev: Eval During Compile,  Up: Byte Compilation

16.6 Compiler Errors
====================

Byte compilation outputs all errors and warnings into the buffer
`*Compile-Log*'.  The messages include file names and line numbers that
identify the location of the problem.  The usual Emacs commands for
operating on compiler diagnostics work properly on these messages.

   However, the warnings about functions that were used but not defined
are always "located" at the end of the file, so these commands won't
find the places they are really used.  To do that, you must search for
the function names.

   You can suppress the compiler warning for calling an undefined
function FUNC by conditionalizing the function call on an `fboundp'
test, like this:

     (if (fboundp 'FUNC) ...(FUNC ...)...)

The call to FUNC must be in the THEN-FORM of the `if', and FUNC must
appear quoted in the call to `fboundp'.  (This feature operates for
`cond' as well.)

   Likewise, you can suppress a compiler warning for an unbound variable
VARIABLE by conditionalizing its use on a `boundp' test, like this:

     (if (boundp 'VARIABLE) ...VARIABLE...)

The reference to VARIABLE must be in the THEN-FORM of the `if', and
VARIABLE must appear quoted in the call to `boundp'.

   You can suppress any compiler warnings using the construct
`with-no-warnings':

 -- Special Form: with-no-warnings body...
     In execution, this is equivalent to `(progn BODY...)', but the
     compiler does not issue warnings for anything that occurs inside
     BODY.

     We recommend that you use this construct around the smallest
     possible piece of code.


File: elisp,  Node: Byte-Code Objects,  Next: Disassembly,  Prev: Compiler Errors,  Up: Byte Compilation

16.7 Byte-Code Function Objects
===============================

Byte-compiled functions have a special data type: they are "byte-code
function objects".

   Internally, a byte-code function object is much like a vector;
however, the evaluator handles this data type specially when it appears
as a function to be called.  The printed representation for a byte-code
function object is like that for a vector, with an additional `#'
before the opening `['.

   A byte-code function object must have at least four elements; there
is no maximum number, but only the first six elements have any normal
use.  They are:

ARGLIST
     The list of argument symbols.

BYTE-CODE
     The string containing the byte-code instructions.

CONSTANTS
     The vector of Lisp objects referenced by the byte code.  These
     include symbols used as function names and variable names.

STACKSIZE
     The maximum stack size this function needs.

DOCSTRING
     The documentation string (if any); otherwise, `nil'.  The value may
     be a number or a list, in case the documentation string is stored
     in a file.  Use the function `documentation' to get the real
     documentation string (*note Accessing Documentation::).

INTERACTIVE
     The interactive spec (if any).  This can be a string or a Lisp
     expression.  It is `nil' for a function that isn't interactive.

   Here's an example of a byte-code function object, in printed
representation.  It is the definition of the command `backward-sexp'.

     #[(&optional arg)
       "^H\204^F^@\301^P\302^H[!\207"
       [arg 1 forward-sexp]
       2
       254435
       "p"]

   The primitive way to create a byte-code object is with
`make-byte-code':

 -- Function: make-byte-code &rest elements
     This function constructs and returns a byte-code function object
     with ELEMENTS as its elements.

   You should not try to come up with the elements for a byte-code
function yourself, because if they are inconsistent, Emacs may crash
when you call the function.  Always leave it to the byte compiler to
create these objects; it makes the elements consistent (we hope).

   You can access the elements of a byte-code object using `aref'; you
can also use `vconcat' to create a vector with the same elements.


File: elisp,  Node: Disassembly,  Prev: Byte-Code Objects,  Up: Byte Compilation

16.8 Disassembled Byte-Code
===========================

People do not write byte-code; that job is left to the byte compiler.
But we provide a disassembler to satisfy a cat-like curiosity.  The
disassembler converts the byte-compiled code into humanly readable form.

   The byte-code interpreter is implemented as a simple stack machine.
It pushes values onto a stack of its own, then pops them off to use them
in calculations whose results are themselves pushed back on the stack.
When a byte-code function returns, it pops a value off the stack and
returns it as the value of the function.

   In addition to the stack, byte-code functions can use, bind, and set
ordinary Lisp variables, by transferring values between variables and
the stack.

 -- Command: disassemble object &optional buffer-or-name
     This command displays the disassembled code for OBJECT.  In
     interactive use, or if BUFFER-OR-NAME is `nil' or omitted, the
     output goes in a buffer named `*Disassemble*'.  If BUFFER-OR-NAME
     is non-`nil', it must be a buffer or the name of an existing
     buffer.  Then the output goes there, at point, and point is left
     before the output.

     The argument OBJECT can be a function name, a lambda expression or
     a byte-code object.  If it is a lambda expression, `disassemble'
     compiles it and disassembles the resulting compiled code.

   Here are two examples of using the `disassemble' function.  We have
added explanatory comments to help you relate the byte-code to the Lisp
source; these do not appear in the output of `disassemble'.  These
examples show unoptimized byte-code.  Nowadays byte-code is usually
optimized, but we did not want to rewrite these examples, since they
still serve their purpose.

     (defun factorial (integer)
       "Compute factorial of an integer."
       (if (= 1 integer) 1
         (* integer (factorial (1- integer)))))
          => factorial

     (factorial 4)
          => 24

     (disassemble 'factorial)
          -| byte-code for factorial:
      doc: Compute factorial of an integer.
      args: (integer)

     0   constant 1              ; Push 1 onto stack.

     1   varref   integer        ; Get value of `integer'
                                 ;   from the environment
                                 ;   and push the value
                                 ;   onto the stack.

     2   eqlsign                 ; Pop top two values off stack,
                                 ;   compare them,
                                 ;   and push result onto stack.

     3   goto-if-nil 10          ; Pop and test top of stack;
                                 ;   if `nil', go to 10,
                                 ;   else continue.

     6   constant 1              ; Push 1 onto top of stack.

     7   goto     17             ; Go to 17 (in this case, 1 will be
                                 ;   returned by the function).

     10  constant *              ; Push symbol `*' onto stack.

     11  varref   integer        ; Push value of `integer' onto stack.

     12  constant factorial      ; Push `factorial' onto stack.

     13  varref   integer        ; Push value of `integer' onto stack.

     14  sub1                    ; Pop `integer', decrement value,
                                 ;   push new value onto stack.

                                 ; Stack now contains:
                                 ;   - decremented value of `integer'
                                 ;   - `factorial'
                                 ;   - value of `integer'
                                 ;   - `*'

     15  call     1              ; Call function `factorial' using
                                 ;   the first (i.e., the top) element
                                 ;   of the stack as the argument;
                                 ;   push returned value onto stack.

                                 ; Stack now contains:
                                 ;   - result of recursive
                                 ;        call to `factorial'
                                 ;   - value of `integer'
                                 ;   - `*'

     16  call     2              ; Using the first two
                                 ;   (i.e., the top two)
                                 ;   elements of the stack
                                 ;   as arguments,
                                 ;   call the function `*',
                                 ;   pushing the result onto the stack.

     17  return                  ; Return the top element
                                 ;   of the stack.
          => nil

   The `silly-loop' function is somewhat more complex:

     (defun silly-loop (n)
       "Return time before and after N iterations of a loop."
       (let ((t1 (current-time-string)))
         (while (> (setq n (1- n))
                   0))
         (list t1 (current-time-string))))
          => silly-loop

     (disassemble 'silly-loop)
          -| byte-code for silly-loop:
      doc: Return time before and after N iterations of a loop.
      args: (n)

     0   constant current-time-string  ; Push
                                       ;   `current-time-string'
                                       ;   onto top of stack.

     1   call     0              ; Call `current-time-string'
                                 ;    with no argument,
                                 ;    pushing result onto stack.

     2   varbind  t1             ; Pop stack and bind `t1'
                                 ;   to popped value.

     3   varref   n              ; Get value of `n' from
                                 ;   the environment and push
                                 ;   the value onto the stack.

     4   sub1                    ; Subtract 1 from top of stack.

     5   dup                     ; Duplicate the top of the stack;
                                 ;   i.e., copy the top of
                                 ;   the stack and push the
                                 ;   copy onto the stack.

     6   varset   n              ; Pop the top of the stack,
                                 ;   and bind `n' to the value.

                                 ; In effect, the sequence `dup varset'
                                 ;   copies the top of the stack
                                 ;   into the value of `n'
                                 ;   without popping it.

     7   constant 0              ; Push 0 onto stack.

     8   gtr                     ; Pop top two values off stack,
                                 ;   test if N is greater than 0
                                 ;   and push result onto stack.

     9   goto-if-nil-else-pop 17 ; Goto 17 if `n' <= 0
                                 ;   (this exits the while loop).
                                 ;   else pop top of stack
                                 ;   and continue

     12  constant nil            ; Push `nil' onto stack
                                 ;   (this is the body of the loop).

     13  discard                 ; Discard result of the body
                                 ;   of the loop (a while loop
                                 ;   is always evaluated for
                                 ;   its side effects).

     14  goto     3              ; Jump back to beginning
                                 ;   of while loop.

     17  discard                 ; Discard result of while loop
                                 ;   by popping top of stack.
                                 ;   This result is the value `nil' that
                                 ;   was not popped by the goto at 9.

     18  varref   t1             ; Push value of `t1' onto stack.

     19  constant current-time-string  ; Push
                                       ;   `current-time-string'
                                       ;   onto top of stack.

     20  call     0              ; Call `current-time-string' again.

     21  list2                   ; Pop top two elements off stack,
                                 ;   create a list of them,
                                 ;   and push list onto stack.

     22  unbind   1              ; Unbind `t1' in local environment.

     23  return                  ; Return value of the top of stack.

          => nil


File: elisp,  Node: Advising Functions,  Next: Debugging,  Prev: Byte Compilation,  Up: Top

17 Advising Emacs Lisp Functions
********************************

The "advice" feature lets you add to the existing definition of a
function, by "advising the function".  This is a cleaner method for a
library to customize functions defined within Emacs--cleaner than
redefining the whole function.

   Each function can have multiple "pieces of advice", separately
defined.  Each defined piece of advice can be "enabled" or "disabled"
explicitly.  All the enabled pieces of advice for any given function
actually take effect when you "activate" advice for that function, or
when you define or redefine the function.  Note that enabling a piece
of advice and activating advice for a function are not the same thing.

   *Usage Note:* Advice is useful for altering the behavior of existing
calls to an existing function.  If you want the new behavior for new
calls, or for key bindings, you should define a new function (or a new
command) which uses the existing function.

   *Usage note:* Advising a function can cause confusion in debugging,
since people who debug calls to the original function may not notice
that it has been modified with advice.  Therefore, if you have the
possibility to change the code of that function (or ask someone to do
so) to run a hook, please solve the problem that way.  Advice should be
reserved for the cases where you cannot get the function changed.

   In particular, this means that a file in Emacs should not put advice
on a function in Emacs.  There are currently a few exceptions to this
convention, but we aim to correct them.

* Menu:

* Simple Advice::           A simple example to explain the basics of advice.
* Defining Advice::         Detailed description of `defadvice'.
* Around-Advice::           Wrapping advice around a function's definition.
* Computed Advice::         ...is to `defadvice' as `fset' is to `defun'.
* Activation of Advice::    Advice doesn't do anything until you activate it.
* Enabling Advice::         You can enable or disable each piece of advice.
* Preactivation::           Preactivation is a way of speeding up the
                              loading of compiled advice.
* Argument Access in Advice:: How advice can access the function's arguments.
* Advising Primitives::     Accessing arguments when advising a primitive.
* Combined Definition::     How advice is implemented.


File: elisp,  Node: Simple Advice,  Next: Defining Advice,  Up: Advising Functions

17.1 A Simple Advice Example
============================

The command `next-line' moves point down vertically one or more lines;
it is the standard binding of `C-n'.  When used on the last line of the
buffer, this command inserts a newline to create a line to move to if
`next-line-add-newlines' is non-`nil' (its default is `nil'.)

   Suppose you wanted to add a similar feature to `previous-line',
which would insert a new line at the beginning of the buffer for the
command to move to (when `next-line-add-newlines' is non-`nil').  How
could you do this?

   You could do it by redefining the whole function, but that is not
modular.  The advice feature provides a cleaner alternative: you can
effectively add your code to the existing function definition, without
actually changing or even seeing that definition.  Here is how to do
this:

     (defadvice previous-line (before next-line-at-end
                                      (&optional arg try-vscroll))
       "Insert an empty line when moving up from the top line."
       (if (and next-line-add-newlines (= arg 1)
                (save-excursion (beginning-of-line) (bobp)))
           (progn
             (beginning-of-line)
             (newline))))

   This expression defines a "piece of advice" for the function
`previous-line'.  This piece of advice is named `next-line-at-end', and
the symbol `before' says that it is "before-advice" which should run
before the regular definition of `previous-line'.  `(&optional arg
try-vscroll)' specifies how the advice code can refer to the function's
arguments.

   When this piece of advice runs, it creates an additional line, in the
situation where that is appropriate, but does not move point to that
line.  This is the correct way to write the advice, because the normal
definition will run afterward and will move back to the newly inserted
line.

   Defining the advice doesn't immediately change the function
`previous-line'.  That happens when you "activate" the advice, like
this:

     (ad-activate 'previous-line)

This is what actually begins to use the advice that has been defined so
far for the function `previous-line'.  Henceforth, whenever that
function is run, whether invoked by the user with `C-p' or `M-x', or
called from Lisp, it runs the advice first, and its regular definition
second.

   This example illustrates before-advice, which is one "class" of
advice: it runs before the function's base definition.  There are two
other advice classes: "after-advice", which runs after the base
definition, and "around-advice", which lets you specify an expression
to wrap around the invocation of the base definition.


File: elisp,  Node: Defining Advice,  Next: Around-Advice,  Prev: Simple Advice,  Up: Advising Functions

17.2 Defining Advice
====================

To define a piece of advice, use the macro `defadvice'.  A call to
`defadvice' has the following syntax, which is based on the syntax of
`defun' and `defmacro', but adds more:

     (defadvice FUNCTION (CLASS NAME
                              [POSITION] [ARGLIST]
                              FLAGS...)
       [DOCUMENTATION-STRING]
       [INTERACTIVE-FORM]
       BODY-FORMS...)

Here, FUNCTION is the name of the function (or macro or special form)
to be advised.  From now on, we will write just "function" when
describing the entity being advised, but this always includes macros and
special forms.

   In place of the argument list in an ordinary definition, an advice
definition calls for several different pieces of information.

   CLASS specifies the "class" of the advice--one of `before', `after',
or `around'.  Before-advice runs before the function itself;
after-advice runs after the function itself; around-advice is wrapped
around the execution of the function itself.  After-advice and
around-advice can override the return value by setting
`ad-return-value'.

 -- Variable: ad-return-value
     While advice is executing, after the function's original
     definition has been executed, this variable holds its return
     value, which will ultimately be returned to the caller after
     finishing all the advice.  After-advice and around-advice can
     arrange to return some other value by storing it in this variable.

   The argument NAME is the name of the advice, a non-`nil' symbol.
The advice name uniquely identifies one piece of advice, within all the
pieces of advice in a particular class for a particular FUNCTION.  The
name allows you to refer to the piece of advice--to redefine it, or to
enable or disable it.

   The optional POSITION specifies where, in the current list of advice
of the specified CLASS, this new advice should be placed.  It should be
either `first', `last' or a number that specifies a zero-based position
(`first' is equivalent to 0).  If no position is specified, the default
is `first'.  Position values outside the range of existing positions in
this class are mapped to the beginning or the end of the range,
whichever is closer.  The POSITION value is ignored when redefining an
existing piece of advice.

   The optional ARGLIST can be used to define the argument list for the
sake of advice.  This becomes the argument list of the combined
definition that is generated in order to run the advice (*note Combined
Definition::).  Therefore, the advice expressions can use the argument
variables in this list to access argument values.

   The argument list used in advice need not be the same as the argument
list used in the original function, but must be compatible with it, so
that it can handle the ways the function is actually called.  If two
pieces of advice for a function both specify an argument list, they must
specify the same argument list.

   *Note Argument Access in Advice::, for more information about
argument lists and advice, and a more flexible way for advice to access
the arguments.

   The remaining elements, FLAGS, are symbols that specify further
information about how to use this piece of advice.  Here are the valid
symbols and their meanings:

`activate'
     Activate the advice for FUNCTION now.  Changes in a function's
     advice always take effect the next time you activate advice for the
     function; this flag says to do so, for FUNCTION, immediately after
     defining this piece of advice.

     This flag has no immediate effect if FUNCTION itself is not
     defined yet (a situation known as "forward advice"), because it is
     impossible to activate an undefined function's advice.  However,
     defining FUNCTION will automatically activate its advice.

`protect'
     Protect this piece of advice against non-local exits and errors in
     preceding code and advice.  Protecting advice places it as a
     cleanup in an `unwind-protect' form, so that it will execute even
     if the previous code gets an error or uses `throw'.  *Note
     Cleanups::.

`compile'
     Compile the combined definition that is used to run the advice.
     This flag is ignored unless `activate' is also specified.  *Note
     Combined Definition::.

`disable'
     Initially disable this piece of advice, so that it will not be used
     unless subsequently explicitly enabled.  *Note Enabling Advice::.

`preactivate'
     Activate advice for FUNCTION when this `defadvice' is compiled or
     macroexpanded.  This generates a compiled advised definition
     according to the current advice state, which will be used during
     activation if appropriate.  *Note Preactivation::.

     This is useful only if this `defadvice' is byte-compiled.

   The optional DOCUMENTATION-STRING serves to document this piece of
advice.  When advice is active for FUNCTION, the documentation for
FUNCTION (as returned by `documentation') combines the documentation
strings of all the advice for FUNCTION with the documentation string of
its original function definition.

   The optional INTERACTIVE-FORM form can be supplied to change the
interactive behavior of the original function.  If more than one piece
of advice has an INTERACTIVE-FORM, then the first one (the one with the
smallest position) found among all the advice takes precedence.

   The possibly empty list of BODY-FORMS specifies the body of the
advice.  The body of an advice can access or change the arguments, the
return value, the binding environment, and perform any other kind of
side effect.

   *Warning:* When you advise a macro, keep in mind that macros are
expanded when a program is compiled, not when a compiled program is run.
All subroutines used by the advice need to be available when the byte
compiler expands the macro.

 -- Command: ad-unadvise function
     This command deletes the advice from FUNCTION.

 -- Command: ad-unadvise-all
     This command deletes all pieces of advice from all functions.


File: elisp,  Node: Around-Advice,  Next: Computed Advice,  Prev: Defining Advice,  Up: Advising Functions

17.3 Around-Advice
==================

Around-advice lets you "wrap" a Lisp expression "around" the original
function definition.  You specify where the original function
definition should go by means of the special symbol `ad-do-it'.  Where
this symbol occurs inside the around-advice body, it is replaced with a
`progn' containing the forms of the surrounded code.  Here is an
example:

     (defadvice foo (around foo-around)
       "Ignore case in `foo'."
       (let ((case-fold-search t))
         ad-do-it))

Its effect is to make sure that case is ignored in searches when the
original definition of `foo' is run.

 -- Variable: ad-do-it
     This is not really a variable, rather a place-holder that looks
     like a variable.  You use it in around-advice to specify the place
     to run the function's original definition and other "earlier"
     around-advice.

   If the around-advice does not use `ad-do-it', then it does not run
the original function definition.  This provides a way to override the
original definition completely.  (It also overrides lower-positioned
pieces of around-advice).

   If the around-advice uses `ad-do-it' more than once, the original
definition is run at each place.  In this way, around-advice can execute
the original definition (and lower-positioned pieces of around-advice)
several times.  Another way to do that is by using `ad-do-it' inside of
a loop.


File: elisp,  Node: Computed Advice,  Next: Activation of Advice,  Prev: Around-Advice,  Up: Advising Functions

17.4 Computed Advice
====================

The macro `defadvice' resembles `defun' in that the code for the
advice, and all other information about it, are explicitly stated in
the source code.  You can also create advice whose details are computed,
using the function `ad-add-advice'.

 -- Function: ad-add-advice function advice class position
     Calling `ad-add-advice' adds ADVICE as a piece of advice to
     FUNCTION in class CLASS.  The argument ADVICE  has this form:

          (NAME PROTECTED ENABLED DEFINITION)

     Here PROTECTED and ENABLED are flags, and DEFINITION is the
     expression that says what the advice should do.  If ENABLED is
     `nil', this piece of advice is initially disabled (*note Enabling
     Advice::).

     If FUNCTION already has one or more pieces of advice in the
     specified CLASS, then POSITION specifies where in the list to put
     the new piece of advice.  The value of POSITION can either be
     `first', `last', or a number (counting from 0 at the beginning of
     the list).  Numbers outside the range are mapped to the beginning
     or the end of the range, whichever is closer.  The POSITION value
     is ignored when redefining an existing piece of advice.

     If FUNCTION already has a piece of ADVICE with the same name, then
     the position argument is ignored and the old advice is replaced
     with the new one.


File: elisp,  Node: Activation of Advice,  Next: Enabling Advice,  Prev: Computed Advice,  Up: Advising Functions

17.5 Activation of Advice
=========================

By default, advice does not take effect when you define it--only when
you "activate" advice for the function that was advised.  However, the
advice will be activated automatically if you define or redefine the
function later.  You can request the activation of advice for a
function when you define the advice, by specifying the `activate' flag
in the `defadvice'.  But normally you activate the advice for a
function by calling the function `ad-activate' or one of the other
activation commands listed below.

   Separating the activation of advice from the act of defining it
permits you to add several pieces of advice to one function
efficiently, without redefining the function over and over as each
advice is added.  More importantly, it permits defining advice for a
function before that function is actually defined.

   When a function's advice is first activated, the function's original
definition is saved, and all enabled pieces of advice for that function
are combined with the original definition to make a new definition.
(Pieces of advice that are currently disabled are not used; see *Note
Enabling Advice::.)  This definition is installed, and optionally
byte-compiled as well, depending on conditions described below.

   In all of the commands to activate advice, if COMPILE is `t' (or
anything but `nil' or a negative number), the command also compiles the
combined definition which implements the advice.  If it is `nil' or a
negative number, what happens depends on
`ad-default-compilation-action' as described below.

 -- Command: ad-activate function &optional compile
     This command activates all the advice defined for FUNCTION.

   Activating advice does nothing if FUNCTION's advice is already
active.  But if there is new advice, added since the previous time you
activated advice for FUNCTION, it activates the new advice.

 -- Command: ad-deactivate function
     This command deactivates the advice for FUNCTION.  

 -- Command: ad-update function &optional compile
     This command activates the advice for FUNCTION if its advice is
     already activated.  This is useful if you change the advice.

 -- Command: ad-activate-all &optional compile
     This command activates the advice for all functions.

 -- Command: ad-deactivate-all
     This command deactivates the advice for all functions.

 -- Command: ad-update-all &optional compile
     This command activates the advice for all functions whose advice
     is already activated.  This is useful if you change the advice of
     some functions.

 -- Command: ad-activate-regexp regexp &optional compile
     This command activates all pieces of advice whose names match
     REGEXP.  More precisely, it activates all advice for any function
     which has at least one piece of advice that matches REGEXP.

 -- Command: ad-deactivate-regexp regexp
     This command deactivates all pieces of advice whose names match
     REGEXP.  More precisely, it deactivates all advice for any
     function which has at least one piece of advice that matches
     REGEXP.

 -- Command: ad-update-regexp regexp &optional compile
     This command activates pieces of advice whose names match REGEXP,
     but only those for functions whose advice is already activated.  

     Reactivating a function's advice is useful for putting into effect
     all the changes that have been made in its advice (including
     enabling and disabling specific pieces of advice; *note Enabling
     Advice::) since the last time it was activated.

 -- Command: ad-start-advice
     Turn on automatic advice activation when a function is defined or
     redefined.  This is the default mode.

 -- Command: ad-stop-advice
     Turn off automatic advice activation when a function is defined or
     redefined.

 -- User Option: ad-default-compilation-action
     This variable controls whether to compile the combined definition
     that results from activating advice for a function.

     A value of `always' specifies to compile unconditionally.  A value
     of `never' specifies never compile the advice.

     A value of `maybe' specifies to compile if the byte-compiler is
     already loaded.  A value of `like-original' specifies to compile
     the advice if the original definition of the advised function is
     compiled or a built-in function.

     This variable takes effect only if the COMPILE argument of
     `ad-activate' (or any of the above functions) did not force
     compilation.

   If the advised definition was constructed during "preactivation"
(*note Preactivation::), then that definition must already be compiled,
because it was constructed during byte-compilation of the file that
contained the `defadvice' with the `preactivate' flag.


File: elisp,  Node: Enabling Advice,  Next: Preactivation,  Prev: Activation of Advice,  Up: Advising Functions

17.6 Enabling and Disabling Advice
==================================

Each piece of advice has a flag that says whether it is enabled or not.
By enabling or disabling a piece of advice, you can turn it on and off
without having to undefine and redefine it.  For example, here is how
to disable a particular piece of advice named `my-advice' for the
function `foo':

     (ad-disable-advice 'foo 'before 'my-advice)

   This function by itself only changes the enable flag for a piece of
advice.  To make the change take effect in the advised definition, you
must activate the advice for `foo' again:

     (ad-activate 'foo)

 -- Command: ad-disable-advice function class name
     This command disables the piece of advice named NAME in class
     CLASS on FUNCTION.

 -- Command: ad-enable-advice function class name
     This command enables the piece of advice named NAME in class CLASS
     on FUNCTION.

   You can also disable many pieces of advice at once, for various
functions, using a regular expression.  As always, the changes take real
effect only when you next reactivate advice for the functions in
question.

 -- Command: ad-disable-regexp regexp
     This command disables all pieces of advice whose names match
     REGEXP, in all classes, on all functions.

 -- Command: ad-enable-regexp regexp
     This command enables all pieces of advice whose names match
     REGEXP, in all classes, on all functions.


File: elisp,  Node: Preactivation,  Next: Argument Access in Advice,  Prev: Enabling Advice,  Up: Advising Functions

17.7 Preactivation
==================

Constructing a combined definition to execute advice is moderately
expensive.  When a library advises many functions, this can make loading
the library slow.  In that case, you can use "preactivation" to
construct suitable combined definitions in advance.

   To use preactivation, specify the `preactivate' flag when you define
the advice with `defadvice'.  This `defadvice' call creates a combined
definition which embodies this piece of advice (whether enabled or not)
plus any other currently enabled advice for the same function, and the
function's own definition.  If the `defadvice' is compiled, that
compiles the combined definition also.

   When the function's advice is subsequently activated, if the enabled
advice for the function matches what was used to make this combined
definition, then the existing combined definition is used, thus avoiding
the need to construct one.  Thus, preactivation never causes wrong
results--but it may fail to do any good, if the enabled advice at the
time of activation doesn't match what was used for preactivation.

   Here are some symptoms that can indicate that a preactivation did not
work properly, because of a mismatch.

   * Activation of the advised function takes longer than usual.

   * The byte-compiler gets loaded while an advised function gets
     activated.

   * `byte-compile' is included in the value of `features' even though
     you did not ever explicitly use the byte-compiler.

   Compiled preactivated advice works properly even if the function
itself is not defined until later; however, the function needs to be
defined when you _compile_ the preactivated advice.

   There is no elegant way to find out why preactivated advice is not
being used.  What you can do is to trace the function
`ad-cache-id-verification-code' (with the function
`trace-function-background') before the advised function's advice is
activated.  After activation, check the value returned by
`ad-cache-id-verification-code' for that function: `verified' means
that the preactivated advice was used, while other values give some
information about why they were considered inappropriate.

   *Warning:* There is one known case that can make preactivation fail,
in that a preconstructed combined definition is used even though it
fails to match the current state of advice.  This can happen when two
packages define different pieces of advice with the same name, in the
same class, for the same function.  But you should avoid that anyway.


File: elisp,  Node: Argument Access in Advice,  Next: Advising Primitives,  Prev: Preactivation,  Up: Advising Functions

17.8 Argument Access in Advice
==============================

The simplest way to access the arguments of an advised function in the
body of a piece of advice is to use the same names that the function
definition uses.  To do this, you need to know the names of the argument
variables of the original function.

   While this simple method is sufficient in many cases, it has a
disadvantage: it is not robust, because it hard-codes the argument names
into the advice.  If the definition of the original function changes,
the advice might break.

   Another method is to specify an argument list in the advice itself.
This avoids the need to know the original function definition's argument
names, but it has a limitation: all the advice on any particular
function must use the same argument list, because the argument list
actually used for all the advice comes from the first piece of advice
for that function.

   A more robust method is to use macros that are translated into the
proper access forms at activation time, i.e., when constructing the
advised definition.  Access macros access actual arguments by position
regardless of how these actual arguments get distributed onto the
argument variables of a function.  This is robust because in Emacs Lisp
the meaning of an argument is strictly determined by its position in the
argument list.

 -- Macro: ad-get-arg position
     This returns the actual argument that was supplied at POSITION.

 -- Macro: ad-get-args position
     This returns the list of actual arguments supplied starting at
     POSITION.

 -- Macro: ad-set-arg position value
     This sets the value of the actual argument at POSITION to VALUE

 -- Macro: ad-set-args position value-list
     This sets the list of actual arguments starting at POSITION to
     VALUE-LIST.

   Now an example.  Suppose the function `foo' is defined as

     (defun foo (x y &optional z &rest r) ...)

and is then called with

     (foo 0 1 2 3 4 5 6)

which means that X is 0, Y is 1, Z is 2 and R is `(3 4 5 6)' within the
body of `foo'.  Here is what `ad-get-arg' and `ad-get-args' return in
this case:

     (ad-get-arg 0) => 0
     (ad-get-arg 1) => 1
     (ad-get-arg 2) => 2
     (ad-get-arg 3) => 3
     (ad-get-args 2) => (2 3 4 5 6)
     (ad-get-args 4) => (4 5 6)

   Setting arguments also makes sense in this example:

     (ad-set-arg 5 "five")

has the effect of changing the sixth argument to `"five"'.  If this
happens in advice executed before the body of `foo' is run, then R will
be `(3 4 "five" 6)' within that body.

   Here is an example of setting a tail of the argument list:

     (ad-set-args 0 '(5 4 3 2 1 0))

If this happens in advice executed before the body of `foo' is run,
then within that body, X will be 5, Y will be 4, Z will be 3, and R
will be `(2 1 0)' inside the body of `foo'.

   These argument constructs are not really implemented as Lisp macros.
Instead they are implemented specially by the advice mechanism.


File: elisp,  Node: Advising Primitives,  Next: Combined Definition,  Prev: Argument Access in Advice,  Up: Advising Functions

17.9 Advising Primitives
========================

Advising a primitive function (also called a "subr") is risky.  Some
primitive functions are used by the advice mechanism; advising them
could cause an infinite recursion.  Also, many primitive functions are
called directly from C code.  Calls to the primitive from Lisp code
will take note of the advice, but calls from C code will ignore the
advice.

   When the advice facility constructs the combined definition, it needs
to know the argument list of the original function.  This is not always
possible for primitive functions.  When advice cannot determine the
argument list, it uses `(&rest ad-subr-args)', which always works but
is inefficient because it constructs a list of the argument values.
You can use `ad-define-subr-args' to declare the proper argument names
for a primitive function:

 -- Function: ad-define-subr-args function arglist
     This function specifies that ARGLIST should be used as the
     argument list for function FUNCTION.

   For example,

     (ad-define-subr-args 'fset '(sym newdef))

specifies the argument list for the function `fset'.


File: elisp,  Node: Combined Definition,  Prev: Advising Primitives,  Up: Advising Functions

17.10 The Combined Definition
=============================

Suppose that a function has N pieces of before-advice (numbered from 0
through N-1), M pieces of around-advice and K pieces of after-advice.
Assuming no piece of advice is protected, the combined definition
produced to implement the advice for a function looks like this:

     (lambda ARGLIST
       [ [ADVISED-DOCSTRING] [(interactive ...)] ]
       (let (ad-return-value)
         before-0-body-form...
              ....
         before-N-1-body-form...
         around-0-body-form...
            around-1-body-form...
                  ....
               around-M-1-body-form...
                  (setq ad-return-value
                        apply original definition to ARGLIST)
               end-of-around-M-1-body-form...
                  ....
            end-of-around-1-body-form...
         end-of-around-0-body-form...
         after-0-body-form...
               ....
         after-K-1-body-form...
         ad-return-value))

   Macros are redefined as macros, which means adding `macro' to the
beginning of the combined definition.

   The interactive form is present if the original function or some
piece of advice specifies one.  When an interactive primitive function
is advised, advice uses a special method: it calls the primitive with
`call-interactively' so that it will read its own arguments.  In this
case, the advice cannot access the arguments.

   The body forms of the various advice in each class are assembled
according to their specified order.  The forms of around-advice L are
included in one of the forms of around-advice L - 1.

   The innermost part of the around advice onion is

     apply original definition to ARGLIST

whose form depends on the type of the original function.  The variable
`ad-return-value' is set to whatever this returns.  The variable is
visible to all pieces of advice, which can access and modify it before
it is actually returned from the advised function.

   The semantic structure of advised functions that contain protected
pieces of advice is the same.  The only difference is that
`unwind-protect' forms ensure that the protected advice gets executed
even if some previous piece of advice had an error or a non-local exit.
If any around-advice is protected, then the whole around-advice onion
is protected as a result.


File: elisp,  Node: Debugging,  Next: Read and Print,  Prev: Advising Functions,  Up: Top

18 Debugging Lisp Programs
**************************

There are three ways to investigate a problem in an Emacs Lisp program,
depending on what you are doing with the program when the problem
appears.

   * If the problem occurs when you run the program, you can use a Lisp
     debugger to investigate what is happening during execution.  In
     addition to the ordinary debugger, Emacs comes with a source-level
     debugger, Edebug.  This chapter describes both of them.

   * If the problem is syntactic, so that Lisp cannot even read the
     program, you can use the Emacs facilities for editing Lisp to
     localize it.

   * If the problem occurs when trying to compile the program with the
     byte compiler, you need to know how to examine the compiler's
     input buffer.

* Menu:

* Debugger::            How the Emacs Lisp debugger is implemented.
* Edebug::		A source-level Emacs Lisp debugger.
* Syntax Errors::       How to find syntax errors.
* Test Coverage::       Ensuring you have tested all branches in your code.
* Compilation Errors::  How to find errors that show up in byte compilation.

   Another useful debugging tool is the dribble file.  When a dribble
file is open, Emacs copies all keyboard input characters to that file.
Afterward, you can examine the file to find out what input was used.
*Note Terminal Input::.

   For debugging problems in terminal descriptions, the
`open-termscript' function can be useful.  *Note Terminal Output::.


File: elisp,  Node: Debugger,  Next: Edebug,  Up: Debugging

18.1 The Lisp Debugger
======================

The ordinary "Lisp debugger" provides the ability to suspend evaluation
of a form.  While evaluation is suspended (a state that is commonly
known as a "break"), you may examine the run time stack, examine the
values of local or global variables, or change those values.  Since a
break is a recursive edit, all the usual editing facilities of Emacs
are available; you can even run programs that will enter the debugger
recursively.  *Note Recursive Editing::.

* Menu:

* Error Debugging::       Entering the debugger when an error happens.
* Infinite Loops::	  Stopping and debugging a program that doesn't exit.
* Function Debugging::    Entering it when a certain function is called.
* Explicit Debug::        Entering it at a certain point in the program.
* Using Debugger::        What the debugger does; what you see while in it.
* Debugger Commands::     Commands used while in the debugger.
* Invoking the Debugger:: How to call the function `debug'.
* Internals of Debugger:: Subroutines of the debugger, and global variables.


File: elisp,  Node: Error Debugging,  Next: Infinite Loops,  Up: Debugger

18.1.1 Entering the Debugger on an Error
----------------------------------------

The most important time to enter the debugger is when a Lisp error
happens.  This allows you to investigate the immediate causes of the
error.

   However, entry to the debugger is not a normal consequence of an
error.  Many commands frequently cause Lisp errors when invoked
inappropriately (such as `C-f' at the end of the buffer), and during
ordinary editing it would be very inconvenient to enter the debugger
each time this happens.  So if you want errors to enter the debugger,
set the variable `debug-on-error' to non-`nil'.  (The command
`toggle-debug-on-error' provides an easy way to do this.)

 -- User Option: debug-on-error
     This variable determines whether the debugger is called when an
     error is signaled and not handled.  If `debug-on-error' is `t', all
     kinds of errors call the debugger (except those listed in
     `debug-ignored-errors').  If it is `nil', none call the debugger.

     The value can also be a list of error conditions that should call
     the debugger.  For example, if you set it to the list
     `(void-variable)', then only errors about a variable that has no
     value invoke the debugger.

     When this variable is non-`nil', Emacs does not create an error
     handler around process filter functions and sentinels.  Therefore,
     errors in these functions also invoke the debugger.  *Note
     Processes::.

 -- User Option: debug-ignored-errors
     This variable specifies certain kinds of errors that should not
     enter the debugger.  Its value is a list of error condition
     symbols and/or regular expressions.  If the error has any of those
     condition symbols, or if the error message matches any of the
     regular expressions, then that error does not enter the debugger,
     regardless of the value of `debug-on-error'.

     The normal value of this variable lists several errors that happen
     often during editing but rarely result from bugs in Lisp programs.
     However, "rarely" is not "never"; if your program fails with an
     error that matches this list, you will need to change this list in
     order to debug the error.  The easiest way is usually to set
     `debug-ignored-errors' to `nil'.

 -- User Option: eval-expression-debug-on-error
     If this variable has a non-`nil' value, then `debug-on-error' is
     set to `t' when evaluating with the command `eval-expression'.  If
     `eval-expression-debug-on-error' is `nil', then the value of
     `debug-on-error' is not changed.  *Note Evaluating Emacs-Lisp
     Expressions: (emacs)Lisp Eval.

 -- User Option: debug-on-signal
     Normally, errors that are caught by `condition-case' never run the
     debugger, even if `debug-on-error' is non-`nil'.  In other words,
     `condition-case' gets a chance to handle the error before the
     debugger gets a chance.

     If you set `debug-on-signal' to a non-`nil' value, then the
     debugger gets the first chance at every error; an error will
     invoke the debugger regardless of any `condition-case', if it fits
     the criteria specified by the values of `debug-on-error' and
     `debug-ignored-errors'.

     *Warning:* This variable is strong medicine!  Various parts of
     Emacs handle errors in the normal course of affairs, and you may
     not even realize that errors happen there.  If you set
     `debug-on-signal' to a non-`nil' value, those errors will enter
     the debugger.

     *Warning:* `debug-on-signal' has no effect when `debug-on-error'
     is `nil'.

   To debug an error that happens during loading of the init file, use
the option `--debug-init'.  This binds `debug-on-error' to `t' while
loading the init file, and bypasses the `condition-case' which normally
catches errors in the init file.

   If your init file sets `debug-on-error', the effect may not last
past the end of loading the init file.  (This is an undesirable
byproduct of the code that implements the `--debug-init' command line
option.)  The best way to make the init file set `debug-on-error'
permanently is with `after-init-hook', like this:

     (add-hook 'after-init-hook
               (lambda () (setq debug-on-error t)))


File: elisp,  Node: Infinite Loops,  Next: Function Debugging,  Prev: Error Debugging,  Up: Debugger

18.1.2 Debugging Infinite Loops
-------------------------------

When a program loops infinitely and fails to return, your first problem
is to stop the loop.  On most operating systems, you can do this with
`C-g', which causes a "quit".

   Ordinary quitting gives no information about why the program was
looping.  To get more information, you can set the variable
`debug-on-quit' to non-`nil'.  Quitting with `C-g' is not considered an
error, and `debug-on-error' has no effect on the handling of `C-g'.
Likewise, `debug-on-quit' has no effect on errors.

   Once you have the debugger running in the middle of the infinite
loop, you can proceed from the debugger using the stepping commands.
If you step through the entire loop, you will probably get enough
information to solve the problem.

 -- User Option: debug-on-quit
     This variable determines whether the debugger is called when `quit'
     is signaled and not handled.  If `debug-on-quit' is non-`nil',
     then the debugger is called whenever you quit (that is, type
     `C-g').  If `debug-on-quit' is `nil', then the debugger is not
     called when you quit.  *Note Quitting::.


File: elisp,  Node: Function Debugging,  Next: Explicit Debug,  Prev: Infinite Loops,  Up: Debugger

18.1.3 Entering the Debugger on a Function Call
-----------------------------------------------

To investigate a problem that happens in the middle of a program, one
useful technique is to enter the debugger whenever a certain function is
called.  You can do this to the function in which the problem occurs,
and then step through the function, or you can do this to a function
called shortly before the problem, step quickly over the call to that
function, and then step through its caller.

 -- Command: debug-on-entry function-name
     This function requests FUNCTION-NAME to invoke the debugger each
     time it is called.  It works by inserting the form
     `(implement-debug-on-entry)' into the function definition as the
     first form.

     Any function or macro defined as Lisp code may be set to break on
     entry, regardless of whether it is interpreted code or compiled
     code.  If the function is a command, it will enter the debugger
     when called from Lisp and when called interactively (after the
     reading of the arguments).  You can also set debug-on-entry for
     primitive functions (i.e., those written in C) this way, but it
     only takes effect when the primitive is called from Lisp code.
     Debug-on-entry is not allowed for special forms.

     When `debug-on-entry' is called interactively, it prompts for
     FUNCTION-NAME in the minibuffer.  If the function is already set
     up to invoke the debugger on entry, `debug-on-entry' does nothing.
     `debug-on-entry' always returns FUNCTION-NAME.

     *Warning:* if you redefine a function after using `debug-on-entry'
     on it, the code to enter the debugger is discarded by the
     redefinition.  In effect, redefining the function cancels the
     break-on-entry feature for that function.

     Here's an example to illustrate use of this function:

          (defun fact (n)
            (if (zerop n) 1
                (* n (fact (1- n)))))
               => fact
          (debug-on-entry 'fact)
               => fact
          (fact 3)

          ------ Buffer: *Backtrace* ------
          Debugger entered--entering a function:
          * fact(3)
            eval((fact 3))
            eval-last-sexp-1(nil)
            eval-last-sexp(nil)
            call-interactively(eval-last-sexp)
          ------ Buffer: *Backtrace* ------

          (symbol-function 'fact)
               => (lambda (n)
                    (debug (quote debug))
                    (if (zerop n) 1 (* n (fact (1- n)))))

 -- Command: cancel-debug-on-entry &optional function-name
     This function undoes the effect of `debug-on-entry' on
     FUNCTION-NAME.  When called interactively, it prompts for
     FUNCTION-NAME in the minibuffer.  If FUNCTION-NAME is omitted or
     `nil', it cancels break-on-entry for all functions.  Calling
     `cancel-debug-on-entry' does nothing to a function which is not
     currently set up to break on entry.


File: elisp,  Node: Explicit Debug,  Next: Using Debugger,  Prev: Function Debugging,  Up: Debugger

18.1.4 Explicit Entry to the Debugger
-------------------------------------

You can cause the debugger to be called at a certain point in your
program by writing the expression `(debug)' at that point.  To do this,
visit the source file, insert the text `(debug)' at the proper place,
and type `C-M-x' (`eval-defun', a Lisp mode key binding).  *Warning:*
if you do this for temporary debugging purposes, be sure to undo this
insertion before you save the file!

   The place where you insert `(debug)' must be a place where an
additional form can be evaluated and its value ignored.  (If the value
of `(debug)' isn't ignored, it will alter the execution of the
program!)  The most common suitable places are inside a `progn' or an
implicit `progn' (*note Sequencing::).


File: elisp,  Node: Using Debugger,  Next: Debugger Commands,  Prev: Explicit Debug,  Up: Debugger

18.1.5 Using the Debugger
-------------------------

When the debugger is entered, it displays the previously selected
buffer in one window and a buffer named `*Backtrace*' in another
window.  The backtrace buffer contains one line for each level of Lisp
function execution currently going on.  At the beginning of this buffer
is a message describing the reason that the debugger was invoked (such
as the error message and associated data, if it was invoked due to an
error).

   The backtrace buffer is read-only and uses a special major mode,
Debugger mode, in which letters are defined as debugger commands.  The
usual Emacs editing commands are available; thus, you can switch windows
to examine the buffer that was being edited at the time of the error,
switch buffers, visit files, or do any other sort of editing.  However,
the debugger is a recursive editing level (*note Recursive Editing::)
and it is wise to go back to the backtrace buffer and exit the debugger
(with the `q' command) when you are finished with it.  Exiting the
debugger gets out of the recursive edit and kills the backtrace buffer.

   The backtrace buffer shows you the functions that are executing and
their argument values.  It also allows you to specify a stack frame by
moving point to the line describing that frame.  (A stack frame is the
place where the Lisp interpreter records information about a particular
invocation of a function.)  The frame whose line point is on is
considered the "current frame".  Some of the debugger commands operate
on the current frame.  If a line starts with a star, that means that
exiting that frame will call the debugger again.  This is useful for
examining the return value of a function.

   If a function name is underlined, that means the debugger knows
where its source code is located.  You can click `Mouse-2' on that
name, or move to it and type <RET>, to visit the source code.

   The debugger itself must be run byte-compiled, since it makes
assumptions about how many stack frames are used for the debugger
itself.  These assumptions are false if the debugger is running
interpreted.


File: elisp,  Node: Debugger Commands,  Next: Invoking the Debugger,  Prev: Using Debugger,  Up: Debugger

18.1.6 Debugger Commands
------------------------

The debugger buffer (in Debugger mode) provides special commands in
addition to the usual Emacs commands.  The most important use of
debugger commands is for stepping through code, so that you can see how
control flows.  The debugger can step through the control structures of
an interpreted function, but cannot do so in a byte-compiled function.
If you would like to step through a byte-compiled function, replace it
with an interpreted definition of the same function.  (To do this,
visit the source for the function and type `C-M-x' on its definition.)
You cannot use the Lisp debugger to step through a primitive function.

   Here is a list of Debugger mode commands:

`c'
     Exit the debugger and continue execution.  When continuing is
     possible, it resumes execution of the program as if the debugger
     had never been entered (aside from any side-effects that you
     caused by changing variable values or data structures while inside
     the debugger).

     Continuing is possible after entry to the debugger due to function
     entry or exit, explicit invocation, or quitting.  You cannot
     continue if the debugger was entered because of an error.

`d'
     Continue execution, but enter the debugger the next time any Lisp
     function is called.  This allows you to step through the
     subexpressions of an expression, seeing what values the
     subexpressions compute, and what else they do.

     The stack frame made for the function call which enters the
     debugger in this way will be flagged automatically so that the
     debugger will be called again when the frame is exited.  You can
     use the `u' command to cancel this flag.

`b'
     Flag the current frame so that the debugger will be entered when
     the frame is exited.  Frames flagged in this way are marked with
     stars in the backtrace buffer.

`u'
     Don't enter the debugger when the current frame is exited.  This
     cancels a `b' command on that frame.  The visible effect is to
     remove the star from the line in the backtrace buffer.

`j'
     Flag the current frame like `b'.  Then continue execution like
     `c', but temporarily disable break-on-entry for all functions that
     are set up to do so by `debug-on-entry'.

`e'
     Read a Lisp expression in the minibuffer, evaluate it, and print
     the value in the echo area.  The debugger alters certain important
     variables, and the current buffer, as part of its operation; `e'
     temporarily restores their values from outside the debugger, so
     you can examine and change them.  This makes the debugger more
     transparent.  By contrast, `M-:' does nothing special in the
     debugger; it shows you the variable values within the debugger.

`R'
     Like `e', but also save the result of evaluation in the buffer
     `*Debugger-record*'.

`q'
     Terminate the program being debugged; return to top-level Emacs
     command execution.

     If the debugger was entered due to a `C-g' but you really want to
     quit, and not debug, use the `q' command.

`r'
     Return a value from the debugger.  The value is computed by
     reading an expression with the minibuffer and evaluating it.

     The `r' command is useful when the debugger was invoked due to exit
     from a Lisp call frame (as requested with `b' or by entering the
     frame with `d'); then the value specified in the `r' command is
     used as the value of that frame.  It is also useful if you call
     `debug' and use its return value.  Otherwise, `r' has the same
     effect as `c', and the specified return value does not matter.

     You can't use `r' when the debugger was entered due to an error.

`l'
     Display a list of functions that will invoke the debugger when
     called.  This is a list of functions that are set to break on
     entry by means of `debug-on-entry'.  *Warning:* if you redefine
     such a function and thus cancel the effect of `debug-on-entry', it
     may erroneously show up in this list.


File: elisp,  Node: Invoking the Debugger,  Next: Internals of Debugger,  Prev: Debugger Commands,  Up: Debugger

18.1.7 Invoking the Debugger
----------------------------

Here we describe in full detail the function `debug' that is used to
invoke the debugger.

 -- Function: debug &rest debugger-args
     This function enters the debugger.  It switches buffers to a buffer
     named `*Backtrace*' (or `*Backtrace*<2>' if it is the second
     recursive entry to the debugger, etc.), and fills it with
     information about the stack of Lisp function calls.  It then
     enters a recursive edit, showing the backtrace buffer in Debugger
     mode.

     The Debugger mode `c', `d', `j', and `r' commands exit the
     recursive edit; then `debug' switches back to the previous buffer
     and returns to whatever called `debug'.  This is the only way the
     function `debug' can return to its caller.

     The use of the DEBUGGER-ARGS is that `debug' displays the rest of
     its arguments at the top of the `*Backtrace*' buffer, so that the
     user can see them.  Except as described below, this is the _only_
     way these arguments are used.

     However, certain values for first argument to `debug' have a
     special significance.  (Normally, these values are used only by the
     internals of Emacs, and not by programmers calling `debug'.)  Here
     is a table of these special values:

    `lambda'
          A first argument of `lambda' means `debug' was called because
          of entry to a function when `debug-on-next-call' was
          non-`nil'.  The debugger displays `Debugger entered--entering
          a function:' as a line of text at the top of the buffer.

    `debug'
          `debug' as first argument means `debug' was called because of
          entry to a function that was set to debug on entry.  The
          debugger displays the string `Debugger entered--entering a
          function:', just as in the `lambda' case.  It also marks the
          stack frame for that function so that it will invoke the
          debugger when exited.

    `t'
          When the first argument is `t', this indicates a call to
          `debug' due to evaluation of a function call form when
          `debug-on-next-call' is non-`nil'.  The debugger displays
          `Debugger entered--beginning evaluation of function call
          form:' as the top line in the buffer.

    `exit'
          When the first argument is `exit', it indicates the exit of a
          stack frame previously marked to invoke the debugger on exit.
          The second argument given to `debug' in this case is the
          value being returned from the frame.  The debugger displays
          `Debugger entered--returning value:' in the top line of the
          buffer, followed by the value being returned.

    `error'
          When the first argument is `error', the debugger indicates
          that it is being entered because an error or `quit' was
          signaled and not handled, by displaying `Debugger
          entered--Lisp error:' followed by the error signaled and any
          arguments to `signal'.  For example,

               (let ((debug-on-error t))
                 (/ 1 0))

               ------ Buffer: *Backtrace* ------
               Debugger entered--Lisp error: (arith-error)
                 /(1 0)
               ...
               ------ Buffer: *Backtrace* ------

          If an error was signaled, presumably the variable
          `debug-on-error' is non-`nil'.  If `quit' was signaled, then
          presumably the variable `debug-on-quit' is non-`nil'.

    `nil'
          Use `nil' as the first of the DEBUGGER-ARGS when you want to
          enter the debugger explicitly.  The rest of the DEBUGGER-ARGS
          are printed on the top line of the buffer.  You can use this
          feature to display messages--for example, to remind yourself
          of the conditions under which `debug' is called.


File: elisp,  Node: Internals of Debugger,  Prev: Invoking the Debugger,  Up: Debugger

18.1.8 Internals of the Debugger
--------------------------------

This section describes functions and variables used internally by the
debugger.

 -- Variable: debugger
     The value of this variable is the function to call to invoke the
     debugger.  Its value must be a function of any number of
     arguments, or, more typically, the name of a function.  This
     function should invoke some kind of debugger.  The default value
     of the variable is `debug'.

     The first argument that Lisp hands to the function indicates why it
     was called.  The convention for arguments is detailed in the
     description of `debug' (*note Invoking the Debugger::).

 -- Command: backtrace
     This function prints a trace of Lisp function calls currently
     active.  This is the function used by `debug' to fill up the
     `*Backtrace*' buffer.  It is written in C, since it must have
     access to the stack to determine which function calls are active.
     The return value is always `nil'.

     In the following example, a Lisp expression calls `backtrace'
     explicitly.  This prints the backtrace to the stream
     `standard-output', which, in this case, is the buffer
     `backtrace-output'.

     Each line of the backtrace represents one function call.  The line
     shows the values of the function's arguments if they are all
     known; if they are still being computed, the line says so.  The
     arguments of special forms are elided.

          (with-output-to-temp-buffer "backtrace-output"
            (let ((var 1))
              (save-excursion
                (setq var (eval '(progn
                                   (1+ var)
                                   (list 'testing (backtrace))))))))

               => (testing nil)

          ----------- Buffer: backtrace-output ------------
            backtrace()
            (list ...computing arguments...)
            (progn ...)
            eval((progn (1+ var) (list (quote testing) (backtrace))))
            (setq ...)
            (save-excursion ...)
            (let ...)
            (with-output-to-temp-buffer ...)
            eval((with-output-to-temp-buffer ...))
            eval-last-sexp-1(nil)
            eval-last-sexp(nil)
            call-interactively(eval-last-sexp)
          ----------- Buffer: backtrace-output ------------

 -- Variable: debug-on-next-call
     If this variable is non-`nil', it says to call the debugger before
     the next `eval', `apply' or `funcall'.  Entering the debugger sets
     `debug-on-next-call' to `nil'.

     The `d' command in the debugger works by setting this variable.

 -- Function: backtrace-debug level flag
     This function sets the debug-on-exit flag of the stack frame LEVEL
     levels down the stack, giving it the value FLAG.  If FLAG is
     non-`nil', this will cause the debugger to be entered when that
     frame later exits.  Even a nonlocal exit through that frame will
     enter the debugger.

     This function is used only by the debugger.

 -- Variable: command-debug-status
     This variable records the debugging status of the current
     interactive command.  Each time a command is called interactively,
     this variable is bound to `nil'.  The debugger can set this
     variable to leave information for future debugger invocations
     during the same command invocation.

     The advantage of using this variable rather than an ordinary global
     variable is that the data will never carry over to a subsequent
     command invocation.

 -- Function: backtrace-frame frame-number
     The function `backtrace-frame' is intended for use in Lisp
     debuggers.  It returns information about what computation is
     happening in the stack frame FRAME-NUMBER levels down.

     If that frame has not evaluated the arguments yet, or is a special
     form, the value is `(nil FUNCTION ARG-FORMS...)'.

     If that frame has evaluated its arguments and called its function
     already, the return value is `(t FUNCTION ARG-VALUES...)'.

     In the return value, FUNCTION is whatever was supplied as the CAR
     of the evaluated list, or a `lambda' expression in the case of a
     macro call.  If the function has a `&rest' argument, that is
     represented as the tail of the list ARG-VALUES.

     If FRAME-NUMBER is out of range, `backtrace-frame' returns `nil'.


File: elisp,  Node: Edebug,  Next: Syntax Errors,  Prev: Debugger,  Up: Debugging

18.2 Edebug
===========

Edebug is a source-level debugger for Emacs Lisp programs with which
you can:

   * Step through evaluation, stopping before and after each expression.

   * Set conditional or unconditional breakpoints.

   * Stop when a specified condition is true (the global break event).

   * Trace slow or fast, stopping briefly at each stop point, or at
     each breakpoint.

   * Display expression results and evaluate expressions as if outside
     of Edebug.

   * Automatically re-evaluate a list of expressions and display their
     results each time Edebug updates the display.

   * Output trace info on function enter and exit.

   * Stop when an error occurs.

   * Display a backtrace, omitting Edebug's own frames.

   * Specify argument evaluation for macros and defining forms.

   * Obtain rudimentary coverage testing and frequency counts.

   The first three sections below should tell you enough about Edebug to
enable you to use it.

* Menu:

* Using Edebug::		Introduction to use of Edebug.
* Instrumenting::		You must instrument your code
				  in order to debug it with Edebug.
* Modes: Edebug Execution Modes. Execution modes, stopping more or less often.
* Jumping::			Commands to jump to a specified place.
* Misc: Edebug Misc.		Miscellaneous commands.
* Breaks::                      Setting breakpoints to make the program stop.
* Trapping Errors::		Trapping errors with Edebug.
* Views: Edebug Views.		Views inside and outside of Edebug.
* Eval: Edebug Eval.		Evaluating expressions within Edebug.
* Eval List::			Expressions whose values are displayed
				  each time you enter Edebug.
* Printing in Edebug::		Customization of printing.
* Trace Buffer::		How to produce trace output in a buffer.
* Coverage Testing::		How to test evaluation coverage.
* The Outside Context::		Data that Edebug saves and restores.
* Edebug and Macros::	        Specifying how to handle macro calls.
* Options: Edebug Options.	Option variables for customizing Edebug.


File: elisp,  Node: Using Edebug,  Next: Instrumenting,  Up: Edebug

18.2.1 Using Edebug
-------------------

To debug a Lisp program with Edebug, you must first "instrument" the
Lisp code that you want to debug.  A simple way to do this is to first
move point into the definition of a function or macro and then do `C-u
C-M-x' (`eval-defun' with a prefix argument).  See *Note
Instrumenting::, for alternative ways to instrument code.

   Once a function is instrumented, any call to the function activates
Edebug.  Depending on which Edebug execution mode you have selected,
activating Edebug may stop execution and let you step through the
function, or it may update the display and continue execution while
checking for debugging commands.  The default execution mode is step,
which stops execution.  *Note Edebug Execution Modes::.

   Within Edebug, you normally view an Emacs buffer showing the source
of the Lisp code you are debugging.  This is referred to as the "source
code buffer", and it is temporarily read-only.

   An arrow in the left fringe indicates the line where the function is
executing.  Point initially shows where within the line the function is
executing, but this ceases to be true if you move point yourself.

   If you instrument the definition of `fac' (shown below) and then
execute `(fac 3)', here is what you would normally see.  Point is at
the open-parenthesis before `if'.

     (defun fac (n)
     =>-!-(if (< 0 n)
           (* n (fac (1- n)))
         1))

   The places within a function where Edebug can stop execution are
called "stop points".  These occur both before and after each
subexpression that is a list, and also after each variable reference.
Here we use periods to show the stop points in the function `fac':

     (defun fac (n)
       .(if .(< 0 n.).
           .(* n. .(fac .(1- n.).).).
         1).)

   The special commands of Edebug are available in the source code
buffer in addition to the commands of Emacs Lisp mode.  For example,
you can type the Edebug command <SPC> to execute until the next stop
point.  If you type <SPC> once after entry to `fac', here is the
display you will see:

     (defun fac (n)
     =>(if -!-(< 0 n)
           (* n (fac (1- n)))
         1))

   When Edebug stops execution after an expression, it displays the
expression's value in the echo area.

   Other frequently used commands are `b' to set a breakpoint at a stop
point, `g' to execute until a breakpoint is reached, and `q' to exit
Edebug and return to the top-level command loop.  Type `?' to display a
list of all Edebug commands.


File: elisp,  Node: Instrumenting,  Next: Edebug Execution Modes,  Prev: Using Edebug,  Up: Edebug

18.2.2 Instrumenting for Edebug
-------------------------------

In order to use Edebug to debug Lisp code, you must first "instrument"
the code.  Instrumenting code inserts additional code into it, to
invoke Edebug at the proper places.

   When you invoke command `C-M-x' (`eval-defun') with a prefix
argument on a function definition, it instruments the definition before
evaluating it.  (This does not modify the source code itself.)  If the
variable `edebug-all-defs' is non-`nil', that inverts the meaning of
the prefix argument: in this case, `C-M-x' instruments the definition
_unless_ it has a prefix argument.  The default value of
`edebug-all-defs' is `nil'.  The command `M-x edebug-all-defs' toggles
the value of the variable `edebug-all-defs'.

   If `edebug-all-defs' is non-`nil', then the commands `eval-region',
`eval-current-buffer', and `eval-buffer' also instrument any
definitions they evaluate.  Similarly, `edebug-all-forms' controls
whether `eval-region' should instrument _any_ form, even non-defining
forms.  This doesn't apply to loading or evaluations in the minibuffer.
The command `M-x edebug-all-forms' toggles this option.

   Another command, `M-x edebug-eval-top-level-form', is available to
instrument any top-level form regardless of the values of
`edebug-all-defs' and `edebug-all-forms'.

   While Edebug is active, the command `I' (`edebug-instrument-callee')
instruments the definition of the function or macro called by the list
form after point, if is not already instrumented.  This is possible
only if Edebug knows where to find the source for that function; for
this reading, after loading Edebug, `eval-region' records the position
of every definition it evaluates, even if not instrumenting it.  See
also the `i' command (*note Jumping::), which steps into the call after
instrumenting the function.

   Edebug knows how to instrument all the standard special forms,
`interactive' forms with an expression argument, anonymous lambda
expressions, and other defining forms.  However, Edebug cannot determine
on its own what a user-defined macro will do with the arguments of a
macro call, so you must provide that information using Edebug
specifications; see *Note Edebug and Macros::, for details.

   When Edebug is about to instrument code for the first time in a
session, it runs the hook `edebug-setup-hook', then sets it to `nil'.
You can use this to load Edebug specifications associated with a
package you are using, but only when you use Edebug.

   To remove instrumentation from a definition, simply re-evaluate its
definition in a way that does not instrument.  There are two ways of
evaluating forms that never instrument them: from a file with `load',
and from the minibuffer with `eval-expression' (`M-:').

   If Edebug detects a syntax error while instrumenting, it leaves point
at the erroneous code and signals an `invalid-read-syntax' error.

   *Note Edebug Eval::, for other evaluation functions available inside
of Edebug.


File: elisp,  Node: Edebug Execution Modes,  Next: Jumping,  Prev: Instrumenting,  Up: Edebug

18.2.3 Edebug Execution Modes
-----------------------------

Edebug supports several execution modes for running the program you are
debugging.  We call these alternatives "Edebug execution modes"; do not
confuse them with major or minor modes.  The current Edebug execution
mode determines how far Edebug continues execution before
stopping--whether it stops at each stop point, or continues to the next
breakpoint, for example--and how much Edebug displays the progress of
the evaluation before it stops.

   Normally, you specify the Edebug execution mode by typing a command
to continue the program in a certain mode.  Here is a table of these
commands; all except for `S' resume execution of the program, at least
for a certain distance.

`S'
     Stop: don't execute any more of the program, but wait for more
     Edebug commands (`edebug-stop').

`<SPC>'
     Step: stop at the next stop point encountered (`edebug-step-mode').

`n'
     Next: stop at the next stop point encountered after an expression
     (`edebug-next-mode').  Also see `edebug-forward-sexp' in *Note
     Jumping::.

`t'
     Trace: pause (normally one second) at each Edebug stop point
     (`edebug-trace-mode').

`T'
     Rapid trace: update the display at each stop point, but don't
     actually pause (`edebug-Trace-fast-mode').

`g'
     Go: run until the next breakpoint (`edebug-go-mode').  *Note
     Breakpoints::.

`c'
     Continue: pause one second at each breakpoint, and then continue
     (`edebug-continue-mode').

`C'
     Rapid continue: move point to each breakpoint, but don't pause
     (`edebug-Continue-fast-mode').

`G'
     Go non-stop: ignore breakpoints (`edebug-Go-nonstop-mode').  You
     can still stop the program by typing `S', or any editing command.

   In general, the execution modes earlier in the above list run the
program more slowly or stop sooner than the modes later in the list.

   While executing or tracing, you can interrupt the execution by typing
any Edebug command.  Edebug stops the program at the next stop point and
then executes the command you typed.  For example, typing `t' during
execution switches to trace mode at the next stop point.  You can use
`S' to stop execution without doing anything else.

   If your function happens to read input, a character you type
intending to interrupt execution may be read by the function instead.
You can avoid such unintended results by paying attention to when your
program wants input.

   Keyboard macros containing the commands in this section do not
completely work: exiting from Edebug, to resume the program, loses track
of the keyboard macro.  This is not easy to fix.  Also, defining or
executing a keyboard macro outside of Edebug does not affect commands
inside Edebug.  This is usually an advantage.  See also the
`edebug-continue-kbd-macro' option (*note Edebug Options::).

   When you enter a new Edebug level, the initial execution mode comes
from the value of the variable `edebug-initial-mode'.  (*Note Edebug
Options::.)  By default, this specifies step mode.  Note that you may
reenter the same Edebug level several times if, for example, an
instrumented function is called several times from one command.

 -- User Option: edebug-sit-for-seconds
     This option specifies how many seconds to wait between execution
     steps in trace mode.  The default is 1 second.


File: elisp,  Node: Jumping,  Next: Edebug Misc,  Prev: Edebug Execution Modes,  Up: Edebug

18.2.4 Jumping
--------------

The commands described in this section execute until they reach a
specified location.  All except `i' make a temporary breakpoint to
establish the place to stop, then switch to go mode.  Any other
breakpoint reached before the intended stop point will also stop
execution.  *Note Breakpoints::, for the details on breakpoints.

   These commands may fail to work as expected in case of nonlocal exit,
as that can bypass the temporary breakpoint where you expected the
program to stop.

`h'
     Proceed to the stop point near where point is (`edebug-goto-here').

`f'
     Run the program for one expression (`edebug-forward-sexp').

`o'
     Run the program until the end of the containing sexp.

`i'
     Step into the function or macro called by the form after point.

   The `h' command proceeds to the stop point at or after the current
location of point, using a temporary breakpoint.

   The `f' command runs the program forward over one expression.  More
precisely, it sets a temporary breakpoint at the position that `C-M-f'
would reach, then executes in go mode so that the program will stop at
breakpoints.

   With a prefix argument N, the temporary breakpoint is placed N sexps
beyond point.  If the containing list ends before N more elements, then
the place to stop is after the containing expression.

   You must check that the position `C-M-f' finds is a place that the
program will really get to.  In `cond', for example, this may not be
true.

   For flexibility, the `f' command does `forward-sexp' starting at
point, rather than at the stop point.  If you want to execute one
expression _from the current stop point_, first type `w', to move point
there, and then type `f'.

   The `o' command continues "out of" an expression.  It places a
temporary breakpoint at the end of the sexp containing point.  If the
containing sexp is a function definition itself, `o' continues until
just before the last sexp in the definition.  If that is where you are
now, it returns from the function and then stops.  In other words, this
command does not exit the currently executing function unless you are
positioned after the last sexp.

   The `i' command steps into the function or macro called by the list
form after point, and stops at its first stop point.  Note that the form
need not be the one about to be evaluated.  But if the form is a
function call about to be evaluated, remember to use this command before
any of the arguments are evaluated, since otherwise it will be too late.

   The `i' command instruments the function or macro it's supposed to
step into, if it isn't instrumented already.  This is convenient, but
keep in mind that the function or macro remains instrumented unless you
explicitly arrange to deinstrument it.


File: elisp,  Node: Edebug Misc,  Next: Breaks,  Prev: Jumping,  Up: Edebug

18.2.5 Miscellaneous Edebug Commands
------------------------------------

Some miscellaneous Edebug commands are described here.

`?'
     Display the help message for Edebug (`edebug-help').

`C-]'
     Abort one level back to the previous command level
     (`abort-recursive-edit').

`q'
     Return to the top level editor command loop (`top-level').  This
     exits all recursive editing levels, including all levels of Edebug
     activity.  However, instrumented code protected with
     `unwind-protect' or `condition-case' forms may resume debugging.

`Q'
     Like `q', but don't stop even for protected code
     (`top-level-nonstop').

`r'
     Redisplay the most recently known expression result in the echo
     area (`edebug-previous-result').

`d'
     Display a backtrace, excluding Edebug's own functions for clarity
     (`edebug-backtrace').

     You cannot use debugger commands in the backtrace buffer in Edebug
     as you would in the standard debugger.

     The backtrace buffer is killed automatically when you continue
     execution.

   You can invoke commands from Edebug that activate Edebug again
recursively.  Whenever Edebug is active, you can quit to the top level
with `q' or abort one recursive edit level with `C-]'.  You can display
a backtrace of all the pending evaluations with `d'.


File: elisp,  Node: Breaks,  Next: Trapping Errors,  Prev: Edebug Misc,  Up: Edebug

18.2.6 Breaks
-------------

Edebug's step mode stops execution when the next stop point is reached.
There are three other ways to stop Edebug execution once it has started:
breakpoints, the global break condition, and source breakpoints.

* Menu:

* Breakpoints::                 Breakpoints at stop points.
* Global Break Condition::	Breaking on an event.
* Source Breakpoints::  	Embedding breakpoints in source code.


File: elisp,  Node: Breakpoints,  Next: Global Break Condition,  Up: Breaks

18.2.6.1 Edebug Breakpoints
...........................

While using Edebug, you can specify "breakpoints" in the program you
are testing: these are places where execution should stop.  You can set
a breakpoint at any stop point, as defined in *Note Using Edebug::.  For
setting and unsetting breakpoints, the stop point that is affected is
the first one at or after point in the source code buffer.  Here are the
Edebug commands for breakpoints:

`b'
     Set a breakpoint at the stop point at or after point
     (`edebug-set-breakpoint').  If you use a prefix argument, the
     breakpoint is temporary--it turns off the first time it stops the
     program.

`u'
     Unset the breakpoint (if any) at the stop point at or after point
     (`edebug-unset-breakpoint').

`x CONDITION <RET>'
     Set a conditional breakpoint which stops the program only if
     evaluating CONDITION produces a non-`nil' value
     (`edebug-set-conditional-breakpoint').  With a prefix argument,
     the breakpoint is temporary.

`B'
     Move point to the next breakpoint in the current definition
     (`edebug-next-breakpoint').

   While in Edebug, you can set a breakpoint with `b' and unset one
with `u'.  First move point to the Edebug stop point of your choice,
then type `b' or `u' to set or unset a breakpoint there.  Unsetting a
breakpoint where none has been set has no effect.

   Re-evaluating or reinstrumenting a definition removes all of its
previous breakpoints.

   A "conditional breakpoint" tests a condition each time the program
gets there.  Any errors that occur as a result of evaluating the
condition are ignored, as if the result were `nil'.  To set a
conditional breakpoint, use `x', and specify the condition expression
in the minibuffer.  Setting a conditional breakpoint at a stop point
that has a previously established conditional breakpoint puts the
previous condition expression in the minibuffer so you can edit it.

   You can make a conditional or unconditional breakpoint "temporary"
by using a prefix argument with the command to set the breakpoint.
When a temporary breakpoint stops the program, it is automatically
unset.

   Edebug always stops or pauses at a breakpoint, except when the Edebug
mode is Go-nonstop.  In that mode, it ignores breakpoints entirely.

   To find out where your breakpoints are, use the `B' command, which
moves point to the next breakpoint following point, within the same
function, or to the first breakpoint if there are no following
breakpoints.  This command does not continue execution--it just moves
point in the buffer.


File: elisp,  Node: Global Break Condition,  Next: Source Breakpoints,  Prev: Breakpoints,  Up: Breaks

18.2.6.2 Global Break Condition
...............................

A "global break condition" stops execution when a specified condition
is satisfied, no matter where that may occur.  Edebug evaluates the
global break condition at every stop point; if it evaluates to a
non-`nil' value, then execution stops or pauses depending on the
execution mode, as if a breakpoint had been hit.  If evaluating the
condition gets an error, execution does not stop.

   The condition expression is stored in
`edebug-global-break-condition'.  You can specify a new expression
using the `X' command from the source code buffer while Edebug is
active, or using `C-x X X' from any buffer at any time, as long as
Edebug is loaded (`edebug-set-global-break-condition').

   The global break condition is the simplest way to find where in your
code some event occurs, but it makes code run much more slowly.  So you
should reset the condition to `nil' when not using it.


File: elisp,  Node: Source Breakpoints,  Prev: Global Break Condition,  Up: Breaks

18.2.6.3 Source Breakpoints
...........................

All breakpoints in a definition are forgotten each time you
reinstrument it.  If you wish to make a breakpoint that won't be
forgotten, you can write a "source breakpoint", which is simply a call
to the function `edebug' in your source code.  You can, of course, make
such a call conditional.  For example, in the `fac' function, you can
insert the first line as shown below, to stop when the argument reaches
zero:

     (defun fac (n)
       (if (= n 0) (edebug))
       (if (< 0 n)
           (* n (fac (1- n)))
         1))

   When the `fac' definition is instrumented and the function is
called, the call to `edebug' acts as a breakpoint.  Depending on the
execution mode, Edebug stops or pauses there.

   If no instrumented code is being executed when `edebug' is called,
that function calls `debug'.


File: elisp,  Node: Trapping Errors,  Next: Edebug Views,  Prev: Breaks,  Up: Edebug

18.2.7 Trapping Errors
----------------------

Emacs normally displays an error message when an error is signaled and
not handled with `condition-case'.  While Edebug is active and
executing instrumented code, it normally responds to all unhandled
errors.  You can customize this with the options `edebug-on-error' and
`edebug-on-quit'; see *Note Edebug Options::.

   When Edebug responds to an error, it shows the last stop point
encountered before the error.  This may be the location of a call to a
function which was not instrumented, and within which the error actually
occurred.  For an unbound variable error, the last known stop point
might be quite distant from the offending variable reference.  In that
case, you might want to display a full backtrace (*note Edebug Misc::).

   If you change `debug-on-error' or `debug-on-quit' while Edebug is
active, these changes will be forgotten when Edebug becomes inactive.
Furthermore, during Edebug's recursive edit, these variables are bound
to the values they had outside of Edebug.


File: elisp,  Node: Edebug Views,  Next: Edebug Eval,  Prev: Trapping Errors,  Up: Edebug

18.2.8 Edebug Views
-------------------

These Edebug commands let you view aspects of the buffer and window
status as they were before entry to Edebug.  The outside window
configuration is the collection of windows and contents that were in
effect outside of Edebug.

`v'
     Switch to viewing the outside window configuration
     (`edebug-view-outside').  Type `C-x X w' to return to Edebug.

`p'
     Temporarily display the outside current buffer with point at its
     outside position (`edebug-bounce-point'), pausing for one second
     before returning to Edebug.  With a prefix argument N, pause for N
     seconds instead.

`w'
     Move point back to the current stop point in the source code buffer
     (`edebug-where').

     If you use this command in a different window displaying the same
     buffer, that window will be used instead to display the current
     definition in the future.

`W'
     Toggle whether Edebug saves and restores the outside window
     configuration (`edebug-toggle-save-windows').

     With a prefix argument, `W' only toggles saving and restoring of
     the selected window.  To specify a window that is not displaying
     the source code buffer, you must use `C-x X W' from the global
     keymap.

   You can view the outside window configuration with `v' or just
bounce to the point in the current buffer with `p', even if it is not
normally displayed.

   After moving point, you may wish to jump back to the stop point.
You can do that with `w' from a source code buffer.  You can jump back
to the stop point in the source code buffer from any buffer using `C-x
X w'.

   Each time you use `W' to turn saving _off_, Edebug forgets the saved
outside window configuration--so that even if you turn saving back
_on_, the current window configuration remains unchanged when you next
exit Edebug (by continuing the program).  However, the automatic
redisplay of `*edebug*' and `*edebug-trace*' may conflict with the
buffers you wish to see unless you have enough windows open.


File: elisp,  Node: Edebug Eval,  Next: Eval List,  Prev: Edebug Views,  Up: Edebug

18.2.9 Evaluation
-----------------

While within Edebug, you can evaluate expressions "as if" Edebug were
not running.  Edebug tries to be invisible to the expression's
evaluation and printing.  Evaluation of expressions that cause side
effects will work as expected, except for changes to data that Edebug
explicitly saves and restores.  *Note The Outside Context::, for details
on this process.

`e EXP <RET>'
     Evaluate expression EXP in the context outside of Edebug
     (`edebug-eval-expression').  That is, Edebug tries to minimize its
     interference with the evaluation.

`M-: EXP <RET>'
     Evaluate expression EXP in the context of Edebug itself.

`C-x C-e'
     Evaluate the expression before point, in the context outside of
     Edebug (`edebug-eval-last-sexp').

   Edebug supports evaluation of expressions containing references to
lexically bound symbols created by the following constructs in `cl.el'
(version 2.03 or later): `lexical-let', `macrolet', and
`symbol-macrolet'.


File: elisp,  Node: Eval List,  Next: Printing in Edebug,  Prev: Edebug Eval,  Up: Edebug

18.2.10 Evaluation List Buffer
------------------------------

You can use the "evaluation list buffer", called `*edebug*', to
evaluate expressions interactively.  You can also set up the
"evaluation list" of expressions to be evaluated automatically each
time Edebug updates the display.

`E'
     Switch to the evaluation list buffer `*edebug*'
     (`edebug-visit-eval-list').

   In the `*edebug*' buffer you can use the commands of Lisp
Interaction mode (*note Lisp Interaction: (emacs)Lisp Interaction.) as
well as these special commands:

`C-j'
     Evaluate the expression before point, in the outside context, and
     insert the value in the buffer (`edebug-eval-print-last-sexp').

`C-x C-e'
     Evaluate the expression before point, in the context outside of
     Edebug (`edebug-eval-last-sexp').

`C-c C-u'
     Build a new evaluation list from the contents of the buffer
     (`edebug-update-eval-list').

`C-c C-d'
     Delete the evaluation list group that point is in
     (`edebug-delete-eval-item').

`C-c C-w'
     Switch back to the source code buffer at the current stop point
     (`edebug-where').

   You can evaluate expressions in the evaluation list window with
`C-j' or `C-x C-e', just as you would in `*scratch*'; but they are
evaluated in the context outside of Edebug.

   The expressions you enter interactively (and their results) are lost
when you continue execution; but you can set up an "evaluation list"
consisting of expressions to be evaluated each time execution stops.

   To do this, write one or more "evaluation list groups" in the
evaluation list buffer.  An evaluation list group consists of one or
more Lisp expressions.  Groups are separated by comment lines.

   The command `C-c C-u' (`edebug-update-eval-list') rebuilds the
evaluation list, scanning the buffer and using the first expression of
each group.  (The idea is that the second expression of the group is the
value previously computed and displayed.)

   Each entry to Edebug redisplays the evaluation list by inserting each
expression in the buffer, followed by its current value.  It also
inserts comment lines so that each expression becomes its own group.
Thus, if you type `C-c C-u' again without changing the buffer text, the
evaluation list is effectively unchanged.

   If an error occurs during an evaluation from the evaluation list, the
error message is displayed in a string as if it were the result.
Therefore, expressions that use variables not currently valid do not
interrupt your debugging.

   Here is an example of what the evaluation list window looks like
after several expressions have been added to it:

     (current-buffer)
     #<buffer *scratch*>
     ;---------------------------------------------------------------
     (selected-window)
     #<window 16 on *scratch*>
     ;---------------------------------------------------------------
     (point)
     196
     ;---------------------------------------------------------------
     bad-var
     "Symbol's value as variable is void: bad-var"
     ;---------------------------------------------------------------
     (recursion-depth)
     0
     ;---------------------------------------------------------------
     this-command
     eval-last-sexp
     ;---------------------------------------------------------------

   To delete a group, move point into it and type `C-c C-d', or simply
delete the text for the group and update the evaluation list with `C-c
C-u'.  To add a new expression to the evaluation list, insert the
expression at a suitable place, insert a new comment line, then type
`C-c C-u'.  You need not insert dashes in the comment line--its
contents don't matter.

   After selecting `*edebug*', you can return to the source code buffer
with `C-c C-w'.  The `*edebug*' buffer is killed when you continue
execution, and recreated next time it is needed.


File: elisp,  Node: Printing in Edebug,  Next: Trace Buffer,  Prev: Eval List,  Up: Edebug

18.2.11 Printing in Edebug
--------------------------

If an expression in your program produces a value containing circular
list structure, you may get an error when Edebug attempts to print it.

   One way to cope with circular structure is to set `print-length' or
`print-level' to truncate the printing.  Edebug does this for you; it
binds `print-length' and `print-level' to 50 if they were `nil'.
(Actually, the variables `edebug-print-length' and `edebug-print-level'
specify the values to use within Edebug.)  *Note Output Variables::.

 -- User Option: edebug-print-length
     If non-`nil', Edebug binds `print-length' to this value while
     printing results.  The default value is `50'.

 -- User Option: edebug-print-level
     If non-`nil', Edebug binds `print-level' to this value while
     printing results.  The default value is `50'.

   You can also print circular structures and structures that share
elements more informatively by binding `print-circle' to a non-`nil'
value.

   Here is an example of code that creates a circular structure:

     (setq a '(x y))
     (setcar a a)

Custom printing prints this as `Result: #1=(#1# y)'.  The `#1='
notation labels the structure that follows it with the label `1', and
the `#1#' notation references the previously labeled structure.  This
notation is used for any shared elements of lists or vectors.

 -- User Option: edebug-print-circle
     If non-`nil', Edebug binds `print-circle' to this value while
     printing results.  The default value is `t'.

   Other programs can also use custom printing; see `cust-print.el' for
details.


File: elisp,  Node: Trace Buffer,  Next: Coverage Testing,  Prev: Printing in Edebug,  Up: Edebug

18.2.12 Trace Buffer
--------------------

Edebug can record an execution trace, storing it in a buffer named
`*edebug-trace*'.  This is a log of function calls and returns, showing
the function names and their arguments and values.  To enable trace
recording, set `edebug-trace' to a non-`nil' value.

   Making a trace buffer is not the same thing as using trace execution
mode (*note Edebug Execution Modes::).

   When trace recording is enabled, each function entry and exit adds
lines to the trace buffer.  A function entry record consists of
`::::{', followed by the function name and argument values.  A function
exit record consists of `::::}', followed by the function name and
result of the function.

   The number of `:'s in an entry shows its recursion depth.  You can
use the braces in the trace buffer to find the matching beginning or
end of function calls.

   You can customize trace recording for function entry and exit by
redefining the functions `edebug-print-trace-before' and
`edebug-print-trace-after'.

 -- Macro: edebug-tracing string body...
     This macro requests additional trace information around the
     execution of the BODY forms.  The argument STRING specifies text
     to put in the trace buffer, after the `{' or `}'.  All the
     arguments are evaluated, and `edebug-tracing' returns the value of
     the last form in BODY.

 -- Function: edebug-trace format-string &rest format-args
     This function inserts text in the trace buffer.  It computes the
     text with `(apply 'format FORMAT-STRING FORMAT-ARGS)'.  It also
     appends a newline to separate entries.

   `edebug-tracing' and `edebug-trace' insert lines in the trace buffer
whenever they are called, even if Edebug is not active.  Adding text to
the trace buffer also scrolls its window to show the last lines
inserted.


File: elisp,  Node: Coverage Testing,  Next: The Outside Context,  Prev: Trace Buffer,  Up: Edebug

18.2.13 Coverage Testing
------------------------

Edebug provides rudimentary coverage testing and display of execution
frequency.

   Coverage testing works by comparing the result of each expression
with the previous result; each form in the program is considered
"covered" if it has returned two different values since you began
testing coverage in the current Emacs session.  Thus, to do coverage
testing on your program, execute it under various conditions and note
whether it behaves correctly; Edebug will tell you when you have tried
enough different conditions that each form has returned two different
values.

   Coverage testing makes execution slower, so it is only done if
`edebug-test-coverage' is non-`nil'.  Frequency counting is performed
for all execution of an instrumented function, even if the execution
mode is Go-nonstop, and regardless of whether coverage testing is
enabled.

   Use `C-x X =' (`edebug-display-freq-count') to display both the
coverage information and the frequency counts for a definition.  Just
`=' (`edebug-temp-display-freq-count') displays the same information
temporarily, only until you type another key.

 -- Command: edebug-display-freq-count
     This command displays the frequency count data for each line of the
     current definition.

     The frequency counts appear as comment lines after each line of
     code, and you can undo all insertions with one `undo' command.  The
     counts appear under the `(' before an expression or the `)' after
     an expression, or on the last character of a variable.  To
     simplify the display, a count is not shown if it is equal to the
     count of an earlier expression on the same line.

     The character `=' following the count for an expression says that
     the expression has returned the same value each time it was
     evaluated.  In other words, it is not yet "covered" for coverage
     testing purposes.

     To clear the frequency count and coverage data for a definition,
     simply reinstrument it with `eval-defun'.

   For example, after evaluating `(fac 5)' with a source breakpoint,
and setting `edebug-test-coverage' to `t', when the breakpoint is
reached, the frequency data looks like this:

     (defun fac (n)
       (if (= n 0) (edebug))
     ;#6           1      = =5
       (if (< 0 n)
     ;#5         =
           (* n (fac (1- n)))
     ;#    5               0
         1))
     ;#   0

   The comment lines show that `fac' was called 6 times.  The first
`if' statement returned 5 times with the same result each time; the
same is true of the condition on the second `if'.  The recursive call
of `fac' did not return at all.


File: elisp,  Node: The Outside Context,  Next: Edebug and Macros,  Prev: Coverage Testing,  Up: Edebug

18.2.14 The Outside Context
---------------------------

Edebug tries to be transparent to the program you are debugging, but it
does not succeed completely.  Edebug also tries to be transparent when
you evaluate expressions with `e' or with the evaluation list buffer,
by temporarily restoring the outside context.  This section explains
precisely what context Edebug restores, and how Edebug fails to be
completely transparent.

* Menu:

* Checking Whether to Stop::	When Edebug decides what to do.
* Edebug Display Update::	When Edebug updates the display.
* Edebug Recursive Edit::	When Edebug stops execution.


File: elisp,  Node: Checking Whether to Stop,  Next: Edebug Display Update,  Up: The Outside Context

18.2.14.1 Checking Whether to Stop
..................................

Whenever Edebug is entered, it needs to save and restore certain data
before even deciding whether to make trace information or stop the
program.

   * `max-lisp-eval-depth' and `max-specpdl-size' are both incremented
     once to reduce Edebug's impact on the stack.  You could, however,
     still run out of stack space when using Edebug.

   * The state of keyboard macro execution is saved and restored.  While
     Edebug is active, `executing-kbd-macro' is bound to `nil' unless
     `edebug-continue-kbd-macro' is non-`nil'.


File: elisp,  Node: Edebug Display Update,  Next: Edebug Recursive Edit,  Prev: Checking Whether to Stop,  Up: The Outside Context

18.2.14.2 Edebug Display Update
...............................

When Edebug needs to display something (e.g., in trace mode), it saves
the current window configuration from "outside" Edebug (*note Window
Configurations::).  When you exit Edebug (by continuing the program),
it restores the previous window configuration.

   Emacs redisplays only when it pauses.  Usually, when you continue
execution, the program re-enters Edebug at a breakpoint or after
stepping, without pausing or reading input in between.  In such cases,
Emacs never gets a chance to redisplay the "outside" configuration.
Consequently, what you see is the same window configuration as the last
time Edebug was active, with no interruption.

   Entry to Edebug for displaying something also saves and restores the
following data (though some of them are deliberately not restored if an
error or quit signal occurs).

   * Which buffer is current, and the positions of point and the mark
     in the current buffer, are saved and restored.

   * The outside window configuration is saved and restored if
     `edebug-save-windows' is non-`nil' (*note Edebug Options::).

     The window configuration is not restored on error or quit, but the
     outside selected window _is_ reselected even on error or quit in
     case a `save-excursion' is active.  If the value of
     `edebug-save-windows' is a list, only the listed windows are saved
     and restored.

     The window start and horizontal scrolling of the source code
     buffer are not restored, however, so that the display remains
     coherent within Edebug.

   * The value of point in each displayed buffer is saved and restored
     if `edebug-save-displayed-buffer-points' is non-`nil'.

   * The variables `overlay-arrow-position' and `overlay-arrow-string'
     are saved and restored.  So you can safely invoke Edebug from the
     recursive edit elsewhere in the same buffer.

   * `cursor-in-echo-area' is locally bound to `nil' so that the cursor
     shows up in the window.


File: elisp,  Node: Edebug Recursive Edit,  Prev: Edebug Display Update,  Up: The Outside Context

18.2.14.3 Edebug Recursive Edit
...............................

When Edebug is entered and actually reads commands from the user, it
saves (and later restores) these additional data:

   * The current match data.  *Note Match Data::.

   * The variables `last-command', `this-command', `last-command-char',
     `last-input-char', `last-input-event', `last-command-event',
     `last-event-frame', `last-nonmenu-event', and `track-mouse'.
     Commands used within Edebug do not affect these variables outside
     of Edebug.

     Executing commands within Edebug can change the key sequence that
     would be returned by `this-command-keys', and there is no way to
     reset the key sequence from Lisp.

     Edebug cannot save and restore the value of
     `unread-command-events'.  Entering Edebug while this variable has a
     nontrivial value can interfere with execution of the program you
     are debugging.

   * Complex commands executed while in Edebug are added to the variable
     `command-history'.  In rare cases this can alter execution.

   * Within Edebug, the recursion depth appears one deeper than the
     recursion depth outside Edebug.  This is not true of the
     automatically updated evaluation list window.

   * `standard-output' and `standard-input' are bound to `nil' by the
     `recursive-edit', but Edebug temporarily restores them during
     evaluations.

   * The state of keyboard macro definition is saved and restored.
     While Edebug is active, `defining-kbd-macro' is bound to
     `edebug-continue-kbd-macro'.


File: elisp,  Node: Edebug and Macros,  Next: Edebug Options,  Prev: The Outside Context,  Up: Edebug

18.2.15 Edebug and Macros
-------------------------

To make Edebug properly instrument expressions that call macros, some
extra care is needed.  This subsection explains the details.

* Menu:

* Instrumenting Macro Calls::   The basic problem.
* Specification List::		How to specify complex patterns of evaluation.
* Backtracking::		What Edebug does when matching fails.
* Specification Examples::	To help understand specifications.


File: elisp,  Node: Instrumenting Macro Calls,  Next: Specification List,  Up: Edebug and Macros

18.2.15.1 Instrumenting Macro Calls
...................................

When Edebug instruments an expression that calls a Lisp macro, it needs
additional information about the macro to do the job properly.  This is
because there is no a-priori way to tell which subexpressions of the
macro call are forms to be evaluated.  (Evaluation may occur explicitly
in the macro body, or when the resulting expansion is evaluated, or any
time later.)

   Therefore, you must define an Edebug specification for each macro
that Edebug will encounter, to explain the format of calls to that
macro.  To do this, add a `debug' declaration to the macro definition.
Here is a simple example that shows the specification for the `for'
example macro (*note Argument Evaluation::).

     (defmacro for (var from init to final do &rest body)
       "Execute a simple \"for\" loop.
     For example, (for i from 1 to 10 do (print i))."
       (declare (debug (symbolp "from" form "to" form "do" &rest form)))
       ...)

   The Edebug specification says which parts of a call to the macro are
forms to be evaluated.  For simple macros, the SPECIFICATION often
looks very similar to the formal argument list of the macro definition,
but specifications are much more general than macro arguments.  *Note
Defining Macros::, for more explanation of the `declare' form.

   You can also define an edebug specification for a macro separately
from the macro definition with `def-edebug-spec'.  Adding `debug'
declarations is preferred, and more convenient, for macro definitions
in Lisp, but `def-edebug-spec' makes it possible to define Edebug
specifications for special forms implemented in C.

 -- Macro: def-edebug-spec macro specification
     Specify which expressions of a call to macro MACRO are forms to be
     evaluated.  SPECIFICATION should be the edebug specification.
     Neither argument is evaluated.

     The MACRO argument can actually be any symbol, not just a macro
     name.

   Here is a table of the possibilities for SPECIFICATION and how each
directs processing of arguments.

`t'
     All arguments are instrumented for evaluation.

`0'
     None of the arguments is instrumented.

a symbol
     The symbol must have an Edebug specification which is used instead.
     This indirection is repeated until another kind of specification is
     found.  This allows you to inherit the specification from another
     macro.

a list
     The elements of the list describe the types of the arguments of a
     calling form.  The possible elements of a specification list are
     described in the following sections.

   If a macro has no Edebug specification, neither through a `debug'
declaration nor through a `def-edebug-spec' call, the variable
`edebug-eval-macro-args' comes into play.  If it is `nil', the default,
none of the arguments is instrumented for evaluation.  If it is
non-`nil', all arguments are instrumented.


File: elisp,  Node: Specification List,  Next: Backtracking,  Prev: Instrumenting Macro Calls,  Up: Edebug and Macros

18.2.15.2 Specification List
............................

A "specification list" is required for an Edebug specification if some
arguments of a macro call are evaluated while others are not.  Some
elements in a specification list match one or more arguments, but others
modify the processing of all following elements.  The latter, called
"specification keywords", are symbols beginning with `&' (such as
`&optional').

   A specification list may contain sublists which match arguments that
are themselves lists, or it may contain vectors used for grouping.
Sublists and groups thus subdivide the specification list into a
hierarchy of levels.  Specification keywords apply only to the
remainder of the sublist or group they are contained in.

   When a specification list involves alternatives or repetition,
matching it against an actual macro call may require backtracking.
*Note Backtracking::, for more details.

   Edebug specifications provide the power of regular expression
matching, plus some context-free grammar constructs: the matching of
sublists with balanced parentheses, recursive processing of forms, and
recursion via indirect specifications.

   Here's a table of the possible elements of a specification list, with
their meanings (see *Note Specification Examples::, for the referenced
examples):

`sexp'
     A single unevaluated Lisp object, which is not instrumented.

`form'
     A single evaluated expression, which is instrumented.

`place'
     A place to store a value, as in the Common Lisp `setf' construct.

`body'
     Short for `&rest form'.  See `&rest' below.

`function-form'
     A function form: either a quoted function symbol, a quoted lambda
     expression, or a form (that should evaluate to a function symbol or
     lambda expression).  This is useful when an argument that's a
     lambda expression might be quoted with `quote' rather than
     `function', since it instruments the body of the lambda expression
     either way.

`lambda-expr'
     A lambda expression with no quoting.

`&optional'
     All following elements in the specification list are optional; as
     soon as one does not match, Edebug stops matching at this level.

     To make just a few elements optional followed by non-optional
     elements, use `[&optional SPECS...]'.  To specify that several
     elements must all match or none, use `&optional [SPECS...]'.  See
     the `defun' example.

`&rest'
     All following elements in the specification list are repeated zero
     or more times.  In the last repetition, however, it is not a
     problem if the expression runs out before matching all of the
     elements of the specification list.

     To repeat only a few elements, use `[&rest SPECS...]'.  To specify
     several elements that must all match on every repetition, use
     `&rest [SPECS...]'.

`&or'
     Each of the following elements in the specification list is an
     alternative.  One of the alternatives must match, or the `&or'
     specification fails.

     Each list element following `&or' is a single alternative.  To
     group two or more list elements as a single alternative, enclose
     them in `[...]'.

`&not'
     Each of the following elements is matched as alternatives as if by
     using `&or', but if any of them match, the specification fails.
     If none of them match, nothing is matched, but the `&not'
     specification succeeds.

`&define'
     Indicates that the specification is for a defining form.  The
     defining form itself is not instrumented (that is, Edebug does not
     stop before and after the defining form), but forms inside it
     typically will be instrumented.  The `&define' keyword should be
     the first element in a list specification.

`nil'
     This is successful when there are no more arguments to match at the
     current argument list level; otherwise it fails.  See sublist
     specifications and the backquote example.

`gate'
     No argument is matched but backtracking through the gate is
     disabled while matching the remainder of the specifications at
     this level.  This is primarily used to generate more specific
     syntax error messages.  See *Note Backtracking::, for more
     details.  Also see the `let' example.

`OTHER-SYMBOL'
     Any other symbol in a specification list may be a predicate or an
     indirect specification.

     If the symbol has an Edebug specification, this "indirect
     specification" should be either a list specification that is used
     in place of the symbol, or a function that is called to process the
     arguments.  The specification may be defined with `def-edebug-spec'
     just as for macros. See the `defun' example.

     Otherwise, the symbol should be a predicate.  The predicate is
     called with the argument and the specification fails if the
     predicate returns `nil'.  In either case, that argument is not
     instrumented.

     Some suitable predicates include `symbolp', `integerp', `stringp',
     `vectorp', and `atom'.

`[ELEMENTS...]'
     A vector of elements groups the elements into a single "group
     specification".  Its meaning has nothing to do with vectors.

`"STRING"'
     The argument should be a symbol named STRING.  This specification
     is equivalent to the quoted symbol, `'SYMBOL', where the name of
     SYMBOL is the STRING, but the string form is preferred.

`(vector ELEMENTS...)'
     The argument should be a vector whose elements must match the
     ELEMENTS in the specification.  See the backquote example.

`(ELEMENTS...)'
     Any other list is a "sublist specification" and the argument must
     be a list whose elements match the specification ELEMENTS.

     A sublist specification may be a dotted list and the corresponding
     list argument may then be a dotted list.  Alternatively, the last
     CDR of a dotted list specification may be another sublist
     specification (via a grouping or an indirect specification, e.g.,
     `(spec .  [(more specs...)])') whose elements match the non-dotted
     list arguments.  This is useful in recursive specifications such
     as in the backquote example.  Also see the description of a `nil'
     specification above for terminating such recursion.

     Note that a sublist specification written as `(specs .  nil)' is
     equivalent to `(specs)', and `(specs .  (sublist-elements...))' is
     equivalent to `(specs sublist-elements...)'.

   Here is a list of additional specifications that may appear only
after `&define'.  See the `defun' example.

`name'
     The argument, a symbol, is the name of the defining form.

     A defining form is not required to have a name field; and it may
     have multiple name fields.

`:name'
     This construct does not actually match an argument.  The element
     following `:name' should be a symbol; it is used as an additional
     name component for the definition.  You can use this to add a
     unique, static component to the name of the definition.  It may be
     used more than once.

`arg'
     The argument, a symbol, is the name of an argument of the defining
     form.  However, lambda-list keywords (symbols starting with `&')
     are not allowed.

`lambda-list'
     This matches a lambda list--the argument list of a lambda
     expression.

`def-body'
     The argument is the body of code in a definition.  This is like
     `body', described above, but a definition body must be instrumented
     with a different Edebug call that looks up information associated
     with the definition.  Use `def-body' for the highest level list of
     forms within the definition.

`def-form'
     The argument is a single, highest-level form in a definition.
     This is like `def-body', except use this to match a single form
     rather than a list of forms.  As a special case, `def-form' also
     means that tracing information is not output when the form is
     executed.  See the `interactive' example.


File: elisp,  Node: Backtracking,  Next: Specification Examples,  Prev: Specification List,  Up: Edebug and Macros

18.2.15.3 Backtracking in Specifications
........................................

If a specification fails to match at some point, this does not
necessarily mean a syntax error will be signaled; instead,
"backtracking" will take place until all alternatives have been
exhausted.  Eventually every element of the argument list must be
matched by some element in the specification, and every required element
in the specification must match some argument.

   When a syntax error is detected, it might not be reported until much
later after higher-level alternatives have been exhausted, and with the
point positioned further from the real error.  But if backtracking is
disabled when an error occurs, it can be reported immediately.  Note
that backtracking is also reenabled automatically in several situations;
it is reenabled when a new alternative is established by `&optional',
`&rest', or `&or', or at the start of processing a sublist, group, or
indirect specification.  The effect of enabling or disabling
backtracking is limited to the remainder of the level currently being
processed and lower levels.

   Backtracking is disabled while matching any of the form
specifications (that is, `form', `body', `def-form', and `def-body').
These specifications will match any form so any error must be in the
form itself rather than at a higher level.

   Backtracking is also disabled after successfully matching a quoted
symbol or string specification, since this usually indicates a
recognized construct.  But if you have a set of alternative constructs
that all begin with the same symbol, you can usually work around this
constraint by factoring the symbol out of the alternatives, e.g.,
`["foo" &or [first case] [second case] ...]'.

   Most needs are satisfied by these two ways that backtracking is
automatically disabled, but occasionally it is useful to explicitly
disable backtracking by using the `gate' specification.  This is useful
when you know that no higher alternatives could apply.  See the example
of the `let' specification.


File: elisp,  Node: Specification Examples,  Prev: Backtracking,  Up: Edebug and Macros

18.2.15.4 Specification Examples
................................

It may be easier to understand Edebug specifications by studying the
examples provided here.

   A `let' special form has a sequence of bindings and a body.  Each of
the bindings is either a symbol or a sublist with a symbol and optional
expression.  In the specification below, notice the `gate' inside of
the sublist to prevent backtracking once a sublist is found.

     (def-edebug-spec let
       ((&rest
         &or symbolp (gate symbolp &optional form))
        body))

   Edebug uses the following specifications for `defun' and `defmacro'
and the associated argument list and `interactive' specifications.  It
is necessary to handle interactive forms specially since an expression
argument is actually evaluated outside of the function body.

     (def-edebug-spec defmacro defun) ; Indirect ref to `defun' spec.
     (def-edebug-spec defun
       (&define name lambda-list
                [&optional stringp]   ; Match the doc string, if present.
                [&optional ("interactive" interactive)]
                def-body))

     (def-edebug-spec lambda-list
       (([&rest arg]
         [&optional ["&optional" arg &rest arg]]
         &optional ["&rest" arg]
         )))

     (def-edebug-spec interactive
       (&optional &or stringp def-form))    ; Notice: `def-form'

   The specification for backquote below illustrates how to match
dotted lists and use `nil' to terminate recursion.  It also illustrates
how components of a vector may be matched.  (The actual specification
defined by Edebug does not support dotted lists because doing so causes
very deep recursion that could fail.)

     (def-edebug-spec ` (backquote-form))   ; Alias just for clarity.

     (def-edebug-spec backquote-form
       (&or ([&or "," ",@"] &or ("quote" backquote-form) form)
            (backquote-form . [&or nil backquote-form])
            (vector &rest backquote-form)
            sexp))


File: elisp,  Node: Edebug Options,  Prev: Edebug and Macros,  Up: Edebug

18.2.16 Edebug Options
----------------------

These options affect the behavior of Edebug:

 -- User Option: edebug-setup-hook
     Functions to call before Edebug is used.  Each time it is set to a
     new value, Edebug will call those functions once and then
     `edebug-setup-hook' is reset to `nil'.  You could use this to load
     up Edebug specifications associated with a package you are using
     but only when you also use Edebug.  *Note Instrumenting::.

 -- User Option: edebug-all-defs
     If this is non-`nil', normal evaluation of defining forms such as
     `defun' and `defmacro' instruments them for Edebug.  This applies
     to `eval-defun', `eval-region', `eval-buffer', and
     `eval-current-buffer'.

     Use the command `M-x edebug-all-defs' to toggle the value of this
     option.  *Note Instrumenting::.

 -- User Option: edebug-all-forms
     If this is non-`nil', the commands `eval-defun', `eval-region',
     `eval-buffer', and `eval-current-buffer' instrument all forms,
     even those that don't define anything.  This doesn't apply to
     loading or evaluations in the minibuffer.

     Use the command `M-x edebug-all-forms' to toggle the value of this
     option.  *Note Instrumenting::.

 -- User Option: edebug-save-windows
     If this is non-`nil', Edebug saves and restores the window
     configuration.  That takes some time, so if your program does not
     care what happens to the window configurations, it is better to
     set this variable to `nil'.

     If the value is a list, only the listed windows are saved and
     restored.

     You can use the `W' command in Edebug to change this variable
     interactively.  *Note Edebug Display Update::.

 -- User Option: edebug-save-displayed-buffer-points
     If this is non-`nil', Edebug saves and restores point in all
     displayed buffers.

     Saving and restoring point in other buffers is necessary if you are
     debugging code that changes the point of a buffer which is
     displayed in a non-selected window.  If Edebug or the user then
     selects the window, point in that buffer will move to the window's
     value of point.

     Saving and restoring point in all buffers is expensive, since it
     requires selecting each window twice, so enable this only if you
     need it.  *Note Edebug Display Update::.

 -- User Option: edebug-initial-mode
     If this variable is non-`nil', it specifies the initial execution
     mode for Edebug when it is first activated.  Possible values are
     `step', `next', `go', `Go-nonstop', `trace', `Trace-fast',
     `continue', and `Continue-fast'.

     The default value is `step'.  *Note Edebug Execution Modes::.

 -- User Option: edebug-trace
     If this is non-`nil', trace each function entry and exit.  Tracing
     output is displayed in a buffer named `*edebug-trace*', one
     function entry or exit per line, indented by the recursion level.

     Also see `edebug-tracing', in *Note Trace Buffer::.

 -- User Option: edebug-test-coverage
     If non-`nil', Edebug tests coverage of all expressions debugged.
     *Note Coverage Testing::.

 -- User Option: edebug-continue-kbd-macro
     If non-`nil', continue defining or executing any keyboard macro
     that is executing outside of Edebug.   Use this with caution since
     it is not debugged.  *Note Edebug Execution Modes::.

 -- User Option: edebug-on-error
     Edebug binds `debug-on-error' to this value, if `debug-on-error'
     was previously `nil'.  *Note Trapping Errors::.

 -- User Option: edebug-on-quit
     Edebug binds `debug-on-quit' to this value, if `debug-on-quit' was
     previously `nil'.  *Note Trapping Errors::.

   If you change the values of `edebug-on-error' or `edebug-on-quit'
while Edebug is active, their values won't be used until the _next_
time Edebug is invoked via a new command.

 -- User Option: edebug-global-break-condition
     If non-`nil', an expression to test for at every stop point.  If
     the result is non-`nil', then break.  Errors are ignored.  *Note
     Global Break Condition::.


File: elisp,  Node: Syntax Errors,  Next: Test Coverage,  Prev: Edebug,  Up: Debugging

18.3 Debugging Invalid Lisp Syntax
==================================

The Lisp reader reports invalid syntax, but cannot say where the real
problem is.  For example, the error "End of file during parsing" in
evaluating an expression indicates an excess of open parentheses (or
square brackets).  The reader detects this imbalance at the end of the
file, but it cannot figure out where the close parenthesis should have
been.  Likewise, "Invalid read syntax: ")"" indicates an excess close
parenthesis or missing open parenthesis, but does not say where the
missing parenthesis belongs.  How, then, to find what to change?

   If the problem is not simply an imbalance of parentheses, a useful
technique is to try `C-M-e' at the beginning of each defun, and see if
it goes to the place where that defun appears to end.  If it does not,
there is a problem in that defun.

   However, unmatched parentheses are the most common syntax errors in
Lisp, and we can give further advice for those cases.  (In addition,
just moving point through the code with Show Paren mode enabled might
find the mismatch.)

* Menu:

* Excess Open::     How to find a spurious open paren or missing close.
* Excess Close::    How to find a spurious close paren or missing open.


File: elisp,  Node: Excess Open,  Next: Excess Close,  Up: Syntax Errors

18.3.1 Excess Open Parentheses
------------------------------

The first step is to find the defun that is unbalanced.  If there is an
excess open parenthesis, the way to do this is to go to the end of the
file and type `C-u C-M-u'.  This will move you to the beginning of the
first defun that is unbalanced.

   The next step is to determine precisely what is wrong.  There is no
way to be sure of this except by studying the program, but often the
existing indentation is a clue to where the parentheses should have
been.  The easiest way to use this clue is to reindent with `C-M-q' and
see what moves.  *But don't do this yet!*  Keep reading, first.

   Before you do this, make sure the defun has enough close parentheses.
Otherwise, `C-M-q' will get an error, or will reindent all the rest of
the file until the end.  So move to the end of the defun and insert a
close parenthesis there.  Don't use `C-M-e' to move there, since that
too will fail to work until the defun is balanced.

   Now you can go to the beginning of the defun and type `C-M-q'.
Usually all the lines from a certain point to the end of the function
will shift to the right.  There is probably a missing close parenthesis,
or a superfluous open parenthesis, near that point.  (However, don't
assume this is true; study the code to make sure.)  Once you have found
the discrepancy, undo the `C-M-q' with `C-_', since the old indentation
is probably appropriate to the intended parentheses.

   After you think you have fixed the problem, use `C-M-q' again.  If
the old indentation actually fit the intended nesting of parentheses,
and you have put back those parentheses, `C-M-q' should not change
anything.


File: elisp,  Node: Excess Close,  Prev: Excess Open,  Up: Syntax Errors

18.3.2 Excess Close Parentheses
-------------------------------

To deal with an excess close parenthesis, first go to the beginning of
the file, then type `C-u -1 C-M-u' to find the end of the first
unbalanced defun.

   Then find the actual matching close parenthesis by typing `C-M-f' at
the beginning of that defun.  This will leave you somewhere short of
the place where the defun ought to end.  It is possible that you will
find a spurious close parenthesis in that vicinity.

   If you don't see a problem at that point, the next thing to do is to
type `C-M-q' at the beginning of the defun.  A range of lines will
probably shift left; if so, the missing open parenthesis or spurious
close parenthesis is probably near the first of those lines.  (However,
don't assume this is true; study the code to make sure.)  Once you have
found the discrepancy, undo the `C-M-q' with `C-_', since the old
indentation is probably appropriate to the intended parentheses.

   After you think you have fixed the problem, use `C-M-q' again.  If
the old indentation actually fits the intended nesting of parentheses,
and you have put back those parentheses, `C-M-q' should not change
anything.


File: elisp,  Node: Test Coverage,  Next: Compilation Errors,  Prev: Syntax Errors,  Up: Debugging

18.4 Test Coverage
==================

You can do coverage testing for a file of Lisp code by loading the
`testcover' library and using the command `M-x testcover-start <RET>
FILE <RET>' to instrument the code.  Then test your code by calling it
one or more times.  Then use the command `M-x testcover-mark-all' to
display colored highlights on the code to show where coverage is
insufficient.  The command `M-x testcover-next-mark' will move point
forward to the next highlighted spot.

   Normally, a red highlight indicates the form was never completely
evaluated; a brown highlight means it always evaluated to the same
value (meaning there has been little testing of what is done with the
result).  However, the red highlight is skipped for forms that can't
possibly complete their evaluation, such as `error'.  The brown
highlight is skipped for forms that are expected to always evaluate to
the same value, such as `(setq x 14)'.

   For difficult cases, you can add do-nothing macros to your code to
give advice to the test coverage tool.

 -- Macro: 1value form
     Evaluate FORM and return its value, but inform coverage testing
     that FORM's value should always be the same.

 -- Macro: noreturn form
     Evaluate FORM, informing coverage testing that FORM should never
     return.  If it ever does return, you get a run-time error.

   Edebug also has a coverage testing feature (*note Coverage
Testing::).  These features partly duplicate each other, and it would
be cleaner to combine them.


File: elisp,  Node: Compilation Errors,  Prev: Test Coverage,  Up: Debugging

18.5 Debugging Problems in Compilation
======================================

When an error happens during byte compilation, it is normally due to
invalid syntax in the program you are compiling.  The compiler prints a
suitable error message in the `*Compile-Log*' buffer, and then stops.
The message may state a function name in which the error was found, or
it may not.  Either way, here is how to find out where in the file the
error occurred.

   What you should do is switch to the buffer ` *Compiler Input*'.
(Note that the buffer name starts with a space, so it does not show up
in `M-x list-buffers'.)  This buffer contains the program being
compiled, and point shows how far the byte compiler was able to read.

   If the error was due to invalid Lisp syntax, point shows exactly
where the invalid syntax was _detected_.  The cause of the error is not
necessarily near by!  Use the techniques in the previous section to find
the error.

   If the error was detected while compiling a form that had been read
successfully, then point is located at the end of the form.  In this
case, this technique can't localize the error precisely, but can still
show you which function to check.


File: elisp,  Node: Read and Print,  Next: Minibuffers,  Prev: Debugging,  Up: Top

19 Reading and Printing Lisp Objects
************************************

"Printing" and "reading" are the operations of converting Lisp objects
to textual form and vice versa.  They use the printed representations
and read syntax described in *Note Lisp Data Types::.

   This chapter describes the Lisp functions for reading and printing.
It also describes "streams", which specify where to get the text (if
reading) or where to put it (if printing).

* Menu:

* Streams Intro::     Overview of streams, reading and printing.
* Input Streams::     Various data types that can be used as input streams.
* Input Functions::   Functions to read Lisp objects from text.
* Output Streams::    Various data types that can be used as output streams.
* Output Functions::  Functions to print Lisp objects as text.
* Output Variables::  Variables that control what the printing functions do.


File: elisp,  Node: Streams Intro,  Next: Input Streams,  Up: Read and Print

19.1 Introduction to Reading and Printing
=========================================

"Reading" a Lisp object means parsing a Lisp expression in textual form
and producing a corresponding Lisp object.  This is how Lisp programs
get into Lisp from files of Lisp code.  We call the text the "read
syntax" of the object.  For example, the text `(a . 5)' is the read
syntax for a cons cell whose CAR is `a' and whose CDR is the number 5.

   "Printing" a Lisp object means producing text that represents that
object--converting the object to its "printed representation" (*note
Printed Representation::).  Printing the cons cell described above
produces the text `(a . 5)'.

   Reading and printing are more or less inverse operations: printing
the object that results from reading a given piece of text often
produces the same text, and reading the text that results from printing
an object usually produces a similar-looking object.  For example,
printing the symbol `foo' produces the text `foo', and reading that text
returns the symbol `foo'.  Printing a list whose elements are `a' and
`b' produces the text `(a b)', and reading that text produces a list
(but not the same list) with elements `a' and `b'.

   However, these two operations are not precisely inverse to each
other.  There are three kinds of exceptions:

   * Printing can produce text that cannot be read.  For example,
     buffers, windows, frames, subprocesses and markers print as text
     that starts with `#'; if you try to read this text, you get an
     error.  There is no way to read those data types.

   * One object can have multiple textual representations.  For example,
     `1' and `01' represent the same integer, and `(a b)' and `(a .
     (b))' represent the same list.  Reading will accept any of the
     alternatives, but printing must choose one of them.

   * Comments can appear at certain points in the middle of an object's
     read sequence without affecting the result of reading it.


File: elisp,  Node: Input Streams,  Next: Input Functions,  Prev: Streams Intro,  Up: Read and Print

19.2 Input Streams
==================

Most of the Lisp functions for reading text take an "input stream" as
an argument.  The input stream specifies where or how to get the
characters of the text to be read.  Here are the possible types of input
stream:

BUFFER
     The input characters are read from BUFFER, starting with the
     character directly after point.  Point advances as characters are
     read.

MARKER
     The input characters are read from the buffer that MARKER is in,
     starting with the character directly after the marker.  The marker
     position advances as characters are read.  The value of point in
     the buffer has no effect when the stream is a marker.

STRING
     The input characters are taken from STRING, starting at the first
     character in the string and using as many characters as required.

FUNCTION
     The input characters are generated by FUNCTION, which must support
     two kinds of calls:

        * When it is called with no arguments, it should return the
          next character.

        * When it is called with one argument (always a character),
          FUNCTION should save the argument and arrange to return it on
          the next call.  This is called "unreading" the character; it
          happens when the Lisp reader reads one character too many and
          wants to "put it back where it came from."  In this case, it
          makes no difference what value FUNCTION returns.

`t'
     `t' used as a stream means that the input is read from the
     minibuffer.  In fact, the minibuffer is invoked once and the text
     given by the user is made into a string that is then used as the
     input stream.  If Emacs is running in batch mode, standard input
     is used instead of the minibuffer.  For example,
          (message "%s" (read t))
     will read a Lisp expression from standard input and print the
     result to standard output.

`nil'
     `nil' supplied as an input stream means to use the value of
     `standard-input' instead; that value is the "default input
     stream", and must be a non-`nil' input stream.

SYMBOL
     A symbol as input stream is equivalent to the symbol's function
     definition (if any).

   Here is an example of reading from a stream that is a buffer, showing
where point is located before and after:

     ---------- Buffer: foo ----------
     This-!- is the contents of foo.
     ---------- Buffer: foo ----------

     (read (get-buffer "foo"))
          => is
     (read (get-buffer "foo"))
          => the

     ---------- Buffer: foo ----------
     This is the-!- contents of foo.
     ---------- Buffer: foo ----------

Note that the first read skips a space.  Reading skips any amount of
whitespace preceding the significant text.

   Here is an example of reading from a stream that is a marker,
initially positioned at the beginning of the buffer shown.  The value
read is the symbol `This'.


     ---------- Buffer: foo ----------
     This is the contents of foo.
     ---------- Buffer: foo ----------

     (setq m (set-marker (make-marker) 1 (get-buffer "foo")))
          => #<marker at 1 in foo>
     (read m)
          => This
     m
          => #<marker at 5 in foo>   ;; Before the first space.

   Here we read from the contents of a string:

     (read "(When in) the course")
          => (When in)

   The following example reads from the minibuffer.  The prompt is:
`Lisp expression: '.  (That is always the prompt used when you read
from the stream `t'.)  The user's input is shown following the prompt.

     (read t)
          => 23
     ---------- Buffer: Minibuffer ----------
     Lisp expression: 23 <RET>
     ---------- Buffer: Minibuffer ----------

   Finally, here is an example of a stream that is a function, named
`useless-stream'.  Before we use the stream, we initialize the variable
`useless-list' to a list of characters.  Then each call to the function
`useless-stream' obtains the next character in the list or unreads a
character by adding it to the front of the list.

     (setq useless-list (append "XY()" nil))
          => (88 89 40 41)

     (defun useless-stream (&optional unread)
       (if unread
           (setq useless-list (cons unread useless-list))
         (prog1 (car useless-list)
                (setq useless-list (cdr useless-list)))))
          => useless-stream

Now we read using the stream thus constructed:

     (read 'useless-stream)
          => XY

     useless-list
          => (40 41)

Note that the open and close parentheses remain in the list.  The Lisp
reader encountered the open parenthesis, decided that it ended the
input, and unread it.  Another attempt to read from the stream at this
point would read `()' and return `nil'.

 -- Function: get-file-char
     This function is used internally as an input stream to read from
     the input file opened by the function `load'.  Don't use this
     function yourself.


File: elisp,  Node: Input Functions,  Next: Output Streams,  Prev: Input Streams,  Up: Read and Print

19.3 Input Functions
====================

This section describes the Lisp functions and variables that pertain to
reading.

   In the functions below, STREAM stands for an input stream (see the
previous section).  If STREAM is `nil' or omitted, it defaults to the
value of `standard-input'.

   An `end-of-file' error is signaled if reading encounters an
unterminated list, vector, or string.

 -- Function: read &optional stream
     This function reads one textual Lisp expression from STREAM,
     returning it as a Lisp object.  This is the basic Lisp input
     function.

 -- Function: read-from-string string &optional start end
     This function reads the first textual Lisp expression from the
     text in STRING.  It returns a cons cell whose CAR is that
     expression, and whose CDR is an integer giving the position of the
     next remaining character in the string (i.e., the first one not
     read).

     If START is supplied, then reading begins at index START in the
     string (where the first character is at index 0).  If you specify
     END, then reading is forced to stop just before that index, as if
     the rest of the string were not there.

     For example:

          (read-from-string "(setq x 55) (setq y 5)")
               => ((setq x 55) . 11)
          (read-from-string "\"A short string\"")
               => ("A short string" . 16)

          ;; Read starting at the first character.
          (read-from-string "(list 112)" 0)
               => ((list 112) . 10)
          ;; Read starting at the second character.
          (read-from-string "(list 112)" 1)
               => (list . 5)
          ;; Read starting at the seventh character,
          ;;   and stopping at the ninth.
          (read-from-string "(list 112)" 6 8)
               => (11 . 8)

 -- Variable: standard-input
     This variable holds the default input stream--the stream that
     `read' uses when the STREAM argument is `nil'.  The default is
     `t', meaning use the minibuffer.


File: elisp,  Node: Output Streams,  Next: Output Functions,  Prev: Input Functions,  Up: Read and Print

19.4 Output Streams
===================

An output stream specifies what to do with the characters produced by
printing.  Most print functions accept an output stream as an optional
argument.  Here are the possible types of output stream:

BUFFER
     The output characters are inserted into BUFFER at point.  Point
     advances as characters are inserted.

MARKER
     The output characters are inserted into the buffer that MARKER
     points into, at the marker position.  The marker position advances
     as characters are inserted.  The value of point in the buffer has
     no effect on printing when the stream is a marker, and this kind
     of printing does not move point (except that if the marker points
     at or before the position of point, point advances with the
     surrounding text, as usual).

FUNCTION
     The output characters are passed to FUNCTION, which is responsible
     for storing them away.  It is called with a single character as
     argument, as many times as there are characters to be output, and
     is responsible for storing the characters wherever you want to put
     them.

`t'
     The output characters are displayed in the echo area.

`nil'
     `nil' specified as an output stream means to use the value of
     `standard-output' instead; that value is the "default output
     stream", and must not be `nil'.

SYMBOL
     A symbol as output stream is equivalent to the symbol's function
     definition (if any).

   Many of the valid output streams are also valid as input streams.
The difference between input and output streams is therefore more a
matter of how you use a Lisp object, than of different types of object.

   Here is an example of a buffer used as an output stream.  Point is
initially located as shown immediately before the `h' in `the'.  At the
end, point is located directly before that same `h'.

     ---------- Buffer: foo ----------
     This is t-!-he contents of foo.
     ---------- Buffer: foo ----------

     (print "This is the output" (get-buffer "foo"))
          => "This is the output"

     ---------- Buffer: foo ----------
     This is t
     "This is the output"
     -!-he contents of foo.
     ---------- Buffer: foo ----------

   Now we show a use of a marker as an output stream.  Initially, the
marker is in buffer `foo', between the `t' and the `h' in the word
`the'.  At the end, the marker has advanced over the inserted text so
that it remains positioned before the same `h'.  Note that the location
of point, shown in the usual fashion, has no effect.

     ---------- Buffer: foo ----------
     This is the -!-output
     ---------- Buffer: foo ----------

     (setq m (copy-marker 10))
          => #<marker at 10 in foo>

     (print "More output for foo." m)
          => "More output for foo."

     ---------- Buffer: foo ----------
     This is t
     "More output for foo."
     he -!-output
     ---------- Buffer: foo ----------

     m
          => #<marker at 34 in foo>

   The following example shows output to the echo area:

     (print "Echo Area output" t)
          => "Echo Area output"
     ---------- Echo Area ----------
     "Echo Area output"
     ---------- Echo Area ----------

   Finally, we show the use of a function as an output stream.  The
function `eat-output' takes each character that it is given and conses
it onto the front of the list `last-output' (*note Building Lists::).
At the end, the list contains all the characters output, but in reverse
order.

     (setq last-output nil)
          => nil

     (defun eat-output (c)
       (setq last-output (cons c last-output)))
          => eat-output

     (print "This is the output" 'eat-output)
          => "This is the output"

     last-output
          => (10 34 116 117 112 116 117 111 32 101 104
         116 32 115 105 32 115 105 104 84 34 10)

Now we can put the output in the proper order by reversing the list:

     (concat (nreverse last-output))
          => "
     \"This is the output\"
     "

Calling `concat' converts the list to a string so you can see its
contents more clearly.


File: elisp,  Node: Output Functions,  Next: Output Variables,  Prev: Output Streams,  Up: Read and Print

19.5 Output Functions
=====================

This section describes the Lisp functions for printing Lisp
objects--converting objects into their printed representation.

   Some of the Emacs printing functions add quoting characters to the
output when necessary so that it can be read properly.  The quoting
characters used are `"' and `\'; they distinguish strings from symbols,
and prevent punctuation characters in strings and symbols from being
taken as delimiters when reading.  *Note Printed Representation::, for
full details.  You specify quoting or no quoting by the choice of
printing function.

   If the text is to be read back into Lisp, then you should print with
quoting characters to avoid ambiguity.  Likewise, if the purpose is to
describe a Lisp object clearly for a Lisp programmer.  However, if the
purpose of the output is to look nice for humans, then it is usually
better to print without quoting.

   Lisp objects can refer to themselves.  Printing a self-referential
object in the normal way would require an infinite amount of text, and
the attempt could cause infinite recursion.  Emacs detects such
recursion and prints `#LEVEL' instead of recursively printing an object
already being printed.  For example, here `#0' indicates a recursive
reference to the object at level 0 of the current print operation:

     (setq foo (list nil))
          => (nil)
     (setcar foo foo)
          => (#0)

   In the functions below, STREAM stands for an output stream.  (See
the previous section for a description of output streams.)  If STREAM
is `nil' or omitted, it defaults to the value of `standard-output'.

 -- Function: print object &optional stream
     The `print' function is a convenient way of printing.  It outputs
     the printed representation of OBJECT to STREAM, printing in
     addition one newline before OBJECT and another after it.  Quoting
     characters are used.  `print' returns OBJECT.  For example:

          (progn (print 'The\ cat\ in)
                 (print "the hat")
                 (print " came back"))
               -|
               -| The\ cat\ in
               -|
               -| "the hat"
               -|
               -| " came back"
               => " came back"

 -- Function: prin1 object &optional stream
     This function outputs the printed representation of OBJECT to
     STREAM.  It does not print newlines to separate output as `print'
     does, but it does use quoting characters just like `print'.  It
     returns OBJECT.

          (progn (prin1 'The\ cat\ in)
                 (prin1 "the hat")
                 (prin1 " came back"))
               -| The\ cat\ in"the hat"" came back"
               => " came back"

 -- Function: princ object &optional stream
     This function outputs the printed representation of OBJECT to
     STREAM.  It returns OBJECT.

     This function is intended to produce output that is readable by
     people, not by `read', so it doesn't insert quoting characters and
     doesn't put double-quotes around the contents of strings.  It does
     not add any spacing between calls.

          (progn
            (princ 'The\ cat)
            (princ " in the \"hat\""))
               -| The cat in the "hat"
               => " in the \"hat\""

 -- Function: terpri &optional stream
     This function outputs a newline to STREAM.  The name stands for
     "terminate print."

 -- Function: write-char character &optional stream
     This function outputs CHARACTER to STREAM.  It returns CHARACTER.

 -- Function: prin1-to-string object &optional noescape
     This function returns a string containing the text that `prin1'
     would have printed for the same argument.

          (prin1-to-string 'foo)
               => "foo"
          (prin1-to-string (mark-marker))
               => "#<marker at 2773 in strings.texi>"

     If NOESCAPE is non-`nil', that inhibits use of quoting characters
     in the output.  (This argument is supported in Emacs versions 19
     and later.)

          (prin1-to-string "foo")
               => "\"foo\""
          (prin1-to-string "foo" t)
               => "foo"

     See `format', in *Note Formatting Strings::, for other ways to
     obtain the printed representation of a Lisp object as a string.

 -- Macro: with-output-to-string body...
     This macro executes the BODY forms with `standard-output' set up
     to feed output into a string.  Then it returns that string.

     For example, if the current buffer name is `foo',

          (with-output-to-string
            (princ "The buffer is ")
            (princ (buffer-name)))

     returns `"The buffer is foo"'.


File: elisp,  Node: Output Variables,  Prev: Output Functions,  Up: Read and Print

19.6 Variables Affecting Output
===============================

 -- Variable: standard-output
     The value of this variable is the default output stream--the stream
     that print functions use when the STREAM argument is `nil'.  The
     default is `t', meaning display in the echo area.

 -- Variable: print-quoted
     If this is non-`nil', that means to print quoted forms using
     abbreviated reader syntax.  `(quote foo)' prints as `'foo',
     `(function foo)' as `#'foo', and backquoted forms print using
     modern backquote syntax.

 -- Variable: print-escape-newlines
     If this variable is non-`nil', then newline characters in strings
     are printed as `\n' and formfeeds are printed as `\f'.  Normally
     these characters are printed as actual newlines and formfeeds.

     This variable affects the print functions `prin1' and `print' that
     print with quoting.  It does not affect `princ'.  Here is an
     example using `prin1':

          (prin1 "a\nb")
               -| "a
               -| b"
               => "a
          b"

          (let ((print-escape-newlines t))
            (prin1 "a\nb"))
               -| "a\nb"
               => "a
          b"

     In the second expression, the local binding of
     `print-escape-newlines' is in effect during the call to `prin1',
     but not during the printing of the result.

 -- Variable: print-escape-nonascii
     If this variable is non-`nil', then unibyte non-ASCII characters
     in strings are unconditionally printed as backslash sequences by
     the print functions `prin1' and `print' that print with quoting.

     Those functions also use backslash sequences for unibyte non-ASCII
     characters, regardless of the value of this variable, when the
     output stream is a multibyte buffer or a marker pointing into one.

 -- Variable: print-escape-multibyte
     If this variable is non-`nil', then multibyte non-ASCII characters
     in strings are unconditionally printed as backslash sequences by
     the print functions `prin1' and `print' that print with quoting.

     Those functions also use backslash sequences for multibyte
     non-ASCII characters, regardless of the value of this variable,
     when the output stream is a unibyte buffer or a marker pointing
     into one.

 -- Variable: print-length
     The value of this variable is the maximum number of elements to
     print in any list, vector or bool-vector.  If an object being
     printed has more than this many elements, it is abbreviated with
     an ellipsis.

     If the value is `nil' (the default), then there is no limit.

          (setq print-length 2)
               => 2
          (print '(1 2 3 4 5))
               -| (1 2 ...)
               => (1 2 ...)

 -- Variable: print-level
     The value of this variable is the maximum depth of nesting of
     parentheses and brackets when printed.  Any list or vector at a
     depth exceeding this limit is abbreviated with an ellipsis.  A
     value of `nil' (which is the default) means no limit.

 -- User Option: eval-expression-print-length
 -- User Option: eval-expression-print-level
     These are the values for `print-length' and `print-level' used by
     `eval-expression', and thus, indirectly, by many interactive
     evaluation commands (*note Evaluating Emacs-Lisp Expressions:
     (emacs)Lisp Eval.).

   These variables are used for detecting and reporting circular and
shared structure:

 -- Variable: print-circle
     If non-`nil', this variable enables detection of circular and
     shared structure in printing.

 -- Variable: print-gensym
     If non-`nil', this variable enables detection of uninterned symbols
     (*note Creating Symbols::) in printing.  When this is enabled,
     uninterned symbols print with the prefix `#:', which tells the Lisp
     reader to produce an uninterned symbol.

 -- Variable: print-continuous-numbering
     If non-`nil', that means number continuously across print calls.
     This affects the numbers printed for `#N=' labels and `#M#'
     references.

     Don't set this variable with `setq'; you should only bind it
     temporarily to `t' with `let'.  When you do that, you should also
     bind `print-number-table' to `nil'.

 -- Variable: print-number-table
     This variable holds a vector used internally by printing to
     implement the `print-circle' feature.  You should not use it except
     to bind it to `nil' when you bind `print-continuous-numbering'.

 -- Variable: float-output-format
     This variable specifies how to print floating point numbers.  Its
     default value is `nil', meaning use the shortest output that
     represents the number without losing information.

     To control output format more precisely, you can put a string in
     this variable.  The string should hold a `%'-specification to be
     used in the C function `sprintf'.  For further restrictions on what
     you can use, see the variable's documentation string.


File: elisp,  Node: Minibuffers,  Next: Command Loop,  Prev: Read and Print,  Up: Top

20 Minibuffers
**************

A "minibuffer" is a special buffer that Emacs commands use to read
arguments more complicated than the single numeric prefix argument.
These arguments include file names, buffer names, and command names (as
in `M-x').  The minibuffer is displayed on the bottom line of the
frame, in the same place as the echo area (*note The Echo Area::), but
only while it is in use for reading an argument.

* Menu:

* Intro to Minibuffers::      Basic information about minibuffers.
* Text from Minibuffer::      How to read a straight text string.
* Object from Minibuffer::    How to read a Lisp object or expression.
* Minibuffer History::	      Recording previous minibuffer inputs
				so the user can reuse them.
* Initial Input::             Specifying initial contents for the minibuffer.
* Completion::                How to invoke and customize completion.
* Yes-or-No Queries::         Asking a question with a simple answer.
* Multiple Queries::	      Asking a series of similar questions.
* Reading a Password::	      Reading a password from the terminal.
* Minibuffer Commands::       Commands used as key bindings in minibuffers.
* Minibuffer Contents::       How such commands access the minibuffer text.
* Minibuffer Windows::        Operating on the special minibuffer windows.
* Recursive Mini::            Whether recursive entry to minibuffer is allowed.
* Minibuffer Misc::           Various customization hooks and variables.


File: elisp,  Node: Intro to Minibuffers,  Next: Text from Minibuffer,  Up: Minibuffers

20.1 Introduction to Minibuffers
================================

In most ways, a minibuffer is a normal Emacs buffer.  Most operations
_within_ a buffer, such as editing commands, work normally in a
minibuffer.  However, many operations for managing buffers do not apply
to minibuffers.  The name of a minibuffer always has the form
` *Minibuf-NUMBER*', and it cannot be changed.  Minibuffers are
displayed only in special windows used only for minibuffers; these
windows always appear at the bottom of a frame.  (Sometimes frames have
no minibuffer window, and sometimes a special kind of frame contains
nothing but a minibuffer window; see *Note Minibuffers and Frames::.)

   The text in the minibuffer always starts with the "prompt string",
the text that was specified by the program that is using the minibuffer
to tell the user what sort of input to type.  This text is marked
read-only so you won't accidentally delete or change it.  It is also
marked as a field (*note Fields::), so that certain motion functions,
including `beginning-of-line', `forward-word', `forward-sentence', and
`forward-paragraph', stop at the boundary between the prompt and the
actual text.  (In older Emacs versions, the prompt was displayed using
a special mechanism and was not part of the buffer contents.)

   The minibuffer's window is normally a single line; it grows
automatically if necessary if the contents require more space.  You can
explicitly resize it temporarily with the window sizing commands; it
reverts to its normal size when the minibuffer is exited.  You can
resize it permanently by using the window sizing commands in the frame's
other window, when the minibuffer is not active.  If the frame contains
just a minibuffer, you can change the minibuffer's size by changing the
frame's size.

   Use of the minibuffer reads input events, and that alters the values
of variables such as `this-command' and `last-command' (*note Command
Loop Info::).  Your program should bind them around the code that uses
the minibuffer, if you do not want that to change them.

   If a command uses a minibuffer while there is an active minibuffer,
this is called a "recursive minibuffer".  The first minibuffer is named
` *Minibuf-0*'.  Recursive minibuffers are named by incrementing the
number at the end of the name.  (The names begin with a space so that
they won't show up in normal buffer lists.)  Of several recursive
minibuffers, the innermost (or most recently entered) is the active
minibuffer.  We usually call this "the" minibuffer.  You can permit or
forbid recursive minibuffers by setting the variable
`enable-recursive-minibuffers' or by putting properties of that name on
command symbols (*note Recursive Mini::).

   Like other buffers, a minibuffer uses a local keymap (*note
Keymaps::) to specify special key bindings.  The function that invokes
the minibuffer also sets up its local map according to the job to be
done.  *Note Text from Minibuffer::, for the non-completion minibuffer
local maps.  *Note Completion Commands::, for the minibuffer local maps
for completion.

   When Emacs is running in batch mode, any request to read from the
minibuffer actually reads a line from the standard input descriptor that
was supplied when Emacs was started.


File: elisp,  Node: Text from Minibuffer,  Next: Object from Minibuffer,  Prev: Intro to Minibuffers,  Up: Minibuffers

20.2 Reading Text Strings with the Minibuffer
=============================================

Most often, the minibuffer is used to read text as a string.  It can
also be used to read a Lisp object in textual form.  The most basic
primitive for minibuffer input is `read-from-minibuffer'; it can do
either one.  There are also specialized commands for reading commands,
variables, file names, etc. (*note Completion::).

   In most cases, you should not call minibuffer input functions in the
middle of a Lisp function.  Instead, do all minibuffer input as part of
reading the arguments for a command, in the `interactive'
specification.  *Note Defining Commands::.

 -- Function: read-from-minibuffer prompt-string &optional
          initial-contents keymap read hist default inherit-input-method
     This function is the most general way to get input through the
     minibuffer.  By default, it accepts arbitrary text and returns it
     as a string; however, if READ is non-`nil', then it uses `read' to
     convert the text into a Lisp object (*note Input Functions::).

     The first thing this function does is to activate a minibuffer and
     display it with PROMPT-STRING as the prompt.  This value must be a
     string.  Then the user can edit text in the minibuffer.

     When the user types a command to exit the minibuffer,
     `read-from-minibuffer' constructs the return value from the text in
     the minibuffer.  Normally it returns a string containing that text.
     However, if READ is non-`nil', `read-from-minibuffer' reads the
     text and returns the resulting Lisp object, unevaluated.  (*Note
     Input Functions::, for information about reading.)

     The argument DEFAULT specifies a default value to make available
     through the history commands.  It should be a string, or `nil'.
     If non-`nil', the user can access it using `next-history-element',
     usually bound in the minibuffer to `M-n'.  If READ is non-`nil',
     then DEFAULT is also used as the input to `read', if the user
     enters empty input.  (If READ is non-`nil' and DEFAULT is `nil',
     empty input results in an `end-of-file' error.)  However, in the
     usual case (where READ is `nil'), `read-from-minibuffer' ignores
     DEFAULT when the user enters empty input and returns an empty
     string, `""'.  In this respect, it is different from all the other
     minibuffer input functions in this chapter.

     If KEYMAP is non-`nil', that keymap is the local keymap to use in
     the minibuffer.  If KEYMAP is omitted or `nil', the value of
     `minibuffer-local-map' is used as the keymap.  Specifying a keymap
     is the most important way to customize the minibuffer for various
     applications such as completion.

     The argument HIST specifies which history list variable to use for
     saving the input and for history commands used in the minibuffer.
     It defaults to `minibuffer-history'.  *Note Minibuffer History::.

     If the variable `minibuffer-allow-text-properties' is non-`nil',
     then the string which is returned includes whatever text
     properties were present in the minibuffer.  Otherwise all the text
     properties are stripped when the value is returned.

     If the argument INHERIT-INPUT-METHOD is non-`nil', then the
     minibuffer inherits the current input method (*note Input
     Methods::) and the setting of `enable-multibyte-characters' (*note
     Text Representations::) from whichever buffer was current before
     entering the minibuffer.

     Use of INITIAL-CONTENTS is mostly deprecated; we recommend using a
     non-`nil' value only in conjunction with specifying a cons cell
     for HIST.  *Note Initial Input::.

 -- Function: read-string prompt &optional initial history default
          inherit-input-method
     This function reads a string from the minibuffer and returns it.
     The arguments PROMPT, INITIAL, HISTORY and INHERIT-INPUT-METHOD
     are used as in `read-from-minibuffer'.  The keymap used is
     `minibuffer-local-map'.

     The optional argument DEFAULT is used as in
     `read-from-minibuffer', except that, if non-`nil', it also
     specifies a default value to return if the user enters null input.
     As in `read-from-minibuffer' it should be a string, or `nil',
     which is equivalent to an empty string.

     This function is a simplified interface to the
     `read-from-minibuffer' function:

          (read-string PROMPT INITIAL HISTORY DEFAULT INHERIT)
          ==
          (let ((value
                 (read-from-minibuffer PROMPT INITIAL nil nil
                                       HISTORY DEFAULT INHERIT)))
            (if (and (equal value "") DEFAULT)
                DEFAULT
              value))

 -- Variable: minibuffer-allow-text-properties
     If this variable is `nil', then `read-from-minibuffer' strips all
     text properties from the minibuffer input before returning it.
     This variable also affects `read-string'.  However,
     `read-no-blanks-input' (see below), as well as `read-minibuffer'
     and related functions (*note Reading Lisp Objects With the
     Minibuffer: Object from Minibuffer.), and all functions that do
     minibuffer input with completion, discard text properties
     unconditionally, regardless of the value of this variable.

 -- Variable: minibuffer-local-map
     This

     is the default local keymap for reading from the minibuffer.  By
     default, it makes the following bindings:

    `C-j'
          `exit-minibuffer'

    <RET>
          `exit-minibuffer'

    `C-g'
          `abort-recursive-edit'

    `M-n'
    <DOWN>
          `next-history-element'

    `M-p'
    <UP>
          `previous-history-element'

    `M-s'
          `next-matching-history-element'

    `M-r'
          `previous-matching-history-element'

 -- Function: read-no-blanks-input prompt &optional initial
          inherit-input-method
     This function reads a string from the minibuffer, but does not
     allow whitespace characters as part of the input: instead, those
     characters terminate the input.  The arguments PROMPT, INITIAL, and
     INHERIT-INPUT-METHOD are used as in `read-from-minibuffer'.

     This is a simplified interface to the `read-from-minibuffer'
     function, and passes the value of the `minibuffer-local-ns-map'
     keymap as the KEYMAP argument for that function.  Since the keymap
     `minibuffer-local-ns-map' does not rebind `C-q', it _is_ possible
     to put a space into the string, by quoting it.

     This function discards text properties, regardless of the value of
     `minibuffer-allow-text-properties'.

          (read-no-blanks-input PROMPT INITIAL)
          ==
          (let (minibuffer-allow-text-properties)
            (read-from-minibuffer PROMPT INITIAL minibuffer-local-ns-map))

 -- Variable: minibuffer-local-ns-map
     This built-in variable is the keymap used as the minibuffer local
     keymap in the function `read-no-blanks-input'.  By default, it
     makes the following bindings, in addition to those of
     `minibuffer-local-map':

    <SPC>
          `exit-minibuffer'

    <TAB>
          `exit-minibuffer'

    `?'
          `self-insert-and-exit'


File: elisp,  Node: Object from Minibuffer,  Next: Minibuffer History,  Prev: Text from Minibuffer,  Up: Minibuffers

20.3 Reading Lisp Objects with the Minibuffer
=============================================

This section describes functions for reading Lisp objects with the
minibuffer.

 -- Function: read-minibuffer prompt &optional initial
     This function reads a Lisp object using the minibuffer, and
     returns it without evaluating it.  The arguments PROMPT and
     INITIAL are used as in `read-from-minibuffer'.

     This is a simplified interface to the `read-from-minibuffer'
     function:

          (read-minibuffer PROMPT INITIAL)
          ==
          (let (minibuffer-allow-text-properties)
            (read-from-minibuffer PROMPT INITIAL nil t))

     Here is an example in which we supply the string `"(testing)"' as
     initial input:

          (read-minibuffer
           "Enter an expression: " (format "%s" '(testing)))

          ;; Here is how the minibuffer is displayed:

          ---------- Buffer: Minibuffer ----------
          Enter an expression: (testing)-!-
          ---------- Buffer: Minibuffer ----------

     The user can type <RET> immediately to use the initial input as a
     default, or can edit the input.

 -- Function: eval-minibuffer prompt &optional initial
     This function reads a Lisp expression using the minibuffer,
     evaluates it, then returns the result.  The arguments PROMPT and
     INITIAL are used as in `read-from-minibuffer'.

     This function simply evaluates the result of a call to
     `read-minibuffer':

          (eval-minibuffer PROMPT INITIAL)
          ==
          (eval (read-minibuffer PROMPT INITIAL))

 -- Function: edit-and-eval-command prompt form
     This function reads a Lisp expression in the minibuffer, and then
     evaluates it.  The difference between this command and
     `eval-minibuffer' is that here the initial FORM is not optional
     and it is treated as a Lisp object to be converted to printed
     representation rather than as a string of text.  It is printed with
     `prin1', so if it is a string, double-quote characters (`"')
     appear in the initial text.  *Note Output Functions::.

     The first thing `edit-and-eval-command' does is to activate the
     minibuffer with PROMPT as the prompt.  Then it inserts the printed
     representation of FORM in the minibuffer, and lets the user edit
     it.  When the user exits the minibuffer, the edited text is read
     with `read' and then evaluated.  The resulting value becomes the
     value of `edit-and-eval-command'.

     In the following example, we offer the user an expression with
     initial text which is a valid form already:

          (edit-and-eval-command "Please edit: " '(forward-word 1))

          ;; After evaluation of the preceding expression,
          ;;   the following appears in the minibuffer:

          ---------- Buffer: Minibuffer ----------
          Please edit: (forward-word 1)-!-
          ---------- Buffer: Minibuffer ----------

     Typing <RET> right away would exit the minibuffer and evaluate the
     expression, thus moving point forward one word.
     `edit-and-eval-command' returns `nil' in this example.


File: elisp,  Node: Minibuffer History,  Next: Initial Input,  Prev: Object from Minibuffer,  Up: Minibuffers

20.4 Minibuffer History
=======================

A "minibuffer history list" records previous minibuffer inputs so the
user can reuse them conveniently.  A history list is actually a symbol,
not a list; it is a variable whose value is a list of strings (previous
inputs), most recent first.

   There are many separate history lists, used for different kinds of
inputs.  It's the Lisp programmer's job to specify the right history
list for each use of the minibuffer.

   You specify the history list with the optional HIST argument to
either `read-from-minibuffer' or `completing-read'.  Here are the
possible values for it:

VARIABLE
     Use VARIABLE (a symbol) as the history list.

(VARIABLE . STARTPOS)
     Use VARIABLE (a symbol) as the history list, and assume that the
     initial history position is STARTPOS (a nonnegative integer).

     Specifying 0 for STARTPOS is equivalent to just specifying the
     symbol VARIABLE.  `previous-history-element' will display the most
     recent element of the history list in the minibuffer.  If you
     specify a positive STARTPOS, the minibuffer history functions
     behave as if `(elt VARIABLE (1- STARTPOS))' were the history
     element currently shown in the minibuffer.

     For consistency, you should also specify that element of the
     history as the initial minibuffer contents, using the INITIAL
     argument to the minibuffer input function (*note Initial Input::).

   If you don't specify HIST, then the default history list
`minibuffer-history' is used.  For other standard history lists, see
below.  You can also create your own history list variable; just
initialize it to `nil' before the first use.

   Both `read-from-minibuffer' and `completing-read' add new elements
to the history list automatically, and provide commands to allow the
user to reuse items on the list.  The only thing your program needs to
do to use a history list is to initialize it and to pass its name to
the input functions when you wish.  But it is safe to modify the list
by hand when the minibuffer input functions are not using it.

   Emacs functions that add a new element to a history list can also
delete old elements if the list gets too long.  The variable
`history-length' specifies the maximum length for most history lists.
To specify a different maximum length for a particular history list,
put the length in the `history-length' property of the history list
symbol.  The variable `history-delete-duplicates' specifies whether to
delete duplicates in history.

 -- Function: add-to-history history-var newelt &optional maxelt
          keep-all
     This function adds a new element NEWELT, if it isn't the empty
     string, to the history list stored in the variable HISTORY-VAR,
     and returns the updated history list.  It limits the list length to
     the value of MAXELT (if non-`nil') or `history-length' (described
     below).  The possible values of MAXELT have the same meaning as
     the values of `history-length'.

     Normally, `add-to-history' removes duplicate members from the
     history list if `history-delete-duplicates' is non-`nil'.
     However, if KEEP-ALL is non-`nil', that says not to remove
     duplicates, and to add NEWELT to the list even if it is empty.

 -- Variable: history-add-new-input
     If the value of this variable is `nil', standard functions that
     read from the minibuffer don't add new elements to the history
     list.  This lets Lisp programs explicitly manage input history by
     using `add-to-history'.  By default, `history-add-new-input' is
     set to a non-`nil' value.

 -- Variable: history-length
     The value of this variable specifies the maximum length for all
     history lists that don't specify their own maximum lengths.  If the
     value is `t', that means there no maximum (don't delete old
     elements).  The value of `history-length' property of the history
     list variable's symbol, if set, overrides this variable for that
     particular history list.

 -- Variable: history-delete-duplicates
     If the value of this variable is `t', that means when adding a new
     history element, all previous identical elements are deleted.

   Here are some of the standard minibuffer history list variables:

 -- Variable: minibuffer-history
     The default history list for minibuffer history input.

 -- Variable: query-replace-history
     A history list for arguments to `query-replace' (and similar
     arguments to other commands).

 -- Variable: file-name-history
     A history list for file-name arguments.

 -- Variable: buffer-name-history
     A history list for buffer-name arguments.

 -- Variable: regexp-history
     A history list for regular expression arguments.

 -- Variable: extended-command-history
     A history list for arguments that are names of extended commands.

 -- Variable: shell-command-history
     A history list for arguments that are shell commands.

 -- Variable: read-expression-history
     A history list for arguments that are Lisp expressions to evaluate.


File: elisp,  Node: Initial Input,  Next: Completion,  Prev: Minibuffer History,  Up: Minibuffers

20.5 Initial Input
==================

Several of the functions for minibuffer input have an argument called
INITIAL or INITIAL-CONTENTS.  This is a mostly-deprecated feature for
specifying that the minibuffer should start out with certain text,
instead of empty as usual.

   If INITIAL is a string, the minibuffer starts out containing the
text of the string, with point at the end, when the user starts to edit
the text.  If the user simply types <RET> to exit the minibuffer, it
will use the initial input string to determine the value to return.

   *We discourage use of a non-`nil' value for INITIAL*, because
initial input is an intrusive interface.  History lists and default
values provide a much more convenient method to offer useful default
inputs to the user.

   There is just one situation where you should specify a string for an
INITIAL argument.  This is when you specify a cons cell for the HIST or
HISTORY argument.  *Note Minibuffer History::.

   INITIAL can also be a cons cell of the form `(STRING . POSITION)'.
This means to insert STRING in the minibuffer but put point at POSITION
within the string's text.

   As a historical accident, POSITION was implemented inconsistently in
different functions.  In `completing-read', POSITION's value is
interpreted as origin-zero; that is, a value of 0 means the beginning
of the string, 1 means after the first character, etc.  In
`read-minibuffer', and the other non-completion minibuffer input
functions that support this argument, 1 means the beginning of the
string 2 means after the first character, etc.

   Use of a cons cell as the value for INITIAL arguments is deprecated
in user code.


File: elisp,  Node: Completion,  Next: Yes-or-No Queries,  Prev: Initial Input,  Up: Minibuffers

20.6 Completion
===============

"Completion" is a feature that fills in the rest of a name starting
from an abbreviation for it.  Completion works by comparing the user's
input against a list of valid names and determining how much of the
name is determined uniquely by what the user has typed.  For example,
when you type `C-x b' (`switch-to-buffer') and then type the first few
letters of the name of the buffer to which you wish to switch, and then
type <TAB> (`minibuffer-complete'), Emacs extends the name as far as it
can.

   Standard Emacs commands offer completion for names of symbols, files,
buffers, and processes; with the functions in this section, you can
implement completion for other kinds of names.

   The `try-completion' function is the basic primitive for completion:
it returns the longest determined completion of a given initial string,
with a given set of strings to match against.

   The function `completing-read' provides a higher-level interface for
completion.  A call to `completing-read' specifies how to determine the
list of valid names.  The function then activates the minibuffer with a
local keymap that binds a few keys to commands useful for completion.
Other functions provide convenient simple interfaces for reading
certain kinds of names with completion.

* Menu:

* Basic Completion::       Low-level functions for completing strings.
                             (These are too low level to use the minibuffer.)
* Minibuffer Completion::  Invoking the minibuffer with completion.
* Completion Commands::    Minibuffer commands that do completion.
* High-Level Completion::  Convenient special cases of completion
                             (reading buffer name, file name, etc.)
* Reading File Names::     Using completion to read file names.
* Programmed Completion::  Writing your own completion-function.


File: elisp,  Node: Basic Completion,  Next: Minibuffer Completion,  Up: Completion

20.6.1 Basic Completion Functions
---------------------------------

The completion functions `try-completion', `all-completions' and
`test-completion' have nothing in themselves to do with minibuffers.
We describe them in this chapter so as to keep them near the
higher-level completion features that do use the minibuffer.

   If you store a completion alist in a variable, you should mark the
variable as "risky" with a non-`nil' `risky-local-variable' property.

 -- Function: try-completion string collection &optional predicate
     This function returns the longest common substring of all possible
     completions of STRING in COLLECTION.  The value of COLLECTION must
     be a list of strings or symbols, an alist, an obarray, a hash
     table, or a function that implements a virtual set of strings (see
     below).

     Completion compares STRING against each of the permissible
     completions specified by COLLECTION; if the beginning of the
     permissible completion equals STRING, it matches.  If no
     permissible completions match, `try-completion' returns `nil'.  If
     only one permissible completion matches, and the match is exact,
     then `try-completion' returns `t'.  Otherwise, the value is the
     longest initial sequence common to all the permissible completions
     that match.

     If COLLECTION is an alist (*note Association Lists::), the
     permissible completions are the elements of the alist that are
     either strings, symbols, or conses whose CAR is a string or symbol.
     Symbols are converted to strings using `symbol-name'.  Other
     elements of the alist are ignored. (Remember that in Emacs Lisp,
     the elements of alists do not _have_ to be conses.)  In
     particular, a list of strings or symbols is allowed, even though
     we usually do not think of such lists as alists.

     If COLLECTION is an obarray (*note Creating Symbols::), the names
     of all symbols in the obarray form the set of permissible
     completions.  The global variable `obarray' holds an obarray
     containing the names of all interned Lisp symbols.

     Note that the only valid way to make a new obarray is to create it
     empty and then add symbols to it one by one using `intern'.  Also,
     you cannot intern a given symbol in more than one obarray.

     If COLLECTION is a hash table, then the keys that are strings are
     the possible completions.  Other keys are ignored.

     You can also use a symbol that is a function as COLLECTION.  Then
     the function is solely responsible for performing completion;
     `try-completion' returns whatever this function returns.  The
     function is called with three arguments: STRING, PREDICATE and
     `nil'.  (The reason for the third argument is so that the same
     function can be used in `all-completions' and do the appropriate
     thing in either case.)  *Note Programmed Completion::.

     If the argument PREDICATE is non-`nil', then it must be a function
     of one argument, unless COLLECTION is a hash table, in which case
     it should be a function of two arguments.  It is used to test each
     possible match, and the match is accepted only if PREDICATE
     returns non-`nil'.  The argument given to PREDICATE is either a
     string or a cons cell (the CAR of which is a string) from the
     alist, or a symbol (_not_ a symbol name) from the obarray.  If
     COLLECTION is a hash table, PREDICATE is called with two
     arguments, the string key and the associated value.

     In addition, to be acceptable, a completion must also match all the
     regular expressions in `completion-regexp-list'.  (Unless
     COLLECTION is a function, in which case that function has to
     handle `completion-regexp-list' itself.)

     In the first of the following examples, the string `foo' is
     matched by three of the alist CARs.  All of the matches begin with
     the characters `fooba', so that is the result.  In the second
     example, there is only one possible match, and it is exact, so the
     value is `t'.

          (try-completion
           "foo"
           '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)))
               => "fooba"

          (try-completion "foo" '(("barfoo" 2) ("foo" 3)))
               => t

     In the following example, numerous symbols begin with the
     characters `forw', and all of them begin with the word `forward'.
     In most of the symbols, this is followed with a `-', but not in
     all, so no more than `forward' can be completed.

          (try-completion "forw" obarray)
               => "forward"

     Finally, in the following example, only two of the three possible
     matches pass the predicate `test' (the string `foobaz' is too
     short).  Both of those begin with the string `foobar'.

          (defun test (s)
            (> (length (car s)) 6))
               => test
          (try-completion
           "foo"
           '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
           'test)
               => "foobar"

 -- Function: all-completions string collection &optional predicate
          nospace
     This function returns a list of all possible completions of
     STRING.  The arguments to this function (aside from NOSPACE) are
     the same as those of `try-completion'.  Also, this function uses
     `completion-regexp-list' in the same way that `try-completion'
     does.  The optional argument NOSPACE only matters if STRING is the
     empty string.  In that case, if NOSPACE is non-`nil', completions
     that start with a space are ignored.

     If COLLECTION is a function, it is called with three arguments:
     STRING, PREDICATE and `t'; then `all-completions' returns whatever
     the function returns.  *Note Programmed Completion::.

     Here is an example, using the function `test' shown in the example
     for `try-completion':

          (defun test (s)
            (> (length (car s)) 6))
               => test

          (all-completions
           "foo"
           '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
           'test)
               => ("foobar1" "foobar2")

 -- Function: test-completion string collection &optional predicate
     This function returns non-`nil' if STRING is a valid completion
     possibility specified by COLLECTION and PREDICATE.  The arguments
     are the same as in `try-completion'.  For instance, if COLLECTION
     is a list of strings, this is true if STRING appears in the list
     and PREDICATE is satisfied.

     This function uses `completion-regexp-list' in the same way that
     `try-completion' does.

     If PREDICATE is non-`nil' and if COLLECTION contains several
     strings that are equal to each other, as determined by
     `compare-strings' according to `completion-ignore-case', then
     PREDICATE should accept either all or none of them.  Otherwise,
     the return value of `test-completion' is essentially unpredictable.

     If COLLECTION is a function, it is called with three arguments,
     the values STRING, PREDICATE and `lambda'; whatever it returns,
     `test-completion' returns in turn.

 -- Variable: completion-ignore-case
     If the value of this variable is non-`nil', Emacs does not
     consider case significant in completion.

 -- Variable: completion-regexp-list
     This is a list of regular expressions.  The completion functions
     only consider a completion acceptable if it matches all regular
     expressions in this list, with `case-fold-search' (*note Searching
     and Case::) bound to the value of `completion-ignore-case'.

 -- Macro: lazy-completion-table var fun
     This macro provides a way to initialize the variable VAR as a
     collection for completion in a lazy way, not computing its actual
     contents until they are first needed.  You use this macro to
     produce a value that you store in VAR.  The actual computation of
     the proper value is done the first time you do completion using
     VAR.  It is done by calling FUN with no arguments.  The value FUN
     returns becomes the permanent value of VAR.

     Here is an example of use:

          (defvar foo (lazy-completion-table foo make-my-alist))


File: elisp,  Node: Minibuffer Completion,  Next: Completion Commands,  Prev: Basic Completion,  Up: Completion

20.6.2 Completion and the Minibuffer
------------------------------------

This section describes the basic interface for reading from the
minibuffer with completion.

 -- Function: completing-read prompt collection &optional predicate
          require-match initial hist default inherit-input-method
     This function reads a string in the minibuffer, assisting the user
     by providing completion.  It activates the minibuffer with prompt
     PROMPT, which must be a string.

     The actual completion is done by passing COLLECTION and PREDICATE
     to the function `try-completion'.  This happens in certain
     commands bound in the local keymaps used for completion.  Some of
     these commands also call `test-completion'.  Thus, if PREDICATE is
     non-`nil', it should be compatible with COLLECTION and
     `completion-ignore-case'.  *Note Definition of test-completion::.

     If REQUIRE-MATCH is `nil', the exit commands work regardless of
     the input in the minibuffer.  If REQUIRE-MATCH is `t', the usual
     minibuffer exit commands won't exit unless the input completes to
     an element of COLLECTION.  If REQUIRE-MATCH is neither `nil' nor
     `t', then the exit commands won't exit unless the input already in
     the buffer matches an element of COLLECTION.

     However, empty input is always permitted, regardless of the value
     of REQUIRE-MATCH; in that case, `completing-read' returns DEFAULT,
     or `""', if DEFAULT is `nil'.  The value of DEFAULT (if non-`nil')
     is also available to the user through the history commands.

     The function `completing-read' uses
     `minibuffer-local-completion-map' as the keymap if REQUIRE-MATCH
     is `nil', and uses `minibuffer-local-must-match-map' if
     REQUIRE-MATCH is non-`nil'.  *Note Completion Commands::.

     The argument HIST specifies which history list variable to use for
     saving the input and for minibuffer history commands.  It defaults
     to `minibuffer-history'.  *Note Minibuffer History::.

     The argument INITIAL is mostly deprecated; we recommend using a
     non-`nil' value only in conjunction with specifying a cons cell
     for HIST.  *Note Initial Input::.  For default input, use DEFAULT
     instead.

     If the argument INHERIT-INPUT-METHOD is non-`nil', then the
     minibuffer inherits the current input method (*note Input
     Methods::) and the setting of `enable-multibyte-characters' (*note
     Text Representations::) from whichever buffer was current before
     entering the minibuffer.

     If the built-in variable `completion-ignore-case' is non-`nil',
     completion ignores case when comparing the input against the
     possible matches.  *Note Basic Completion::.  In this mode of
     operation, PREDICATE must also ignore case, or you will get
     surprising results.

     Here's an example of using `completing-read':

          (completing-read
           "Complete a foo: "
           '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
           nil t "fo")

          ;; After evaluation of the preceding expression,
          ;;   the following appears in the minibuffer:

          ---------- Buffer: Minibuffer ----------
          Complete a foo: fo-!-
          ---------- Buffer: Minibuffer ----------

     If the user then types `<DEL> <DEL> b <RET>', `completing-read'
     returns `barfoo'.

     The `completing-read' function binds variables to pass information
     to the commands that actually do completion.  They are described
     in the following section.


File: elisp,  Node: Completion Commands,  Next: High-Level Completion,  Prev: Minibuffer Completion,  Up: Completion

20.6.3 Minibuffer Commands that Do Completion
---------------------------------------------

This section describes the keymaps, commands and user options used in
the minibuffer to do completion.  The description refers to the
situation when Partial Completion mode is disabled (as it is by
default).  When enabled, this minor mode uses its own alternatives to
some of the commands described below.  *Note Completion Options:
(emacs)Completion Options, for a short description of Partial
Completion mode.

 -- Variable: minibuffer-completion-table
     The value of this variable is the collection used for completion in
     the minibuffer.  This is the global variable that contains what
     `completing-read' passes to `try-completion'.  It is used by
     minibuffer completion commands such as `minibuffer-complete-word'.

 -- Variable: minibuffer-completion-predicate
     This variable's value is the predicate that `completing-read'
     passes to `try-completion'.  The variable is also used by the other
     minibuffer completion functions.

 -- Variable: minibuffer-completion-confirm
     When the value of this variable is non-`nil', Emacs asks for
     confirmation of a completion before exiting the minibuffer.
     `completing-read' binds this variable, and the function
     `minibuffer-complete-and-exit' checks the value before exiting.

 -- Command: minibuffer-complete-word
     This function completes the minibuffer contents by at most a single
     word.  Even if the minibuffer contents have only one completion,
     `minibuffer-complete-word' does not add any characters beyond the
     first character that is not a word constituent.  *Note Syntax
     Tables::.

 -- Command: minibuffer-complete
     This function completes the minibuffer contents as far as possible.

 -- Command: minibuffer-complete-and-exit
     This function completes the minibuffer contents, and exits if
     confirmation is not required, i.e., if
     `minibuffer-completion-confirm' is `nil'.  If confirmation _is_
     required, it is given by repeating this command immediately--the
     command is programmed to work without confirmation when run twice
     in succession.

 -- Command: minibuffer-completion-help
     This function creates a list of the possible completions of the
     current minibuffer contents.  It works by calling `all-completions'
     using the value of the variable `minibuffer-completion-table' as
     the COLLECTION argument, and the value of
     `minibuffer-completion-predicate' as the PREDICATE argument.  The
     list of completions is displayed as text in a buffer named
     `*Completions*'.

 -- Function: display-completion-list completions &optional
          common-substring
     This function displays COMPLETIONS to the stream in
     `standard-output', usually a buffer.  (*Note Read and Print::, for
     more information about streams.)  The argument COMPLETIONS is
     normally a list of completions just returned by `all-completions',
     but it does not have to be.  Each element may be a symbol or a
     string, either of which is simply printed.  It can also be a list
     of two strings, which is printed as if the strings were
     concatenated.  The first of the two strings is the actual
     completion, the second string serves as annotation.

     The argument COMMON-SUBSTRING is the prefix that is common to all
     the completions.  With normal Emacs completion, it is usually the
     same as the string that was completed.  `display-completion-list'
     uses this to highlight text in the completion list for better
     visual feedback.  This is not needed in the minibuffer; for
     minibuffer completion, you can pass `nil'.

     This function is called by `minibuffer-completion-help'.  The most
     common way to use it is together with
     `with-output-to-temp-buffer', like this:

          (with-output-to-temp-buffer "*Completions*"
            (display-completion-list
              (all-completions (buffer-string) my-alist)
              (buffer-string)))

 -- User Option: completion-auto-help
     If this variable is non-`nil', the completion commands
     automatically display a list of possible completions whenever
     nothing can be completed because the next character is not
     uniquely determined.

 -- Variable: minibuffer-local-completion-map
     `completing-read' uses this value as the local keymap when an
     exact match of one of the completions is not required.  By
     default, this keymap makes the following bindings:

    `?'
          `minibuffer-completion-help'

    <SPC>
          `minibuffer-complete-word'

    <TAB>
          `minibuffer-complete'

     with other characters bound as in `minibuffer-local-map' (*note
     Definition of minibuffer-local-map::).

 -- Variable: minibuffer-local-must-match-map
     `completing-read' uses this value as the local keymap when an
     exact match of one of the completions is required.  Therefore, no
     keys are bound to `exit-minibuffer', the command that exits the
     minibuffer unconditionally.  By default, this keymap makes the
     following bindings:

    `?'
          `minibuffer-completion-help'

    <SPC>
          `minibuffer-complete-word'

    <TAB>
          `minibuffer-complete'

    `C-j'
          `minibuffer-complete-and-exit'

    <RET>
          `minibuffer-complete-and-exit'

     with other characters bound as in `minibuffer-local-map'.

 -- Variable: minibuffer-local-filename-completion-map
     This is like `minibuffer-local-completion-map' except that it does
     not bind <SPC>.  This keymap is used by the function
     `read-file-name'.

 -- Variable: minibuffer-local-must-match-filename-map
     This is like `minibuffer-local-must-match-map' except that it does
     not bind <SPC>.  This keymap is used by the function
     `read-file-name'.


File: elisp,  Node: High-Level Completion,  Next: Reading File Names,  Prev: Completion Commands,  Up: Completion

20.6.4 High-Level Completion  Functions
---------------------------------------

This section describes the higher-level convenient functions for
reading certain sorts of names with completion.

   In most cases, you should not call these functions in the middle of a
Lisp function.  When possible, do all minibuffer input as part of
reading the arguments for a command, in the `interactive'
specification.  *Note Defining Commands::.

 -- Function: read-buffer prompt &optional default existing
     This function reads the name of a buffer and returns it as a
     string.  The argument DEFAULT is the default name to use, the
     value to return if the user exits with an empty minibuffer.  If
     non-`nil', it should be a string or a buffer.  It is mentioned in
     the prompt, but is not inserted in the minibuffer as initial input.

     The argument PROMPT should be a string ending with a colon and a
     space.  If DEFAULT is non-`nil', the function inserts it in PROMPT
     before the colon to follow the convention for reading from the
     minibuffer with a default value (*note Programming Tips::).

     If EXISTING is non-`nil', then the name specified must be that of
     an existing buffer.  The usual commands to exit the minibuffer do
     not exit if the text is not valid, and <RET> does completion to
     attempt to find a valid name.  If EXISTING is neither `nil' nor
     `t', confirmation is required after completion.  (However, DEFAULT
     is not checked for validity; it is returned, whatever it is, if
     the user exits with the minibuffer empty.)

     In the following example, the user enters `minibuffer.t', and then
     types <RET>.  The argument EXISTING is `t', and the only buffer
     name starting with the given input is `minibuffer.texi', so that
     name is the value.

          (read-buffer "Buffer name: " "foo" t)
          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears,
          ;;   with an empty minibuffer:

          ---------- Buffer: Minibuffer ----------
          Buffer name (default foo): -!-
          ---------- Buffer: Minibuffer ----------

          ;; The user types `minibuffer.t <RET>'.
               => "minibuffer.texi"

 -- Variable: read-buffer-function
     This variable specifies how to read buffer names.  For example, if
     you set this variable to `iswitchb-read-buffer', all Emacs commands
     that call `read-buffer' to read a buffer name will actually use the
     `iswitchb' package to read it.

 -- Function: read-command prompt &optional default
     This function reads the name of a command and returns it as a Lisp
     symbol.  The argument PROMPT is used as in `read-from-minibuffer'.
     Recall that a command is anything for which `commandp' returns
     `t', and a command name is a symbol for which `commandp' returns
     `t'.  *Note Interactive Call::.

     The argument DEFAULT specifies what to return if the user enters
     null input.  It can be a symbol or a string; if it is a string,
     `read-command' interns it before returning it.  If DEFAULT is
     `nil', that means no default has been specified; then if the user
     enters null input, the return value is `(intern "")', that is, a
     symbol whose name is an empty string.

          (read-command "Command name? ")

          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears with an empty minibuffer:

          ---------- Buffer: Minibuffer ----------
          Command name?
          ---------- Buffer: Minibuffer ----------

     If the user types `forward-c <RET>', then this function returns
     `forward-char'.

     The `read-command' function is a simplified interface to
     `completing-read'.  It uses the variable `obarray' so as to
     complete in the set of extant Lisp symbols, and it uses the
     `commandp' predicate so as to accept only command names:

          (read-command PROMPT)
          ==
          (intern (completing-read PROMPT obarray
                                   'commandp t nil))

 -- Function: read-variable prompt &optional default
     This function reads the name of a user variable and returns it as a
     symbol.

     The argument DEFAULT specifies what to return if the user enters
     null input.  It can be a symbol or a string; if it is a string,
     `read-variable' interns it before returning it.  If DEFAULT is
     `nil', that means no default has been specified; then if the user
     enters null input, the return value is `(intern "")'.

          (read-variable "Variable name? ")

          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears,
          ;;   with an empty minibuffer:

          ---------- Buffer: Minibuffer ----------
          Variable name? -!-
          ---------- Buffer: Minibuffer ----------

     If the user then types `fill-p <RET>', `read-variable' returns
     `fill-prefix'.

     In general, `read-variable' is similar to `read-command', but uses
     the predicate `user-variable-p' instead of `commandp':

          (read-variable PROMPT)
          ==
          (intern
           (completing-read PROMPT obarray
                            'user-variable-p t nil))

   See also the functions `read-coding-system' and
`read-non-nil-coding-system', in *Note User-Chosen Coding Systems::,
and `read-input-method-name', in *Note Input Methods::.


File: elisp,  Node: Reading File Names,  Next: Programmed Completion,  Prev: High-Level Completion,  Up: Completion

20.6.5 Reading File Names
-------------------------

Here is another high-level completion function, designed for reading a
file name.  It provides special features including automatic insertion
of the default directory.

 -- Function: read-file-name prompt &optional directory default
          existing initial predicate
     This function reads a file name in the minibuffer, prompting with
     PROMPT and providing completion.

     If EXISTING is non-`nil', then the user must specify the name of
     an existing file; <RET> performs completion to make the name valid
     if possible, and then refuses to exit if it is not valid.  If the
     value of EXISTING is neither `nil' nor `t', then <RET> also
     requires confirmation after completion.  If EXISTING is `nil',
     then the name of a nonexistent file is acceptable.

     `read-file-name' uses `minibuffer-local-filename-completion-map'
     as the keymap if EXISTING is `nil', and uses
     `minibuffer-local-must-match-filename-map' if EXISTING is
     non-`nil'.  *Note Completion Commands::.

     The argument DIRECTORY specifies the directory to use for
     completion of relative file names.  It should be an absolute
     directory name.  If `insert-default-directory' is non-`nil',
     DIRECTORY is also inserted in the minibuffer as initial input.  It
     defaults to the current buffer's value of `default-directory'.

     If you specify INITIAL, that is an initial file name to insert in
     the buffer (after DIRECTORY, if that is inserted).  In this case,
     point goes at the beginning of INITIAL.  The default for INITIAL
     is `nil'--don't insert any file name.  To see what INITIAL does,
     try the command `C-x C-v'.  *Please note:* we recommend using
     DEFAULT rather than INITIAL in most cases.

     If DEFAULT is non-`nil', then the function returns DEFAULT if the
     user exits the minibuffer with the same non-empty contents that
     `read-file-name' inserted initially.  The initial minibuffer
     contents are always non-empty if `insert-default-directory' is
     non-`nil', as it is by default.  DEFAULT is not checked for
     validity, regardless of the value of EXISTING.  However, if
     EXISTING is non-`nil', the initial minibuffer contents should be a
     valid file (or directory) name.  Otherwise `read-file-name'
     attempts completion if the user exits without any editing, and
     does not return DEFAULT.  DEFAULT is also available through the
     history commands.

     If DEFAULT is `nil', `read-file-name' tries to find a substitute
     default to use in its place, which it treats in exactly the same
     way as if it had been specified explicitly.  If DEFAULT is `nil',
     but INITIAL is non-`nil', then the default is the absolute file
     name obtained from DIRECTORY and INITIAL.  If both DEFAULT and
     INITIAL are `nil' and the buffer is visiting a file,
     `read-file-name' uses the absolute file name of that file as
     default.  If the buffer is not visiting a file, then there is no
     default.  In that case, if the user types <RET> without any
     editing, `read-file-name' simply returns the pre-inserted contents
     of the minibuffer.

     If the user types <RET> in an empty minibuffer, this function
     returns an empty string, regardless of the value of EXISTING.
     This is, for instance, how the user can make the current buffer
     visit no file using `M-x set-visited-file-name'.

     If PREDICATE is non-`nil', it specifies a function of one argument
     that decides which file names are acceptable completion
     possibilities.  A file name is an acceptable value if PREDICATE
     returns non-`nil' for it.

     `read-file-name' does not automatically expand file names.  You
     must call `expand-file-name' yourself if an absolute file name is
     required.

     Here is an example:

          (read-file-name "The file is ")

          ;; After evaluation of the preceding expression,
          ;;   the following appears in the minibuffer:

          ---------- Buffer: Minibuffer ----------
          The file is /gp/gnu/elisp/-!-
          ---------- Buffer: Minibuffer ----------

     Typing `manual <TAB>' results in the following:

          ---------- Buffer: Minibuffer ----------
          The file is /gp/gnu/elisp/manual.texi-!-
          ---------- Buffer: Minibuffer ----------

     If the user types <RET>, `read-file-name' returns the file name as
     the string `"/gp/gnu/elisp/manual.texi"'.

 -- Variable: read-file-name-function
     If non-`nil', this should be a function that accepts the same
     arguments as `read-file-name'.  When `read-file-name' is called,
     it calls this function with the supplied arguments instead of
     doing its usual work.

 -- Variable: read-file-name-completion-ignore-case
     If this variable is non-`nil', `read-file-name' ignores case when
     performing completion.

 -- Function: read-directory-name prompt &optional directory default
          existing initial
     This function is like `read-file-name' but allows only directory
     names as completion possibilities.

     If DEFAULT is `nil' and INITIAL is non-`nil',
     `read-directory-name' constructs a substitute default by combining
     DIRECTORY (or the current buffer's default directory if DIRECTORY
     is `nil') and INITIAL.  If both DEFAULT and INITIAL are `nil',
     this function uses DIRECTORY as substitute default, or the current
     buffer's default directory if DIRECTORY is `nil'.

 -- User Option: insert-default-directory
     This variable is used by `read-file-name', and thus, indirectly,
     by most commands reading file names.  (This includes all commands
     that use the code letters `f' or `F' in their interactive form.
     *Note Code Characters for interactive: Interactive Codes.)  Its
     value controls whether `read-file-name' starts by placing the name
     of the default directory in the minibuffer, plus the initial file
     name if any.  If the value of this variable is `nil', then
     `read-file-name' does not place any initial input in the
     minibuffer (unless you specify initial input with the INITIAL
     argument).  In that case, the default directory is still used for
     completion of relative file names, but is not displayed.

     If this variable is `nil' and the initial minibuffer contents are
     empty, the user may have to explicitly fetch the next history
     element to access a default value.  If the variable is non-`nil',
     the initial minibuffer contents are always non-empty and the user
     can always request a default value by immediately typing <RET> in
     an unedited minibuffer.  (See above.)

     For example:

          ;; Here the minibuffer starts out with the default directory.
          (let ((insert-default-directory t))
            (read-file-name "The file is "))

          ---------- Buffer: Minibuffer ----------
          The file is ~lewis/manual/-!-
          ---------- Buffer: Minibuffer ----------

          ;; Here the minibuffer is empty and only the prompt
          ;;   appears on its line.
          (let ((insert-default-directory nil))
            (read-file-name "The file is "))

          ---------- Buffer: Minibuffer ----------
          The file is -!-
          ---------- Buffer: Minibuffer ----------


File: elisp,  Node: Programmed Completion,  Prev: Reading File Names,  Up: Completion

20.6.6 Programmed Completion
----------------------------

Sometimes it is not possible to create an alist or an obarray
containing all the intended possible completions.  In such a case, you
can supply your own function to compute the completion of a given
string.  This is called "programmed completion".

   To use this feature, pass a symbol with a function definition as the
COLLECTION argument to `completing-read'.  The function
`completing-read' arranges to pass your completion function along to
`try-completion' and `all-completions', which will then let your
function do all the work.

   The completion function should accept three arguments:

   * The string to be completed.

   * The predicate function to filter possible matches, or `nil' if
     none.  Your function should call the predicate for each possible
     match, and ignore the possible match if the predicate returns
     `nil'.

   * A flag specifying the type of operation.

   There are three flag values for three operations:

   * `nil' specifies `try-completion'.  The completion function should
     return the completion of the specified string, or `t' if the
     string is a unique and exact match already, or `nil' if the string
     matches no possibility.

     If the string is an exact match for one possibility, but also
     matches other longer possibilities, the function should return the
     string, not `t'.

   * `t' specifies `all-completions'.  The completion function should
     return a list of all possible completions of the specified string.

   * `lambda' specifies `test-completion'.  The completion function
     should return `t' if the specified string is an exact match for
     some possibility; `nil' otherwise.

   It would be consistent and clean for completion functions to allow
lambda expressions (lists that are functions) as well as function
symbols as COLLECTION, but this is impossible.  Lists as completion
tables already have other meanings, and it would be unreliable to treat
one differently just because it is also a possible function.  So you
must arrange for any function you wish to use for completion to be
encapsulated in a symbol.

   Emacs uses programmed completion when completing file names.  *Note
File Name Completion::.

 -- Macro: dynamic-completion-table function
     This macro is a convenient way to write a function that can act as
     programmed completion function.  The argument FUNCTION should be a
     function that takes one argument, a string, and returns an alist of
     possible completions of it.  You can think of
     `dynamic-completion-table' as a transducer between that interface
     and the interface for programmed completion functions.


File: elisp,  Node: Yes-or-No Queries,  Next: Multiple Queries,  Prev: Completion,  Up: Minibuffers

20.7 Yes-or-No Queries
======================

This section describes functions used to ask the user a yes-or-no
question.  The function `y-or-n-p' can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences.  `yes-or-no-p' is suitable for more
momentous questions, since it requires three or four characters to
answer.

   If either of these functions is called in a command that was invoked
using the mouse--more precisely, if `last-nonmenu-event' (*note Command
Loop Info::) is either `nil' or a list--then it uses a dialog box or
pop-up menu to ask the question.  Otherwise, it uses keyboard input.
You can force use of the mouse or use of keyboard input by binding
`last-nonmenu-event' to a suitable value around the call.

   Strictly speaking, `yes-or-no-p' uses the minibuffer and `y-or-n-p'
does not; but it seems best to describe them together.

 -- Function: y-or-n-p prompt
     This function asks the user a question, expecting input in the echo
     area.  It returns `t' if the user types `y', `nil' if the user
     types `n'.  This function also accepts <SPC> to mean yes and <DEL>
     to mean no.  It accepts `C-]' to mean "quit," like `C-g', because
     the question might look like a minibuffer and for that reason the
     user might try to use `C-]' to get out.  The answer is a single
     character, with no <RET> needed to terminate it.  Upper and lower
     case are equivalent.

     "Asking the question" means printing PROMPT in the echo area,
     followed by the string `(y or n) '.  If the input is not one of
     the expected answers (`y', `n', `<SPC>', `<DEL>', or something
     that quits), the function responds `Please answer y or n.', and
     repeats the request.

     This function does not actually use the minibuffer, since it does
     not allow editing of the answer.  It actually uses the echo area
     (*note The Echo Area::), which uses the same screen space as the
     minibuffer.  The cursor moves to the echo area while the question
     is being asked.

     The answers and their meanings, even `y' and `n', are not
     hardwired.  The keymap `query-replace-map' specifies them.  *Note
     Search and Replace::.

     In the following example, the user first types `q', which is
     invalid.  At the next prompt the user types `y'.

          (y-or-n-p "Do you need a lift? ")

          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears in the echo area:

          ---------- Echo area ----------
          Do you need a lift? (y or n)
          ---------- Echo area ----------

          ;; If the user then types `q', the following appears:

          ---------- Echo area ----------
          Please answer y or n.  Do you need a lift? (y or n)
          ---------- Echo area ----------

          ;; When the user types a valid answer,
          ;;   it is displayed after the question:

          ---------- Echo area ----------
          Do you need a lift? (y or n) y
          ---------- Echo area ----------

     We show successive lines of echo area messages, but only one
     actually appears on the screen at a time.

 -- Function: y-or-n-p-with-timeout prompt seconds default-value
     Like `y-or-n-p', except that if the user fails to answer within
     SECONDS seconds, this function stops waiting and returns
     DEFAULT-VALUE.  It works by setting up a timer; see *Note Timers::.
     The argument SECONDS may be an integer or a floating point number.

 -- Function: yes-or-no-p prompt
     This function asks the user a question, expecting input in the
     minibuffer.  It returns `t' if the user enters `yes', `nil' if the
     user types `no'.  The user must type <RET> to finalize the
     response.  Upper and lower case are equivalent.

     `yes-or-no-p' starts by displaying PROMPT in the echo area,
     followed by `(yes or no) '.  The user must type one of the
     expected responses; otherwise, the function responds `Please answer
     yes or no.', waits about two seconds and repeats the request.

     `yes-or-no-p' requires more work from the user than `y-or-n-p' and
     is appropriate for more crucial decisions.

     Here is an example:

          (yes-or-no-p "Do you really want to remove everything? ")

          ;; After evaluation of the preceding expression,
          ;;   the following prompt appears,
          ;;   with an empty minibuffer:

          ---------- Buffer: minibuffer ----------
          Do you really want to remove everything? (yes or no)
          ---------- Buffer: minibuffer ----------

     If the user first types `y <RET>', which is invalid because this
     function demands the entire word `yes', it responds by displaying
     these prompts, with a brief pause between them:

          ---------- Buffer: minibuffer ----------
          Please answer yes or no.
          Do you really want to remove everything? (yes or no)
          ---------- Buffer: minibuffer ----------


File: elisp,  Node: Multiple Queries,  Next: Reading a Password,  Prev: Yes-or-No Queries,  Up: Minibuffers

20.8 Asking Multiple Y-or-N Questions
=====================================

When you have a series of similar questions to ask, such as "Do you
want to save this buffer" for each buffer in turn, you should use
`map-y-or-n-p' to ask the collection of questions, rather than asking
each question individually.  This gives the user certain convenient
facilities such as the ability to answer the whole series at once.

 -- Function: map-y-or-n-p prompter actor list &optional help
          action-alist no-cursor-in-echo-area
     This function asks the user a series of questions, reading a
     single-character answer in the echo area for each one.

     The value of LIST specifies the objects to ask questions about.
     It should be either a list of objects or a generator function.  If
     it is a function, it should expect no arguments, and should return
     either the next object to ask about, or `nil' meaning stop asking
     questions.

     The argument PROMPTER specifies how to ask each question.  If
     PROMPTER is a string, the question text is computed like this:

          (format PROMPTER OBJECT)

     where OBJECT is the next object to ask about (as obtained from
     LIST).

     If not a string, PROMPTER should be a function of one argument
     (the next object to ask about) and should return the question
     text.  If the value is a string, that is the question to ask the
     user.  The function can also return `t' meaning do act on this
     object (and don't ask the user), or `nil' meaning ignore this
     object (and don't ask the user).

     The argument ACTOR says how to act on the answers that the user
     gives.  It should be a function of one argument, and it is called
     with each object that the user says yes for.  Its argument is
     always an object obtained from LIST.

     If the argument HELP is given, it should be a list of this form:

          (SINGULAR PLURAL ACTION)

     where SINGULAR is a string containing a singular noun that
     describes the objects conceptually being acted on, PLURAL is the
     corresponding plural noun, and ACTION is a transitive verb
     describing what ACTOR does.

     If you don't specify HELP, the default is `("object" "objects"
     "act on")'.

     Each time a question is asked, the user may enter `y', `Y', or
     <SPC> to act on that object; `n', `N', or <DEL> to skip that
     object; `!' to act on all following objects; <ESC> or `q' to exit
     (skip all following objects); `.' (period) to act on the current
     object and then exit; or `C-h' to get help.  These are the same
     answers that `query-replace' accepts.  The keymap
     `query-replace-map' defines their meaning for `map-y-or-n-p' as
     well as for `query-replace'; see *Note Search and Replace::.

     You can use ACTION-ALIST to specify additional possible answers
     and what they mean.  It is an alist of elements of the form `(CHAR
     FUNCTION HELP)', each of which defines one additional answer.  In
     this element, CHAR is a character (the answer); FUNCTION is a
     function of one argument (an object from LIST); HELP is a string.

     When the user responds with CHAR, `map-y-or-n-p' calls FUNCTION.
     If it returns non-`nil', the object is considered "acted upon,"
     and `map-y-or-n-p' advances to the next object in LIST.  If it
     returns `nil', the prompt is repeated for the same object.

     Normally, `map-y-or-n-p' binds `cursor-in-echo-area' while
     prompting.  But if NO-CURSOR-IN-ECHO-AREA is non-`nil', it does
     not do that.

     If `map-y-or-n-p' is called in a command that was invoked using the
     mouse--more precisely, if `last-nonmenu-event' (*note Command Loop
     Info::) is either `nil' or a list--then it uses a dialog box or
     pop-up menu to ask the question.  In this case, it does not use
     keyboard input or the echo area.  You can force use of the mouse
     or use of keyboard input by binding `last-nonmenu-event' to a
     suitable value around the call.

     The return value of `map-y-or-n-p' is the number of objects acted
     on.


File: elisp,  Node: Reading a Password,  Next: Minibuffer Commands,  Prev: Multiple Queries,  Up: Minibuffers

20.9 Reading a Password
=======================

To read a password to pass to another program, you can use the function
`read-passwd'.

 -- Function: read-passwd prompt &optional confirm default
     This function reads a password, prompting with PROMPT.  It does
     not echo the password as the user types it; instead, it echoes `.'
     for each character in the password.

     The optional argument CONFIRM, if non-`nil', says to read the
     password twice and insist it must be the same both times.  If it
     isn't the same, the user has to type it over and over until the
     last two times match.

     The optional argument DEFAULT specifies the default password to
     return if the user enters empty input.  If DEFAULT is `nil', then
     `read-passwd' returns the null string in that case.


File: elisp,  Node: Minibuffer Commands,  Next: Minibuffer Contents,  Prev: Reading a Password,  Up: Minibuffers

20.10 Minibuffer Commands
=========================

This section describes some commands meant for use in the minibuffer.

 -- Command: exit-minibuffer
     This command exits the active minibuffer.  It is normally bound to
     keys in minibuffer local keymaps.

 -- Command: self-insert-and-exit
     This command exits the active minibuffer after inserting the last
     character typed on the keyboard (found in `last-command-char';
     *note Command Loop Info::).

 -- Command: previous-history-element n
     This command replaces the minibuffer contents with the value of the
     Nth previous (older) history element.

 -- Command: next-history-element n
     This command replaces the minibuffer contents with the value of the
     Nth more recent history element.

 -- Command: previous-matching-history-element pattern n
     This command replaces the minibuffer contents with the value of the
     Nth previous (older) history element that matches PATTERN (a
     regular expression).

 -- Command: next-matching-history-element pattern n
     This command replaces the minibuffer contents with the value of the
     Nth next (newer) history element that matches PATTERN (a regular
     expression).


File: elisp,  Node: Minibuffer Windows,  Next: Recursive Mini,  Prev: Minibuffer Contents,  Up: Minibuffers

20.11 Minibuffer Windows
========================

These functions access and select minibuffer windows and test whether
they are active.

 -- Function: active-minibuffer-window
     This function returns the currently active minibuffer window, or
     `nil' if none is currently active.

 -- Function: minibuffer-window &optional frame
     This function returns the minibuffer window used for frame FRAME.
     If FRAME is `nil', that stands for the current frame.  Note that
     the minibuffer window used by a frame need not be part of that
     frame--a frame that has no minibuffer of its own necessarily uses
     some other frame's minibuffer window.

 -- Function: set-minibuffer-window window
     This function specifies WINDOW as the minibuffer window to use.
     This affects where the minibuffer is displayed if you put text in
     it without invoking the usual minibuffer commands.  It has no
     effect on the usual minibuffer input functions because they all
     start by choosing the minibuffer window according to the current
     frame.

 -- Function: window-minibuffer-p &optional window
     This function returns non-`nil' if WINDOW is a minibuffer window.
     WINDOW defaults to the selected window.

   It is not correct to determine whether a given window is a
minibuffer by comparing it with the result of `(minibuffer-window)',
because there can be more than one minibuffer window if there is more
than one frame.

 -- Function: minibuffer-window-active-p window
     This function returns non-`nil' if WINDOW, assumed to be a
     minibuffer window, is currently active.


File: elisp,  Node: Minibuffer Contents,  Next: Minibuffer Windows,  Prev: Minibuffer Commands,  Up: Minibuffers

20.12 Minibuffer Contents
=========================

These functions access the minibuffer prompt and contents.

 -- Function: minibuffer-prompt
     This function returns the prompt string of the currently active
     minibuffer.  If no minibuffer is active, it returns `nil'.

 -- Function: minibuffer-prompt-end
     This function returns the current position of the end of the
     minibuffer prompt, if a minibuffer is current.  Otherwise, it
     returns the minimum valid buffer position.

 -- Function: minibuffer-prompt-width
     This function returns the current display-width of the minibuffer
     prompt, if a minibuffer is current.  Otherwise, it returns zero.

 -- Function: minibuffer-contents
     This function returns the editable contents of the minibuffer
     (that is, everything except the prompt) as a string, if a
     minibuffer is current.  Otherwise, it returns the entire contents
     of the current buffer.

 -- Function: minibuffer-contents-no-properties
     This is like `minibuffer-contents', except that it does not copy
     text properties, just the characters themselves.  *Note Text
     Properties::.

 -- Function: minibuffer-completion-contents
     This is like `minibuffer-contents', except that it returns only
     the contents before point.  That is the part that completion
     commands operate on.  *Note Minibuffer Completion::.

 -- Function: delete-minibuffer-contents
     This function erases the editable contents of the minibuffer (that
     is, everything except the prompt), if a minibuffer is current.
     Otherwise, it erases the entire current buffer.


File: elisp,  Node: Recursive Mini,  Next: Minibuffer Misc,  Prev: Minibuffer Windows,  Up: Minibuffers

20.13 Recursive Minibuffers
===========================

These functions and variables deal with recursive minibuffers (*note
Recursive Editing::):

 -- Function: minibuffer-depth
     This function returns the current depth of activations of the
     minibuffer, a nonnegative integer.  If no minibuffers are active,
     it returns zero.

 -- User Option: enable-recursive-minibuffers
     If this variable is non-`nil', you can invoke commands (such as
     `find-file') that use minibuffers even while the minibuffer window
     is active.  Such invocation produces a recursive editing level for
     a new minibuffer.  The outer-level minibuffer is invisible while
     you are editing the inner one.

     If this variable is `nil', you cannot invoke minibuffer commands
     when the minibuffer window is active, not even if you switch to
     another window to do it.

   If a command name has a property `enable-recursive-minibuffers' that
is non-`nil', then the command can use the minibuffer to read arguments
even if it is invoked from the minibuffer.  A command can also achieve
this by binding `enable-recursive-minibuffers' to `t' in the
interactive declaration (*note Using Interactive::).  The minibuffer
command `next-matching-history-element' (normally `M-s' in the
minibuffer) does the latter.


File: elisp,  Node: Minibuffer Misc,  Prev: Recursive Mini,  Up: Minibuffers

20.14 Minibuffer Miscellany
===========================

 -- Function: minibufferp &optional buffer-or-name
     This function returns non-`nil' if BUFFER-OR-NAME is a minibuffer.
     If BUFFER-OR-NAME is omitted, it tests the current buffer.

 -- Variable: minibuffer-setup-hook
     This is a normal hook that is run whenever the minibuffer is
     entered.  *Note Hooks::.

 -- Variable: minibuffer-exit-hook
     This is a normal hook that is run whenever the minibuffer is
     exited.  *Note Hooks::.

 -- Variable: minibuffer-help-form
     The current value of this variable is used to rebind `help-form'
     locally inside the minibuffer (*note Help Functions::).

 -- Variable: minibuffer-scroll-window
     If the value of this variable is non-`nil', it should be a window
     object.  When the function `scroll-other-window' is called in the
     minibuffer, it scrolls this window.

 -- Function: minibuffer-selected-window
     This function returns the window which was selected when the
     minibuffer was entered.  If selected window is not a minibuffer
     window, it returns `nil'.

 -- User Option: max-mini-window-height
     This variable specifies the maximum height for resizing minibuffer
     windows.  If a float, it specifies a fraction of the height of the
     frame.  If an integer, it specifies a number of lines.

 -- Function: minibuffer-message string
     This function displays STRING temporarily at the end of the
     minibuffer text, for two seconds, or until the next input event
     arrives, whichever comes first.


File: elisp,  Node: Command Loop,  Next: Keymaps,  Prev: Minibuffers,  Up: Top

21 Command Loop
***************

When you run Emacs, it enters the "editor command loop" almost
immediately.  This loop reads key sequences, executes their definitions,
and displays the results.  In this chapter, we describe how these things
are done, and the subroutines that allow Lisp programs to do them.

* Menu:

* Command Overview::    How the command loop reads commands.
* Defining Commands::   Specifying how a function should read arguments.
* Interactive Call::    Calling a command, so that it will read arguments.
* Distinguish Interactive::     Making a command distinguish interactive calls.
* Command Loop Info::   Variables set by the command loop for you to examine.
* Adjusting Point::     Adjustment of point after a command.
* Input Events::	What input looks like when you read it.
* Reading Input::       How to read input events from the keyboard or mouse.
* Special Events::      Events processed immediately and individually.
* Waiting::             Waiting for user input or elapsed time.
* Quitting::            How C-g works.  How to catch or defer quitting.
* Prefix Command Arguments::    How the commands to set prefix args work.
* Recursive Editing::   Entering a recursive edit,
                          and why you usually shouldn't.
* Disabling Commands::  How the command loop handles disabled commands.
* Command History::     How the command history is set up, and how accessed.
* Keyboard Macros::     How keyboard macros are implemented.


File: elisp,  Node: Command Overview,  Next: Defining Commands,  Up: Command Loop

21.1 Command Loop Overview
==========================

The first thing the command loop must do is read a key sequence, which
is a sequence of events that translates into a command.  It does this by
calling the function `read-key-sequence'.  Your Lisp code can also call
this function (*note Key Sequence Input::).  Lisp programs can also do
input at a lower level with `read-event' (*note Reading One Event::) or
discard pending input with `discard-input' (*note Event Input Misc::).

   The key sequence is translated into a command through the currently
active keymaps.  *Note Key Lookup::, for information on how this is
done.  The result should be a keyboard macro or an interactively
callable function.  If the key is `M-x', then it reads the name of
another command, which it then calls.  This is done by the command
`execute-extended-command' (*note Interactive Call::).

   To execute a command requires first reading the arguments for it.
This is done by calling `command-execute' (*note Interactive Call::).
For commands written in Lisp, the `interactive' specification says how
to read the arguments.  This may use the prefix argument (*note Prefix
Command Arguments::) or may read with prompting in the minibuffer
(*note Minibuffers::).  For example, the command `find-file' has an
`interactive' specification which says to read a file name using the
minibuffer.  The command's function body does not use the minibuffer;
if you call this command from Lisp code as a function, you must supply
the file name string as an ordinary Lisp function argument.

   If the command is a string or vector (i.e., a keyboard macro) then
`execute-kbd-macro' is used to execute it.  You can call this function
yourself (*note Keyboard Macros::).

   To terminate the execution of a running command, type `C-g'.  This
character causes "quitting" (*note Quitting::).

 -- Variable: pre-command-hook
     The editor command loop runs this normal hook before each command.
     At that time, `this-command' contains the command that is about to
     run, and `last-command' describes the previous command.  *Note
     Command Loop Info::.

 -- Variable: post-command-hook
     The editor command loop runs this normal hook after each command
     (including commands terminated prematurely by quitting or by
     errors), and also when the command loop is first entered.  At that
     time, `this-command' refers to the command that just ran, and
     `last-command' refers to the command before that.

   Quitting is suppressed while running `pre-command-hook' and
`post-command-hook'.  If an error happens while executing one of these
hooks, it terminates execution of the hook, and clears the hook
variable to `nil' so as to prevent an infinite loop of errors.

   A request coming into the Emacs server (*note Emacs Server:
(emacs)Emacs Server.) runs these two hooks just as a keyboard command
does.


File: elisp,  Node: Defining Commands,  Next: Interactive Call,  Prev: Command Overview,  Up: Command Loop

21.2 Defining Commands
======================

A Lisp function becomes a command when its body contains, at top level,
a form that calls the special form `interactive'.  This form does
nothing when actually executed, but its presence serves as a flag to
indicate that interactive calling is permitted.  Its argument controls
the reading of arguments for an interactive call.

* Menu:

* Using Interactive::     General rules for `interactive'.
* Interactive Codes::     The standard letter-codes for reading arguments
                             in various ways.
* Interactive Examples::  Examples of how to read interactive arguments.


File: elisp,  Node: Using Interactive,  Next: Interactive Codes,  Up: Defining Commands

21.2.1 Using `interactive'
--------------------------

This section describes how to write the `interactive' form that makes a
Lisp function an interactively-callable command, and how to examine a
command's `interactive' form.

 -- Special Form: interactive arg-descriptor
     This special form declares that the function in which it appears
     is a command, and that it may therefore be called interactively
     (via `M-x' or by entering a key sequence bound to it).  The
     argument ARG-DESCRIPTOR declares how to compute the arguments to
     the command when the command is called interactively.

     A command may be called from Lisp programs like any other
     function, but then the caller supplies the arguments and
     ARG-DESCRIPTOR has no effect.

     The `interactive' form has its effect because the command loop
     (actually, its subroutine `call-interactively') scans through the
     function definition looking for it, before calling the function.
     Once the function is called, all its body forms including the
     `interactive' form are executed, but at this time `interactive'
     simply returns `nil' without even evaluating its argument.

   There are three possibilities for the argument ARG-DESCRIPTOR:

   * It may be omitted or `nil'; then the command is called with no
     arguments.  This leads quickly to an error if the command requires
     one or more arguments.

   * It may be a string; then its contents should consist of a code
     character followed by a prompt (which some code characters use and
     some ignore).  The prompt ends either with the end of the string
     or with a newline.  Here is a simple example:

          (interactive "bFrobnicate buffer: ")

     The code letter `b' says to read the name of an existing buffer,
     with completion.  The buffer name is the sole argument passed to
     the command.  The rest of the string is a prompt.

     If there is a newline character in the string, it terminates the
     prompt.  If the string does not end there, then the rest of the
     string should contain another code character and prompt,
     specifying another argument.  You can specify any number of
     arguments in this way.

     The prompt string can use `%' to include previous argument values
     (starting with the first argument) in the prompt.  This is done
     using `format' (*note Formatting Strings::).  For example, here is
     how you could read the name of an existing buffer followed by a
     new name to give to that buffer:

          (interactive "bBuffer to rename: \nsRename buffer %s to: ")

     If the first character in the string is `*', then an error is
     signaled if the buffer is read-only.

     If the first character in the string is `@', and if the key
     sequence used to invoke the command includes any mouse events, then
     the window associated with the first of those events is selected
     before the command is run.

     You can use `*' and `@' together; the order does not matter.
     Actual reading of arguments is controlled by the rest of the prompt
     string (starting with the first character that is not `*' or `@').

   * It may be a Lisp expression that is not a string; then it should
     be a form that is evaluated to get a list of arguments to pass to
     the command.  Usually this form will call various functions to
     read input from the user, most often through the minibuffer (*note
     Minibuffers::) or directly from the keyboard (*note Reading
     Input::).

     Providing point or the mark as an argument value is also common,
     but if you do this _and_ read input (whether using the minibuffer
     or not), be sure to get the integer values of point or the mark
     after reading.  The current buffer may be receiving subprocess
     output; if subprocess output arrives while the command is waiting
     for input, it could relocate point and the mark.

     Here's an example of what _not_ to do:

          (interactive
           (list (region-beginning) (region-end)
                 (read-string "Foo: " nil 'my-history)))

     Here's how to avoid the problem, by examining point and the mark
     after reading the keyboard input:

          (interactive
           (let ((string (read-string "Foo: " nil 'my-history)))
             (list (region-beginning) (region-end) string)))

     *Warning:* the argument values should not include any data types
     that can't be printed and then read.  Some facilities save
     `command-history' in a file to be read in the subsequent sessions;
     if a command's arguments contain a data type that prints using
     `#<...>' syntax, those facilities won't work.

     There are, however, a few exceptions: it is ok to use a limited
     set of expressions such as `(point)', `(mark)',
     `(region-beginning)', and `(region-end)', because Emacs recognizes
     them specially and puts the expression (rather than its value)
     into the command history.  To see whether the expression you wrote
     is one of these exceptions, run the command, then examine `(car
     command-history)'.

 -- Function: interactive-form function
     This function returns the `interactive' form of FUNCTION.  If
     FUNCTION is an interactively callable function (*note Interactive
     Call::), the value is the command's `interactive' form
     `(interactive SPEC)', which specifies how to compute its
     arguments.  Otherwise, the value is `nil'.  If FUNCTION is a
     symbol, its function definition is used.


File: elisp,  Node: Interactive Codes,  Next: Interactive Examples,  Prev: Using Interactive,  Up: Defining Commands

21.2.2 Code Characters for `interactive'
----------------------------------------

The code character descriptions below contain a number of key words,
defined here as follows:

Completion
     Provide completion.  <TAB>, <SPC>, and <RET> perform name
     completion because the argument is read using `completing-read'
     (*note Completion::).  `?' displays a list of possible completions.

Existing
     Require the name of an existing object.  An invalid name is not
     accepted; the commands to exit the minibuffer do not exit if the
     current input is not valid.

Default
     A default value of some sort is used if the user enters no text in
     the minibuffer.  The default depends on the code character.

No I/O
     This code letter computes an argument without reading any input.
     Therefore, it does not use a prompt string, and any prompt string
     you supply is ignored.

     Even though the code letter doesn't use a prompt string, you must
     follow it with a newline if it is not the last code character in
     the string.

Prompt
     A prompt immediately follows the code character.  The prompt ends
     either with the end of the string or with a newline.

Special
     This code character is meaningful only at the beginning of the
     interactive string, and it does not look for a prompt or a newline.
     It is a single, isolated character.

   Here are the code character descriptions for use with `interactive':

`*'
     Signal an error if the current buffer is read-only.  Special.

`@'
     Select the window mentioned in the first mouse event in the key
     sequence that invoked this command.  Special.

`a'
     A function name (i.e., a symbol satisfying `fboundp').  Existing,
     Completion, Prompt.

`b'
     The name of an existing buffer.  By default, uses the name of the
     current buffer (*note Buffers::).  Existing, Completion, Default,
     Prompt.

`B'
     A buffer name.  The buffer need not exist.  By default, uses the
     name of a recently used buffer other than the current buffer.
     Completion, Default, Prompt.

`c'
     A character.  The cursor does not move into the echo area.  Prompt.

`C'
     A command name (i.e., a symbol satisfying `commandp').  Existing,
     Completion, Prompt.

`d'
     The position of point, as an integer (*note Point::).  No I/O.

`D'
     A directory name.  The default is the current default directory of
     the current buffer, `default-directory' (*note File Name
     Expansion::).  Existing, Completion, Default, Prompt.

`e'
     The first or next mouse event in the key sequence that invoked the
     command.  More precisely, `e' gets events that are lists, so you
     can look at the data in the lists.  *Note Input Events::.  No I/O.

     You can use `e' more than once in a single command's interactive
     specification.  If the key sequence that invoked the command has N
     events that are lists, the Nth `e' provides the Nth such event.
     Events that are not lists, such as function keys and ASCII
     characters, do not count where `e' is concerned.

`f'
     A file name of an existing file (*note File Names::).  The default
     directory is `default-directory'.  Existing, Completion, Default,
     Prompt.

`F'
     A file name.  The file need not exist.  Completion, Default,
     Prompt.

`G'
     A file name.  The file need not exist.  If the user enters just a
     directory name, then the value is just that directory name, with no
     file name within the directory added.  Completion, Default, Prompt.

`i'
     An irrelevant argument.  This code always supplies `nil' as the
     argument's value.  No I/O.

`k'
     A key sequence (*note Key Sequences::).  This keeps reading events
     until a command (or undefined command) is found in the current key
     maps.  The key sequence argument is represented as a string or
     vector.  The cursor does not move into the echo area.  Prompt.

     If `k' reads a key sequence that ends with a down-event, it also
     reads and discards the following up-event.  You can get access to
     that up-event with the `U' code character.

     This kind of input is used by commands such as `describe-key' and
     `global-set-key'.

`K'
     A key sequence, whose definition you intend to change.  This works
     like `k', except that it suppresses, for the last input event in
     the key sequence, the conversions that are normally used (when
     necessary) to convert an undefined key into a defined one.

`m'
     The position of the mark, as an integer.  No I/O.

`M'
     Arbitrary text, read in the minibuffer using the current buffer's
     input method, and returned as a string (*note Input Methods:
     (emacs)Input Methods.).  Prompt.

`n'
     A number, read with the minibuffer.  If the input is not a number,
     the user has to try again.  `n' never uses the prefix argument.
     Prompt.

`N'
     The numeric prefix argument; but if there is no prefix argument,
     read a number as with `n'.  The value is always a number.  *Note
     Prefix Command Arguments::.  Prompt.

`p'
     The numeric prefix argument.  (Note that this `p' is lower case.)
     No I/O.

`P'
     The raw prefix argument.  (Note that this `P' is upper case.)  No
     I/O.

`r'
     Point and the mark, as two numeric arguments, smallest first.
     This is the only code letter that specifies two successive
     arguments rather than one.  No I/O.

`s'
     Arbitrary text, read in the minibuffer and returned as a string
     (*note Text from Minibuffer::).  Terminate the input with either
     `C-j' or <RET>.  (`C-q' may be used to include either of these
     characters in the input.)  Prompt.

`S'
     An interned symbol whose name is read in the minibuffer.  Any
     whitespace character terminates the input.  (Use `C-q' to include
     whitespace in the string.)  Other characters that normally
     terminate a symbol (e.g., parentheses and brackets) do not do so
     here.  Prompt.

`U'
     A key sequence or `nil'.  Can be used after a `k' or `K' argument
     to get the up-event that was discarded (if any) after `k' or `K'
     read a down-event.  If no up-event has been discarded, `U'
     provides `nil' as the argument.  No I/O.

`v'
     A variable declared to be a user option (i.e., satisfying the
     predicate `user-variable-p').  This reads the variable using
     `read-variable'.  *Note Definition of read-variable::.  Existing,
     Completion, Prompt.

`x'
     A Lisp object, specified with its read syntax, terminated with a
     `C-j' or <RET>.  The object is not evaluated.  *Note Object from
     Minibuffer::.  Prompt.

`X'
     A Lisp form's value.  `X' reads as `x' does, then evaluates the
     form so that its value becomes the argument for the command.
     Prompt.

`z'
     A coding system name (a symbol).  If the user enters null input,
     the argument value is `nil'.  *Note Coding Systems::.  Completion,
     Existing, Prompt.

`Z'
     A coding system name (a symbol)--but only if this command has a
     prefix argument.  With no prefix argument, `Z' provides `nil' as
     the argument value.  Completion, Existing, Prompt.


File: elisp,  Node: Interactive Examples,  Prev: Interactive Codes,  Up: Defining Commands

21.2.3 Examples of Using `interactive'
--------------------------------------

Here are some examples of `interactive':

     (defun foo1 ()              ; `foo1' takes no arguments,
         (interactive)           ;   just moves forward two words.
         (forward-word 2))
          => foo1

     (defun foo2 (n)             ; `foo2' takes one argument,
         (interactive "p")       ;   which is the numeric prefix.
         (forward-word (* 2 n)))
          => foo2

     (defun foo3 (n)             ; `foo3' takes one argument,
         (interactive "nCount:") ;   which is read with the Minibuffer.
         (forward-word (* 2 n)))
          => foo3

     (defun three-b (b1 b2 b3)
       "Select three existing buffers.
     Put them into three windows, selecting the last one."
         (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:")
         (delete-other-windows)
         (split-window (selected-window) 8)
         (switch-to-buffer b1)
         (other-window 1)
         (split-window (selected-window) 8)
         (switch-to-buffer b2)
         (other-window 1)
         (switch-to-buffer b3))
          => three-b
     (three-b "*scratch*" "declarations.texi" "*mail*")
          => nil


File: elisp,  Node: Interactive Call,  Next: Distinguish Interactive,  Prev: Defining Commands,  Up: Command Loop

21.3 Interactive Call
=====================

After the command loop has translated a key sequence into a command it
invokes that command using the function `command-execute'.  If the
command is a function, `command-execute' calls `call-interactively',
which reads the arguments and calls the command.  You can also call
these functions yourself.

 -- Function: commandp object &optional for-call-interactively
     Returns `t' if OBJECT is suitable for calling interactively; that
     is, if OBJECT is a command.  Otherwise, returns `nil'.

     The interactively callable objects include strings and vectors
     (treated as keyboard macros), lambda expressions that contain a
     top-level call to `interactive', byte-code function objects made
     from such lambda expressions, autoload objects that are declared
     as interactive (non-`nil' fourth argument to `autoload'), and some
     of the primitive functions.

     A symbol satisfies `commandp' if its function definition satisfies
     `commandp'.  Keys and keymaps are not commands.  Rather, they are
     used to look up commands (*note Keymaps::).

     If FOR-CALL-INTERACTIVELY is non-`nil', then `commandp' returns
     `t' only for objects that `call-interactively' could call--thus,
     not for keyboard macros.

     See `documentation' in *Note Accessing Documentation::, for a
     realistic example of using `commandp'.

 -- Function: call-interactively command &optional record-flag keys
     This function calls the interactively callable function COMMAND,
     reading arguments according to its interactive calling
     specifications.  It returns whatever COMMAND returns.  An error is
     signaled if COMMAND is not a function or if it cannot be called
     interactively (i.e., is not a command).  Note that keyboard macros
     (strings and vectors) are not accepted, even though they are
     considered commands, because they are not functions.  If COMMAND
     is a symbol, then `call-interactively' uses its function
     definition.

     If RECORD-FLAG is non-`nil', then this command and its arguments
     are unconditionally added to the list `command-history'.
     Otherwise, the command is added only if it uses the minibuffer to
     read an argument.  *Note Command History::.

     The argument KEYS, if given, should be a vector which specifies
     the sequence of events to supply if the command inquires which
     events were used to invoke it.  If KEYS is omitted or `nil', the
     default is the return value of `this-command-keys-vector'.  *Note
     Definition of this-command-keys-vector::.

 -- Function: command-execute command &optional record-flag keys special
     This function executes COMMAND.  The argument COMMAND must satisfy
     the `commandp' predicate; i.e., it must be an interactively
     callable function or a keyboard macro.

     A string or vector as COMMAND is executed with
     `execute-kbd-macro'.  A function is passed to
     `call-interactively', along with the optional RECORD-FLAG and KEYS.

     A symbol is handled by using its function definition in its place.
     A symbol with an `autoload' definition counts as a command if it
     was declared to stand for an interactively callable function.
     Such a definition is handled by loading the specified library and
     then rechecking the definition of the symbol.

     The argument SPECIAL, if given, means to ignore the prefix
     argument and not clear it.  This is used for executing special
     events (*note Special Events::).

 -- Command: execute-extended-command prefix-argument
     This function reads a command name from the minibuffer using
     `completing-read' (*note Completion::).  Then it uses
     `command-execute' to call the specified command.  Whatever that
     command returns becomes the value of `execute-extended-command'.

     If the command asks for a prefix argument, it receives the value
     PREFIX-ARGUMENT.  If `execute-extended-command' is called
     interactively, the current raw prefix argument is used for
     PREFIX-ARGUMENT, and thus passed on to whatever command is run.

     `execute-extended-command' is the normal definition of `M-x', so
     it uses the string `M-x ' as a prompt.  (It would be better to
     take the prompt from the events used to invoke
     `execute-extended-command', but that is painful to implement.)  A
     description of the value of the prefix argument, if any, also
     becomes part of the prompt.

          (execute-extended-command 3)
          ---------- Buffer: Minibuffer ----------
          3 M-x forward-word RET
          ---------- Buffer: Minibuffer ----------
               => t


File: elisp,  Node: Distinguish Interactive,  Next: Command Loop Info,  Prev: Interactive Call,  Up: Command Loop

21.4 Distinguish Interactive Calls
==================================

Sometimes a command should display additional visual feedback (such as
an informative message in the echo area) for interactive calls only.
There are three ways to do this.  The recommended way to test whether
the function was called using `call-interactively' is to give it an
optional argument `print-message' and use the `interactive' spec to
make it non-`nil' in interactive calls.  Here's an example:

     (defun foo (&optional print-message)
       (interactive "p")
       (when print-message
         (message "foo")))

We use `"p"' because the numeric prefix argument is never `nil'.
Defined in this way, the function does display the message when called
from a keyboard macro.

   The above method with the additional argument is usually best,
because it allows callers to say "treat this call as interactive."  But
you can also do the job in a simpler way by testing
`called-interactively-p'.

 -- Function: called-interactively-p
     This function returns `t' when the calling function was called
     using `call-interactively'.

     If the containing function was called by Lisp evaluation (or with
     `apply' or `funcall'), then it was not called interactively.

   Here's an example of using `called-interactively-p':

     (defun foo ()
       (interactive)
       (when (called-interactively-p)
         (message "foo"))
       'haha)
          => foo

     ;; Type `M-x foo'.
          -| foo

     (foo)
          => haha

   Here is another example that contrasts direct and indirect calls to
`called-interactively-p'.

     (defun bar ()
       (interactive)
       (setq foobar (list (foo) (called-interactively-p))))
          => bar

     ;; Type `M-x bar'.
     ;; This does not display a message.

     foobar
          => (nil t)

   If you want to treat commands run in keyboard macros just like calls
from Lisp programs, test `interactive-p' instead of
`called-interactively-p'.

 -- Function: interactive-p
     This function returns `t' if the containing function (the one
     whose code includes the call to `interactive-p') was called in
     direct response to user input.  This means that it was called with
     the function `call-interactively', and that a keyboard macro is
     not running, and that Emacs is not running in batch mode.


File: elisp,  Node: Command Loop Info,  Next: Adjusting Point,  Prev: Distinguish Interactive,  Up: Command Loop

21.5 Information from the Command Loop
======================================

The editor command loop sets several Lisp variables to keep status
records for itself and for commands that are run.  With the exception of
`this-command' and `last-command' it's generally a bad idea to change
any of these variables in a Lisp program.

 -- Variable: last-command
     This variable records the name of the previous command executed by
     the command loop (the one before the current command).  Normally
     the value is a symbol with a function definition, but this is not
     guaranteed.

     The value is copied from `this-command' when a command returns to
     the command loop, except when the command has specified a prefix
     argument for the following command.

     This variable is always local to the current terminal and cannot be
     buffer-local.  *Note Multiple Displays::.

 -- Variable: real-last-command
     This variable is set up by Emacs just like `last-command', but
     never altered by Lisp programs.

 -- Variable: last-repeatable-command
     This variable stores the most recently executed command that was
     not part of an input event.  This is the command `repeat' will try
     to repeat, *Note Repeating: (emacs)Repeating.

 -- Variable: this-command
     This variable records the name of the command now being executed by
     the editor command loop.  Like `last-command', it is normally a
     symbol with a function definition.

     The command loop sets this variable just before running a command,
     and copies its value into `last-command' when the command finishes
     (unless the command specified a prefix argument for the following
     command).

     Some commands set this variable during their execution, as a flag
     for whatever command runs next.  In particular, the functions for
     killing text set `this-command' to `kill-region' so that any kill
     commands immediately following will know to append the killed text
     to the previous kill.

   If you do not want a particular command to be recognized as the
previous command in the case where it got an error, you must code that
command to prevent this.  One way is to set `this-command' to `t' at the
beginning of the command, and set `this-command' back to its proper
value at the end, like this:

     (defun foo (args...)
       (interactive ...)
       (let ((old-this-command this-command))
         (setq this-command t)
         ...do the work...
         (setq this-command old-this-command)))

We do not bind `this-command' with `let' because that would restore the
old value in case of error--a feature of `let' which in this case does
precisely what we want to avoid.

 -- Variable: this-original-command
     This has the same value as `this-command' except when command
     remapping occurs (*note Remapping Commands::).  In that case,
     `this-command' gives the command actually run (the result of
     remapping), and `this-original-command' gives the command that was
     specified to run but remapped into another command.

 -- Function: this-command-keys
     This function returns a string or vector containing the key
     sequence that invoked the present command, plus any previous
     commands that generated the prefix argument for this command.  Any
     events read by the command using `read-event' without a timeout
     get tacked on to the end.

     However, if the command has called `read-key-sequence', it returns
     the last read key sequence.  *Note Key Sequence Input::.  The
     value is a string if all events in the sequence were characters
     that fit in a string.  *Note Input Events::.

          (this-command-keys)
          ;; Now use `C-u C-x C-e' to evaluate that.
               => "^U^X^E"

 -- Function: this-command-keys-vector
     Like `this-command-keys', except that it always returns the events
     in a vector, so you don't need to deal with the complexities of
     storing input events in a string (*note Strings of Events::).

 -- Function: clear-this-command-keys &optional keep-record
     This function empties out the table of events for
     `this-command-keys' to return.  Unless KEEP-RECORD is non-`nil',
     it also empties the records that the function `recent-keys' (*note
     Recording Input::) will subsequently return.  This is useful after
     reading a password, to prevent the password from echoing
     inadvertently as part of the next command in certain cases.

 -- Variable: last-nonmenu-event
     This variable holds the last input event read as part of a key
     sequence, not counting events resulting from mouse menus.

     One use of this variable is for telling `x-popup-menu' where to pop
     up a menu.  It is also used internally by `y-or-n-p' (*note
     Yes-or-No Queries::).

 -- Variable: last-command-event
 -- Variable: last-command-char
     This variable is set to the last input event that was read by the
     command loop as part of a command.  The principal use of this
     variable is in `self-insert-command', which uses it to decide which
     character to insert.

          last-command-event
          ;; Now use `C-u C-x C-e' to evaluate that.
               => 5

     The value is 5 because that is the ASCII code for `C-e'.

     The alias `last-command-char' exists for compatibility with Emacs
     version 18.

 -- Variable: last-event-frame
     This variable records which frame the last input event was
     directed to.  Usually this is the frame that was selected when the
     event was generated, but if that frame has redirected input focus
     to another frame, the value is the frame to which the event was
     redirected.  *Note Input Focus::.

     If the last event came from a keyboard macro, the value is `macro'.


File: elisp,  Node: Adjusting Point,  Next: Input Events,  Prev: Command Loop Info,  Up: Command Loop

21.6 Adjusting Point After Commands
===================================

It is not easy to display a value of point in the middle of a sequence
of text that has the `display', `composition' or `intangible' property,
or is invisible.  Therefore, after a command finishes and returns to
the command loop, if point is within such a sequence, the command loop
normally moves point to the edge of the sequence.

   A command can inhibit this feature by setting the variable
`disable-point-adjustment':

 -- Variable: disable-point-adjustment
     If this variable is non-`nil' when a command returns to the
     command loop, then the command loop does not check for those text
     properties, and does not move point out of sequences that have
     them.

     The command loop sets this variable to `nil' before each command,
     so if a command sets it, the effect applies only to that command.

 -- Variable: global-disable-point-adjustment
     If you set this variable to a non-`nil' value, the feature of
     moving point out of these sequences is completely turned off.


File: elisp,  Node: Input Events,  Next: Reading Input,  Prev: Adjusting Point,  Up: Command Loop

21.7 Input Events
=================

The Emacs command loop reads a sequence of "input events" that
represent keyboard or mouse activity.  The events for keyboard activity
are characters or symbols; mouse events are always lists.  This section
describes the representation and meaning of input events in detail.

 -- Function: eventp object
     This function returns non-`nil' if OBJECT is an input event or
     event type.

     Note that any symbol might be used as an event or an event type.
     `eventp' cannot distinguish whether a symbol is intended by Lisp
     code to be used as an event.  Instead, it distinguishes whether the
     symbol has actually been used in an event that has been read as
     input in the current Emacs session.  If a symbol has not yet been
     so used, `eventp' returns `nil'.

* Menu:

* Keyboard Events::		Ordinary characters--keys with symbols on them.
* Function Keys::		Function keys--keys with names, not symbols.
* Mouse Events::                Overview of mouse events.
* Click Events::		Pushing and releasing a mouse button.
* Drag Events::			Moving the mouse before releasing the button.
* Button-Down Events::		A button was pushed and not yet released.
* Repeat Events::               Double and triple click (or drag, or down).
* Motion Events::		Just moving the mouse, not pushing a button.
* Focus Events::		Moving the mouse between frames.
* Misc Events::                 Other events the system can generate.
* Event Examples::		Examples of the lists for mouse events.
* Classifying Events::		Finding the modifier keys in an event symbol.
				Event types.
* Accessing Mouse::		Functions to extract info from mouse events.
* Accessing Scroll::		Functions to get info from scroll bar events.
* Strings of Events::           Special considerations for putting
				  keyboard character events in a string.


File: elisp,  Node: Keyboard Events,  Next: Function Keys,  Up: Input Events

21.7.1 Keyboard Events
----------------------

There are two kinds of input you can get from the keyboard: ordinary
keys, and function keys.  Ordinary keys correspond to characters; the
events they generate are represented in Lisp as characters.  The event
type of a character event is the character itself (an integer); see
*Note Classifying Events::.

   An input character event consists of a "basic code" between 0 and
524287, plus any or all of these "modifier bits":

meta
     The 2**27 bit in the character code indicates a character typed
     with the meta key held down.

control
     The 2**26 bit in the character code indicates a non-ASCII control
     character.

     ASCII control characters such as `C-a' have special basic codes of
     their own, so Emacs needs no special bit to indicate them.  Thus,
     the code for `C-a' is just 1.

     But if you type a control combination not in ASCII, such as `%'
     with the control key, the numeric value you get is the code for
     `%' plus 2**26 (assuming the terminal supports non-ASCII control
     characters).

shift
     The 2**25 bit in the character code indicates an ASCII control
     character typed with the shift key held down.

     For letters, the basic code itself indicates upper versus lower
     case; for digits and punctuation, the shift key selects an
     entirely different character with a different basic code.  In
     order to keep within the ASCII character set whenever possible,
     Emacs avoids using the 2**25 bit for those characters.

     However, ASCII provides no way to distinguish `C-A' from `C-a', so
     Emacs uses the 2**25 bit in `C-A' and not in `C-a'.

hyper
     The 2**24 bit in the character code indicates a character typed
     with the hyper key held down.

super
     The 2**23 bit in the character code indicates a character typed
     with the super key held down.

alt
     The 2**22 bit in the character code indicates a character typed
     with the alt key held down.  (On some terminals, the key labeled
     <ALT> is actually the meta key.)

   It is best to avoid mentioning specific bit numbers in your program.
To test the modifier bits of a character, use the function
`event-modifiers' (*note Classifying Events::).  When making key
bindings, you can use the read syntax for characters with modifier bits
(`\C-', `\M-', and so on).  For making key bindings with `define-key',
you can use lists such as `(control hyper ?x)' to specify the
characters (*note Changing Key Bindings::).  The function
`event-convert-list' converts such a list into an event type (*note
Classifying Events::).


File: elisp,  Node: Function Keys,  Next: Mouse Events,  Prev: Keyboard Events,  Up: Input Events

21.7.2 Function Keys
--------------------

Most keyboards also have "function keys"--keys that have names or
symbols that are not characters.  Function keys are represented in Emacs
Lisp as symbols; the symbol's name is the function key's label, in lower
case.  For example, pressing a key labeled <F1> places the symbol `f1'
in the input stream.

   The event type of a function key event is the event symbol itself.
*Note Classifying Events::.

   Here are a few special cases in the symbol-naming convention for
function keys:

`backspace', `tab', `newline', `return', `delete'
     These keys correspond to common ASCII control characters that have
     special keys on most keyboards.

     In ASCII, `C-i' and <TAB> are the same character.  If the terminal
     can distinguish between them, Emacs conveys the distinction to
     Lisp programs by representing the former as the integer 9, and the
     latter as the symbol `tab'.

     Most of the time, it's not useful to distinguish the two.  So
     normally `function-key-map' (*note Translation Keymaps::) is set
     up to map `tab' into 9.  Thus, a key binding for character code 9
     (the character `C-i') also applies to `tab'.  Likewise for the
     other symbols in this group.  The function `read-char' likewise
     converts these events into characters.

     In ASCII, <BS> is really `C-h'.  But `backspace' converts into the
     character code 127 (<DEL>), not into code 8 (<BS>).  This is what
     most users prefer.

`left', `up', `right', `down'
     Cursor arrow keys

`kp-add', `kp-decimal', `kp-divide', ...
     Keypad keys (to the right of the regular keyboard).

`kp-0', `kp-1', ...
     Keypad keys with digits.

`kp-f1', `kp-f2', `kp-f3', `kp-f4'
     Keypad PF keys.

`kp-home', `kp-left', `kp-up', `kp-right', `kp-down'
     Keypad arrow keys.  Emacs normally translates these into the
     corresponding non-keypad keys `home', `left', ...

`kp-prior', `kp-next', `kp-end', `kp-begin', `kp-insert', `kp-delete'
     Additional keypad duplicates of keys ordinarily found elsewhere.
     Emacs normally translates these into the like-named non-keypad
     keys.

   You can use the modifier keys <ALT>, <CTRL>, <HYPER>, <META>,
<SHIFT>, and <SUPER> with function keys.  The way to represent them is
with prefixes in the symbol name:

`A-'
     The alt modifier.

`C-'
     The control modifier.

`H-'
     The hyper modifier.

`M-'
     The meta modifier.

`S-'
     The shift modifier.

`s-'
     The super modifier.

   Thus, the symbol for the key <F3> with <META> held down is `M-f3'.
When you use more than one prefix, we recommend you write them in
alphabetical order; but the order does not matter in arguments to the
key-binding lookup and modification functions.


File: elisp,  Node: Mouse Events,  Next: Click Events,  Prev: Function Keys,  Up: Input Events

21.7.3 Mouse Events
-------------------

Emacs supports four kinds of mouse events: click events, drag events,
button-down events, and motion events.  All mouse events are represented
as lists.  The CAR of the list is the event type; this says which mouse
button was involved, and which modifier keys were used with it.  The
event type can also distinguish double or triple button presses (*note
Repeat Events::).  The rest of the list elements give position and time
information.

   For key lookup, only the event type matters: two events of the same
type necessarily run the same command.  The command can access the full
values of these events using the `e' interactive code.  *Note
Interactive Codes::.

   A key sequence that starts with a mouse event is read using the
keymaps of the buffer in the window that the mouse was in, not the
current buffer.  This does not imply that clicking in a window selects
that window or its buffer--that is entirely under the control of the
command binding of the key sequence.


File: elisp,  Node: Click Events,  Next: Drag Events,  Prev: Mouse Events,  Up: Input Events

21.7.4 Click Events
-------------------

When the user presses a mouse button and releases it at the same
location, that generates a "click" event.  All mouse click event share
the same format:

     (EVENT-TYPE POSITION CLICK-COUNT)

EVENT-TYPE
     This is a symbol that indicates which mouse button was used.  It is
     one of the symbols `mouse-1', `mouse-2', ..., where the buttons
     are numbered left to right.

     You can also use prefixes `A-', `C-', `H-', `M-', `S-' and `s-'
     for modifiers alt, control, hyper, meta, shift and super, just as
     you would with function keys.

     This symbol also serves as the event type of the event.  Key
     bindings describe events by their types; thus, if there is a key
     binding for `mouse-1', that binding would apply to all events whose
     EVENT-TYPE is `mouse-1'.

POSITION
     This is the position where the mouse click occurred.  The actual
     format of POSITION depends on what part of a window was clicked
     on.  The various formats are described below.

CLICK-COUNT
     This is the number of rapid repeated presses so far of the same
     mouse button.  *Note Repeat Events::.

   For mouse click events in the text area, mode line, header line, or
in the marginal areas, POSITION has this form:

     (WINDOW POS-OR-AREA (X . Y) TIMESTAMP
      OBJECT TEXT-POS (COL . ROW)
      IMAGE (DX . DY) (WIDTH . HEIGHT))

WINDOW
     This is the window in which the click occurred.

POS-OR-AREA
     This is the buffer position of the character clicked on in the text
     area, or if clicked outside the text area, it is the window area in
     which the click occurred.  It is one of the symbols `mode-line',
     `header-line', `vertical-line', `left-margin', `right-margin',
     `left-fringe', or `right-fringe'.

X, Y
     These are the pixel-denominated coordinates of the click, relative
     to the top left corner of WINDOW, which is `(0 . 0)'.  For the
     mode or header line, Y does not have meaningful data.  For the
     vertical line, X does not have meaningful data.

TIMESTAMP
     This is the time at which the event occurred, in milliseconds.

OBJECT
     This is the object on which the click occurred.  It is either
     `nil' if there is no string property, or it has the form (STRING .
     STRING-POS) when there is a string-type text property at the click
     position.

STRING
     This is the string on which the click occurred, including any
     properties.

STRING-POS
     This is the position in the string on which the click occurred,
     relevant if properties at the click need to be looked up.

TEXT-POS
     For clicks on a marginal area or on a fringe, this is the buffer
     position of the first visible character in the corresponding line
     in the window.  For other events, it is the current buffer
     position in the window.

COL, ROW
     These are the actual coordinates of the glyph under the X, Y
     position, possibly padded with default character width glyphs if X
     is beyond the last glyph on the line.

IMAGE
     This is the image object on which the click occurred.  It is either
     `nil' if there is no image at the position clicked on, or it is an
     image object as returned by `find-image' if click was in an image.

DX, DY
     These are the pixel-denominated coordinates of the click, relative
     to the top left corner of OBJECT, which is `(0 . 0)'.  If OBJECT
     is `nil', the coordinates are relative to the top left corner of
     the character glyph clicked on.

   For mouse clicks on a scroll-bar, POSITION has this form:

     (WINDOW AREA (PORTION . WHOLE) TIMESTAMP PART)

WINDOW
     This is the window whose scroll-bar was clicked on.

AREA
     This is the scroll bar where the click occurred.  It is one of the
     symbols `vertical-scroll-bar' or `horizontal-scroll-bar'.

PORTION
     This is the distance of the click from the top or left end of the
     scroll bar.

WHOLE
     This is the length of the entire scroll bar.

TIMESTAMP
     This is the time at which the event occurred, in milliseconds.

PART
     This is the part of the scroll-bar which was clicked on.  It is one
     of the symbols `above-handle', `handle', `below-handle', `up',
     `down', `top', `bottom', and `end-scroll'.

   In one special case, BUFFER-POS is a list containing a symbol (one
of the symbols listed above) instead of just the symbol.  This happens
after the imaginary prefix keys for the event are inserted into the
input stream.  *Note Key Sequence Input::.


File: elisp,  Node: Drag Events,  Next: Button-Down Events,  Prev: Click Events,  Up: Input Events

21.7.5 Drag Events
------------------

With Emacs, you can have a drag event without even changing your
clothes.  A "drag event" happens every time the user presses a mouse
button and then moves the mouse to a different character position before
releasing the button.  Like all mouse events, drag events are
represented in Lisp as lists.  The lists record both the starting mouse
position and the final position, like this:

     (EVENT-TYPE
      (WINDOW1 BUFFER-POS1 (X1 . Y1) TIMESTAMP1)
      (WINDOW2 BUFFER-POS2 (X2 . Y2) TIMESTAMP2)
      CLICK-COUNT)

   For a drag event, the name of the symbol EVENT-TYPE contains the
prefix `drag-'.  For example, dragging the mouse with button 2 held
down generates a `drag-mouse-2' event.  The second and third elements
of the event give the starting and ending position of the drag.  Aside
from that, the data have the same meanings as in a click event (*note
Click Events::).  You can access the second element of any mouse event
in the same way, with no need to distinguish drag events from others.

   The `drag-' prefix follows the modifier key prefixes such as `C-'
and `M-'.

   If `read-key-sequence' receives a drag event that has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position.  This means that you don't have to distinguish between click
and drag events unless you want to.


File: elisp,  Node: Button-Down Events,  Next: Repeat Events,  Prev: Drag Events,  Up: Input Events

21.7.6 Button-Down Events
-------------------------

Click and drag events happen when the user releases a mouse button.
They cannot happen earlier, because there is no way to distinguish a
click from a drag until the button is released.

   If you want to take action as soon as a button is pressed, you need
to handle "button-down" events.(1)  These occur as soon as a button is
pressed.  They are represented by lists that look exactly like click
events (*note Click Events::), except that the EVENT-TYPE symbol name
contains the prefix `down-'.  The `down-' prefix follows modifier key
prefixes such as `C-' and `M-'.

   The function `read-key-sequence' ignores any button-down events that
don't have command bindings; therefore, the Emacs command loop ignores
them too.  This means that you need not worry about defining
button-down events unless you want them to do something.  The usual
reason to define a button-down event is so that you can track mouse
motion (by reading motion events) until the button is released.  *Note
Motion Events::.

   ---------- Footnotes ----------

   (1) Button-down is the conservative antithesis of drag.


File: elisp,  Node: Repeat Events,  Next: Motion Events,  Prev: Button-Down Events,  Up: Input Events

21.7.7 Repeat Events
--------------------

If you press the same mouse button more than once in quick succession
without moving the mouse, Emacs generates special "repeat" mouse events
for the second and subsequent presses.

   The most common repeat events are "double-click" events.  Emacs
generates a double-click event when you click a button twice; the event
happens when you release the button (as is normal for all click events).

   The event type of a double-click event contains the prefix
`double-'.  Thus, a double click on the second mouse button with <meta>
held down comes to the Lisp program as `M-double-mouse-2'.  If a
double-click event has no binding, the binding of the corresponding
ordinary click event is used to execute it.  Thus, you need not pay
attention to the double click feature unless you really want to.

   When the user performs a double click, Emacs generates first an
ordinary click event, and then a double-click event.  Therefore, you
must design the command binding of the double click event to assume
that the single-click command has already run.  It must produce the
desired results of a double click, starting from the results of a
single click.

   This is convenient, if the meaning of a double click somehow "builds
on" the meaning of a single click--which is recommended user interface
design practice for double clicks.

   If you click a button, then press it down again and start moving the
mouse with the button held down, then you get a "double-drag" event
when you ultimately release the button.  Its event type contains
`double-drag' instead of just `drag'.  If a double-drag event has no
binding, Emacs looks for an alternate binding as if the event were an
ordinary drag.

   Before the double-click or double-drag event, Emacs generates a
"double-down" event when the user presses the button down for the
second time.  Its event type contains `double-down' instead of just
`down'.  If a double-down event has no binding, Emacs looks for an
alternate binding as if the event were an ordinary button-down event.
If it finds no binding that way either, the double-down event is
ignored.

   To summarize, when you click a button and then press it again right
away, Emacs generates a down event and a click event for the first
click, a double-down event when you press the button again, and finally
either a double-click or a double-drag event.

   If you click a button twice and then press it again, all in quick
succession, Emacs generates a "triple-down" event, followed by either a
"triple-click" or a "triple-drag".  The event types of these events
contain `triple' instead of `double'.  If any triple event has no
binding, Emacs uses the binding that it would use for the corresponding
double event.

   If you click a button three or more times and then press it again,
the events for the presses beyond the third are all triple events.
Emacs does not have separate event types for quadruple, quintuple, etc.
events.  However, you can look at the event list to find out precisely
how many times the button was pressed.

 -- Function: event-click-count event
     This function returns the number of consecutive button presses
     that led up to EVENT.  If EVENT is a double-down, double-click or
     double-drag event, the value is 2.  If EVENT is a triple event,
     the value is 3 or greater.  If EVENT is an ordinary mouse event
     (not a repeat event), the value is 1.

 -- User Option: double-click-fuzz
     To generate repeat events, successive mouse button presses must be
     at approximately the same screen position.  The value of
     `double-click-fuzz' specifies the maximum number of pixels the
     mouse may be moved (horizontally or vertically) between two
     successive clicks to make a double-click.

     This variable is also the threshold for motion of the mouse to
     count as a drag.

 -- User Option: double-click-time
     To generate repeat events, the number of milliseconds between
     successive button presses must be less than the value of
     `double-click-time'.  Setting `double-click-time' to `nil'
     disables multi-click detection entirely.  Setting it to `t'
     removes the time limit; Emacs then detects multi-clicks by
     position only.


File: elisp,  Node: Motion Events,  Next: Focus Events,  Prev: Repeat Events,  Up: Input Events

21.7.8 Motion Events
--------------------

Emacs sometimes generates "mouse motion" events to describe motion of
the mouse without any button activity.  Mouse motion events are
represented by lists that look like this:

     (mouse-movement (WINDOW BUFFER-POS (X . Y) TIMESTAMP))

   The second element of the list describes the current position of the
mouse, just as in a click event (*note Click Events::).

   The special form `track-mouse' enables generation of motion events
within its body.  Outside of `track-mouse' forms, Emacs does not
generate events for mere motion of the mouse, and these events do not
appear.  *Note Mouse Tracking::.


File: elisp,  Node: Focus Events,  Next: Misc Events,  Prev: Motion Events,  Up: Input Events

21.7.9 Focus Events
-------------------

Window systems provide general ways for the user to control which window
gets keyboard input.  This choice of window is called the "focus".
When the user does something to switch between Emacs frames, that
generates a "focus event".  The normal definition of a focus event, in
the global keymap, is to select a new frame within Emacs, as the user
would expect.  *Note Input Focus::.

   Focus events are represented in Lisp as lists that look like this:

     (switch-frame NEW-FRAME)

where NEW-FRAME is the frame switched to.

   Most X window managers are set up so that just moving the mouse into
a window is enough to set the focus there.  Emacs appears to do this,
because it changes the cursor to solid in the new frame.  However, there
is no need for the Lisp program to know about the focus change until
some other kind of input arrives.  So Emacs generates a focus event only
when the user actually types a keyboard key or presses a mouse button in
the new frame; just moving the mouse between frames does not generate a
focus event.

   A focus event in the middle of a key sequence would garble the
sequence.  So Emacs never generates a focus event in the middle of a key
sequence.  If the user changes focus in the middle of a key
sequence--that is, after a prefix key--then Emacs reorders the events
so that the focus event comes either before or after the multi-event key
sequence, and not within it.


File: elisp,  Node: Misc Events,  Next: Event Examples,  Prev: Focus Events,  Up: Input Events

21.7.10 Miscellaneous System Events
-----------------------------------

A few other event types represent occurrences within the system.

`(delete-frame (FRAME))'
     This kind of event indicates that the user gave the window manager
     a command to delete a particular window, which happens to be an
     Emacs frame.

     The standard definition of the `delete-frame' event is to delete
     FRAME.

`(iconify-frame (FRAME))'
     This kind of event indicates that the user iconified FRAME using
     the window manager.  Its standard definition is `ignore'; since the
     frame has already been iconified, Emacs has no work to do.  The
     purpose of this event type is so that you can keep track of such
     events if you want to.

`(make-frame-visible (FRAME))'
     This kind of event indicates that the user deiconified FRAME using
     the window manager.  Its standard definition is `ignore'; since the
     frame has already been made visible, Emacs has no work to do.

`(wheel-up POSITION)'

`(wheel-down POSITION)'
     These kinds of event are generated by moving a mouse wheel.  Their
     usual meaning is a kind of scroll or zoom.

     The element POSITION is a list describing the position of the
     event, in the same format as used in a mouse-click event.

     This kind of event is generated only on some kinds of systems. On
     some systems, `mouse-4' and `mouse-5' are used instead.  For
     portable code, use the variables `mouse-wheel-up-event' and
     `mouse-wheel-down-event' defined in `mwheel.el' to determine what
     event types to expect for the mouse wheel.

`(drag-n-drop POSITION FILES)'
     This kind of event is generated when a group of files is selected
     in an application outside of Emacs, and then dragged and dropped
     onto an Emacs frame.

     The element POSITION is a list describing the position of the
     event, in the same format as used in a mouse-click event, and
     FILES is the list of file names that were dragged and dropped.
     The usual way to handle this event is by visiting these files.

     This kind of event is generated, at present, only on some kinds of
     systems.

`help-echo'
     This kind of event is generated when a mouse pointer moves onto a
     portion of buffer text which has a `help-echo' text property.  The
     generated event has this form:

          (help-echo FRAME HELP WINDOW OBJECT POS)

     The precise meaning of the event parameters and the way these
     parameters are used to display the help-echo text are described in
     *Note Text help-echo::.

`sigusr1'
`sigusr2'
     These events are generated when the Emacs process receives the
     signals `SIGUSR1' and `SIGUSR2'.  They contain no additional data
     because signals do not carry additional information.

     To catch a user signal, bind the corresponding event to an
     interactive command in the `special-event-map' (*note Active
     Keymaps::).  The command is called with no arguments, and the
     specific signal event is available in `last-input-event'.  For
     example:

          (defun sigusr-handler ()
            (interactive)
            (message "Caught signal %S" last-input-event))

          (define-key special-event-map [sigusr1] 'sigusr-handler)

     To test the signal handler, you can make Emacs send a signal to
     itself:

          (signal-process (emacs-pid) 'sigusr1)

   If one of these events arrives in the middle of a key sequence--that
is, after a prefix key--then Emacs reorders the events so that this
event comes either before or after the multi-event key sequence, not
within it.


File: elisp,  Node: Event Examples,  Next: Classifying Events,  Prev: Misc Events,  Up: Input Events

21.7.11 Event Examples
----------------------

If the user presses and releases the left mouse button over the same
location, that generates a sequence of events like this:

     (down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
     (mouse-1      (#<window 18 on NEWS> 2613 (0 . 38) -864180))

   While holding the control key down, the user might hold down the
second mouse button, and drag the mouse from one line to the next.
That produces two events, as shown here:

     (C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
     (C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
                     (#<window 18 on NEWS> 3510 (0 . 28) -729648))

   While holding down the meta and shift keys, the user might press the
second mouse button on the window's mode line, and then drag the mouse
into another window.  That produces a pair of events like these:

     (M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
     (M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
                       (#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
                        -453816))

   To handle a SIGUSR1 signal, define an interactive function, and bind
it to the `signal usr1' event sequence:

     (defun usr1-handler ()
       (interactive)
       (message "Got USR1 signal"))
     (global-set-key [signal usr1] 'usr1-handler)


File: elisp,  Node: Classifying Events,  Next: Accessing Mouse,  Prev: Event Examples,  Up: Input Events

21.7.12 Classifying Events
--------------------------

Every event has an "event type", which classifies the event for key
binding purposes.  For a keyboard event, the event type equals the
event value; thus, the event type for a character is the character, and
the event type for a function key symbol is the symbol itself.  For
events that are lists, the event type is the symbol in the CAR of the
list.  Thus, the event type is always a symbol or a character.

   Two events of the same type are equivalent where key bindings are
concerned; thus, they always run the same command.  That does not
necessarily mean they do the same things, however, as some commands look
at the whole event to decide what to do.  For example, some commands use
the location of a mouse event to decide where in the buffer to act.

   Sometimes broader classifications of events are useful.  For example,
you might want to ask whether an event involved the <META> key,
regardless of which other key or mouse button was used.

   The functions `event-modifiers' and `event-basic-type' are provided
to get such information conveniently.

 -- Function: event-modifiers event
     This function returns a list of the modifiers that EVENT has.  The
     modifiers are symbols; they include `shift', `control', `meta',
     `alt', `hyper' and `super'.  In addition, the modifiers list of a
     mouse event symbol always contains one of `click', `drag', and
     `down'.  For double or triple events, it also contains `double' or
     `triple'.

     The argument EVENT may be an entire event object, or just an event
     type.  If EVENT is a symbol that has never been used in an event
     that has been read as input in the current Emacs session, then
     `event-modifiers' can return `nil', even when EVENT actually has
     modifiers.

     Here are some examples:

          (event-modifiers ?a)
               => nil
          (event-modifiers ?A)
               => (shift)
          (event-modifiers ?\C-a)
               => (control)
          (event-modifiers ?\C-%)
               => (control)
          (event-modifiers ?\C-\S-a)
               => (control shift)
          (event-modifiers 'f5)
               => nil
          (event-modifiers 's-f5)
               => (super)
          (event-modifiers 'M-S-f5)
               => (meta shift)
          (event-modifiers 'mouse-1)
               => (click)
          (event-modifiers 'down-mouse-1)
               => (down)

     The modifiers list for a click event explicitly contains `click',
     but the event symbol name itself does not contain `click'.

 -- Function: event-basic-type event
     This function returns the key or mouse button that EVENT
     describes, with all modifiers removed.  The EVENT argument is as
     in `event-modifiers'.  For example:

          (event-basic-type ?a)
               => 97
          (event-basic-type ?A)
               => 97
          (event-basic-type ?\C-a)
               => 97
          (event-basic-type ?\C-\S-a)
               => 97
          (event-basic-type 'f5)
               => f5
          (event-basic-type 's-f5)
               => f5
          (event-basic-type 'M-S-f5)
               => f5
          (event-basic-type 'down-mouse-1)
               => mouse-1

 -- Function: mouse-movement-p object
     This function returns non-`nil' if OBJECT is a mouse movement
     event.

 -- Function: event-convert-list list
     This function converts a list of modifier names and a basic event
     type to an event type which specifies all of them.  The basic
     event type must be the last element of the list.  For example,

          (event-convert-list '(control ?a))
               => 1
          (event-convert-list '(control meta ?a))
               => -134217727
          (event-convert-list '(control super f1))
               => C-s-f1


File: elisp,  Node: Accessing Mouse,  Next: Accessing Scroll,  Prev: Classifying Events,  Up: Input Events

21.7.13 Accessing Mouse Events
------------------------------

This section describes convenient functions for accessing the data in a
mouse button or motion event.

   These two functions return the starting or ending position of a
mouse-button event, as a list of this form:

     (WINDOW POS-OR-AREA (X . Y) TIMESTAMP
      OBJECT TEXT-POS (COL . ROW)
      IMAGE (DX . DY) (WIDTH . HEIGHT))

 -- Function: event-start event
     This returns the starting position of EVENT.

     If EVENT is a click or button-down event, this returns the
     location of the event.  If EVENT is a drag event, this returns the
     drag's starting position.

 -- Function: event-end event
     This returns the ending position of EVENT.

     If EVENT is a drag event, this returns the position where the user
     released the mouse button.  If EVENT is a click or button-down
     event, the value is actually the starting position, which is the
     only position such events have.

   These functions take a position list as described above, and return
various parts of it.

 -- Function: posn-window position
     Return the window that POSITION is in.

 -- Function: posn-area position
     Return the window area recorded in POSITION.  It returns `nil'
     when the event occurred in the text area of the window; otherwise,
     it is a symbol identifying the area in which the event occurred.

 -- Function: posn-point position
     Return the buffer position in POSITION.  When the event occurred
     in the text area of the window, in a marginal area, or on a fringe,
     this is an integer specifying a buffer position.  Otherwise, the
     value is undefined.

 -- Function: posn-x-y position
     Return the pixel-based x and y coordinates in POSITION, as a cons
     cell `(X . Y)'.  These coordinates are relative to the window
     given by `posn-window'.

     This example shows how to convert these window-relative coordinates
     into frame-relative coordinates:

          (defun frame-relative-coordinates (position)
            "Return frame-relative coordinates from POSITION."
            (let* ((x-y (posn-x-y position))
                   (window (posn-window position))
                   (edges (window-inside-pixel-edges window)))
              (cons (+ (car x-y) (car edges))
                    (+ (cdr x-y) (cadr edges)))))

 -- Function: posn-col-row position
     Return the row and column (in units of the frame's default
     character height and width) of POSITION, as a cons cell `(COL .
     ROW)'.  These are computed from the X and Y values actually found
     in POSITION.

 -- Function: posn-actual-col-row position
     Return the actual row and column in POSITION, as a cons cell `(COL
     . ROW)'.  The values are the actual row number in the window, and
     the actual character number in that row.  It returns `nil' if
     POSITION does not include actual positions values.  You can use
     `posn-col-row' to get approximate values.

 -- Function: posn-string position
     Return the string object in POSITION, either `nil', or a cons cell
     `(STRING . STRING-POS)'.

 -- Function: posn-image position
     Return the image object in POSITION, either `nil', or an image
     `(image ...)'.

 -- Function: posn-object position
     Return the image or string object in POSITION, either `nil', an
     image `(image ...)', or a cons cell `(STRING . STRING-POS)'.

 -- Function: posn-object-x-y position
     Return the pixel-based x and y coordinates relative to the upper
     left corner of the object in POSITION as a cons cell `(DX . DY)'.
     If the POSITION is a buffer position, return the relative position
     in the character at that position.

 -- Function: posn-object-width-height position
     Return the pixel width and height of the object in POSITION as a
     cons cell `(WIDTH . HEIGHT)'.  If the POSITION is a buffer
     position, return the size of the character at that position.

 -- Function: posn-timestamp position
     Return the timestamp in POSITION.  This is the time at which the
     event occurred, in milliseconds.

   These functions compute a position list given particular buffer
position or screen position.  You can access the data in this position
list with the functions described above.

 -- Function: posn-at-point &optional pos window
     This function returns a position list for position POS in WINDOW.
     POS defaults to point in WINDOW; WINDOW defaults to the selected
     window.

     `posn-at-point' returns `nil' if POS is not visible in WINDOW.

 -- Function: posn-at-x-y x y &optional frame-or-window whole
     This function returns position information corresponding to pixel
     coordinates X and Y in a specified frame or window,
     FRAME-OR-WINDOW, which defaults to the selected window.  The
     coordinates X and Y are relative to the frame or window used.  If
     WHOLE is `nil', the coordinates are relative to the window text
     area, otherwise they are relative to the entire window area
     including scroll bars, margins and fringes.


File: elisp,  Node: Accessing Scroll,  Next: Strings of Events,  Prev: Accessing Mouse,  Up: Input Events

21.7.14 Accessing Scroll Bar Events
-----------------------------------

These functions are useful for decoding scroll bar events.

 -- Function: scroll-bar-event-ratio event
     This function returns the fractional vertical position of a scroll
     bar event within the scroll bar.  The value is a cons cell
     `(PORTION . WHOLE)' containing two integers whose ratio is the
     fractional position.

 -- Function: scroll-bar-scale ratio total
     This function multiplies (in effect) RATIO by TOTAL, rounding the
     result to an integer.  The argument RATIO is not a number, but
     rather a pair `(NUM . DENOM)'--typically a value returned by
     `scroll-bar-event-ratio'.

     This function is handy for scaling a position on a scroll bar into
     a buffer position.  Here's how to do that:

          (+ (point-min)
             (scroll-bar-scale
                (posn-x-y (event-start event))
                (- (point-max) (point-min))))

     Recall that scroll bar events have two integers forming a ratio,
     in place of a pair of x and y coordinates.


File: elisp,  Node: Strings of Events,  Prev: Accessing Scroll,  Up: Input Events

21.7.15 Putting Keyboard Events in Strings
------------------------------------------

In most of the places where strings are used, we conceptualize the
string as containing text characters--the same kind of characters found
in buffers or files.  Occasionally Lisp programs use strings that
conceptually contain keyboard characters; for example, they may be key
sequences or keyboard macro definitions.  However, storing keyboard
characters in a string is a complex matter, for reasons of historical
compatibility, and it is not always possible.

   We recommend that new programs avoid dealing with these complexities
by not storing keyboard events in strings.  Here is how to do that:

   * Use vectors instead of strings for key sequences, when you plan to
     use them for anything other than as arguments to `lookup-key' and
     `define-key'.  For example, you can use `read-key-sequence-vector'
     instead of `read-key-sequence', and `this-command-keys-vector'
     instead of `this-command-keys'.

   * Use vectors to write key sequence constants containing meta
     characters, even when passing them directly to `define-key'.

   * When you have to look at the contents of a key sequence that might
     be a string, use `listify-key-sequence' (*note Event Input Misc::)
     first, to convert it to a list.

   The complexities stem from the modifier bits that keyboard input
characters can include.  Aside from the Meta modifier, none of these
modifier bits can be included in a string, and the Meta modifier is
allowed only in special cases.

   The earliest GNU Emacs versions represented meta characters as codes
in the range of 128 to 255.  At that time, the basic character codes
ranged from 0 to 127, so all keyboard character codes did fit in a
string.  Many Lisp programs used `\M-' in string constants to stand for
meta characters, especially in arguments to `define-key' and similar
functions, and key sequences and sequences of events were always
represented as strings.

   When we added support for larger basic character codes beyond 127,
and additional modifier bits, we had to change the representation of
meta characters.  Now the flag that represents the Meta modifier in a
character is 2**27 and such numbers cannot be included in a string.

   To support programs with `\M-' in string constants, there are
special rules for including certain meta characters in a string.  Here
are the rules for interpreting a string as a sequence of input
characters:

   * If the keyboard character value is in the range of 0 to 127, it
     can go in the string unchanged.

   * The meta variants of those characters, with codes in the range of
     2**27 to 2**27+127, can also go in the string, but you must change
     their numeric values.  You must set the 2**7 bit instead of the
     2**27 bit, resulting in a value between 128 and 255.  Only a
     unibyte string can include these codes.

   * Non-ASCII characters above 256 can be included in a multibyte
     string.

   * Other keyboard character events cannot fit in a string.  This
     includes keyboard events in the range of 128 to 255.

   Functions such as `read-key-sequence' that construct strings of
keyboard input characters follow these rules: they construct vectors
instead of strings, when the events won't fit in a string.

   When you use the read syntax `\M-' in a string, it produces a code
in the range of 128 to 255--the same code that you get if you modify
the corresponding keyboard event to put it in the string.  Thus, meta
events in strings work consistently regardless of how they get into the
strings.

   However, most programs would do well to avoid these issues by
following the recommendations at the beginning of this section.


File: elisp,  Node: Reading Input,  Next: Special Events,  Prev: Input Events,  Up: Command Loop

21.8 Reading Input
==================

The editor command loop reads key sequences using the function
`read-key-sequence', which uses `read-event'.  These and other
functions for event input are also available for use in Lisp programs.
See also `momentary-string-display' in *Note Temporary Displays::, and
`sit-for' in *Note Waiting::.  *Note Terminal Input::, for functions
and variables for controlling terminal input modes and debugging
terminal input.

   For higher-level input facilities, see *Note Minibuffers::.

* Menu:

* Key Sequence Input::		How to read one key sequence.
* Reading One Event::		How to read just one event.
* Event Mod::                   How Emacs modifies events as they are read.
* Invoking the Input Method::   How reading an event uses the input method.
* Quoted Character Input::	Asking the user to specify a character.
* Event Input Misc::    	How to reread or throw away input events.


File: elisp,  Node: Key Sequence Input,  Next: Reading One Event,  Up: Reading Input

21.8.1 Key Sequence Input
-------------------------

The command loop reads input a key sequence at a time, by calling
`read-key-sequence'.  Lisp programs can also call this function; for
example, `describe-key' uses it to read the key to describe.

 -- Function: read-key-sequence prompt &optional continue-echo
          dont-downcase-last switch-frame-ok command-loop
     This function reads a key sequence and returns it as a string or
     vector.  It keeps reading events until it has accumulated a
     complete key sequence; that is, enough to specify a non-prefix
     command using the currently active keymaps.  (Remember that a key
     sequence that starts with a mouse event is read using the keymaps
     of the buffer in the window that the mouse was in, not the current
     buffer.)

     If the events are all characters and all can fit in a string, then
     `read-key-sequence' returns a string (*note Strings of Events::).
     Otherwise, it returns a vector, since a vector can hold all kinds
     of events--characters, symbols, and lists.  The elements of the
     string or vector are the events in the key sequence.

     Reading a key sequence includes translating the events in various
     ways.  *Note Translation Keymaps::.

     The argument PROMPT is either a string to be displayed in the echo
     area as a prompt, or `nil', meaning not to display a prompt.  The
     argument CONTINUE-ECHO, if non-`nil', means to echo this key as a
     continuation of the previous key.

     Normally any upper case event is converted to lower case if the
     original event is undefined and the lower case equivalent is
     defined.  The argument DONT-DOWNCASE-LAST, if non-`nil', means do
     not convert the last event to lower case.  This is appropriate for
     reading a key sequence to be defined.

     The argument SWITCH-FRAME-OK, if non-`nil', means that this
     function should process a `switch-frame' event if the user
     switches frames before typing anything.  If the user switches
     frames in the middle of a key sequence, or at the start of the
     sequence but SWITCH-FRAME-OK is `nil', then the event will be put
     off until after the current key sequence.

     The argument COMMAND-LOOP, if non-`nil', means that this key
     sequence is being read by something that will read commands one
     after another.  It should be `nil' if the caller will read just
     one key sequence.

     In the following example, Emacs displays the prompt `?' in the
     echo area, and then the user types `C-x C-f'.

          (read-key-sequence "?")

          ---------- Echo Area ----------
          ?C-x C-f
          ---------- Echo Area ----------

               => "^X^F"

     The function `read-key-sequence' suppresses quitting: `C-g' typed
     while reading with this function works like any other character,
     and does not set `quit-flag'.  *Note Quitting::.

 -- Function: read-key-sequence-vector prompt &optional continue-echo
          dont-downcase-last switch-frame-ok command-loop
     This is like `read-key-sequence' except that it always returns the
     key sequence as a vector, never as a string.  *Note Strings of
     Events::.

   If an input character is upper-case (or has the shift modifier) and
has no key binding, but its lower-case equivalent has one, then
`read-key-sequence' converts the character to lower case.  Note that
`lookup-key' does not perform case conversion in this way.

   The function `read-key-sequence' also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely.  It also reshuffles focus events and
miscellaneous window events so that they never appear in a key sequence
with any other events.

   When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event type shows nothing special--it is the
same symbol that would normally represent that combination of mouse
button and modifier keys.  The information about the window part is kept
elsewhere in the event--in the coordinates.  But `read-key-sequence'
translates this information into imaginary "prefix keys," all of which
are symbols: `header-line', `horizontal-scroll-bar', `menu-bar',
`mode-line', `vertical-line', and `vertical-scroll-bar'.  You can define
meanings for mouse clicks in special window parts by defining key
sequences using these imaginary prefix keys.

   For example, if you call `read-key-sequence' and then click the
mouse on the window's mode line, you get two events, like this:

     (read-key-sequence "Click on the mode line: ")
          => [mode-line
              (mouse-1
               (#<window 6 on NEWS> mode-line
                (40 . 63) 5959987))]

 -- Variable: num-input-keys
     This variable's value is the number of key sequences processed so
     far in this Emacs session.  This includes key sequences read from
     the terminal and key sequences read from keyboard macros being
     executed.


File: elisp,  Node: Reading One Event,  Next: Event Mod,  Prev: Key Sequence Input,  Up: Reading Input

21.8.2 Reading One Event
------------------------

The lowest level functions for command input are those that read a
single event.

   None of the three functions below suppresses quitting.

 -- Function: read-event &optional prompt inherit-input-method seconds
     This function reads and returns the next event of command input,
     waiting if necessary until an event is available.  Events can come
     directly from the user or from a keyboard macro.

     If the optional argument PROMPT is non-`nil', it should be a
     string to display in the echo area as a prompt.  Otherwise,
     `read-event' does not display any message to indicate it is waiting
     for input; instead, it prompts by echoing: it displays
     descriptions of the events that led to or were read by the current
     command.  *Note The Echo Area::.

     If INHERIT-INPUT-METHOD is non-`nil', then the current input
     method (if any) is employed to make it possible to enter a
     non-ASCII character.  Otherwise, input method handling is disabled
     for reading this event.

     If `cursor-in-echo-area' is non-`nil', then `read-event' moves the
     cursor temporarily to the echo area, to the end of any message
     displayed there.  Otherwise `read-event' does not move the cursor.

     If SECONDS is non-`nil', it should be a number specifying the
     maximum time to wait for input, in seconds.  If no input arrives
     within that time, `read-event' stops waiting and returns `nil'.  A
     floating-point value for SECONDS means to wait for a fractional
     number of seconds.  Some systems support only a whole number of
     seconds; on these systems, SECONDS is rounded down.  If SECONDS is
     `nil', `read-event' waits as long as necessary for input to arrive.

     If SECONDS is `nil', Emacs is considered idle while waiting for
     user input to arrive.  Idle timers--those created with
     `run-with-idle-timer' (*note Idle Timers::)--can run during this
     period.  However, if SECONDS is non-`nil', the state of idleness
     remains unchanged.  If Emacs is non-idle when `read-event' is
     called, it remains non-idle throughout the operation of
     `read-event'; if Emacs is idle (which can happen if the call
     happens inside an idle timer), it remains idle.

     If `read-event' gets an event that is defined as a help character,
     then in some cases `read-event' processes the event directly
     without returning.  *Note Help Functions::.  Certain other events,
     called "special events", are also processed directly within
     `read-event' (*note Special Events::).

     Here is what happens if you call `read-event' and then press the
     right-arrow function key:

          (read-event)
               => right

 -- Function: read-char &optional prompt inherit-input-method seconds
     This function reads and returns a character of command input.  If
     the user generates an event which is not a character (i.e. a mouse
     click or function key event), `read-char' signals an error.  The
     arguments work as in `read-event'.

     In the first example, the user types the character `1' (ASCII code
     49).  The second example shows a keyboard macro definition that
     calls `read-char' from the minibuffer using `eval-expression'.
     `read-char' reads the keyboard macro's very next character, which
     is `1'.  Then `eval-expression' displays its return value in the
     echo area.

          (read-char)
               => 49

          ;; We assume here you use `M-:' to evaluate this.
          (symbol-function 'foo)
               => "^[:(read-char)^M1"
          (execute-kbd-macro 'foo)
               -| 49
               => nil

 -- Function: read-char-exclusive &optional prompt inherit-input-method
          seconds
     This function reads and returns a character of command input.  If
     the user generates an event which is not a character,
     `read-char-exclusive' ignores it and reads another event, until it
     gets a character.  The arguments work as in `read-event'.

 -- Variable: num-nonmacro-input-events
     This variable holds the total number of input events received so
     far from the terminal--not counting those generated by keyboard
     macros.


File: elisp,  Node: Event Mod,  Next: Invoking the Input Method,  Prev: Reading One Event,  Up: Reading Input

21.8.3 Modifying and Translating Input Events
---------------------------------------------

Emacs modifies every event it reads according to
`extra-keyboard-modifiers', then translates it through
`keyboard-translate-table' (if applicable), before returning it from
`read-event'.

 -- Variable: extra-keyboard-modifiers
     This variable lets Lisp programs "press" the modifier keys on the
     keyboard.  The value is a character.  Only the modifiers of the
     character matter.  Each time the user types a keyboard key, it is
     altered as if those modifier keys were held down.  For instance, if
     you bind `extra-keyboard-modifiers' to `?\C-\M-a', then all
     keyboard input characters typed during the scope of the binding
     will have the control and meta modifiers applied to them.  The
     character `?\C-@', equivalent to the integer 0, does not count as
     a control character for this purpose, but as a character with no
     modifiers.  Thus, setting `extra-keyboard-modifiers' to zero
     cancels any modification.

     When using a window system, the program can "press" any of the
     modifier keys in this way.  Otherwise, only the <CTL> and <META>
     keys can be virtually pressed.

     Note that this variable applies only to events that really come
     from the keyboard, and has no effect on mouse events or any other
     events.

 -- Variable: keyboard-translate-table
     This variable is the translate table for keyboard characters.  It
     lets you reshuffle the keys on the keyboard without changing any
     command bindings.  Its value is normally a char-table, or else
     `nil'.  (It can also be a string or vector, but this is considered
     obsolete.)

     If `keyboard-translate-table' is a char-table (*note
     Char-Tables::), then each character read from the keyboard is
     looked up in this char-table.  If the value found there is
     non-`nil', then it is used instead of the actual input character.

     Note that this translation is the first thing that happens to a
     character after it is read from the terminal.  Record-keeping
     features such as `recent-keys' and dribble files record the
     characters after translation.

     Note also that this translation is done before the characters are
     supplied to input methods (*note Input Methods::).  Use
     `translation-table-for-input' (*note Translation of Characters::),
     if you want to translate characters after input methods operate.

 -- Function: keyboard-translate from to
     This function modifies `keyboard-translate-table' to translate
     character code FROM into character code TO.  It creates the
     keyboard translate table if necessary.

   Here's an example of using the `keyboard-translate-table' to make
`C-x', `C-c' and `C-v' perform the cut, copy and paste operations:

     (keyboard-translate ?\C-x 'control-x)
     (keyboard-translate ?\C-c 'control-c)
     (keyboard-translate ?\C-v 'control-v)
     (global-set-key [control-x] 'kill-region)
     (global-set-key [control-c] 'kill-ring-save)
     (global-set-key [control-v] 'yank)

On a graphical terminal that supports extended ASCII input, you can
still get the standard Emacs meanings of one of those characters by
typing it with the shift key.  That makes it a different character as
far as keyboard translation is concerned, but it has the same usual
meaning.

   *Note Translation Keymaps::, for mechanisms that translate event
sequences at the level of `read-key-sequence'.


File: elisp,  Node: Invoking the Input Method,  Next: Quoted Character Input,  Prev: Event Mod,  Up: Reading Input

21.8.4 Invoking the Input Method
--------------------------------

The event-reading functions invoke the current input method, if any
(*note Input Methods::).  If the value of `input-method-function' is
non-`nil', it should be a function; when `read-event' reads a printing
character (including <SPC>) with no modifier bits, it calls that
function, passing the character as an argument.

 -- Variable: input-method-function
     If this is non-`nil', its value specifies the current input method
     function.

     *Warning:* don't bind this variable with `let'.  It is often
     buffer-local, and if you bind it around reading input (which is
     exactly when you _would_ bind it), switching buffers
     asynchronously while Emacs is waiting will cause the value to be
     restored in the wrong buffer.

   The input method function should return a list of events which should
be used as input.  (If the list is `nil', that means there is no input,
so `read-event' waits for another event.)  These events are processed
before the events in `unread-command-events' (*note Event Input
Misc::).  Events returned by the input method function are not passed
to the input method function again, even if they are printing
characters with no modifier bits.

   If the input method function calls `read-event' or
`read-key-sequence', it should bind `input-method-function' to `nil'
first, to prevent recursion.

   The input method function is not called when reading the second and
subsequent events of a key sequence.  Thus, these characters are not
subject to input method processing.  The input method function should
test the values of `overriding-local-map' and
`overriding-terminal-local-map'; if either of these variables is
non-`nil', the input method should put its argument into a list and
return that list with no further processing.


File: elisp,  Node: Quoted Character Input,  Next: Event Input Misc,  Prev: Invoking the Input Method,  Up: Reading Input

21.8.5 Quoted Character Input
-----------------------------

You can use the function `read-quoted-char' to ask the user to specify
a character, and allow the user to specify a control or meta character
conveniently, either literally or as an octal character code.  The
command `quoted-insert' uses this function.

 -- Function: read-quoted-char &optional prompt
     This function is like `read-char', except that if the first
     character read is an octal digit (0-7), it reads any number of
     octal digits (but stopping if a non-octal digit is found), and
     returns the character represented by that numeric character code.
     If the character that terminates the sequence of octal digits is
     <RET>, it is discarded.  Any other terminating character is used
     as input after this function returns.

     Quitting is suppressed when the first character is read, so that
     the user can enter a `C-g'.  *Note Quitting::.

     If PROMPT is supplied, it specifies a string for prompting the
     user.  The prompt string is always displayed in the echo area,
     followed by a single `-'.

     In the following example, the user types in the octal number 177
     (which is 127 in decimal).

          (read-quoted-char "What character")

          ---------- Echo Area ----------
          What character 1 7 7-
          ---------- Echo Area ----------

               => 127


File: elisp,  Node: Event Input Misc,  Prev: Quoted Character Input,  Up: Reading Input

21.8.6 Miscellaneous Event Input Features
-----------------------------------------

This section describes how to "peek ahead" at events without using them
up, how to check for pending input, and how to discard pending input.
See also the function `read-passwd' (*note Reading a Password::).

 -- Variable: unread-command-events
     This variable holds a list of events waiting to be read as command
     input.  The events are used in the order they appear in the list,
     and removed one by one as they are used.

     The variable is needed because in some cases a function reads an
     event and then decides not to use it.  Storing the event in this
     variable causes it to be processed normally, by the command loop
     or by the functions to read command input.

     For example, the function that implements numeric prefix arguments
     reads any number of digits.  When it finds a non-digit event, it
     must unread the event so that it can be read normally by the
     command loop.  Likewise, incremental search uses this feature to
     unread events with no special meaning in a search, because these
     events should exit the search and then execute normally.

     The reliable and easy way to extract events from a key sequence so
     as to put them in `unread-command-events' is to use
     `listify-key-sequence' (*note Strings of Events::).

     Normally you add events to the front of this list, so that the
     events most recently unread will be reread first.

     Events read from this list are not normally added to the current
     command's key sequence (as returned by e.g. `this-command-keys'),
     as the events will already have been added once as they were read
     for the first time.  An element of the form `(`t' . EVENT)' forces
     EVENT to be added to the current command's key sequence.

 -- Function: listify-key-sequence key
     This function converts the string or vector KEY to a list of
     individual events, which you can put in `unread-command-events'.

 -- Variable: unread-command-char
     This variable holds a character to be read as command input.  A
     value of -1 means "empty."

     This variable is mostly obsolete now that you can use
     `unread-command-events' instead; it exists only to support programs
     written for Emacs versions 18 and earlier.

 -- Function: input-pending-p
     This function determines whether any command input is currently
     available to be read.  It returns immediately, with value `t' if
     there is available input, `nil' otherwise.  On rare occasions it
     may return `t' when no input is available.

 -- Variable: last-input-event
 -- Variable: last-input-char
     This variable records the last terminal input event read, whether
     as part of a command or explicitly by a Lisp program.

     In the example below, the Lisp program reads the character `1',
     ASCII code 49.  It becomes the value of `last-input-event', while
     `C-e' (we assume `C-x C-e' command is used to evaluate this
     expression) remains the value of `last-command-event'.

          (progn (print (read-char))
                 (print last-command-event)
                 last-input-event)
               -| 49
               -| 5
               => 49

     The alias `last-input-char' exists for compatibility with Emacs
     version 18.

 -- Macro: while-no-input body...
     This construct runs the BODY forms and returns the value of the
     last one--but only if no input arrives.  If any input arrives
     during the execution of the BODY forms, it aborts them (working
     much like a quit).  The `while-no-input' form returns `nil' if
     aborted by a real quit, and returns `t' if aborted by arrival of
     other input.

     If a part of BODY binds `inhibit-quit' to non-`nil', arrival of
     input during those parts won't cause an abort until the end of
     that part.

     If you want to be able to distinguish all possible values computed
     by BODY from both kinds of abort conditions, write the code like
     this:

          (while-no-input
            (list
              (progn . BODY)))

 -- Function: discard-input
     This function discards the contents of the terminal input buffer
     and cancels any keyboard macro that might be in the process of
     definition.  It returns `nil'.

     In the following example, the user may type a number of characters
     right after starting the evaluation of the form.  After the
     `sleep-for' finishes sleeping, `discard-input' discards any
     characters typed during the sleep.

          (progn (sleep-for 2)
                 (discard-input))
               => nil


File: elisp,  Node: Special Events,  Next: Waiting,  Prev: Reading Input,  Up: Command Loop

21.9 Special Events
===================

Special events are handled at a very low level--as soon as they are
read.  The `read-event' function processes these events itself, and
never returns them.  Instead, it keeps waiting for the first event that
is not special and returns that one.

   Events that are handled in this way do not echo, they are never
grouped into key sequences, and they never appear in the value of
`last-command-event' or `(this-command-keys)'.  They do not discard a
numeric argument, they cannot be unread with `unread-command-events',
they may not appear in a keyboard macro, and they are not recorded in a
keyboard macro while you are defining one.

   These events do, however, appear in `last-input-event' immediately
after they are read, and this is the way for the event's definition to
find the actual event.

   The events types `iconify-frame', `make-frame-visible',
`delete-frame', `drag-n-drop', and user signals like `sigusr1' are
normally handled in this way.  The keymap which defines how to handle
special events--and which events are special--is in the variable
`special-event-map' (*note Active Keymaps::).


File: elisp,  Node: Waiting,  Next: Quitting,  Prev: Special Events,  Up: Command Loop

21.10 Waiting for Elapsed Time or Input
=======================================

The wait functions are designed to wait for a certain amount of time to
pass or until there is input.  For example, you may wish to pause in
the middle of a computation to allow the user time to view the display.
`sit-for' pauses and updates the screen, and returns immediately if
input comes in, while `sleep-for' pauses without updating the screen.

 -- Function: sit-for seconds &optional nodisp
     This function performs redisplay (provided there is no pending
     input from the user), then waits SECONDS seconds, or until input is
     available.  The usual purpose of `sit-for' is to give the user
     time to read text that you display.  The value is `t' if `sit-for'
     waited the full time with no input arriving (*note Event Input
     Misc::).  Otherwise, the value is `nil'.

     The argument SECONDS need not be an integer.  If it is a floating
     point number, `sit-for' waits for a fractional number of seconds.
     Some systems support only a whole number of seconds; on these
     systems, SECONDS is rounded down.

     The expression `(sit-for 0)' is equivalent to `(redisplay)', i.e.
     it requests a redisplay, without any delay, if there is no pending
     input.  *Note Forcing Redisplay::.

     If NODISP is non-`nil', then `sit-for' does not redisplay, but it
     still returns as soon as input is available (or when the timeout
     elapses).

     In batch mode (*note Batch Mode::), `sit-for' cannot be
     interrupted, even by input from the standard input descriptor.  It
     is thus equivalent to `sleep-for', which is described below.

     It is also possible to call `sit-for' with three arguments, as
     `(sit-for SECONDS MILLISEC NODISP)', but that is considered
     obsolete.

 -- Function: sleep-for seconds &optional millisec
     This function simply pauses for SECONDS seconds without updating
     the display.  It pays no attention to available input.  It returns
     `nil'.

     The argument SECONDS need not be an integer.  If it is a floating
     point number, `sleep-for' waits for a fractional number of seconds.
     Some systems support only a whole number of seconds; on these
     systems, SECONDS is rounded down.

     The optional argument MILLISEC specifies an additional waiting
     period measured in milliseconds.  This adds to the period
     specified by SECONDS.  If the system doesn't support waiting
     fractions of a second, you get an error if you specify nonzero
     MILLISEC.

     Use `sleep-for' when you wish to guarantee a delay.

   *Note Time of Day::, for functions to get the current time.


File: elisp,  Node: Quitting,  Next: Prefix Command Arguments,  Prev: Waiting,  Up: Command Loop

21.11 Quitting
==============

Typing `C-g' while a Lisp function is running causes Emacs to "quit"
whatever it is doing.  This means that control returns to the innermost
active command loop.

   Typing `C-g' while the command loop is waiting for keyboard input
does not cause a quit; it acts as an ordinary input character.  In the
simplest case, you cannot tell the difference, because `C-g' normally
runs the command `keyboard-quit', whose effect is to quit.  However,
when `C-g' follows a prefix key, they combine to form an undefined key.
The effect is to cancel the prefix key as well as any prefix argument.

   In the minibuffer, `C-g' has a different definition: it aborts out
of the minibuffer.  This means, in effect, that it exits the minibuffer
and then quits.  (Simply quitting would return to the command loop
_within_ the minibuffer.)  The reason why `C-g' does not quit directly
when the command reader is reading input is so that its meaning can be
redefined in the minibuffer in this way.  `C-g' following a prefix key
is not redefined in the minibuffer, and it has its normal effect of
canceling the prefix key and prefix argument.  This too would not be
possible if `C-g' always quit directly.

   When `C-g' does directly quit, it does so by setting the variable
`quit-flag' to `t'.  Emacs checks this variable at appropriate times
and quits if it is not `nil'.  Setting `quit-flag' non-`nil' in any way
thus causes a quit.

   At the level of C code, quitting cannot happen just anywhere; only
at the special places that check `quit-flag'.  The reason for this is
that quitting at other places might leave an inconsistency in Emacs's
internal state.  Because quitting is delayed until a safe place,
quitting cannot make Emacs crash.

   Certain functions such as `read-key-sequence' or `read-quoted-char'
prevent quitting entirely even though they wait for input.  Instead of
quitting, `C-g' serves as the requested input.  In the case of
`read-key-sequence', this serves to bring about the special behavior of
`C-g' in the command loop.  In the case of `read-quoted-char', this is
so that `C-q' can be used to quote a `C-g'.

   You can prevent quitting for a portion of a Lisp function by binding
the variable `inhibit-quit' to a non-`nil' value.  Then, although `C-g'
still sets `quit-flag' to `t' as usual, the usual result of this--a
quit--is prevented.  Eventually, `inhibit-quit' will become `nil'
again, such as when its binding is unwound at the end of a `let' form.
At that time, if `quit-flag' is still non-`nil', the requested quit
happens immediately.  This behavior is ideal when you wish to make sure
that quitting does not happen within a "critical section" of the
program.

   In some functions (such as `read-quoted-char'), `C-g' is handled in
a special way that does not involve quitting.  This is done by reading
the input with `inhibit-quit' bound to `t', and setting `quit-flag' to
`nil' before `inhibit-quit' becomes `nil' again.  This excerpt from the
definition of `read-quoted-char' shows how this is done; it also shows
that normal quitting is permitted after the first character of input.

     (defun read-quoted-char (&optional prompt)
       "...DOCUMENTATION..."
       (let ((message-log-max nil) done (first t) (code 0) char)
         (while (not done)
           (let ((inhibit-quit first)
                 ...)
     	(and prompt (message "%s-" prompt))
     	(setq char (read-event))
     	(if inhibit-quit (setq quit-flag nil)))
           ...set the variable `code'...)
         code))

 -- Variable: quit-flag
     If this variable is non-`nil', then Emacs quits immediately, unless
     `inhibit-quit' is non-`nil'.  Typing `C-g' ordinarily sets
     `quit-flag' non-`nil', regardless of `inhibit-quit'.

 -- Variable: inhibit-quit
     This variable determines whether Emacs should quit when `quit-flag'
     is set to a value other than `nil'.  If `inhibit-quit' is
     non-`nil', then `quit-flag' has no special effect.

 -- Macro: with-local-quit body...
     This macro executes BODY forms in sequence, but allows quitting, at
     least locally, within BODY even if `inhibit-quit' was non-`nil'
     outside this construct.  It returns the value of the last form in
     BODY, unless exited by quitting, in which case it returns `nil'.

     If `inhibit-quit' is `nil' on entry to `with-local-quit', it only
     executes the BODY, and setting `quit-flag' causes a normal quit.
     However, if `inhibit-quit' is non-`nil' so that ordinary quitting
     is delayed, a non-`nil' `quit-flag' triggers a special kind of
     local quit.  This ends the execution of BODY and exits the
     `with-local-quit' body with `quit-flag' still non-`nil', so that
     another (ordinary) quit will happen as soon as that is allowed.
     If `quit-flag' is already non-`nil' at the beginning of BODY, the
     local quit happens immediately and the body doesn't execute at all.

     This macro is mainly useful in functions that can be called from
     timers, process filters, process sentinels, `pre-command-hook',
     `post-command-hook', and other places where `inhibit-quit' is
     normally bound to `t'.

 -- Command: keyboard-quit
     This function signals the `quit' condition with `(signal 'quit
     nil)'.  This is the same thing that quitting does.  (See `signal'
     in *Note Errors::.)

   You can specify a character other than `C-g' to use for quitting.
See the function `set-input-mode' in *Note Terminal Input::.


File: elisp,  Node: Prefix Command Arguments,  Next: Recursive Editing,  Prev: Quitting,  Up: Command Loop

21.12 Prefix Command Arguments
==============================

Most Emacs commands can use a "prefix argument", a number specified
before the command itself.  (Don't confuse prefix arguments with prefix
keys.)  The prefix argument is at all times represented by a value,
which may be `nil', meaning there is currently no prefix argument.
Each command may use the prefix argument or ignore it.

   There are two representations of the prefix argument: "raw" and
"numeric".  The editor command loop uses the raw representation
internally, and so do the Lisp variables that store the information, but
commands can request either representation.

   Here are the possible values of a raw prefix argument:

   * `nil', meaning there is no prefix argument.  Its numeric value is
     1, but numerous commands make a distinction between `nil' and the
     integer 1.

   * An integer, which stands for itself.

   * A list of one element, which is an integer.  This form of prefix
     argument results from one or a succession of `C-u''s with no
     digits.  The numeric value is the integer in the list, but some
     commands make a distinction between such a list and an integer
     alone.

   * The symbol `-'.  This indicates that `M--' or `C-u -' was typed,
     without following digits.  The equivalent numeric value is -1, but
     some commands make a distinction between the integer -1 and the
     symbol `-'.

   We illustrate these possibilities by calling the following function
with various prefixes:

     (defun display-prefix (arg)
       "Display the value of the raw prefix arg."
       (interactive "P")
       (message "%s" arg))

Here are the results of calling `display-prefix' with various raw
prefix arguments:

             M-x display-prefix  -| nil

     C-u     M-x display-prefix  -| (4)

     C-u C-u M-x display-prefix  -| (16)

     C-u 3   M-x display-prefix  -| 3

     M-3     M-x display-prefix  -| 3      ; (Same as `C-u 3'.)

     C-u -   M-x display-prefix  -| -

     M--     M-x display-prefix  -| -      ; (Same as `C-u -'.)

     C-u - 7 M-x display-prefix  -| -7

     M-- 7   M-x display-prefix  -| -7     ; (Same as `C-u -7'.)

   Emacs uses two variables to store the prefix argument: `prefix-arg'
and `current-prefix-arg'.  Commands such as `universal-argument' that
set up prefix arguments for other commands store them in `prefix-arg'.
In contrast, `current-prefix-arg' conveys the prefix argument to the
current command, so setting it has no effect on the prefix arguments
for future commands.

   Normally, commands specify which representation to use for the prefix
argument, either numeric or raw, in the `interactive' specification.
(*Note Using Interactive::.)  Alternatively, functions may look at the
value of the prefix argument directly in the variable
`current-prefix-arg', but this is less clean.

 -- Function: prefix-numeric-value arg
     This function returns the numeric meaning of a valid raw prefix
     argument value, ARG.  The argument may be a symbol, a number, or a
     list.  If it is `nil', the value 1 is returned; if it is `-', the
     value -1 is returned; if it is a number, that number is returned;
     if it is a list, the CAR of that list (which should be a number) is
     returned.

 -- Variable: current-prefix-arg
     This variable holds the raw prefix argument for the _current_
     command.  Commands may examine it directly, but the usual method
     for accessing it is with `(interactive "P")'.

 -- Variable: prefix-arg
     The value of this variable is the raw prefix argument for the
     _next_ editing command.  Commands such as `universal-argument'
     that specify prefix arguments for the following command work by
     setting this variable.

 -- Variable: last-prefix-arg
     The raw prefix argument value used by the previous command.

   The following commands exist to set up prefix arguments for the
following command.  Do not call them for any other reason.

 -- Command: universal-argument
     This command reads input and specifies a prefix argument for the
     following command.  Don't call this command yourself unless you
     know what you are doing.

 -- Command: digit-argument arg
     This command adds to the prefix argument for the following
     command.  The argument ARG is the raw prefix argument as it was
     before this command; it is used to compute the updated prefix
     argument.  Don't call this command yourself unless you know what
     you are doing.

 -- Command: negative-argument arg
     This command adds to the numeric argument for the next command.
     The argument ARG is the raw prefix argument as it was before this
     command; its value is negated to form the new prefix argument.
     Don't call this command yourself unless you know what you are
     doing.


File: elisp,  Node: Recursive Editing,  Next: Disabling Commands,  Prev: Prefix Command Arguments,  Up: Command Loop

21.13 Recursive Editing
=======================

The Emacs command loop is entered automatically when Emacs starts up.
This top-level invocation of the command loop never exits; it keeps
running as long as Emacs does.  Lisp programs can also invoke the
command loop.  Since this makes more than one activation of the command
loop, we call it "recursive editing".  A recursive editing level has
the effect of suspending whatever command invoked it and permitting the
user to do arbitrary editing before resuming that command.

   The commands available during recursive editing are the same ones
available in the top-level editing loop and defined in the keymaps.
Only a few special commands exit the recursive editing level; the others
return to the recursive editing level when they finish.  (The special
commands for exiting are always available, but they do nothing when
recursive editing is not in progress.)

   All command loops, including recursive ones, set up all-purpose error
handlers so that an error in a command run from the command loop will
not exit the loop.

   Minibuffer input is a special kind of recursive editing.  It has a
few special wrinkles, such as enabling display of the minibuffer and the
minibuffer window, but fewer than you might suppose.  Certain keys
behave differently in the minibuffer, but that is only because of the
minibuffer's local map; if you switch windows, you get the usual Emacs
commands.

   To invoke a recursive editing level, call the function
`recursive-edit'.  This function contains the command loop; it also
contains a call to `catch' with tag `exit', which makes it possible to
exit the recursive editing level by throwing to `exit' (*note Catch and
Throw::).  If you throw a value other than `t', then `recursive-edit'
returns normally to the function that called it.  The command `C-M-c'
(`exit-recursive-edit') does this.  Throwing a `t' value causes
`recursive-edit' to quit, so that control returns to the command loop
one level up.  This is called "aborting", and is done by `C-]'
(`abort-recursive-edit').

   Most applications should not use recursive editing, except as part of
using the minibuffer.  Usually it is more convenient for the user if you
change the major mode of the current buffer temporarily to a special
major mode, which should have a command to go back to the previous mode.
(The `e' command in Rmail uses this technique.)  Or, if you wish to
give the user different text to edit "recursively," create and select a
new buffer in a special mode.  In this mode, define a command to
complete the processing and go back to the previous buffer.  (The `m'
command in Rmail does this.)

   Recursive edits are useful in debugging.  You can insert a call to
`debug' into a function definition as a sort of breakpoint, so that you
can look around when the function gets there.  `debug' invokes a
recursive edit but also provides the other features of the debugger.

   Recursive editing levels are also used when you type `C-r' in
`query-replace' or use `C-x q' (`kbd-macro-query').

 -- Function: recursive-edit
     This function invokes the editor command loop.  It is called
     automatically by the initialization of Emacs, to let the user begin
     editing.  When called from a Lisp program, it enters a recursive
     editing level.

     If the current buffer is not the same as the selected window's
     buffer, `recursive-edit' saves and restores the current buffer.
     Otherwise, if you switch buffers, the buffer you switched to is
     current after `recursive-edit' returns.

     In the following example, the function `simple-rec' first advances
     point one word, then enters a recursive edit, printing out a
     message in the echo area.  The user can then do any editing
     desired, and then type `C-M-c' to exit and continue executing
     `simple-rec'.

          (defun simple-rec ()
            (forward-word 1)
            (message "Recursive edit in progress")
            (recursive-edit)
            (forward-word 1))
               => simple-rec
          (simple-rec)
               => nil

 -- Command: exit-recursive-edit
     This function exits from the innermost recursive edit (including
     minibuffer input).  Its definition is effectively `(throw 'exit
     nil)'.

 -- Command: abort-recursive-edit
     This function aborts the command that requested the innermost
     recursive edit (including minibuffer input), by signaling `quit'
     after exiting the recursive edit.  Its definition is effectively
     `(throw 'exit t)'.  *Note Quitting::.

 -- Command: top-level
     This function exits all recursive editing levels; it does not
     return a value, as it jumps completely out of any computation
     directly back to the main command loop.

 -- Function: recursion-depth
     This function returns the current depth of recursive edits.  When
     no recursive edit is active, it returns 0.


File: elisp,  Node: Disabling Commands,  Next: Command History,  Prev: Recursive Editing,  Up: Command Loop

21.14 Disabling Commands
========================

"Disabling a command" marks the command as requiring user confirmation
before it can be executed.  Disabling is used for commands which might
be confusing to beginning users, to prevent them from using the
commands by accident.

   The low-level mechanism for disabling a command is to put a
non-`nil' `disabled' property on the Lisp symbol for the command.
These properties are normally set up by the user's init file (*note
Init File::) with Lisp expressions such as this:

     (put 'upcase-region 'disabled t)

For a few commands, these properties are present by default (you can
remove them in your init file if you wish).

   If the value of the `disabled' property is a string, the message
saying the command is disabled includes that string.  For example:

     (put 'delete-region 'disabled
          "Text deleted this way cannot be yanked back!\n")

   *Note Disabling: (emacs)Disabling, for the details on what happens
when a disabled command is invoked interactively.  Disabling a command
has no effect on calling it as a function from Lisp programs.

 -- Command: enable-command command
     Allow COMMAND (a symbol) to be executed without special
     confirmation from now on, and alter the user's init file (*note
     Init File::) so that this will apply to future sessions.

 -- Command: disable-command command
     Require special confirmation to execute COMMAND from now on, and
     alter the user's init file so that this will apply to future
     sessions.

 -- Variable: disabled-command-function
     The value of this variable should be a function.  When the user
     invokes a disabled command interactively, this function is called
     instead of the disabled command.  It can use `this-command-keys'
     to determine what the user typed to run the command, and thus find
     the command itself.

     The value may also be `nil'.  Then all commands work normally,
     even disabled ones.

     By default, the value is a function that asks the user whether to
     proceed.


File: elisp,  Node: Command History,  Next: Keyboard Macros,  Prev: Disabling Commands,  Up: Command Loop

21.15 Command History
=====================

The command loop keeps a history of the complex commands that have been
executed, to make it convenient to repeat these commands.  A "complex
command" is one for which the interactive argument reading uses the
minibuffer.  This includes any `M-x' command, any `M-:' command, and
any command whose `interactive' specification reads an argument from
the minibuffer.  Explicit use of the minibuffer during the execution of
the command itself does not cause the command to be considered complex.

 -- Variable: command-history
     This variable's value is a list of recent complex commands, each
     represented as a form to evaluate.  It continues to accumulate all
     complex commands for the duration of the editing session, but when
     it reaches the maximum size (*note Minibuffer History::), the
     oldest elements are deleted as new ones are added.

          command-history
          => ((switch-to-buffer "chistory.texi")
              (describe-key "^X^[")
              (visit-tags-table "~/emacs/src/")
              (find-tag "repeat-complex-command"))

   This history list is actually a special case of minibuffer history
(*note Minibuffer History::), with one special twist: the elements are
expressions rather than strings.

   There are a number of commands devoted to the editing and recall of
previous commands.  The commands `repeat-complex-command', and
`list-command-history' are described in the user manual (*note
Repetition: (emacs)Repetition.).  Within the minibuffer, the usual
minibuffer history commands are available.


File: elisp,  Node: Keyboard Macros,  Prev: Command History,  Up: Command Loop

21.16 Keyboard Macros
=====================

A "keyboard macro" is a canned sequence of input events that can be
considered a command and made the definition of a key.  The Lisp
representation of a keyboard macro is a string or vector containing the
events.  Don't confuse keyboard macros with Lisp macros (*note
Macros::).

 -- Function: execute-kbd-macro kbdmacro &optional count loopfunc
     This function executes KBDMACRO as a sequence of events.  If
     KBDMACRO is a string or vector, then the events in it are executed
     exactly as if they had been input by the user.  The sequence is
     _not_ expected to be a single key sequence; normally a keyboard
     macro definition consists of several key sequences concatenated.

     If KBDMACRO is a symbol, then its function definition is used in
     place of KBDMACRO.  If that is another symbol, this process
     repeats.  Eventually the result should be a string or vector.  If
     the result is not a symbol, string, or vector, an error is
     signaled.

     The argument COUNT is a repeat count; KBDMACRO is executed that
     many times.  If COUNT is omitted or `nil', KBDMACRO is executed
     once.  If it is 0, KBDMACRO is executed over and over until it
     encounters an error or a failing search.

     If LOOPFUNC is non-`nil', it is a function that is called, without
     arguments, prior to each iteration of the macro.  If LOOPFUNC
     returns `nil', then this stops execution of the macro.

     *Note Reading One Event::, for an example of using
     `execute-kbd-macro'.

 -- Variable: executing-kbd-macro
     This variable contains the string or vector that defines the
     keyboard macro that is currently executing.  It is `nil' if no
     macro is currently executing.  A command can test this variable so
     as to behave differently when run from an executing macro.  Do not
     set this variable yourself.

 -- Variable: defining-kbd-macro
     This variable is non-`nil' if and only if a keyboard macro is
     being defined.  A command can test this variable so as to behave
     differently while a macro is being defined.  The value is `append'
     while appending to the definition of an existing macro.  The
     commands `start-kbd-macro', `kmacro-start-macro' and
     `end-kbd-macro' set this variable--do not set it yourself.

     The variable is always local to the current terminal and cannot be
     buffer-local.  *Note Multiple Displays::.

 -- Variable: last-kbd-macro
     This variable is the definition of the most recently defined
     keyboard macro.  Its value is a string or vector, or `nil'.

     The variable is always local to the current terminal and cannot be
     buffer-local.  *Note Multiple Displays::.

 -- Variable: kbd-macro-termination-hook
     This normal hook (*note Standard Hooks::) is run when a keyboard
     macro terminates, regardless of what caused it to terminate
     (reaching the macro end or an error which ended the macro
     prematurely).


File: elisp,  Node: Keymaps,  Next: Modes,  Prev: Command Loop,  Up: Top

22 Keymaps
**********

The command bindings of input events are recorded in data structures
called "keymaps".  Each entry in a keymap associates (or "binds") an
individual event type, either to another keymap or to a command.  When
an event type is bound to a keymap, that keymap is used to look up the
next input event; this continues until a command is found.  The whole
process is called "key lookup".

* Menu:

* Key Sequences::        	Key sequences as Lisp objects.
* Keymap Basics::               Basic concepts of keymaps.
* Format of Keymaps::		What a keymap looks like as a Lisp object.
* Creating Keymaps:: 		Functions to create and copy keymaps.
* Inheritance and Keymaps::	How one keymap can inherit the bindings
				   of another keymap.
* Prefix Keys::                 Defining a key with a keymap as its definition.
* Active Keymaps::              How Emacs searches the active keymaps
                                   for a key binding.
* Searching Keymaps::           A pseudo-Lisp summary of searching active maps.
* Controlling Active Maps::     Each buffer has a local keymap
                                   to override the standard (global) bindings.
				   A minor mode can also override them.
* Key Lookup::                  Finding a key's binding in one keymap.
* Functions for Key Lookup::    How to request key lookup.
* Changing Key Bindings::       Redefining a key in a keymap.
* Remapping Commands::          A keymap can translate one command to another.
* Translation Keymaps::         Keymaps for translating sequences of events.
* Key Binding Commands::        Interactive interfaces for redefining keys.
* Scanning Keymaps::            Looking through all keymaps, for printing help.
* Menu Keymaps::		Defining a menu as a keymap.


File: elisp,  Node: Key Sequences,  Next: Keymap Basics,  Up: Keymaps

22.1 Key Sequences
==================

A "key sequence", or "key" for short, is a sequence of one or more
input events that form a unit.  Input events include characters,
function keys, and mouse actions (*note Input Events::).  The Emacs
Lisp representation for a key sequence is a string or vector.  Unless
otherwise stated, any Emacs Lisp function that accepts a key sequence
as an argument can handle both representations.

   In the string representation, alphanumeric characters ordinarily
stand for themselves; for example, `"a"' represents `a' and `"2"'
represents `2'.  Control character events are prefixed by the substring
`"\C-"', and meta characters by `"\M-"'; for example, `"\C-x"'
represents the key `C-x'.  In addition, the <TAB>, <RET>, <ESC>, and
<DEL> events are represented by `"\t"', `"\r"', `"\e"', and `"\d"'
respectively.  The string representation of a complete key sequence is
the concatenation of the string representations of the constituent
events; thus, `"\C-xl"' represents the key sequence `C-x l'.

   Key sequences containing function keys, mouse button events, or
non-ASCII characters such as `C-=' or `H-a' cannot be represented as
strings; they have to be represented as vectors.

   In the vector representation, each element of the vector represents
an input event, in its Lisp form.  *Note Input Events::.  For example,
the vector `[?\C-x ?l]' represents the key sequence `C-x l'.

   For examples of key sequences written in string and vector
representations, *Note Init Rebinding: (emacs)Init Rebinding.

 -- Macro: kbd keyseq-text
     This macro converts the text KEYSEQ-TEXT (a string constant) into
     a key sequence (a string or vector constant).  The contents of
     KEYSEQ-TEXT should describe the key sequence using almost the same
     syntax used in this manual.  More precisely, it uses the same
     syntax that Edit Macro mode uses for editing keyboard macros
     (*note Edit Keyboard Macro: (emacs)Edit Keyboard Macro.); you must
     surround function key names with `<...>'.

          (kbd "C-x") => "\C-x"
          (kbd "C-x C-f") => "\C-x\C-f"
          (kbd "C-x 4 C-f") => "\C-x4\C-f"
          (kbd "X") => "X"
          (kbd "RET") => "\^M"
          (kbd "C-c SPC") => "\C-c "
          (kbd "<f1> SPC") => [f1 32]
          (kbd "C-M-<down>") => [C-M-down]

     This macro is not meant for use with arguments that vary--only
     with string constants.


File: elisp,  Node: Keymap Basics,  Next: Format of Keymaps,  Prev: Key Sequences,  Up: Keymaps

22.2 Keymap Basics
==================

A keymap is a Lisp data structure that specifies "key bindings" for
various key sequences.

   A single keymap directly specifies definitions for individual
events.  When a key sequence consists of a single event, its binding in
a keymap is the keymap's definition for that event.  The binding of a
longer key sequence is found by an iterative process: first find the
definition of the first event (which must itself be a keymap); then
find the second event's definition in that keymap, and so on until all
the events in the key sequence have been processed.

   If the binding of a key sequence is a keymap, we call the key
sequence a "prefix key".  Otherwise, we call it a "complete key"
(because no more events can be added to it).  If the binding is `nil',
we call the key "undefined".  Examples of prefix keys are `C-c', `C-x',
and `C-x 4'.  Examples of defined complete keys are `X', <RET>, and
`C-x 4 C-f'.  Examples of undefined complete keys are `C-x C-g', and
`C-c 3'.  *Note Prefix Keys::, for more details.

   The rule for finding the binding of a key sequence assumes that the
intermediate bindings (found for the events before the last) are all
keymaps; if this is not so, the sequence of events does not form a
unit--it is not really one key sequence.  In other words, removing one
or more events from the end of any valid key sequence must always yield
a prefix key.  For example, `C-f C-n' is not a key sequence; `C-f' is
not a prefix key, so a longer sequence starting with `C-f' cannot be a
key sequence.

   The set of possible multi-event key sequences depends on the bindings
for prefix keys; therefore, it can be different for different keymaps,
and can change when bindings are changed.  However, a one-event sequence
is always a key sequence, because it does not depend on any prefix keys
for its well-formedness.

   At any time, several primary keymaps are "active"--that is, in use
for finding key bindings.  These are the "global map", which is shared
by all buffers; the "local keymap", which is usually associated with a
specific major mode; and zero or more "minor mode keymaps", which
belong to currently enabled minor modes.  (Not all minor modes have
keymaps.)  The local keymap bindings shadow (i.e., take precedence
over) the corresponding global bindings.  The minor mode keymaps shadow
both local and global keymaps.  *Note Active Keymaps::, for details.


File: elisp,  Node: Format of Keymaps,  Next: Creating Keymaps,  Prev: Keymap Basics,  Up: Keymaps

22.3 Format of Keymaps
======================

Each keymap is a list whose CAR is the symbol `keymap'.  The remaining
elements of the list define the key bindings of the keymap.  A symbol
whose function definition is a keymap is also a keymap.  Use the
function `keymapp' (see below) to test whether an object is a keymap.

   Several kinds of elements may appear in a keymap, after the symbol
`keymap' that begins it:

`(TYPE . BINDING)'
     This specifies one binding, for events of type TYPE.  Each
     ordinary binding applies to events of a particular "event type",
     which is always a character or a symbol.  *Note Classifying
     Events::.  In this kind of binding, BINDING is a command.

`(TYPE ITEM-NAME [CACHE] . BINDING)'
     This specifies a binding which is also a simple menu item that
     displays as ITEM-NAME in the menu.  CACHE, if present, caches
     certain information for display in the menu.  *Note Simple Menu
     Items::.

`(TYPE ITEM-NAME HELP-STRING [CACHE] . BINDING)'
     This is a simple menu item with help string HELP-STRING.

`(TYPE menu-item . DETAILS)'
     This specifies a binding which is also an extended menu item.  This
     allows use of other features.  *Note Extended Menu Items::.

`(t . BINDING)'
     This specifies a "default key binding"; any event not bound by
     other elements of the keymap is given BINDING as its binding.
     Default bindings allow a keymap to bind all possible event types
     without having to enumerate all of them.  A keymap that has a
     default binding completely masks any lower-precedence keymap,
     except for events explicitly bound to `nil' (see below).

`CHAR-TABLE'
     If an element of a keymap is a char-table, it counts as holding
     bindings for all character events with no modifier bits (*note
     modifier bits::): element N is the binding for the character with
     code N.  This is a compact way to record lots of bindings.  A
     keymap with such a char-table is called a "full keymap".  Other
     keymaps are called "sparse keymaps".

`STRING'
     Aside from elements that specify bindings for keys, a keymap can
     also have a string as an element.  This is called the "overall
     prompt string" and makes it possible to use the keymap as a menu.
     *Note Defining Menus::.

   When the binding is `nil', it doesn't constitute a definition but it
does take precedence over a default binding or a binding in the parent
keymap.  On the other hand, a binding of `nil' does _not_ override
lower-precedence keymaps; thus, if the local map gives a binding of
`nil', Emacs uses the binding from the global map.

   Keymaps do not directly record bindings for the meta characters.
Instead, meta characters are regarded for purposes of key lookup as
sequences of two characters, the first of which is <ESC> (or whatever
is currently the value of `meta-prefix-char').  Thus, the key `M-a' is
internally represented as `<ESC> a', and its global binding is found at
the slot for `a' in `esc-map' (*note Prefix Keys::).

   This conversion applies only to characters, not to function keys or
other input events; thus, `M-<end>' has nothing to do with `<ESC>
<end>'.

   Here as an example is the local keymap for Lisp mode, a sparse
keymap.  It defines bindings for <DEL> and <TAB>, plus `C-c C-l',
`M-C-q', and `M-C-x'.

     lisp-mode-map
     =>
     (keymap
      (3 keymap
         ;; C-c C-z
         (26 . run-lisp))
      (27 keymap
          ;; `M-C-x', treated as `<ESC> C-x'
          (24 . lisp-send-defun)
          keymap
          ;; `M-C-q', treated as `<ESC> C-q'
          (17 . indent-sexp))
      ;; This part is inherited from `lisp-mode-shared-map'.
      keymap
      ;; <DEL>
      (127 . backward-delete-char-untabify)
      (27 keymap
          ;; `M-C-q', treated as `<ESC> C-q'
          (17 . indent-sexp))
      (9 . lisp-indent-line))

 -- Function: keymapp object
     This function returns `t' if OBJECT is a keymap, `nil' otherwise.
     More precisely, this function tests for a list whose CAR is
     `keymap', or for a symbol whose function definition satisfies
     `keymapp'.

          (keymapp '(keymap))
              => t
          (fset 'foo '(keymap))
          (keymapp 'foo)
              => t
          (keymapp (current-global-map))
              => t


File: elisp,  Node: Creating Keymaps,  Next: Inheritance and Keymaps,  Prev: Format of Keymaps,  Up: Keymaps

22.4 Creating Keymaps
=====================

Here we describe the functions for creating keymaps.

 -- Function: make-sparse-keymap &optional prompt
     This function creates and returns a new sparse keymap with no
     entries.  (A sparse keymap is the kind of keymap you usually
     want.)  The new keymap does not contain a char-table, unlike
     `make-keymap', and does not bind any events.

          (make-sparse-keymap)
              => (keymap)

     If you specify PROMPT, that becomes the overall prompt string for
     the keymap.  You should specify this only for menu keymaps (*note
     Defining Menus::).  A keymap with an overall prompt string will
     always present a mouse menu or a keyboard menu if it is active for
     looking up the next input event.  Don't specify an overall prompt
     string for the main map of a major or minor mode, because that
     would cause the command loop to present a keyboard menu every time.

 -- Function: make-keymap &optional prompt
     This function creates and returns a new full keymap.  That keymap
     contains a char-table (*note Char-Tables::) with slots for all
     characters without modifiers.  The new keymap initially binds all
     these characters to `nil', and does not bind any other kind of
     event.  The argument PROMPT specifies a prompt string, as in
     `make-sparse-keymap'.

          (make-keymap)
              => (keymap #^[t nil nil nil ... nil nil keymap])

     A full keymap is more efficient than a sparse keymap when it holds
     lots of bindings; for just a few, the sparse keymap is better.

 -- Function: copy-keymap keymap
     This function returns a copy of KEYMAP.  Any keymaps that appear
     directly as bindings in KEYMAP are also copied recursively, and so
     on to any number of levels.  However, recursive copying does not
     take place when the definition of a character is a symbol whose
     function definition is a keymap; the same symbol appears in the
     new copy.

          (setq map (copy-keymap (current-local-map)))
          => (keymap
               ;; (This implements meta characters.)
               (27 keymap
                   (83 . center-paragraph)
                   (115 . center-line))
               (9 . tab-to-tab-stop))

          (eq map (current-local-map))
              => nil
          (equal map (current-local-map))
              => t


File: elisp,  Node: Inheritance and Keymaps,  Next: Prefix Keys,  Prev: Creating Keymaps,  Up: Keymaps

22.5 Inheritance and Keymaps
============================

A keymap can inherit the bindings of another keymap, which we call the
"parent keymap".  Such a keymap looks like this:

     (keymap ELEMENTS... . PARENT-KEYMAP)

The effect is that this keymap inherits all the bindings of
PARENT-KEYMAP, whatever they may be at the time a key is looked up, but
can add to them or override them with ELEMENTS.

   If you change the bindings in PARENT-KEYMAP using `define-key' or
other key-binding functions, these changed bindings are visible in the
inheriting keymap, unless shadowed by the bindings made by ELEMENTS.
The converse is not true: if you use `define-key' to change bindings in
the inheriting keymap, these changes are recorded in ELEMENTS, but have
no effect on PARENT-KEYMAP.

   The proper way to construct a keymap with a parent is to use
`set-keymap-parent'; if you have code that directly constructs a keymap
with a parent, please convert the program to use `set-keymap-parent'
instead.

 -- Function: keymap-parent keymap
     This returns the parent keymap of KEYMAP.  If KEYMAP has no
     parent, `keymap-parent' returns `nil'.

 -- Function: set-keymap-parent keymap parent
     This sets the parent keymap of KEYMAP to PARENT, and returns
     PARENT.  If PARENT is `nil', this function gives KEYMAP no parent
     at all.

     If KEYMAP has submaps (bindings for prefix keys), they too receive
     new parent keymaps that reflect what PARENT specifies for those
     prefix keys.

   Here is an example showing how to make a keymap that inherits from
`text-mode-map':

     (let ((map (make-sparse-keymap)))
       (set-keymap-parent map text-mode-map)
       map)

   A non-sparse keymap can have a parent too, but this is not very
useful.  A non-sparse keymap always specifies something as the binding
for every numeric character code without modifier bits, even if it is
`nil', so these character's bindings are never inherited from the
parent keymap.


File: elisp,  Node: Prefix Keys,  Next: Active Keymaps,  Prev: Inheritance and Keymaps,  Up: Keymaps

22.6 Prefix Keys
================

A "prefix key" is a key sequence whose binding is a keymap.  The keymap
defines what to do with key sequences that extend the prefix key.  For
example, `C-x' is a prefix key, and it uses a keymap that is also
stored in the variable `ctl-x-map'.  This keymap defines bindings for
key sequences starting with `C-x'.

   Some of the standard Emacs prefix keys use keymaps that are also
found in Lisp variables:

   * `esc-map' is the global keymap for the <ESC> prefix key.  Thus,
     the global definitions of all meta characters are actually found
     here.  This map is also the function definition of `ESC-prefix'.

   * `help-map' is the global keymap for the `C-h' prefix key.

   * `mode-specific-map' is the global keymap for the prefix key `C-c'.
     This map is actually global, not mode-specific, but its name
     provides useful information about `C-c' in the output of `C-h b'
     (`display-bindings'), since the main use of this prefix key is for
     mode-specific bindings.

   * `ctl-x-map' is the global keymap used for the `C-x' prefix key.
     This map is found via the function cell of the symbol
     `Control-X-prefix'.

   * `mule-keymap' is the global keymap used for the `C-x <RET>' prefix
     key.

   * `ctl-x-4-map' is the global keymap used for the `C-x 4' prefix key.

   * `ctl-x-5-map' is the global keymap used for the `C-x 5' prefix key.

   * `2C-mode-map' is the global keymap used for the `C-x 6' prefix key.

   * `vc-prefix-map' is the global keymap used for the `C-x v' prefix
     key.

   * `facemenu-keymap' is the global keymap used for the `M-o' prefix
     key.

   * The other Emacs prefix keys are `M-g', `C-x @', `C-x a i', `C-x
     <ESC>' and `<ESC> <ESC>'.  They use keymaps that have no special
     names.

   The keymap binding of a prefix key is used for looking up the event
that follows the prefix key.  (It may instead be a symbol whose function
definition is a keymap.  The effect is the same, but the symbol serves
as a name for the prefix key.)  Thus, the binding of `C-x' is the
symbol `Control-X-prefix', whose function cell holds the keymap for
`C-x' commands.  (The same keymap is also the value of `ctl-x-map'.)

   Prefix key definitions can appear in any active keymap.  The
definitions of `C-c', `C-x', `C-h' and <ESC> as prefix keys appear in
the global map, so these prefix keys are always available.  Major and
minor modes can redefine a key as a prefix by putting a prefix key
definition for it in the local map or the minor mode's map.  *Note
Active Keymaps::.

   If a key is defined as a prefix in more than one active map, then its
various definitions are in effect merged: the commands defined in the
minor mode keymaps come first, followed by those in the local map's
prefix definition, and then by those from the global map.

   In the following example, we make `C-p' a prefix key in the local
keymap, in such a way that `C-p' is identical to `C-x'.  Then the
binding for `C-p C-f' is the function `find-file', just like `C-x C-f'.
The key sequence `C-p 6' is not found in any active keymap.

     (use-local-map (make-sparse-keymap))
         => nil
     (local-set-key "\C-p" ctl-x-map)
         => nil
     (key-binding "\C-p\C-f")
         => find-file

     (key-binding "\C-p6")
         => nil

 -- Function: define-prefix-command symbol &optional mapvar prompt
     This function prepares SYMBOL for use as a prefix key's binding:
     it creates a sparse keymap and stores it as SYMBOL's function
     definition.  Subsequently binding a key sequence to SYMBOL will
     make that key sequence into a prefix key.  The return value is
     `symbol'.

     This function also sets SYMBOL as a variable, with the keymap as
     its value.  But if MAPVAR is non-`nil', it sets MAPVAR as a
     variable instead.

     If PROMPT is non-`nil', that becomes the overall prompt string for
     the keymap.  The prompt string should be given for menu keymaps
     (*note Defining Menus::).


File: elisp,  Node: Active Keymaps,  Next: Searching Keymaps,  Prev: Prefix Keys,  Up: Keymaps

22.7 Active Keymaps
===================

Emacs normally contains many keymaps; at any given time, just a few of
them are "active", meaning that they participate in the interpretation
of user input.  All the active keymaps are used together to determine
what command to execute when a key is entered.

   Normally the active keymaps are the `keymap' property keymap, the
keymaps of any enabled minor modes, the current buffer's local keymap,
and the global keymap, in that order.  Emacs searches for each input
key sequence in all these keymaps.  *Note Searching Keymaps::, for more
details of this procedure.

   When the key sequence starts with a mouse event (optionally preceded
by a symbolic prefix), the active keymaps are determined based on the
position in that event.  If the event happened on a string embedded
with a `display', `before-string', or `after-string' property (*note
Special Properties::), the non-`nil' map properties of the string
override those of the buffer.

   The "global keymap" holds the bindings of keys that are defined
regardless of the current buffer, such as `C-f'.  The variable
`global-map' holds this keymap, which is always active.

   Each buffer may have another keymap, its "local keymap", which may
contain new or overriding definitions for keys.  The current buffer's
local keymap is always active except when `overriding-local-map'
overrides it.  The `local-map' text or overlay property can specify an
alternative local keymap for certain parts of the buffer; see *Note
Special Properties::.

   Each minor mode can have a keymap; if it does, the keymap is active
when the minor mode is enabled.  Modes for emulation can specify
additional active keymaps through the variable
`emulation-mode-map-alists'.

   The highest precedence normal keymap comes from the `keymap' text or
overlay property.  If that is non-`nil', it is the first keymap to be
processed, in normal circumstances.

   However, there are also special ways for programs to substitute
other keymaps for some of those.  The variable `overriding-local-map',
if non-`nil', specifies a keymap that replaces all the usual active
keymaps except the global keymap.  Another way to do this is with
`overriding-terminal-local-map'; it operates on a per-terminal basis.
These variables are documented below.

   Since every buffer that uses the same major mode normally uses the
same local keymap, you can think of the keymap as local to the mode.  A
change to the local keymap of a buffer (using `local-set-key', for
example) is seen also in the other buffers that share that keymap.

   The local keymaps that are used for Lisp mode and some other major
modes exist even if they have not yet been used.  These local keymaps
are the values of variables such as `lisp-mode-map'.  For most major
modes, which are less frequently used, the local keymap is constructed
only when the mode is used for the first time in a session.

   The minibuffer has local keymaps, too; they contain various
completion and exit commands.  *Note Intro to Minibuffers::.

   Emacs has other keymaps that are used in a different way--translating
events within `read-key-sequence'.  *Note Translation Keymaps::.

   *Note Standard Keymaps::, for a list of standard keymaps.

 -- Function: current-active-maps &optional olp
     This returns the list of active keymaps that would be used by the
     command loop in the current circumstances to look up a key
     sequence.  Normally it ignores `overriding-local-map' and
     `overriding-terminal-local-map', but if OLP is non-`nil' then it
     pays attention to them.

 -- Function: key-binding key &optional accept-defaults no-remap
          position
     This function returns the binding for KEY according to the current
     active keymaps.  The result is `nil' if KEY is undefined in the
     keymaps.

     The argument ACCEPT-DEFAULTS controls checking for default
     bindings, as in `lookup-key' (*note Functions for Key Lookup::).

     When commands are remapped (*note Remapping Commands::),
     `key-binding' normally processes command remappings so as to
     returns the remapped command that will actually be executed.
     However, if NO-REMAP is non-`nil', `key-binding' ignores
     remappings and returns the binding directly specified for KEY.

     If KEY starts with a mouse event (perhaps following a prefix
     event), the maps to be consulted are determined based on the
     event's position.  Otherwise, they are determined based on the
     value of point.  However, you can override either of them by
     specifying POSITION.  If POSITION is non-`nil', it should be
     either a buffer position or an event position like the value of
     `event-start'.  Then the maps consulted are determined based on
     POSITION.

     An error is signaled if KEY is not a string or a vector.

          (key-binding "\C-x\C-f")
              => find-file


File: elisp,  Node: Searching Keymaps,  Next: Controlling Active Maps,  Prev: Active Keymaps,  Up: Keymaps

22.8 Searching the Active Keymaps
=================================

After translation of event subsequences (*note Translation Keymaps::)
Emacs looks for them in the active keymaps.  Here is a pseudo-Lisp
description of the order and conditions for searching them:

     (or (if overriding-terminal-local-map
             (FIND-IN overriding-terminal-local-map)
           (if overriding-local-map
               (FIND-IN overriding-local-map)
             (or (FIND-IN (get-char-property (point) 'keymap))
                 (FIND-IN-ANY emulation-mode-map-alists)
                 (FIND-IN-ANY minor-mode-overriding-map-alist)
                 (FIND-IN-ANY minor-mode-map-alist)
                 (if (get-text-property (point) 'local-map)
                     (FIND-IN (get-char-property (point) 'local-map))
                   (FIND-IN (current-local-map))))))
         (FIND-IN (current-global-map)))

The FIND-IN and FIND-IN-ANY are pseudo functions that search in one
keymap and in an alist of keymaps, respectively.  (Searching a single
keymap for a binding is called "key lookup"; see *Note Key Lookup::.)
If the key sequence starts with a mouse event, or a symbolic prefix
event followed by a mouse event, that event's position is used instead
of point and the current buffer.  Mouse events on an embedded string
use non-`nil' text properties from that string instead of the buffer.

  1. The function finally found may be remapped (*note Remapping
     Commands::).

  2. Characters that are bound to `self-insert-command' are translated
     according to `translation-table-for-input' before insertion.

  3. `current-active-maps' returns a list of the currently active
     keymaps at point.

  4. When a match is found (*note Key Lookup::), if the binding in the
     keymap is a function, the search is over.  However if the keymap
     entry is a symbol with a value or a string, Emacs replaces the
     input key sequences with the variable's value or the string, and
     restarts the search of the active keymaps.


File: elisp,  Node: Controlling Active Maps,  Next: Key Lookup,  Prev: Searching Keymaps,  Up: Keymaps

22.9 Controlling the Active Keymaps
===================================

 -- Variable: global-map
     This variable contains the default global keymap that maps Emacs
     keyboard input to commands.  The global keymap is normally this
     keymap.  The default global keymap is a full keymap that binds
     `self-insert-command' to all of the printing characters.

     It is normal practice to change the bindings in the global keymap,
     but you should not assign this variable any value other than the
     keymap it starts out with.

 -- Function: current-global-map
     This function returns the current global keymap.  This is the same
     as the value of `global-map' unless you change one or the other.

          (current-global-map)
          => (keymap [set-mark-command beginning-of-line ...
                      delete-backward-char])

 -- Function: current-local-map
     This function returns the current buffer's local keymap, or `nil'
     if it has none.  In the following example, the keymap for the
     `*scratch*' buffer (using Lisp Interaction mode) is a sparse keymap
     in which the entry for <ESC>, ASCII code 27, is another sparse
     keymap.

          (current-local-map)
          => (keymap
              (10 . eval-print-last-sexp)
              (9 . lisp-indent-line)
              (127 . backward-delete-char-untabify)
              (27 keymap
                  (24 . eval-defun)
                  (17 . indent-sexp)))

 -- Function: current-minor-mode-maps
     This function returns a list of the keymaps of currently enabled
     minor modes.

 -- Function: use-global-map keymap
     This function makes KEYMAP the new current global keymap.  It
     returns `nil'.

     It is very unusual to change the global keymap.

 -- Function: use-local-map keymap
     This function makes KEYMAP the new local keymap of the current
     buffer.  If KEYMAP is `nil', then the buffer has no local keymap.
     `use-local-map' returns `nil'.  Most major mode commands use this
     function.

 -- Variable: minor-mode-map-alist
     This variable is an alist describing keymaps that may or may not be
     active according to the values of certain variables.  Its elements
     look like this:

          (VARIABLE . KEYMAP)

     The keymap KEYMAP is active whenever VARIABLE has a non-`nil'
     value.  Typically VARIABLE is the variable that enables or
     disables a minor mode.  *Note Keymaps and Minor Modes::.

     Note that elements of `minor-mode-map-alist' do not have the same
     structure as elements of `minor-mode-alist'.  The map must be the
     CDR of the element; a list with the map as the second element will
     not do.  The CDR can be either a keymap (a list) or a symbol whose
     function definition is a keymap.

     When more than one minor mode keymap is active, the earlier one in
     `minor-mode-map-alist' takes priority.  But you should design
     minor modes so that they don't interfere with each other.  If you
     do this properly, the order will not matter.

     See *Note Keymaps and Minor Modes::, for more information about
     minor modes.  See also `minor-mode-key-binding' (*note Functions
     for Key Lookup::).

 -- Variable: minor-mode-overriding-map-alist
     This variable allows major modes to override the key bindings for
     particular minor modes.  The elements of this alist look like the
     elements of `minor-mode-map-alist': `(VARIABLE . KEYMAP)'.

     If a variable appears as an element of
     `minor-mode-overriding-map-alist', the map specified by that
     element totally replaces any map specified for the same variable in
     `minor-mode-map-alist'.

     `minor-mode-overriding-map-alist' is automatically buffer-local in
     all buffers.

 -- Variable: overriding-local-map
     If non-`nil', this variable holds a keymap to use instead of the
     buffer's local keymap, any text property or overlay keymaps, and
     any minor mode keymaps.  This keymap, if specified, overrides all
     other maps that would have been active, except for the current
     global map.

 -- Variable: overriding-terminal-local-map
     If non-`nil', this variable holds a keymap to use instead of
     `overriding-local-map', the buffer's local keymap, text property
     or overlay keymaps, and all the minor mode keymaps.

     This variable is always local to the current terminal and cannot be
     buffer-local.  *Note Multiple Displays::.  It is used to implement
     incremental search mode.

 -- Variable: overriding-local-map-menu-flag
     If this variable is non-`nil', the value of `overriding-local-map'
     or `overriding-terminal-local-map' can affect the display of the
     menu bar.  The default value is `nil', so those map variables have
     no effect on the menu bar.

     Note that these two map variables do affect the execution of key
     sequences entered using the menu bar, even if they do not affect
     the menu bar display.  So if a menu bar key sequence comes in, you
     should clear the variables before looking up and executing that
     key sequence.  Modes that use the variables would typically do
     this anyway; normally they respond to events that they do not
     handle by "unreading" them and exiting.

 -- Variable: special-event-map
     This variable holds a keymap for special events.  If an event type
     has a binding in this keymap, then it is special, and the binding
     for the event is run directly by `read-event'.  *Note Special
     Events::.

 -- Variable: emulation-mode-map-alists
     This variable holds a list of keymap alists to use for emulations
     modes.  It is intended for modes or packages using multiple
     minor-mode keymaps.  Each element is a keymap alist which has the
     same format and meaning as `minor-mode-map-alist', or a symbol
     with a variable binding which is such an alist.  The "active"
     keymaps in each alist are used before `minor-mode-map-alist' and
     `minor-mode-overriding-map-alist'.


File: elisp,  Node: Key Lookup,  Next: Functions for Key Lookup,  Prev: Controlling Active Maps,  Up: Keymaps

22.10 Key Lookup
================

"Key lookup" is the process of finding the binding of a key sequence
from a given keymap.  The execution or use of the binding is not part
of key lookup.

   Key lookup uses just the event type of each event in the key
sequence; the rest of the event is ignored.  In fact, a key sequence
used for key lookup may designate a mouse event with just its types (a
symbol) instead of the entire event (a list).  *Note Input Events::.
Such a "key sequence" is insufficient for `command-execute' to run, but
it is sufficient for looking up or rebinding a key.

   When the key sequence consists of multiple events, key lookup
processes the events sequentially: the binding of the first event is
found, and must be a keymap; then the second event's binding is found in
that keymap, and so on until all the events in the key sequence are used
up.  (The binding thus found for the last event may or may not be a
keymap.)  Thus, the process of key lookup is defined in terms of a
simpler process for looking up a single event in a keymap.  How that is
done depends on the type of object associated with the event in that
keymap.

   Let's use the term "keymap entry" to describe the value found by
looking up an event type in a keymap.  (This doesn't include the item
string and other extra elements in a keymap element for a menu item,
because `lookup-key' and other key lookup functions don't include them
in the returned value.)  While any Lisp object may be stored in a keymap
as a keymap entry, not all make sense for key lookup.  Here is a table
of the meaningful types of keymap entries:

`nil'
     `nil' means that the events used so far in the lookup form an
     undefined key.  When a keymap fails to mention an event type at
     all, and has no default binding, that is equivalent to a binding
     of `nil' for that event type.

COMMAND
     The events used so far in the lookup form a complete key, and
     COMMAND is its binding.  *Note What Is a Function::.

ARRAY
     The array (either a string or a vector) is a keyboard macro.  The
     events used so far in the lookup form a complete key, and the
     array is its binding.  See *Note Keyboard Macros::, for more
     information.

KEYMAP
     The events used so far in the lookup form a prefix key.  The next
     event of the key sequence is looked up in KEYMAP.

LIST
     The meaning of a list depends on what it contains:

        * If the CAR of LIST is the symbol `keymap', then the list is a
          keymap, and is treated as a keymap (see above).

        * If the CAR of LIST is `lambda', then the list is a lambda
          expression.  This is presumed to be a function, and is treated
          as such (see above).  In order to execute properly as a key
          binding, this function must be a command--it must have an
          `interactive' specification.  *Note Defining Commands::.

        * If the CAR of LIST is a keymap and the CDR is an event type,
          then this is an "indirect entry":

               (OTHERMAP . OTHERTYPE)

          When key lookup encounters an indirect entry, it looks up
          instead the binding of OTHERTYPE in OTHERMAP and uses that.

          This feature permits you to define one key as an alias for
          another key.  For example, an entry whose CAR is the keymap
          called `esc-map' and whose CDR is 32 (the code for <SPC>)
          means, "Use the global binding of `Meta-<SPC>', whatever that
          may be."

SYMBOL
     The function definition of SYMBOL is used in place of SYMBOL.  If
     that too is a symbol, then this process is repeated, any number of
     times.  Ultimately this should lead to an object that is a keymap,
     a command, or a keyboard macro.  A list is allowed if it is a
     keymap or a command, but indirect entries are not understood when
     found via symbols.

     Note that keymaps and keyboard macros (strings and vectors) are not
     valid functions, so a symbol with a keymap, string, or vector as
     its function definition is invalid as a function.  It is, however,
     valid as a key binding.  If the definition is a keyboard macro,
     then the symbol is also valid as an argument to `command-execute'
     (*note Interactive Call::).

     The symbol `undefined' is worth special mention: it means to treat
     the key as undefined.  Strictly speaking, the key is defined, and
     its binding is the command `undefined'; but that command does the
     same thing that is done automatically for an undefined key: it
     rings the bell (by calling `ding') but does not signal an error.

     `undefined' is used in local keymaps to override a global key
     binding and make the key "undefined" locally.  A local binding of
     `nil' would fail to do this because it would not override the
     global binding.

ANYTHING ELSE
     If any other type of object is found, the events used so far in the
     lookup form a complete key, and the object is its binding, but the
     binding is not executable as a command.

   In short, a keymap entry may be a keymap, a command, a keyboard
macro, a symbol that leads to one of them, or an indirection or `nil'.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap.  This map is the normal value
of `emacs-lisp-mode-map'.  Note that 9 is the code for <TAB>, 127 for
<DEL>, 27 for <ESC>, 17 for `C-q' and 24 for `C-x'.

     (keymap (9 . lisp-indent-line)
             (127 . backward-delete-char-untabify)
             (27 keymap (17 . indent-sexp) (24 . eval-defun)))


File: elisp,  Node: Functions for Key Lookup,  Next: Changing Key Bindings,  Prev: Key Lookup,  Up: Keymaps

22.11 Functions for Key Lookup
==============================

Here are the functions and variables pertaining to key lookup.

 -- Function: lookup-key keymap key &optional accept-defaults
     This function returns the definition of KEY in KEYMAP.  All the
     other functions described in this chapter that look up keys use
     `lookup-key'.  Here are examples:

          (lookup-key (current-global-map) "\C-x\C-f")
              => find-file
          (lookup-key (current-global-map) (kbd "C-x C-f"))
              => find-file
          (lookup-key (current-global-map) "\C-x\C-f12345")
              => 2

     If the string or vector KEY is not a valid key sequence according
     to the prefix keys specified in KEYMAP, it must be "too long" and
     have extra events at the end that do not fit into a single key
     sequence.  Then the value is a number, the number of events at the
     front of KEY that compose a complete key.

     If ACCEPT-DEFAULTS is non-`nil', then `lookup-key' considers
     default bindings as well as bindings for the specific events in
     KEY.  Otherwise, `lookup-key' reports only bindings for the
     specific sequence KEY, ignoring default bindings except when you
     explicitly ask about them.  (To do this, supply `t' as an element
     of KEY; see *Note Format of Keymaps::.)

     If KEY contains a meta character (not a function key), that
     character is implicitly replaced by a two-character sequence: the
     value of `meta-prefix-char', followed by the corresponding non-meta
     character.  Thus, the first example below is handled by conversion
     into the second example.

          (lookup-key (current-global-map) "\M-f")
              => forward-word
          (lookup-key (current-global-map) "\ef")
              => forward-word

     Unlike `read-key-sequence', this function does not modify the
     specified events in ways that discard information (*note Key
     Sequence Input::).  In particular, it does not convert letters to
     lower case and it does not change drag events to clicks.

 -- Command: undefined
     Used in keymaps to undefine keys.  It calls `ding', but does not
     cause an error.

 -- Function: local-key-binding key &optional accept-defaults
     This function returns the binding for KEY in the current local
     keymap, or `nil' if it is undefined there.

     The argument ACCEPT-DEFAULTS controls checking for default
     bindings, as in `lookup-key' (above).

 -- Function: global-key-binding key &optional accept-defaults
     This function returns the binding for command KEY in the current
     global keymap, or `nil' if it is undefined there.

     The argument ACCEPT-DEFAULTS controls checking for default
     bindings, as in `lookup-key' (above).

 -- Function: minor-mode-key-binding key &optional accept-defaults
     This function returns a list of all the active minor mode bindings
     of KEY.  More precisely, it returns an alist of pairs `(MODENAME .
     BINDING)', where MODENAME is the variable that enables the minor
     mode, and BINDING is KEY's binding in that mode.  If KEY has no
     minor-mode bindings, the value is `nil'.

     If the first binding found is not a prefix definition (a keymap or
     a symbol defined as a keymap), all subsequent bindings from other
     minor modes are omitted, since they would be completely shadowed.
     Similarly, the list omits non-prefix bindings that follow prefix
     bindings.

     The argument ACCEPT-DEFAULTS controls checking for default
     bindings, as in `lookup-key' (above).

 -- Variable: meta-prefix-char
     This variable is the meta-prefix character code.  It is used for
     translating a meta character to a two-character sequence so it can
     be looked up in a keymap.  For useful results, the value should be
     a prefix event (*note Prefix Keys::).  The default value is 27,
     which is the ASCII code for <ESC>.

     As long as the value of `meta-prefix-char' remains 27, key lookup
     translates `M-b' into `<ESC> b', which is normally defined as the
     `backward-word' command.  However, if you were to set
     `meta-prefix-char' to 24, the code for `C-x', then Emacs will
     translate `M-b' into `C-x b', whose standard binding is the
     `switch-to-buffer' command.  (Don't actually do this!)  Here is an
     illustration of what would happen:

          meta-prefix-char                    ; The default value.
               => 27
          (key-binding "\M-b")
               => backward-word
          ?\C-x                               ; The print representation
               => 24                          ;   of a character.
          (setq meta-prefix-char 24)
               => 24
          (key-binding "\M-b")
               => switch-to-buffer            ; Now, typing `M-b' is
                                              ;   like typing `C-x b'.

          (setq meta-prefix-char 27)          ; Avoid confusion!
               => 27                          ; Restore the default value!

     This translation of one event into two happens only for
     characters, not for other kinds of input events.  Thus, `M-<F1>',
     a function key, is not converted into `<ESC> <F1>'.


File: elisp,  Node: Changing Key Bindings,  Next: Remapping Commands,  Prev: Functions for Key Lookup,  Up: Keymaps

22.12 Changing Key Bindings
===========================

The way to rebind a key is to change its entry in a keymap.  If you
change a binding in the global keymap, the change is effective in all
buffers (though it has no direct effect in buffers that shadow the
global binding with a local one).  If you change the current buffer's
local map, that usually affects all buffers using the same major mode.
The `global-set-key' and `local-set-key' functions are convenient
interfaces for these operations (*note Key Binding Commands::).  You
can also use `define-key', a more general function; then you must
specify explicitly the map to change.

   When choosing the key sequences for Lisp programs to rebind, please
follow the Emacs conventions for use of various keys (*note Key Binding
Conventions::).

   In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (*note String Type::).
The syntax `\C-' means that the following character is a control
character and `\M-' means that the following character is a meta
character.  Thus, the string `"\M-x"' is read as containing a single
`M-x', `"\C-f"' is read as containing a single `C-f', and `"\M-\C-x"'
and `"\C-\M-x"' are both read as containing a single `C-M-x'.  You can
also use this escape syntax in vectors, as well as others that aren't
allowed in strings; one example is `[?\C-\H-x home]'.  *Note Character
Type::.

   The key definition and lookup functions accept an alternate syntax
for event types in a key sequence that is a vector: you can use a list
containing modifier names plus one base event (a character or function
key name).  For example, `(control ?a)' is equivalent to `?\C-a' and
`(hyper control left)' is equivalent to `C-H-left'.  One advantage of
such lists is that the precise numeric codes for the modifier bits
don't appear in compiled files.

   The functions below signal an error if KEYMAP is not a keymap, or if
KEY is not a string or vector representing a key sequence.  You can use
event types (symbols) as shorthand for events that are lists.  The
`kbd' macro (*note Key Sequences::) is a convenient way to specify the
key sequence.

 -- Function: define-key keymap key binding
     This function sets the binding for KEY in KEYMAP.  (If KEY is more
     than one event long, the change is actually made in another keymap
     reached from KEYMAP.)  The argument BINDING can be any Lisp
     object, but only certain types are meaningful.  (For a list of
     meaningful types, see *Note Key Lookup::.)  The value returned by
     `define-key' is BINDING.

     If KEY is `[t]', this sets the default binding in KEYMAP.  When an
     event has no binding of its own, the Emacs command loop uses the
     keymap's default binding, if there is one.

     Every prefix of KEY must be a prefix key (i.e., bound to a keymap)
     or undefined; otherwise an error is signaled.  If some prefix of
     KEY is undefined, then `define-key' defines it as a prefix key so
     that the rest of KEY can be defined as specified.

     If there was previously no binding for KEY in KEYMAP, the new
     binding is added at the beginning of KEYMAP.  The order of
     bindings in a keymap makes no difference for keyboard input, but it
     does matter for menu keymaps (*note Menu Keymaps::).

   This example creates a sparse keymap and makes a number of bindings
in it:

     (setq map (make-sparse-keymap))
         => (keymap)
     (define-key map "\C-f" 'forward-char)
         => forward-char
     map
         => (keymap (6 . forward-char))

     ;; Build sparse submap for `C-x' and bind `f' in that.
     (define-key map (kbd "C-x f") 'forward-word)
         => forward-word
     map
     => (keymap
         (24 keymap                ; C-x
             (102 . forward-word)) ;      f
         (6 . forward-char))       ; C-f

     ;; Bind `C-p' to the `ctl-x-map'.
     (define-key map (kbd "C-p") ctl-x-map)
     ;; `ctl-x-map'
     => [nil ... find-file ... backward-kill-sentence]

     ;; Bind `C-f' to `foo' in the `ctl-x-map'.
     (define-key map (kbd "C-p C-f") 'foo)
     => 'foo
     map
     => (keymap     ; Note `foo' in `ctl-x-map'.
         (16 keymap [nil ... foo ... backward-kill-sentence])
         (24 keymap
             (102 . forward-word))
         (6 . forward-char))

Note that storing a new binding for `C-p C-f' actually works by
changing an entry in `ctl-x-map', and this has the effect of changing
the bindings of both `C-p C-f' and `C-x C-f' in the default global map.

   The function `substitute-key-definition' scans a keymap for keys
that have a certain binding and rebinds them with a different binding.
Another feature which is cleaner and can often produce the same results
to remap one command into another (*note Remapping Commands::).

 -- Function: substitute-key-definition olddef newdef keymap &optional
          oldmap
     This function replaces OLDDEF with NEWDEF for any keys in KEYMAP
     that were bound to OLDDEF.  In other words, OLDDEF is replaced
     with NEWDEF wherever it appears.  The function returns `nil'.

     For example, this redefines `C-x C-f', if you do it in an Emacs
     with standard bindings:

          (substitute-key-definition
           'find-file 'find-file-read-only (current-global-map))

     If OLDMAP is non-`nil', that changes the behavior of
     `substitute-key-definition': the bindings in OLDMAP determine
     which keys to rebind.  The rebindings still happen in KEYMAP, not
     in OLDMAP.  Thus, you can change one map under the control of the
     bindings in another.  For example,

          (substitute-key-definition
            'delete-backward-char 'my-funny-delete
            my-map global-map)

     puts the special deletion command in `my-map' for whichever keys
     are globally bound to the standard deletion command.

     Here is an example showing a keymap before and after substitution:

          (setq map '(keymap
                      (?1 . olddef-1)
                      (?2 . olddef-2)
                      (?3 . olddef-1)))
          => (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))

          (substitute-key-definition 'olddef-1 'newdef map)
          => nil
          map
          => (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))

 -- Function: suppress-keymap keymap &optional nodigits
     This function changes the contents of the full keymap KEYMAP by
     remapping `self-insert-command' to the command `undefined' (*note
     Remapping Commands::).  This has the effect of undefining all
     printing characters, thus making ordinary insertion of text
     impossible.  `suppress-keymap' returns `nil'.

     If NODIGITS is `nil', then `suppress-keymap' defines digits to run
     `digit-argument', and `-' to run `negative-argument'.  Otherwise
     it makes them undefined like the rest of the printing characters.

     The `suppress-keymap' function does not make it impossible to
     modify a buffer, as it does not suppress commands such as `yank'
     and `quoted-insert'.  To prevent any modification of a buffer, make
     it read-only (*note Read Only Buffers::).

     Since this function modifies KEYMAP, you would normally use it on
     a newly created keymap.  Operating on an existing keymap that is
     used for some other purpose is likely to cause trouble; for
     example, suppressing `global-map' would make it impossible to use
     most of Emacs.

     Most often, `suppress-keymap' is used to initialize local keymaps
     of modes such as Rmail and Dired where insertion of text is not
     desirable and the buffer is read-only.  Here is an example taken
     from the file `emacs/lisp/dired.el', showing how the local keymap
     for Dired mode is set up:

          (setq dired-mode-map (make-keymap))
          (suppress-keymap dired-mode-map)
          (define-key dired-mode-map "r" 'dired-rename-file)
          (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted)
          (define-key dired-mode-map "d" 'dired-flag-file-deleted)
          (define-key dired-mode-map "v" 'dired-view-file)
          (define-key dired-mode-map "e" 'dired-find-file)
          (define-key dired-mode-map "f" 'dired-find-file)
          ...


File: elisp,  Node: Remapping Commands,  Next: Translation Keymaps,  Prev: Changing Key Bindings,  Up: Keymaps

22.13 Remapping Commands
========================

A special kind of key binding, using a special "key sequence" which
includes a command name, has the effect of "remapping" that command
into another.  Here's how it works.  You make a key binding for a key
sequence that starts with the dummy event `remap', followed by the
command name you want to remap.  Specify the remapped definition as the
definition in this binding.  The remapped definition is usually a
command name, but it can be any valid definition for a key binding.

   Here's an example.  Suppose that My mode uses special commands
`my-kill-line' and `my-kill-word', which should be invoked instead of
`kill-line' and `kill-word'.  It can establish this by making these two
command-remapping bindings in its keymap:

     (define-key my-mode-map [remap kill-line] 'my-kill-line)
     (define-key my-mode-map [remap kill-word] 'my-kill-word)

   Whenever `my-mode-map' is an active keymap, if the user types `C-k',
Emacs will find the standard global binding of `kill-line' (assuming
nobody has changed it).  But `my-mode-map' remaps `kill-line' to
`my-kill-line', so instead of running `kill-line', Emacs runs
`my-kill-line'.

   Remapping only works through a single level.  In other words,

     (define-key my-mode-map [remap kill-line] 'my-kill-line)
     (define-key my-mode-map [remap my-kill-line] 'my-other-kill-line)

does not have the effect of remapping `kill-line' into
`my-other-kill-line'.  If an ordinary key binding specifies
`kill-line', this keymap will remap it to `my-kill-line'; if an
ordinary binding specifies `my-kill-line', this keymap will remap it to
`my-other-kill-line'.

 -- Function: command-remapping command &optional position keymaps
     This function returns the remapping for COMMAND (a symbol), given
     the current active keymaps.  If COMMAND is not remapped (which is
     the usual situation), or not a symbol, the function returns `nil'.
     `position' can optionally specify a buffer position or an event
     position to determine the keymaps to use, as in `key-binding'.

     If the optional argument `keymaps' is non-`nil', it specifies a
     list of keymaps to search in.  This argument is ignored if
     `position' is non-`nil'.


File: elisp,  Node: Translation Keymaps,  Next: Key Binding Commands,  Prev: Remapping Commands,  Up: Keymaps

22.14 Keymaps for Translating Sequences of Events
=================================================

This section describes keymaps that are used during reading a key
sequence, to translate certain event sequences into others.
`read-key-sequence' checks every subsequence of the key sequence being
read, as it is read, against `function-key-map' and then against
`key-translation-map'.

 -- Variable: function-key-map
     This variable holds a keymap that describes the character
     sequences sent by function keys on an ordinary character terminal.
     This keymap has the same structure as other keymaps, but is used
     differently: it specifies translations to make while reading key
     sequences, rather than bindings for key sequences.

     If `function-key-map' "binds" a key sequence K to a vector V, then
     when K appears as a subsequence _anywhere_ in a key sequence, it
     is replaced with the events in V.

     For example, VT100 terminals send `<ESC> O P' when the keypad
     <PF1> key is pressed.  Therefore, we want Emacs to translate that
     sequence of events into the single event `pf1'.  We accomplish
     this by "binding" `<ESC> O P' to `[pf1]' in `function-key-map',
     when using a VT100.

     Thus, typing `C-c <PF1>' sends the character sequence `C-c <ESC> O
     P'; later the function `read-key-sequence' translates this back
     into `C-c <PF1>', which it returns as the vector `[?\C-c pf1]'.

     Entries in `function-key-map' are ignored if they conflict with
     bindings made in the minor mode, local, or global keymaps.  The
     intent is that the character sequences that function keys send
     should not have command bindings in their own right--but if they
     do, the ordinary bindings take priority.

     The value of `function-key-map' is usually set up automatically
     according to the terminal's Terminfo or Termcap entry, but
     sometimes those need help from terminal-specific Lisp files.
     Emacs comes with terminal-specific files for many common
     terminals; their main purpose is to make entries in
     `function-key-map' beyond those that can be deduced from Termcap
     and Terminfo.  *Note Terminal-Specific::.

 -- Variable: key-translation-map
     This variable is another keymap used just like `function-key-map'
     to translate input events into other events.  It differs from
     `function-key-map' in two ways:

        * `key-translation-map' goes to work after `function-key-map' is
          finished; it receives the results of translation by
          `function-key-map'.

        * Non-prefix bindings in `key-translation-map' override actual
          key bindings.  For example, if `C-x f' has a non-prefix
          binding in `key-translation-map', that translation takes
          effect even though `C-x f' also has a key binding in the
          global map.

     Note however that actual key bindings can have an effect on
     `key-translation-map', even though they are overridden by it.
     Indeed, actual key bindings override `function-key-map' and thus
     may alter the key sequence that `key-translation-map' receives.
     Clearly, it is better to avoid this type of situation.

     The intent of `key-translation-map' is for users to map one
     character set to another, including ordinary characters normally
     bound to `self-insert-command'.

   You can use `function-key-map' or `key-translation-map' for more
than simple aliases, by using a function, instead of a key sequence, as
the "translation" of a key.  Then this function is called to compute
the translation of that key.

   The key translation function receives one argument, which is the
prompt that was specified in `read-key-sequence'--or `nil' if the key
sequence is being read by the editor command loop.  In most cases you
can ignore the prompt value.

   If the function reads input itself, it can have the effect of
altering the event that follows.  For example, here's how to define
`C-c h' to turn the character that follows into a Hyper character:

     (defun hyperify (prompt)
       (let ((e (read-event)))
         (vector (if (numberp e)
                     (logior (lsh 1 24) e)
                   (if (memq 'hyper (event-modifiers e))
                       e
                     (add-event-modifier "H-" e))))))

     (defun add-event-modifier (string e)
       (let ((symbol (if (symbolp e) e (car e))))
         (setq symbol (intern (concat string
                                      (symbol-name symbol))))
         (if (symbolp e)
             symbol
           (cons symbol (cdr e)))))

     (define-key function-key-map "\C-ch" 'hyperify)

   If you have enabled keyboard character set decoding using
`set-keyboard-coding-system', decoding is done after the translations
listed above.  *Note Terminal I/O Encoding::.  However, in future Emacs
versions, character set decoding may be done at an earlier stage.


File: elisp,  Node: Key Binding Commands,  Next: Scanning Keymaps,  Prev: Translation Keymaps,  Up: Keymaps

22.15 Commands for Binding Keys
===============================

This section describes some convenient interactive interfaces for
changing key bindings.  They work by calling `define-key'.

   People often use `global-set-key' in their init files (*note Init
File::) for simple customization.  For example,

     (global-set-key (kbd "C-x C-\\") 'next-line)

or

     (global-set-key [?\C-x ?\C-\\] 'next-line)

or

     (global-set-key [(control ?x) (control ?\\)] 'next-line)

redefines `C-x C-\' to move down a line.

     (global-set-key [M-mouse-1] 'mouse-set-point)

redefines the first (leftmost) mouse button, entered with the Meta key,
to set point where you click.

   Be careful when using non-ASCII text characters in Lisp
specifications of keys to bind.  If these are read as multibyte text, as
they usually will be in a Lisp file (*note Loading Non-ASCII::), you
must type the keys as multibyte too.  For instance, if you use this:

     (global-set-key "o"" 'my-function) ; bind o-umlaut

or

     (global-set-key ?o" 'my-function) ; bind o-umlaut

and your language environment is multibyte Latin-1, these commands
actually bind the multibyte character with code 2294, not the unibyte
Latin-1 character with code 246 (`M-v').  In order to use this binding,
you need to enter the multibyte Latin-1 character as keyboard input.
One way to do this is by using an appropriate input method (*note Input
Methods: (emacs)Input Methods.).

   If you want to use a unibyte character in the key binding, you can
construct the key sequence string using `multibyte-char-to-unibyte' or
`string-make-unibyte' (*note Converting Representations::).

 -- Command: global-set-key key binding
     This function sets the binding of KEY in the current global map to
     BINDING.

          (global-set-key KEY BINDING)
          ==
          (define-key (current-global-map) KEY BINDING)

 -- Command: global-unset-key key
     This function removes the binding of KEY from the current global
     map.

     One use of this function is in preparation for defining a longer
     key that uses KEY as a prefix--which would not be allowed if KEY
     has a non-prefix binding.  For example:

          (global-unset-key "\C-l")
              => nil
          (global-set-key "\C-l\C-l" 'redraw-display)
              => nil

     This function is implemented simply using `define-key':

          (global-unset-key KEY)
          ==
          (define-key (current-global-map) KEY nil)

 -- Command: local-set-key key binding
     This function sets the binding of KEY in the current local keymap
     to BINDING.

          (local-set-key KEY BINDING)
          ==
          (define-key (current-local-map) KEY BINDING)

 -- Command: local-unset-key key
     This function removes the binding of KEY from the current local
     map.

          (local-unset-key KEY)
          ==
          (define-key (current-local-map) KEY nil)


File: elisp,  Node: Scanning Keymaps,  Next: Menu Keymaps,  Prev: Key Binding Commands,  Up: Keymaps

22.16 Scanning Keymaps
======================

This section describes functions used to scan all the current keymaps
for the sake of printing help information.

 -- Function: accessible-keymaps keymap &optional prefix
     This function returns a list of all the keymaps that can be
     reached (via zero or more prefix keys) from KEYMAP.  The value is
     an association list with elements of the form `(KEY .  MAP)',
     where KEY is a prefix key whose definition in KEYMAP is MAP.

     The elements of the alist are ordered so that the KEY increases in
     length.  The first element is always `([] . KEYMAP)', because the
     specified keymap is accessible from itself with a prefix of no
     events.

     If PREFIX is given, it should be a prefix key sequence; then
     `accessible-keymaps' includes only the submaps whose prefixes start
     with PREFIX.  These elements look just as they do in the value of
     `(accessible-keymaps)'; the only difference is that some elements
     are omitted.

     In the example below, the returned alist indicates that the key
     <ESC>, which is displayed as `^[', is a prefix key whose
     definition is the sparse keymap `(keymap (83 . center-paragraph)
     (115 . foo))'.

          (accessible-keymaps (current-local-map))
          =>(([] keymap
                (27 keymap   ; Note this keymap for <ESC> is repeated below.
                    (83 . center-paragraph)
                    (115 . center-line))
                (9 . tab-to-tab-stop))

             ("^[" keymap
              (83 . center-paragraph)
              (115 . foo)))

     In the following example, `C-h' is a prefix key that uses a sparse
     keymap starting with `(keymap (118 . describe-variable)...)'.
     Another prefix, `C-x 4', uses a keymap which is also the value of
     the variable `ctl-x-4-map'.  The event `mode-line' is one of
     several dummy events used as prefixes for mouse actions in special
     parts of a window.

          (accessible-keymaps (current-global-map))
          => (([] keymap [set-mark-command beginning-of-line ...
                             delete-backward-char])
              ("^H" keymap (118 . describe-variable) ...
               (8 . help-for-help))
              ("^X" keymap [x-flush-mouse-queue ...
               backward-kill-sentence])
              ("^[" keymap [mark-sexp backward-sexp ...
               backward-kill-word])
              ("^X4" keymap (15 . display-buffer) ...)
              ([mode-line] keymap
               (S-mouse-2 . mouse-split-window-horizontally) ...))

     These are not all the keymaps you would see in actuality.

 -- Function: map-keymap function keymap
     The function `map-keymap' calls FUNCTION once for each binding in
     KEYMAP.  It passes two arguments, the event type and the value of
     the binding.  If KEYMAP has a parent, the parent's bindings are
     included as well.  This works recursively: if the parent has
     itself a parent, then the grandparent's bindings are also included
     and so on.

     This function is the cleanest way to examine all the bindings in a
     keymap.

 -- Function: where-is-internal command &optional keymap firstonly
          noindirect no-remap
     This function is a subroutine used by the `where-is' command
     (*note Help: (emacs)Help.).  It returns a list of all key
     sequences (of any length) that are bound to COMMAND in a set of
     keymaps.

     The argument COMMAND can be any object; it is compared with all
     keymap entries using `eq'.

     If KEYMAP is `nil', then the maps used are the current active
     keymaps, disregarding `overriding-local-map' (that is, pretending
     its value is `nil').  If KEYMAP is a keymap, then the maps
     searched are KEYMAP and the global keymap.  If KEYMAP is a list of
     keymaps, only those keymaps are searched.

     Usually it's best to use `overriding-local-map' as the expression
     for KEYMAP.  Then `where-is-internal' searches precisely the
     keymaps that are active.  To search only the global map, pass
     `(keymap)' (an empty keymap) as KEYMAP.

     If FIRSTONLY is `non-ascii', then the value is a single vector
     representing the first key sequence found, rather than a list of
     all possible key sequences.  If FIRSTONLY is `t', then the value
     is the first key sequence, except that key sequences consisting
     entirely of ASCII characters (or meta variants of ASCII
     characters) are preferred to all other key sequences and that the
     return value can never be a menu binding.

     If NOINDIRECT is non-`nil', `where-is-internal' doesn't follow
     indirect keymap bindings.  This makes it possible to search for an
     indirect definition itself.

     When command remapping is in effect (*note Remapping Commands::),
     `where-is-internal' figures out when a command will be run due to
     remapping and reports keys accordingly.  It also returns `nil' if
     COMMAND won't really be run because it has been remapped to some
     other command.  However, if NO-REMAP is non-`nil'.
     `where-is-internal' ignores remappings.

          (where-is-internal 'describe-function)
              => ([8 102] [f1 102] [help 102]
                   [menu-bar help-menu describe describe-function])

 -- Command: describe-bindings &optional prefix buffer-or-name
     This function creates a listing of all current key bindings, and
     displays it in a buffer named `*Help*'.  The text is grouped by
     modes--minor modes first, then the major mode, then global
     bindings.

     If PREFIX is non-`nil', it should be a prefix key; then the
     listing includes only keys that start with PREFIX.

     The listing describes meta characters as <ESC> followed by the
     corresponding non-meta character.

     When several characters with consecutive ASCII codes have the same
     definition, they are shown together, as `FIRSTCHAR..LASTCHAR'.  In
     this instance, you need to know the ASCII codes to understand
     which characters this means.  For example, in the default global
     map, the characters `<SPC> .. ~' are described by a single line.
     <SPC> is ASCII 32, `~' is ASCII 126, and the characters between
     them include all the normal printing characters, (e.g., letters,
     digits, punctuation, etc.); all these characters are bound to
     `self-insert-command'.

     If BUFFER-OR-NAME is non-`nil', it should be a buffer or a buffer
     name.  Then `describe-bindings' lists that buffer's bindings,
     instead of the current buffer's.


File: elisp,  Node: Menu Keymaps,  Prev: Scanning Keymaps,  Up: Keymaps

22.17 Menu Keymaps
==================

A keymap can operate as a menu as well as defining bindings for
keyboard keys and mouse buttons.  Menus are usually actuated with the
mouse, but they can function with the keyboard also.  If a menu keymap
is active for the next input event, that activates the keyboard menu
feature.

* Menu:

* Defining Menus::		How to make a keymap that defines a menu.
* Mouse Menus::			How users actuate the menu with the mouse.
* Keyboard Menus::		How users actuate the menu with the keyboard.
* Menu Example::		Making a simple menu.
* Menu Bar::			How to customize the menu bar.
* Tool Bar::                    A tool bar is a row of images.
* Modifying Menus::             How to add new items to a menu.


File: elisp,  Node: Defining Menus,  Next: Mouse Menus,  Up: Menu Keymaps

22.17.1 Defining Menus
----------------------

A keymap acts as a menu if it has an "overall prompt string", which is
a string that appears as an element of the keymap.  (*Note Format of
Keymaps::.)  The string should describe the purpose of the menu's
commands.  Emacs displays the overall prompt string as the menu title
in some cases, depending on the toolkit (if any) used for displaying
menus.(1)  Keyboard menus also display the overall prompt string.

   The easiest way to construct a keymap with a prompt string is to
specify the string as an argument when you call `make-keymap',
`make-sparse-keymap' (*note Creating Keymaps::), or
`define-prefix-command' (*note Definition of define-prefix-command::).
If you do not want the keymap to operate as a menu, don't specify a
prompt string for it.

 -- Function: keymap-prompt keymap
     This function returns the overall prompt string of KEYMAP, or
     `nil' if it has none.

   The menu's items are the bindings in the keymap.  Each binding
associates an event type to a definition, but the event types have no
significance for the menu appearance.  (Usually we use pseudo-events,
symbols that the keyboard cannot generate, as the event types for menu
item bindings.)  The menu is generated entirely from the bindings that
correspond in the keymap to these events.

   The order of items in the menu is the same as the order of bindings
in the keymap.  Since `define-key' puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order.  When you add an item to
an existing menu, you can specify its position in the menu using
`define-key-after' (*note Modifying Menus::).

* Menu:

* Simple Menu Items::       A simple kind of menu key binding,
                              limited in capabilities.
* Extended Menu Items::     More powerful menu item definitions
                              let you specify keywords to enable
                              various features.
* Menu Separators::         Drawing a horizontal line through a menu.
* Alias Menu Items::        Using command aliases in menu items.

   ---------- Footnotes ----------

   (1) It is required for menus which do not use a toolkit, e.g. under
MS-DOS.


File: elisp,  Node: Simple Menu Items,  Next: Extended Menu Items,  Up: Defining Menus

22.17.1.1 Simple Menu Items
...........................

The simpler (and original) way to define a menu item is to bind some
event type (it doesn't matter what event type) to a binding like this:

     (ITEM-STRING . REAL-BINDING)

The CAR, ITEM-STRING, is the string to be displayed in the menu.  It
should be short--preferably one to three words.  It should describe the
action of the command it corresponds to.  Note that it is not generally
possible to display non-ASCII text in menus.  It will work for keyboard
menus and will work to a large extent when Emacs is built with the Gtk+
toolkit.(1)

   You can also supply a second string, called the help string, as
follows:

     (ITEM-STRING HELP . REAL-BINDING)

HELP specifies a "help-echo" string to display while the mouse is on
that item in the same way as `help-echo' text properties (*note Help
display::).

   As far as `define-key' is concerned, ITEM-STRING and HELP-STRING are
part of the event's binding.  However, `lookup-key' returns just
REAL-BINDING, and only REAL-BINDING is used for executing the key.

   If REAL-BINDING is `nil', then ITEM-STRING appears in the menu but
cannot be selected.

   If REAL-BINDING is a symbol and has a non-`nil' `menu-enable'
property, that property is an expression that controls whether the menu
item is enabled.  Every time the keymap is used to display a menu,
Emacs evaluates the expression, and it enables the menu item only if
the expression's value is non-`nil'.  When a menu item is disabled, it
is displayed in a "fuzzy" fashion, and cannot be selected.

   The menu bar does not recalculate which items are enabled every time
you look at a menu.  This is because the X toolkit requires the whole
tree of menus in advance.  To force recalculation of the menu bar, call
`force-mode-line-update' (*note Mode Line Format::).

   You've probably noticed that menu items show the equivalent keyboard
key sequence (if any) to invoke the same command.  To save time on
recalculation, menu display caches this information in a sublist in the
binding, like this:

     (ITEM-STRING [HELP] (KEY-BINDING-DATA) . REAL-BINDING)

Don't put these sublists in the menu item yourself; menu display
calculates them automatically.  Don't mention keyboard equivalents in
the item strings themselves, since that is redundant.

   ---------- Footnotes ----------

   (1) In this case, the text is first encoded using the `utf-8' coding
system and then rendered by the toolkit as it sees fit.


File: elisp,  Node: Extended Menu Items,  Next: Menu Separators,  Prev: Simple Menu Items,  Up: Defining Menus

22.17.1.2 Extended Menu Items
.............................

An extended-format menu item is a more flexible and also cleaner
alternative to the simple format.  You define an event type with a
binding that's a list starting with the symbol `menu-item'.  For a
non-selectable string, the binding looks like this:

     (menu-item ITEM-NAME)

A string starting with two or more dashes specifies a separator line;
see *Note Menu Separators::.

   To define a real menu item which can be selected, the extended format
binding looks like this:

     (menu-item ITEM-NAME REAL-BINDING
         . ITEM-PROPERTY-LIST)

Here, ITEM-NAME is an expression which evaluates to the menu item
string.  Thus, the string need not be a constant.  The third element,
REAL-BINDING, is the command to execute.  The tail of the list,
ITEM-PROPERTY-LIST, has the form of a property list which contains
other information.

   When an equivalent keyboard key binding is cached, the extended menu
item binding looks like this:

     (menu-item ITEM-NAME REAL-BINDING (KEY-BINDING-DATA)
         . ITEM-PROPERTY-LIST)

   Here is a table of the properties that are supported:

`:enable FORM'
     The result of evaluating FORM determines whether the item is
     enabled (non-`nil' means yes).  If the item is not enabled, you
     can't really click on it.

`:visible FORM'
     The result of evaluating FORM determines whether the item should
     actually appear in the menu (non-`nil' means yes).  If the item
     does not appear, then the menu is displayed as if this item were
     not defined at all.

`:help HELP'
     The value of this property, HELP, specifies a "help-echo" string
     to display while the mouse is on that item.  This is displayed in
     the same way as `help-echo' text properties (*note Help display::).
     Note that this must be a constant string, unlike the `help-echo'
     property for text and overlays.

`:button (TYPE . SELECTED)'
     This property provides a way to define radio buttons and toggle
     buttons.  The CAR, TYPE, says which: it should be `:toggle' or
     `:radio'.  The CDR, SELECTED, should be a form; the result of
     evaluating it says whether this button is currently selected.

     A "toggle" is a menu item which is labeled as either "on" or "off"
     according to the value of SELECTED.  The command itself should
     toggle SELECTED, setting it to `t' if it is `nil', and to `nil' if
     it is `t'.  Here is how the menu item to toggle the
     `debug-on-error' flag is defined:

          (menu-item "Debug on Error" toggle-debug-on-error
                     :button (:toggle
                              . (and (boundp 'debug-on-error)
                                     debug-on-error)))

     This works because `toggle-debug-on-error' is defined as a command
     which toggles the variable `debug-on-error'.

     "Radio buttons" are a group of menu items, in which at any time one
     and only one is "selected."  There should be a variable whose value
     says which one is selected at any time.  The SELECTED form for
     each radio button in the group should check whether the variable
     has the right value for selecting that button.  Clicking on the
     button should set the variable so that the button you clicked on
     becomes selected.

`:key-sequence KEY-SEQUENCE'
     This property specifies which key sequence is likely to be bound
     to the same command invoked by this menu item.  If you specify the
     right key sequence, that makes preparing the menu for display run
     much faster.

     If you specify the wrong key sequence, it has no effect; before
     Emacs displays KEY-SEQUENCE in the menu, it verifies that
     KEY-SEQUENCE is really equivalent to this menu item.

`:key-sequence nil'
     This property indicates that there is normally no key binding
     which is equivalent to this menu item.  Using this property saves
     time in preparing the menu for display, because Emacs does not
     need to search the keymaps for a keyboard equivalent for this menu
     item.

     However, if the user has rebound this item's definition to a key
     sequence, Emacs ignores the `:keys' property and finds the keyboard
     equivalent anyway.

`:keys STRING'
     This property specifies that STRING is the string to display as
     the keyboard equivalent for this menu item.  You can use the
     `\\[...]' documentation construct in STRING.

`:filter FILTER-FN'
     This property provides a way to compute the menu item dynamically.
     The property value FILTER-FN should be a function of one argument;
     when it is called, its argument will be REAL-BINDING.  The
     function should return the binding to use instead.

     Emacs can call this function at any time that it does redisplay or
     operates on menu data structures, so you should write it so it can
     safely be called at any time.


File: elisp,  Node: Menu Separators,  Next: Alias Menu Items,  Prev: Extended Menu Items,  Up: Defining Menus

22.17.1.3 Menu Separators
.........................

A menu separator is a kind of menu item that doesn't display any
text--instead, it divides the menu into subparts with a horizontal line.
A separator looks like this in the menu keymap:

     (menu-item SEPARATOR-TYPE)

where SEPARATOR-TYPE is a string starting with two or more dashes.

   In the simplest case, SEPARATOR-TYPE consists of only dashes.  That
specifies the default kind of separator.  (For compatibility, `""' and
`-' also count as separators.)

   Certain other values of SEPARATOR-TYPE specify a different style of
separator.  Here is a table of them:

`"--no-line"'
`"--space"'
     An extra vertical space, with no actual line.

`"--single-line"'
     A single line in the menu's foreground color.

`"--double-line"'
     A double line in the menu's foreground color.

`"--single-dashed-line"'
     A single dashed line in the menu's foreground color.

`"--double-dashed-line"'
     A double dashed line in the menu's foreground color.

`"--shadow-etched-in"'
     A single line with a 3D sunken appearance.  This is the default,
     used separators consisting of dashes only.

`"--shadow-etched-out"'
     A single line with a 3D raised appearance.

`"--shadow-etched-in-dash"'
     A single dashed line with a 3D sunken appearance.

`"--shadow-etched-out-dash"'
     A single dashed line with a 3D raised appearance.

`"--shadow-double-etched-in"'
     Two lines with a 3D sunken appearance.

`"--shadow-double-etched-out"'
     Two lines with a 3D raised appearance.

`"--shadow-double-etched-in-dash"'
     Two dashed lines with a 3D sunken appearance.

`"--shadow-double-etched-out-dash"'
     Two dashed lines with a 3D raised appearance.

   You can also give these names in another style, adding a colon after
the double-dash and replacing each single dash with capitalization of
the following word.  Thus, `"--:singleLine"', is equivalent to
`"--single-line"'.

   Some systems and display toolkits don't really handle all of these
separator types.  If you use a type that isn't supported, the menu
displays a similar kind of separator that is supported.


File: elisp,  Node: Alias Menu Items,  Prev: Menu Separators,  Up: Defining Menus

22.17.1.4 Alias Menu Items
..........................

Sometimes it is useful to make menu items that use the "same" command
but with different enable conditions.  The best way to do this in Emacs
now is with extended menu items; before that feature existed, it could
be done by defining alias commands and using them in menu items.
Here's an example that makes two aliases for `toggle-read-only' and
gives them different enable conditions:

     (defalias 'make-read-only 'toggle-read-only)
     (put 'make-read-only 'menu-enable '(not buffer-read-only))
     (defalias 'make-writable 'toggle-read-only)
     (put 'make-writable 'menu-enable 'buffer-read-only)

   When using aliases in menus, often it is useful to display the
equivalent key bindings for the "real" command name, not the aliases
(which typically don't have any key bindings except for the menu
itself).  To request this, give the alias symbol a non-`nil'
`menu-alias' property.  Thus,

     (put 'make-read-only 'menu-alias t)
     (put 'make-writable 'menu-alias t)

causes menu items for `make-read-only' and `make-writable' to show the
keyboard bindings for `toggle-read-only'.


File: elisp,  Node: Mouse Menus,  Next: Keyboard Menus,  Prev: Defining Menus,  Up: Menu Keymaps

22.17.2 Menus and the Mouse
---------------------------

The usual way to make a menu keymap produce a menu is to make it the
definition of a prefix key.  (A Lisp program can explicitly pop up a
menu and receive the user's choice--see *Note Pop-Up Menus::.)

   If the prefix key ends with a mouse event, Emacs handles the menu
keymap by popping up a visible menu, so that the user can select a
choice with the mouse.  When the user clicks on a menu item, the event
generated is whatever character or symbol has the binding that brought
about that menu item.  (A menu item may generate a series of events if
the menu has multiple levels or comes from the menu bar.)

   It's often best to use a button-down event to trigger the menu.  Then
the user can select a menu item by releasing the button.

   A single keymap can appear as multiple menu panes, if you explicitly
arrange for this.  The way to do this is to make a keymap for each pane,
then create a binding for each of those maps in the main keymap of the
menu.  Give each of these bindings an item string that starts with `@'.
The rest of the item string becomes the name of the pane.  See the
file `lisp/mouse.el' for an example of this.  Any ordinary bindings
with `@'-less item strings are grouped into one pane, which appears
along with the other panes explicitly created for the submaps.

   X toolkit menus don't have panes; instead, they can have submenus.
Every nested keymap becomes a submenu, whether the item string starts
with `@' or not.  In a toolkit version of Emacs, the only thing special
about `@' at the beginning of an item string is that the `@' doesn't
appear in the menu item.

   Multiple keymaps that define the same menu prefix key produce
separate panes or separate submenus.


File: elisp,  Node: Keyboard Menus,  Next: Menu Example,  Prev: Mouse Menus,  Up: Menu Keymaps

22.17.3 Menus and the Keyboard
------------------------------

When a prefix key ending with a keyboard event (a character or function
key) has a definition that is a menu keymap, the keymap operates as a
keyboard menu; the user specifies the next event by choosing a menu
item with the keyboard.

   Emacs displays the keyboard menu with the map's overall prompt
string, followed by the alternatives (the item strings of the map's
bindings), in the echo area.  If the bindings don't all fit at once,
the user can type <SPC> to see the next line of alternatives.
Successive uses of <SPC> eventually get to the end of the menu and then
cycle around to the beginning.  (The variable `menu-prompt-more-char'
specifies which character is used for this; <SPC> is the default.)

   When the user has found the desired alternative from the menu, he or
she should type the corresponding character--the one whose binding is
that alternative.

   This way of using menus in an Emacs-like editor was inspired by the
Hierarkey system.

 -- Variable: menu-prompt-more-char
     This variable specifies the character to use to ask to see the
     next line of a menu.  Its initial value is 32, the code for <SPC>.


File: elisp,  Node: Menu Example,  Next: Menu Bar,  Prev: Keyboard Menus,  Up: Menu Keymaps

22.17.4 Menu Example
--------------------

Here is a complete example of defining a menu keymap.  It is the
definition of the `Replace' submenu in the `Edit' menu in the menu bar,
and it uses the extended menu item format (*note Extended Menu
Items::).  First we create the keymap, and give it a name:

     (defvar menu-bar-replace-menu (make-sparse-keymap "Replace"))

Next we define the menu items:

     (define-key menu-bar-replace-menu [tags-repl-continue]
       '(menu-item "Continue Replace" tags-loop-continue
     	      :help "Continue last tags replace operation"))
     (define-key menu-bar-replace-menu [tags-repl]
       '(menu-item "Replace in tagged files" tags-query-replace
     	      :help "Interactively replace a regexp in all tagged files"))
     (define-key menu-bar-replace-menu [separator-replace-tags]
       '(menu-item "--"))
     ;; ...

Note the symbols which the bindings are "made for"; these appear inside
square brackets, in the key sequence being defined.  In some cases,
this symbol is the same as the command name; sometimes it is different.
These symbols are treated as "function keys," but they are not real
function keys on the keyboard.  They do not affect the functioning of
the menu itself, but they are "echoed" in the echo area when the user
selects from the menu, and they appear in the output of `where-is' and
`apropos'.

   The menu in this example is intended for use with the mouse.  If a
menu is intended for use with the keyboard, that is, if it is bound to
a key sequence ending with a keyboard event, then the menu items should
be bound to characters or "real" function keys, that can be typed with
the keyboard.

   The binding whose definition is `("--")' is a separator line.  Like
a real menu item, the separator has a key symbol, in this case
`separator-replace-tags'.  If one menu has two separators, they must
have two different key symbols.

   Here is how we make this menu appear as an item in the parent menu:

     (define-key menu-bar-edit-menu [replace]
       (list 'menu-item "Replace" menu-bar-replace-menu))

Note that this incorporates the submenu keymap, which is the value of
the variable `menu-bar-replace-menu', rather than the symbol
`menu-bar-replace-menu' itself.  Using that symbol in the parent menu
item would be meaningless because `menu-bar-replace-menu' is not a
command.

   If you wanted to attach the same replace menu to a mouse click, you
can do it this way:

     (define-key global-map [C-S-down-mouse-1]
        menu-bar-replace-menu)


File: elisp,  Node: Menu Bar,  Next: Tool Bar,  Prev: Menu Example,  Up: Menu Keymaps

22.17.5 The Menu Bar
--------------------

Most window systems allow each frame to have a "menu bar"--a
permanently displayed menu stretching horizontally across the top of the
frame.  The items of the menu bar are the subcommands of the fake
"function key" `menu-bar', as defined in the active keymaps.

   To add an item to the menu bar, invent a fake "function key" of your
own (let's call it KEY), and make a binding for the key sequence
`[menu-bar KEY]'.  Most often, the binding is a menu keymap, so that
pressing a button on the menu bar item leads to another menu.

   When more than one active keymap defines the same fake function key
for the menu bar, the item appears just once.  If the user clicks on
that menu bar item, it brings up a single, combined menu containing all
the subcommands of that item--the global subcommands, the local
subcommands, and the minor mode subcommands.

   The variable `overriding-local-map' is normally ignored when
determining the menu bar contents.  That is, the menu bar is computed
from the keymaps that would be active if `overriding-local-map' were
`nil'.  *Note Active Keymaps::.

   In order for a frame to display a menu bar, its `menu-bar-lines'
parameter must be greater than zero.  Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame.  We
recommend 1 or 2 as the value of `menu-bar-lines'.  *Note Layout
Parameters::.

   Here's an example of setting up a menu bar item:

     (modify-frame-parameters (selected-frame)
                              '((menu-bar-lines . 2)))

     ;; Make a menu keymap (with a prompt string)
     ;; and make it the menu bar item's definition.
     (define-key global-map [menu-bar words]
       (cons "Words" (make-sparse-keymap "Words")))

     ;; Define specific subcommands in this menu.
     (define-key global-map
       [menu-bar words forward]
       '("Forward word" . forward-word))
     (define-key global-map
       [menu-bar words backward]
       '("Backward word" . backward-word))

   A local keymap can cancel a menu bar item made by the global keymap
by rebinding the same fake function key with `undefined' as the
binding.  For example, this is how Dired suppresses the `Edit' menu bar
item:

     (define-key dired-mode-map [menu-bar edit] 'undefined)

`edit' is the fake function key used by the global map for the `Edit'
menu bar item.  The main reason to suppress a global menu bar item is
to regain space for mode-specific items.

 -- Variable: menu-bar-final-items
     Normally the menu bar shows global items followed by items defined
     by the local maps.

     This variable holds a list of fake function keys for items to
     display at the end of the menu bar rather than in normal sequence.
     The default value is `(help-menu)'; thus, the `Help' menu item
     normally appears at the end of the menu bar, following local menu
     items.

 -- Variable: menu-bar-update-hook
     This normal hook is run by redisplay to update the menu bar
     contents, before redisplaying the menu bar.  You can use it to
     update submenus whose contents should vary.  Since this hook is
     run frequently, we advise you to ensure that the functions it
     calls do not take much time in the usual case.


File: elisp,  Node: Tool Bar,  Next: Modifying Menus,  Prev: Menu Bar,  Up: Menu Keymaps

22.17.6 Tool bars
-----------------

A "tool bar" is a row of icons at the top of a frame, that execute
commands when you click on them--in effect, a kind of graphical menu
bar.

   The frame parameter `tool-bar-lines' (X resource `toolBar') controls
how many lines' worth of height to reserve for the tool bar.  A zero
value suppresses the tool bar.  If the value is nonzero, and
`auto-resize-tool-bars' is non-`nil', the tool bar expands and
contracts automatically as needed to hold the specified contents.

   If the value of `auto-resize-tool-bars' is `grow-only', the tool bar
expands automatically, but does not contract automatically.  To
contract the tool bar, the user has to redraw the frame by entering
`C-l'.

   The tool bar contents are controlled by a menu keymap attached to a
fake "function key" called `tool-bar' (much like the way the menu bar
is controlled).  So you define a tool bar item using `define-key', like
this:

     (define-key global-map [tool-bar KEY] ITEM)

where KEY is a fake "function key" to distinguish this item from other
items, and ITEM is a menu item key binding (*note Extended Menu
Items::), which says how to display this item and how it behaves.

   The usual menu keymap item properties, `:visible', `:enable',
`:button', and `:filter', are useful in tool bar bindings and have
their normal meanings.  The REAL-BINDING in the item must be a command,
not a keymap; in other words, it does not work to define a tool bar
icon as a prefix key.

   The `:help' property specifies a "help-echo" string to display while
the mouse is on that item.  This is displayed in the same way as
`help-echo' text properties (*note Help display::).

   In addition, you should use the `:image' property; this is how you
specify the image to display in the tool bar:

`:image IMAGE'
     IMAGES is either a single image specification or a vector of four
     image specifications.  If you use a vector of four, one of them is
     used, depending on circumstances:

    item 0
          Used when the item is enabled and selected.

    item 1
          Used when the item is enabled and deselected.

    item 2
          Used when the item is disabled and selected.

    item 3
          Used when the item is disabled and deselected.

   If IMAGE is a single image specification, Emacs draws the tool bar
button in disabled state by applying an edge-detection algorithm to the
image.

   The default tool bar is defined so that items specific to editing do
not appear for major modes whose command symbol has a `mode-class'
property of `special' (*note Major Mode Conventions::).  Major modes
may add items to the global bar by binding `[tool-bar FOO]' in their
local map.  It makes sense for some major modes to replace the default
tool bar items completely, since not many can be accommodated
conveniently, and the default bindings make this easy by using an
indirection through `tool-bar-map'.

 -- Variable: tool-bar-map
     By default, the global map binds `[tool-bar]' as follows:
          (global-set-key [tool-bar]
          		'(menu-item "tool bar" ignore
          			    :filter (lambda (ignore) tool-bar-map)))
     Thus the tool bar map is derived dynamically from the value of
     variable `tool-bar-map' and you should normally adjust the default
     (global) tool bar by changing that map.  Major modes may replace
     the global bar completely by making `tool-bar-map' buffer-local
     and set to a keymap containing only the desired items.  Info mode
     provides an example.

   There are two convenience functions for defining tool bar items, as
follows.

 -- Function: tool-bar-add-item icon def key &rest props
     This function adds an item to the tool bar by modifying
     `tool-bar-map'.  The image to use is defined by ICON, which is the
     base name of an XPM, XBM or PBM image file to be located by
     `find-image'.  Given a value `"exit"', say, `exit.xpm', `exit.pbm'
     and `exit.xbm' would be searched for in that order on a color
     display.  On a monochrome display, the search order is `.pbm',
     `.xbm' and `.xpm'.  The binding to use is the command DEF, and KEY
     is the fake function key symbol in the prefix keymap.  The
     remaining arguments PROPS are additional property list elements to
     add to the menu item specification.

     To define items in some local map, bind `tool-bar-map' with `let'
     around calls of this function:
          (defvar foo-tool-bar-map
            (let ((tool-bar-map (make-sparse-keymap)))
              (tool-bar-add-item ...)
              ...
              tool-bar-map))

 -- Function: tool-bar-add-item-from-menu command icon &optional map
          &rest props
     This function is a convenience for defining tool bar items which
     are consistent with existing menu bar bindings.  The binding of
     COMMAND is looked up in the menu bar in MAP (default `global-map')
     and modified to add an image specification for ICON, which is
     found in the same way as by `tool-bar-add-item'.  The resulting
     binding is then placed in `tool-bar-map', so use this function
     only for global tool bar items.

     MAP must contain an appropriate keymap bound to `[menu-bar]'.  The
     remaining arguments PROPS are additional property list elements to
     add to the menu item specification.

 -- Function: tool-bar-local-item-from-menu command icon in-map
          &optional from-map &rest props
     This function is used for making non-global tool bar items.  Use it
     like `tool-bar-add-item-from-menu' except that IN-MAP specifies
     the local map to make the definition in.  The argument FROM-MAP is
     like the MAP argument of `tool-bar-add-item-from-menu'.

 -- Variable: auto-resize-tool-bar
     If this variable is non-`nil', the tool bar automatically resizes
     to show all defined tool bar items--but not larger than a quarter
     of the frame's height.

     If the value is `grow-only', the tool bar expands automatically,
     but does not contract automatically.  To contract the tool bar, the
     user has to redraw the frame by entering `C-l'.

 -- Variable: auto-raise-tool-bar-buttons
     If this variable is non-`nil', tool bar items display in raised
     form when the mouse moves over them.

 -- Variable: tool-bar-button-margin
     This variable specifies an extra margin to add around tool bar
     items.  The value is an integer, a number of pixels.  The default
     is 4.

 -- Variable: tool-bar-button-relief
     This variable specifies the shadow width for tool bar items.  The
     value is an integer, a number of pixels.  The default is 1.

 -- Variable: tool-bar-border
     This variable specifies the height of the border drawn below the
     tool bar area.  An integer value specifies height as a number of
     pixels.  If the value is one of `internal-border-width' (the
     default) or `border-width', the tool bar border height corresponds
     to the corresponding frame parameter.

   You can define a special meaning for clicking on a tool bar item with
the shift, control, meta, etc., modifiers.  You do this by setting up
additional items that relate to the original item through the fake
function keys.  Specifically, the additional items should use the
modified versions of the same fake function key used to name the
original item.

   Thus, if the original item was defined this way,

     (define-key global-map [tool-bar shell]
       '(menu-item "Shell" shell
                   :image (image :type xpm :file "shell.xpm")))

then here is how you can define clicking on the same tool bar image with
the shift modifier:

     (define-key global-map [tool-bar S-shell] 'some-command)

   *Note Function Keys::, for more information about how to add
modifiers to function keys.


File: elisp,  Node: Modifying Menus,  Prev: Tool Bar,  Up: Menu Keymaps

22.17.7 Modifying Menus
-----------------------

When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items.  If you
use `define-key' to add the item, it normally goes at the front of the
menu.  To put it elsewhere in the menu, use `define-key-after':

 -- Function: define-key-after map key binding &optional after
     Define a binding in MAP for KEY, with value BINDING, just like
     `define-key', but position the binding in MAP after the binding
     for the event AFTER.  The argument KEY should be of length one--a
     vector or string with just one element.  But AFTER should be a
     single event type--a symbol or a character, not a sequence.  The
     new binding goes after the binding for AFTER.  If AFTER is `t' or
     is omitted, then the new binding goes last, at the end of the
     keymap.  However, new bindings are added before any inherited
     keymap.

     Here is an example:

          (define-key-after my-menu [drink]
            '("Drink" . drink-command) 'eat)

     makes a binding for the fake function key <DRINK> and puts it
     right after the binding for <EAT>.

     Here is how to insert an item called `Work' in the `Signals' menu
     of Shell mode, after the item `break':

          (define-key-after
            (lookup-key shell-mode-map [menu-bar signals])
            [work] '("Work" . work-command) 'break)


File: elisp,  Node: Modes,  Next: Documentation,  Prev: Keymaps,  Up: Top

23 Major and Minor Modes
************************

A "mode" is a set of definitions that customize Emacs and can be turned
on and off while you edit.  There are two varieties of modes: "major
modes", which are mutually exclusive and used for editing particular
kinds of text, and "minor modes", which provide features that users can
enable individually.

   This chapter describes how to write both major and minor modes, how
to indicate them in the mode line, and how they run hooks supplied by
the user.  For related topics such as keymaps and syntax tables, see
*Note Keymaps::, and *Note Syntax Tables::.

* Menu:

* Hooks::              How to use hooks; how to write code that provides hooks.
* Major Modes::        Defining major modes.
* Minor Modes::        Defining minor modes.
* Mode Line Format::   Customizing the text that appears in the mode line.
* Imenu::              How a mode can provide a menu
                         of definitions in the buffer.
* Font Lock Mode::     How modes can highlight text according to syntax.
* Desktop Save Mode::  How modes can have buffer state saved between
                         Emacs sessions.


File: elisp,  Node: Hooks,  Next: Major Modes,  Up: Modes

23.1 Hooks
==========

A "hook" is a variable where you can store a function or functions to
be called on a particular occasion by an existing program.  Emacs
provides hooks for the sake of customization.  Most often, hooks are set
up in the init file (*note Init File::), but Lisp programs can set them
also.  *Note Standard Hooks::, for a list of standard hook variables.

   Most of the hooks in Emacs are "normal hooks".  These variables
contain lists of functions to be called with no arguments.  By
convention, whenever the hook name ends in `-hook', that tells you it
is normal.  We try to make all hooks normal, as much as possible, so
that you can use them in a uniform way.

   Every major mode function is supposed to run a normal hook called
the "mode hook" as the one of the last steps of initialization.  This
makes it easy for a user to customize the behavior of the mode, by
overriding the buffer-local variable assignments already made by the
mode.  Most minor mode functions also run a mode hook at the end.  But
hooks are used in other contexts too.  For example, the hook
`suspend-hook' runs just before Emacs suspends itself (*note Suspending
Emacs::).

   The recommended way to add a hook function to a normal hook is by
calling `add-hook' (see below).  The hook functions may be any of the
valid kinds of functions that `funcall' accepts (*note What Is a
Function::).  Most normal hook variables are initially void; `add-hook'
knows how to deal with this.  You can add hooks either globally or
buffer-locally with `add-hook'.

   If the hook variable's name does not end with `-hook', that
indicates it is probably an "abnormal hook".  That means the hook
functions are called with arguments, or their return values are used in
some way.  The hook's documentation says how the functions are called.
You can use `add-hook' to add a function to an abnormal hook, but you
must write the function to follow the hook's calling convention.

   By convention, abnormal hook names end in `-functions' or `-hooks'.
If the variable's name ends in `-function', then its value is just a
single function, not a list of functions.

   Here's an example that uses a mode hook to turn on Auto Fill mode
when in Lisp Interaction mode:

     (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)

   At the appropriate time, Emacs uses the `run-hooks' function to run
particular hooks.

 -- Function: run-hooks &rest hookvars
     This function takes one or more normal hook variable names as
     arguments, and runs each hook in turn.  Each argument should be a
     symbol that is a normal hook variable.  These arguments are
     processed in the order specified.

     If a hook variable has a non-`nil' value, that value should be a
     list of functions.  `run-hooks' calls all the functions, one by
     one, with no arguments.

     The hook variable's value can also be a single function--either a
     lambda expression or a symbol with a function definition--which
     `run-hooks' calls.  But this usage is obsolete.

 -- Function: run-hook-with-args hook &rest args
     This function is the way to run an abnormal hook and always call
     all of the hook functions.  It calls each of the hook functions
     one by one, passing each of them the arguments ARGS.

 -- Function: run-hook-with-args-until-failure hook &rest args
     This function is the way to run an abnormal hook until one of the
     hook functions fails.  It calls each of the hook functions,
     passing each of them the arguments ARGS, until some hook function
     returns `nil'.  It then stops and returns `nil'.  If none of the
     hook functions return `nil', it returns a non-`nil' value.

 -- Function: run-hook-with-args-until-success hook &rest args
     This function is the way to run an abnormal hook until a hook
     function succeeds.  It calls each of the hook functions, passing
     each of them the arguments ARGS, until some hook function returns
     non-`nil'.  Then it stops, and returns whatever was returned by
     the last hook function that was called.  If all hook functions
     return `nil', it returns `nil' as well.

 -- Function: add-hook hook function &optional append local
     This function is the handy way to add function FUNCTION to hook
     variable HOOK.  You can use it for abnormal hooks as well as for
     normal hooks.  FUNCTION can be any Lisp function that can accept
     the proper number of arguments for HOOK.  For example,

          (add-hook 'text-mode-hook 'my-text-hook-function)

     adds `my-text-hook-function' to the hook called `text-mode-hook'.

     If FUNCTION is already present in HOOK (comparing using `equal'),
     then `add-hook' does not add it a second time.

     It is best to design your hook functions so that the order in
     which they are executed does not matter.  Any dependence on the
     order is "asking for trouble."  However, the order is predictable:
     normally, FUNCTION goes at the front of the hook list, so it will
     be executed first (barring another `add-hook' call).  If the
     optional argument APPEND is non-`nil', the new hook function goes
     at the end of the hook list and will be executed last.

     `add-hook' can handle the cases where HOOK is void or its value is
     a single function; it sets or changes the value to a list of
     functions.

     If LOCAL is non-`nil', that says to add FUNCTION to the
     buffer-local hook list instead of to the global hook list.  If
     needed, this makes the hook buffer-local and adds `t' to the
     buffer-local value.  The latter acts as a flag to run the hook
     functions in the default value as well as in the local value.

 -- Function: remove-hook hook function &optional local
     This function removes FUNCTION from the hook variable HOOK.  It
     compares FUNCTION with elements of HOOK using `equal', so it works
     for both symbols and lambda expressions.

     If LOCAL is non-`nil', that says to remove FUNCTION from the
     buffer-local hook list instead of from the global hook list.


File: elisp,  Node: Major Modes,  Next: Minor Modes,  Prev: Hooks,  Up: Modes

23.2 Major Modes
================

Major modes specialize Emacs for editing particular kinds of text.
Each buffer has only one major mode at a time.  For each major mode
there is a function to switch to that mode in the current buffer; its
name should end in `-mode'.  These functions work by setting
buffer-local variable bindings and other data associated with the
buffer, such as a local keymap.  The effect lasts until you switch to
another major mode in the same buffer.

* Menu:

* Major Mode Basics::
* Major Mode Conventions::  Coding conventions for keymaps, etc.
* Auto Major Mode::         How Emacs chooses the major mode automatically.
* Mode Help::               Finding out how to use a mode.
* Derived Modes::           Defining a new major mode based on another major
                              mode.
* Generic Modes::           Defining a simple major mode that supports
                              comment syntax and Font Lock mode.
* Mode Hooks::              Hooks run at the end of major mode functions.
* Example Major Modes::     Text mode and Lisp modes.


File: elisp,  Node: Major Mode Basics,  Next: Major Mode Conventions,  Up: Major Modes

23.2.1 Major Mode Basics
------------------------

The least specialized major mode is called "Fundamental mode".  This
mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
default state.  All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
`C-j' (`eval-print-last-sexp'), <TAB> (`lisp-indent-line'), and other
keys.

   When you need to write several editing commands to help you perform a
specialized editing task, creating a new major mode is usually a good
idea.  In practice, writing a major mode is easy (in contrast to
writing a minor mode, which is often difficult).

   If the new mode is similar to an old one, it is often unwise to
modify the old one to serve two purposes, since it may become harder to
use and maintain.  Instead, copy and rename an existing major mode
definition and alter the copy--or use `define-derived-mode' to define a
"derived mode" (*note Derived Modes::).  For example, Rmail Edit mode
is a major mode that is very similar to Text mode except that it
provides two additional commands.  Its definition is distinct from that
of Text mode, but uses that of Text mode.

   Even if the new mode is not an obvious derivative of any other mode,
it is convenient to use `define-derived-mode' with a `nil' parent
argument, since it automatically enforces the most important coding
conventions for you.

   For a very simple programming language major mode that handles
comments and fontification, you can use `define-generic-mode'.  *Note
Generic Modes::.

   Rmail Edit mode offers an example of changing the major mode
temporarily for a buffer, so it can be edited in a different way (with
ordinary Emacs commands rather than Rmail commands).  In such cases, the
temporary major mode usually provides a command to switch back to the
buffer's usual mode (Rmail mode, in this case).  You might be tempted to
present the temporary redefinitions inside a recursive edit and restore
the usual ones when the user exits; but this is a bad idea because it
constrains the user's options when it is done in more than one buffer:
recursive edits must be exited most-recently-entered first.  Using an
alternative major mode avoids this limitation.  *Note Recursive
Editing::.

   The standard GNU Emacs Lisp library directory tree contains the code
for several major modes, in files such as `text-mode.el', `texinfo.el',
`lisp-mode.el', `c-mode.el', and `rmail.el'.  They are found in various
subdirectories of the `lisp' directory.  You can study these libraries
to see how modes are written.  Text mode is perhaps the simplest major
mode aside from Fundamental mode.  Rmail mode is a complicated and
specialized mode.


File: elisp,  Node: Major Mode Conventions,  Next: Auto Major Mode,  Prev: Major Mode Basics,  Up: Major Modes

23.2.2 Major Mode Conventions
-----------------------------

The code for existing major modes follows various coding conventions,
including conventions for local keymap and syntax table initialization,
global names, and hooks.  Please follow these conventions when you
define a new major mode.  (Fundamental mode is an exception to many of
these conventions, because its definition is to present the global
state of Emacs.)

   This list of conventions is only partial, because each major mode
should aim for consistency in general with other Emacs major modes.
This makes Emacs as a whole more coherent.  It is impossible to list
here all the possible points where this issue might come up; if the
Emacs developers point out an area where your major mode deviates from
the usual conventions, please make it compatible.

   * Define a command whose name ends in `-mode', with no arguments,
     that switches to the new mode in the current buffer.  This command
     should set up the keymap, syntax table, and buffer-local variables
     in an existing buffer, without changing the buffer's contents.

   * Write a documentation string for this command that describes the
     special commands available in this mode.  `C-h m'
     (`describe-mode') in your mode will display this string.

     The documentation string may include the special documentation
     substrings, `\[COMMAND]', `\{KEYMAP}', and `\<KEYMAP>', which
     enable the documentation to adapt automatically to the user's own
     key bindings.  *Note Keys in Documentation::.

   * The major mode command should start by calling
     `kill-all-local-variables'.  This runs the normal hook
     `change-major-mode-hook', then gets rid of the buffer-local
     variables of the major mode previously in effect.  *Note Creating
     Buffer-Local::.

   * The major mode command should set the variable `major-mode' to the
     major mode command symbol.  This is how `describe-mode' discovers
     which documentation to print.

   * The major mode command should set the variable `mode-name' to the
     "pretty" name of the mode, as a string.  This string appears in the
     mode line.

   * Since all global names are in the same name space, all the global
     variables, constants, and functions that are part of the mode
     should have names that start with the major mode name (or with an
     abbreviation of it if the name is long).  *Note Coding
     Conventions::.

   * In a major mode for editing some kind of structured text, such as a
     programming language, indentation of text according to structure is
     probably useful.  So the mode should set `indent-line-function' to
     a suitable function, and probably customize other variables for
     indentation.

   * The major mode should usually have its own keymap, which is used
     as the local keymap in all buffers in that mode.  The major mode
     command should call `use-local-map' to install this local map.
     *Note Active Keymaps::, for more information.

     This keymap should be stored permanently in a global variable named
     `MODENAME-mode-map'.  Normally the library that defines the mode
     sets this variable.

     *Note Tips for Defining::, for advice about how to write the code
     to set up the mode's keymap variable.

   * The key sequences bound in a major mode keymap should usually
     start with `C-c', followed by a control character, a digit, or `{',
     `}', `<', `>', `:' or `;'.  The other punctuation characters are
     reserved for minor modes, and ordinary letters are reserved for
     users.

     A major mode can also rebind the keys `M-n', `M-p' and `M-s'.  The
     bindings for `M-n' and `M-p' should normally be some kind of
     "moving forward and backward," but this does not necessarily mean
     cursor motion.

     It is legitimate for a major mode to rebind a standard key
     sequence if it provides a command that does "the same job" in a
     way better suited to the text this mode is used for.  For example,
     a major mode for editing a programming language might redefine
     `C-M-a' to "move to the beginning of a function" in a way that
     works better for that language.

     It is also legitimate for a major mode to rebind a standard key
     sequence whose standard meaning is rarely useful in that mode.  For
     instance, minibuffer modes rebind `M-r', whose standard meaning is
     rarely of any use in the minibuffer.  Major modes such as Dired or
     Rmail that do not allow self-insertion of text can reasonably
     redefine letters and other printing characters as special commands.

   * Major modes modes for editing text should not define <RET> to do
     anything other than insert a newline.  However, it is ok for
     specialized modes for text that users don't directly edit, such as
     Dired and Info modes, to redefine <RET> to do something entirely
     different.

   * Major modes should not alter options that are primarily a matter
     of user preference, such as whether Auto-Fill mode is enabled.
     Leave this to each user to decide.  However, a major mode should
     customize other variables so that Auto-Fill mode will work
     usefully _if_ the user decides to use it.

   * The mode may have its own syntax table or may share one with other
     related modes.  If it has its own syntax table, it should store
     this in a variable named `MODENAME-mode-syntax-table'.  *Note
     Syntax Tables::.

   * If the mode handles a language that has a syntax for comments, it
     should set the variables that define the comment syntax.  *Note
     Options Controlling Comments: (emacs)Options for Comments.

   * The mode may have its own abbrev table or may share one with other
     related modes.  If it has its own abbrev table, it should store
     this in a variable named `MODENAME-mode-abbrev-table'.  If the
     major mode command defines any abbrevs itself, it should pass `t'
     for the SYSTEM-FLAG argument to `define-abbrev'.  *Note Defining
     Abbrevs::.

   * The mode should specify how to do highlighting for Font Lock mode,
     by setting up a buffer-local value for the variable
     `font-lock-defaults' (*note Font Lock Mode::).

   * The mode should specify how Imenu should find the definitions or
     sections of a buffer, by setting up a buffer-local value for the
     variable `imenu-generic-expression', for the two variables
     `imenu-prev-index-position-function' and
     `imenu-extract-index-name-function', or for the variable
     `imenu-create-index-function' (*note Imenu::).

   * The mode can specify a local value for
     `eldoc-documentation-function' to tell ElDoc mode how to handle
     this mode.

   * Use `defvar' or `defcustom' to set mode-related variables, so that
     they are not reinitialized if they already have a value.  (Such
     reinitialization could discard customizations made by the user.)

   * To make a buffer-local binding for an Emacs customization
     variable, use `make-local-variable' in the major mode command, not
     `make-variable-buffer-local'.  The latter function would make the
     variable local to every buffer in which it is subsequently set,
     which would affect buffers that do not use this mode.  It is
     undesirable for a mode to have such global effects.  *Note
     Buffer-Local Variables::.

     With rare exceptions, the only reasonable way to use
     `make-variable-buffer-local' in a Lisp package is for a variable
     which is used only within that package.  Using it on a variable
     used by other packages would interfere with them.

   * Each major mode should have a normal "mode hook" named
     `MODENAME-mode-hook'.  The very last thing the major mode command
     should do is to call `run-mode-hooks'.  This runs the mode hook,
     and then runs the normal hook `after-change-major-mode-hook'.
     *Note Mode Hooks::.

   * The major mode command may start by calling some other major mode
     command (called the "parent mode") and then alter some of its
     settings.  A mode that does this is called a "derived mode".  The
     recommended way to define one is to use `define-derived-mode', but
     this is not required.  Such a mode should call the parent mode
     command inside a `delay-mode-hooks' form.  (Using
     `define-derived-mode' does this automatically.)  *Note Derived
     Modes::, and *Note Mode Hooks::.

   * If something special should be done if the user switches a buffer
     from this mode to any other major mode, this mode can set up a
     buffer-local value for `change-major-mode-hook' (*note Creating
     Buffer-Local::).

   * If this mode is appropriate only for specially-prepared text, then
     the major mode command symbol should have a property named
     `mode-class' with value `special', put on as follows:

          (put 'funny-mode 'mode-class 'special)

     This tells Emacs that new buffers created while the current buffer
     is in Funny mode should not inherit Funny mode, in case
     `default-major-mode' is `nil'.  Modes such as Dired, Rmail, and
     Buffer List use this feature.

   * If you want to make the new mode the default for files with certain
     recognizable names, add an element to `auto-mode-alist' to select
     the mode for those file names (*note Auto Major Mode::).  If you
     define the mode command to autoload, you should add this element in
     the same file that calls `autoload'.  If you use an autoload
     cookie for the mode command, you can also use an autoload cookie
     for the form that adds the element (*note autoload cookie::).  If
     you do not autoload the mode command, it is sufficient to add the
     element in the file that contains the mode definition.

   * In the comments that document the file, you should provide a sample
     `autoload' form and an example of how to add to `auto-mode-alist',
     that users can include in their init files (*note Init File::).

   * The top-level forms in the file defining the mode should be
     written so that they may be evaluated more than once without
     adverse consequences.  Even if you never load the file more than
     once, someone else will.


File: elisp,  Node: Auto Major Mode,  Next: Mode Help,  Prev: Major Mode Conventions,  Up: Major Modes

23.2.3 How Emacs Chooses a Major Mode
-------------------------------------

Based on information in the file name or in the file itself, Emacs
automatically selects a major mode for the new buffer when a file is
visited.  It also processes local variables specified in the file text.

 -- Command: fundamental-mode
     Fundamental mode is a major mode that is not specialized for
     anything in particular.  Other major modes are defined in effect
     by comparison with this one--their definitions say what to change,
     starting from Fundamental mode.  The `fundamental-mode' function
     does _not_ run any mode hooks; you're not supposed to customize
     it.  (If you want Emacs to behave differently in Fundamental mode,
     change the _global_ state of Emacs.)

 -- Command: normal-mode &optional find-file
     This function establishes the proper major mode and buffer-local
     variable bindings for the current buffer.  First it calls
     `set-auto-mode' (see below), then it runs `hack-local-variables'
     to parse, and bind or evaluate as appropriate, the file's local
     variables (*note File Local Variables::).

     If the FIND-FILE argument to `normal-mode' is non-`nil',
     `normal-mode' assumes that the `find-file' function is calling it.
     In this case, it may process local variables in the `-*-' line or
     at the end of the file.  The variable `enable-local-variables'
     controls whether to do so.  *Note Local Variables in Files:
     (emacs)File Variables, for the syntax of the local variables
     section of a file.

     If you run `normal-mode' interactively, the argument FIND-FILE is
     normally `nil'.  In this case, `normal-mode' unconditionally
     processes any file local variables.

     If `normal-mode' processes the local variables list and this list
     specifies a major mode, that mode overrides any mode chosen by
     `set-auto-mode'.  If neither `set-auto-mode' nor
     `hack-local-variables' specify a major mode, the buffer stays in
     the major mode determined by `default-major-mode' (see below).

     `normal-mode' uses `condition-case' around the call to the major
     mode function, so errors are caught and reported as a `File mode
     specification error',  followed by the original error message.

 -- Function: set-auto-mode &optional keep-mode-if-same
     This function selects the major mode that is appropriate for the
     current buffer.  It bases its decision (in order of precedence) on
     the `-*-' line, on the `#!' line (using `interpreter-mode-alist'),
     on the text at the beginning of the buffer (using
     `magic-mode-alist'), and finally on the visited file name (using
     `auto-mode-alist').  *Note How Major Modes are Chosen:
     (emacs)Choosing Modes.  However, this function does not look for
     the `mode:' local variable near the end of a file; the
     `hack-local-variables' function does that.  If
     `enable-local-variables' is `nil', `set-auto-mode' does not check
     the `-*-' line for a mode tag either.

     If KEEP-MODE-IF-SAME is non-`nil', this function does not call the
     mode command if the buffer is already in the proper major mode.
     For instance, `set-visited-file-name' sets this to `t' to avoid
     killing buffer local variables that the user may have set.

 -- User Option: default-major-mode
     This variable holds the default major mode for new buffers.  The
     standard value is `fundamental-mode'.

     If the value of `default-major-mode' is `nil', Emacs uses the
     (previously) current buffer's major mode as the default major mode
     of a new buffer.  However, if that major mode symbol has a
     `mode-class' property with value `special', then it is not used
     for new buffers; Fundamental mode is used instead.  The modes that
     have this property are those such as Dired and Rmail that are
     useful only with text that has been specially prepared.

 -- Function: set-buffer-major-mode buffer
     This function sets the major mode of BUFFER to the value of
     `default-major-mode'; if that variable is `nil', it uses the
     current buffer's major mode (if that is suitable).  As an
     exception, if BUFFER's name is `*scratch*', it sets the mode to
     `initial-major-mode'.

     The low-level primitives for creating buffers do not use this
     function, but medium-level commands such as `switch-to-buffer' and
     `find-file-noselect' use it whenever they create buffers.

 -- User Option: initial-major-mode
     The value of this variable determines the major mode of the initial
     `*scratch*' buffer.  The value should be a symbol that is a major
     mode command.  The default value is `lisp-interaction-mode'.

 -- Variable: interpreter-mode-alist
     This variable specifies major modes to use for scripts that
     specify a command interpreter in a `#!' line.  Its value is an
     alist with elements of the form `(INTERPRETER . MODE)'; for
     example, `("perl" . perl-mode)' is one element present by default.
     The element says to use mode MODE if the file specifies an
     interpreter which matches INTERPRETER.

 -- Variable: magic-mode-alist
     This variable's value is an alist with elements of the form
     `(REGEXP .  FUNCTION)', where REGEXP is a regular expression and
     FUNCTION is a function or `nil'.  After visiting a file,
     `set-auto-mode' calls FUNCTION if the text at the beginning of the
     buffer matches REGEXP and FUNCTION is non-`nil'; if FUNCTION is
     `nil', `auto-mode-alist' gets to decide the mode.

 -- Variable: magic-fallback-mode-alist
     This works like `magic-mode-alist', except that it is handled only
     if `auto-mode-alist' does not specify a mode for this file.

 -- Variable: auto-mode-alist
     This variable contains an association list of file name patterns
     (regular expressions) and corresponding major mode commands.
     Usually, the file name patterns test for suffixes, such as `.el'
     and `.c', but this need not be the case.  An ordinary element of
     the alist looks like `(REGEXP .  MODE-FUNCTION)'.

     For example,

          (("\\`/tmp/fol/" . text-mode)
           ("\\.texinfo\\'" . texinfo-mode)
           ("\\.texi\\'" . texinfo-mode)
           ("\\.el\\'" . emacs-lisp-mode)
           ("\\.c\\'" . c-mode)
           ("\\.h\\'" . c-mode)
           ...)

     When you visit a file whose expanded file name (*note File Name
     Expansion::), with version numbers and backup suffixes removed
     using `file-name-sans-versions' (*note File Name Components::),
     matches a REGEXP, `set-auto-mode' calls the corresponding
     MODE-FUNCTION.  This feature enables Emacs to select the proper
     major mode for most files.

     If an element of `auto-mode-alist' has the form `(REGEXP FUNCTION
     t)', then after calling FUNCTION, Emacs searches `auto-mode-alist'
     again for a match against the portion of the file name that did
     not match before.  This feature is useful for uncompression
     packages: an entry of the form `("\\.gz\\'" FUNCTION t)' can
     uncompress the file and then put the uncompressed file in the
     proper mode according to the name sans `.gz'.

     Here is an example of how to prepend several pattern pairs to
     `auto-mode-alist'.  (You might use this sort of expression in your
     init file.)

          (setq auto-mode-alist
            (append
             ;; File name (within directory) starts with a dot.
             '(("/\\.[^/]*\\'" . fundamental-mode)
               ;; File name has no dot.
               ("[^\\./]*\\'" . fundamental-mode)
               ;; File name ends in `.C'.
               ("\\.C\\'" . c++-mode))
             auto-mode-alist))


File: elisp,  Node: Mode Help,  Next: Derived Modes,  Prev: Auto Major Mode,  Up: Major Modes

23.2.4 Getting Help about a Major Mode
--------------------------------------

The `describe-mode' function is used to provide information about major
modes.  It is normally called with `C-h m'.  The `describe-mode'
function uses the value of `major-mode', which is why every major mode
function needs to set the `major-mode' variable.

 -- Command: describe-mode
     This function displays the documentation of the current major mode.

     The `describe-mode' function calls the `documentation' function
     using the value of `major-mode' as an argument.  Thus, it displays
     the documentation string of the major mode function.  (*Note
     Accessing Documentation::.)

 -- Variable: major-mode
     This buffer-local variable holds the symbol for the current
     buffer's major mode.  This symbol should have a function
     definition that is the command to switch to that major mode.  The
     `describe-mode' function uses the documentation string of the
     function as the documentation of the major mode.


File: elisp,  Node: Derived Modes,  Next: Generic Modes,  Prev: Mode Help,  Up: Major Modes

23.2.5 Defining Derived Modes
-----------------------------

It's often useful to define a new major mode in terms of an existing
one.  An easy way to do this is to use `define-derived-mode'.

 -- Macro: define-derived-mode variant parent name docstring
          keyword-args... body...
     This construct defines VARIANT as a major mode command, using NAME
     as the string form of the mode name.  VARIANT and PARENT should be
     unquoted symbols.

     The new command VARIANT is defined to call the function PARENT,
     then override certain aspects of that parent mode:

        * The new mode has its own sparse keymap, named `VARIANT-map'.
          `define-derived-mode' makes the parent mode's keymap the
          parent of the new map, unless `VARIANT-map' is already set
          and already has a parent.

        * The new mode has its own syntax table, kept in the variable
          `VARIANT-syntax-table', unless you override this using the
          `:syntax-table' keyword (see below).  `define-derived-mode'
          makes the parent mode's syntax-table the parent of
          `VARIANT-syntax-table', unless the latter is already set and
          already has a parent different from the standard syntax table.

        * The new mode has its own abbrev table, kept in the variable
          `VARIANT-abbrev-table', unless you override this using the
          `:abbrev-table' keyword (see below).

        * The new mode has its own mode hook, `VARIANT-hook'.  It runs
          this hook, after running the hooks of its ancestor modes, with
          `run-mode-hooks', as the last thing it does. *Note Mode
          Hooks::.

     In addition, you can specify how to override other aspects of
     PARENT with BODY.  The command VARIANT evaluates the forms in BODY
     after setting up all its usual overrides, just before running the
     mode hooks.

     You can also specify `nil' for PARENT.  This gives the new mode no
     parent.  Then `define-derived-mode' behaves as described above,
     but, of course, omits all actions connected with PARENT.

     The argument DOCSTRING specifies the documentation string for the
     new mode.  `define-derived-mode' adds some general information
     about the mode's hook, followed by the mode's keymap, at the end
     of this docstring.  If you omit DOCSTRING, `define-derived-mode'
     generates a documentation string.

     The KEYWORD-ARGS are pairs of keywords and values.  The values are
     evaluated.  The following keywords are currently supported:

    `:syntax-table'
          You can use this to explicitly specify a syntax table for the
          new mode.  If you specify a `nil' value, the new mode uses
          the same syntax table as PARENT, or the standard syntax table
          if PARENT is `nil'.  (Note that this does _not_ follow the
          convention used for non-keyword arguments that a `nil' value
          is equivalent with not specifying the argument.)

    `:abbrev-table'
          You can use this to explicitly specify an abbrev table for
          the new mode.  If you specify a `nil' value, the new mode
          uses the same abbrev table as PARENT, or
          `fundamental-mode-abbrev-table' if PARENT is `nil'.  (Again,
          a `nil' value is _not_ equivalent to not specifying this
          keyword.)

    `:group'
          If this is specified, the value should be the customization
          group for this mode.  (Not all major modes have one.)  Only
          the (still experimental and unadvertised) command
          `customize-mode' currently uses this.  `define-derived-mode'
          does _not_ automatically define the specified customization
          group.

     Here is a hypothetical example:

          (define-derived-mode hypertext-mode
            text-mode "Hypertext"
            "Major mode for hypertext.
          \\{hypertext-mode-map}"
            (setq case-fold-search nil))

          (define-key hypertext-mode-map
            [down-mouse-3] 'do-hyper-link)

     Do not write an `interactive' spec in the definition;
     `define-derived-mode' does that automatically.


File: elisp,  Node: Generic Modes,  Next: Mode Hooks,  Prev: Derived Modes,  Up: Major Modes

23.2.6 Generic Modes
--------------------

"Generic modes" are simple major modes with basic support for comment
syntax and Font Lock mode.  To define a generic mode, use the macro
`define-generic-mode'.  See the file `generic-x.el' for some examples
of the use of `define-generic-mode'.

 -- Macro: define-generic-mode mode comment-list keyword-list
          font-lock-list auto-mode-list function-list &optional
          docstring
     This macro defines a generic mode command named MODE (a symbol,
     not quoted).  The optional argument DOCSTRING is the documentation
     for the mode command.  If you do not supply it,
     `define-generic-mode' generates one by default.

     The argument COMMENT-LIST is a list in which each element is
     either a character, a string of one or two characters, or a cons
     cell.  A character or a string is set up in the mode's syntax
     table as a "comment starter."  If the entry is a cons cell, the
     CAR is set up as a "comment starter" and the CDR as a "comment
     ender."  (Use `nil' for the latter if you want comments to end at
     the end of the line.)  Note that the syntax table mechanism has
     limitations about what comment starters and enders are actually
     possible.  *Note Syntax Tables::.

     The argument KEYWORD-LIST is a list of keywords to highlight with
     `font-lock-keyword-face'.  Each keyword should be a string.
     Meanwhile, FONT-LOCK-LIST is a list of additional expressions to
     highlight.  Each element of this list should have the same form as
     an element of `font-lock-keywords'.  *Note Search-based
     Fontification::.

     The argument AUTO-MODE-LIST is a list of regular expressions to
     add to the variable `auto-mode-alist'.  They are added by the
     execution of the `define-generic-mode' form, not by expanding the
     macro call.

     Finally, FUNCTION-LIST is a list of functions for the mode command
     to call for additional setup.  It calls these functions just
     before it runs the mode hook variable `MODE-hook'.


File: elisp,  Node: Mode Hooks,  Next: Example Major Modes,  Prev: Generic Modes,  Up: Major Modes

23.2.7 Mode Hooks
-----------------

Every major mode function should finish by running its mode hook and
the mode-independent normal hook `after-change-major-mode-hook'.  It
does this by calling `run-mode-hooks'.  If the major mode is a derived
mode, that is if it calls another major mode (the parent mode) in its
body, it should do this inside `delay-mode-hooks' so that the parent
won't run these hooks itself.  Instead, the derived mode's call to
`run-mode-hooks' runs the parent's mode hook too.  *Note Major Mode
Conventions::.

   Emacs versions before Emacs 22 did not have `delay-mode-hooks'.
When user-implemented major modes have not been updated to use it, they
won't entirely follow these conventions: they may run the parent's mode
hook too early, or fail to run `after-change-major-mode-hook'.  If you
encounter such a major mode, please correct it to follow these
conventions.

   When you defined a major mode using `define-derived-mode', it
automatically makes sure these conventions are followed.  If you define
a major mode "by hand," not using `define-derived-mode', use the
following functions to handle these conventions automatically.

 -- Function: run-mode-hooks &rest hookvars
     Major modes should run their mode hook using this function.  It is
     similar to `run-hooks' (*note Hooks::), but it also runs
     `after-change-major-mode-hook'.

     When this function is called during the execution of a
     `delay-mode-hooks' form, it does not run the hooks immediately.
     Instead, it arranges for the next call to `run-mode-hooks' to run
     them.

 -- Macro: delay-mode-hooks body...
     When one major mode command calls another, it should do so inside
     of `delay-mode-hooks'.

     This macro executes BODY, but tells all `run-mode-hooks' calls
     during the execution of BODY to delay running their hooks.  The
     hooks will actually run during the next call to `run-mode-hooks'
     after the end of the `delay-mode-hooks' construct.

 -- Variable: after-change-major-mode-hook
     This is a normal hook run by `run-mode-hooks'.  It is run at the
     very end of every properly-written major mode function.


File: elisp,  Node: Example Major Modes,  Prev: Mode Hooks,  Up: Major Modes

23.2.8 Major Mode Examples
--------------------------

Text mode is perhaps the simplest mode besides Fundamental mode.  Here
are excerpts from  `text-mode.el' that illustrate many of the
conventions listed above:

     ;; Create the syntax table for this mode.
     (defvar text-mode-syntax-table
       (let ((st (make-syntax-table)))
         (modify-syntax-entry ?\" ".   " st)
         (modify-syntax-entry ?\\ ".   " st)
         ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'.
         (modify-syntax-entry ?' "w p" st)
         st)
       "Syntax table used while in `text-mode'.")

     ;; Create the keymap for this mode.
     (defvar text-mode-map
       (let ((map (make-sparse-keymap)))
         (define-key map "\e\t" 'ispell-complete-word)
         (define-key map "\es" 'center-line)
         (define-key map "\eS" 'center-paragraph)
         map)
       "Keymap for `text-mode'.
     Many other modes, such as Mail mode, Outline mode
     and Indented Text mode, inherit all the commands
     defined in this map.")

   Here is how the actual mode command is defined now:

     (define-derived-mode text-mode nil "Text"
       "Major mode for editing text written for humans to read.
     In this mode, paragraphs are delimited only by blank or white lines.
     You can thus get the full benefit of adaptive filling
      (see the variable `adaptive-fill-mode').
     \\{text-mode-map}
     Turning on Text mode runs the normal hook `text-mode-hook'."
       (make-local-variable 'text-mode-variant)
       (setq text-mode-variant t)
       ;; These two lines are a feature added recently.
       (set (make-local-variable 'require-final-newline)
            mode-require-final-newline)
       (set (make-local-variable 'indent-line-function) 'indent-relative))

(The last line is redundant nowadays, since `indent-relative' is the
default value, and we'll delete it in a future version.)

   Here is how it was defined formerly, before `define-derived-mode'
existed:

     ;; This isn't needed nowadays, since `define-derived-mode' does it.
     (defvar text-mode-abbrev-table nil
       "Abbrev table used while in text mode.")
     (define-abbrev-table 'text-mode-abbrev-table ())

     (defun text-mode ()
       "Major mode for editing text intended for humans to read...
      Special commands: \\{text-mode-map}
     Turning on text-mode runs the hook `text-mode-hook'."
       (interactive)
       (kill-all-local-variables)
       (use-local-map text-mode-map)
       (setq local-abbrev-table text-mode-abbrev-table)
       (set-syntax-table text-mode-syntax-table)
       ;; These four lines are absent from the current version
       ;; not because this is done some other way, but rather
       ;; because nowadays Text mode uses the normal definition of paragraphs.
       (make-local-variable 'paragraph-start)
       (setq paragraph-start (concat "[ \t]*$\\|" page-delimiter))
       (make-local-variable 'paragraph-separate)
       (setq paragraph-separate paragraph-start)
       (make-local-variable 'indent-line-function)
       (setq indent-line-function 'indent-relative-maybe)
       (setq mode-name "Text")
       (setq major-mode 'text-mode)
       (run-mode-hooks 'text-mode-hook)) ; Finally, this permits the user to
                                         ;   customize the mode with a hook.

   The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp
Interaction mode) have more features than Text mode and the code is
correspondingly more complicated.  Here are excerpts from
`lisp-mode.el' that illustrate how these modes are written.

     ;; Create mode-specific table variables.
     (defvar lisp-mode-syntax-table nil "")
     (defvar lisp-mode-abbrev-table nil "")

     (defvar emacs-lisp-mode-syntax-table
       (let ((table (make-syntax-table)))
         (let ((i 0))

           ;; Set syntax of chars up to `0' to say they are
           ;;   part of symbol names but not words.
           ;;   (The digit `0' is `48' in the ASCII character set.)
           (while (< i ?0)
     	(modify-syntax-entry i "_   " table)
     	(setq i (1+ i)))
           ;; ... similar code follows for other character ranges.
           ;; Then set the syntax codes for characters that are special in Lisp.
           (modify-syntax-entry ?  "    " table)
           (modify-syntax-entry ?\t "    " table)
           (modify-syntax-entry ?\f "    " table)
           (modify-syntax-entry ?\n ">   " table)
           ;; Give CR the same syntax as newline, for selective-display.
           (modify-syntax-entry ?\^m ">   " table)
           (modify-syntax-entry ?\; "<   " table)
           (modify-syntax-entry ?` "'   " table)
           (modify-syntax-entry ?' "'   " table)
           (modify-syntax-entry ?, "'   " table)
           ;; ...likewise for many other characters...
           (modify-syntax-entry ?\( "()  " table)
           (modify-syntax-entry ?\) ")(  " table)
           (modify-syntax-entry ?\[ "(]  " table)
           (modify-syntax-entry ?\] ")[  " table))
         table))
     ;; Create an abbrev table for lisp-mode.
     (define-abbrev-table 'lisp-mode-abbrev-table ())

   The three modes for Lisp share much of their code.  For instance,
each calls the following function to set various variables:

     (defun lisp-mode-variables (lisp-syntax)
       (when lisp-syntax
         (set-syntax-table lisp-mode-syntax-table))
       (setq local-abbrev-table lisp-mode-abbrev-table)
       ...

   In Lisp and most programming languages, we want the paragraph
commands to treat only blank lines as paragraph separators.  And the
modes should understand the Lisp conventions for comments.  The rest of
`lisp-mode-variables' sets this up:

       (make-local-variable 'paragraph-start)
       (setq paragraph-start (concat page-delimiter "\\|$" ))
       (make-local-variable 'paragraph-separate)
       (setq paragraph-separate paragraph-start)
       ...
       (make-local-variable 'comment-indent-function)
       (setq comment-indent-function 'lisp-comment-indent))
       ...

   Each of the different Lisp modes has a slightly different keymap.
For example, Lisp mode binds `C-c C-z' to `run-lisp', but the other
Lisp modes do not.  However, all Lisp modes have some commands in
common.  The following code sets up the common commands:

     (defvar shared-lisp-mode-map ()
       "Keymap for commands shared by all sorts of Lisp modes.")

     ;; Putting this `if' after the `defvar' is an older style.
     (if shared-lisp-mode-map
         ()
        (setq shared-lisp-mode-map (make-sparse-keymap))
        (define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp)
        (define-key shared-lisp-mode-map "\177"
                    'backward-delete-char-untabify))

And here is the code to set up the keymap for Lisp mode:

     (defvar lisp-mode-map ()
       "Keymap for ordinary Lisp mode...")

     (if lisp-mode-map
         ()
       (setq lisp-mode-map (make-sparse-keymap))
       (set-keymap-parent lisp-mode-map shared-lisp-mode-map)
       (define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun)
       (define-key lisp-mode-map "\C-c\C-z" 'run-lisp))

   Finally, here is the complete major mode function definition for
Lisp mode.

     (defun lisp-mode ()
       "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
     Commands:
     Delete converts tabs to spaces as it moves back.
     Blank lines separate paragraphs.  Semicolons start comments.
     \\{lisp-mode-map}
     Note that `run-lisp' may be used either to start an inferior Lisp job
     or to switch back to an existing one.

     Entry to this mode calls the value of `lisp-mode-hook'
     if that value is non-nil."
       (interactive)
       (kill-all-local-variables)
       (use-local-map lisp-mode-map)          ; Select the mode's keymap.
       (setq major-mode 'lisp-mode)           ; This is how `describe-mode'
                                              ;   finds out what to describe.
       (setq mode-name "Lisp")                ; This goes into the mode line.
       (lisp-mode-variables t)                ; This defines various variables.
       (make-local-variable 'comment-start-skip)
       (setq comment-start-skip
             "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *")
       (make-local-variable 'font-lock-keywords-case-fold-search)
       (setq font-lock-keywords-case-fold-search t)
       (setq imenu-case-fold-search t)
       (set-syntax-table lisp-mode-syntax-table)
       (run-mode-hooks 'lisp-mode-hook))      ; This permits the user to use a
                                              ;   hook to customize the mode.


File: elisp,  Node: Minor Modes,  Next: Mode Line Format,  Prev: Major Modes,  Up: Modes

23.3 Minor Modes
================

A "minor mode" provides features that users may enable or disable
independently of the choice of major mode.  Minor modes can be enabled
individually or in combination.  Minor modes would be better named
"generally available, optional feature modes," except that such a name
would be unwieldy.

   A minor mode is not usually meant as a variation of a single major
mode.  Usually they are general and can apply to many major modes.  For
example, Auto Fill mode works with any major mode that permits text
insertion.  To be general, a minor mode must be effectively independent
of the things major modes do.

   A minor mode is often much more difficult to implement than a major
mode.  One reason is that you should be able to activate and deactivate
minor modes in any order.  A minor mode should be able to have its
desired effect regardless of the major mode and regardless of the other
minor modes in effect.

   Often the biggest problem in implementing a minor mode is finding a
way to insert the necessary hook into the rest of Emacs.  Minor mode
keymaps make this easier than it used to be.

 -- Variable: minor-mode-list
     The value of this variable is a list of all minor mode commands.

* Menu:

* Minor Mode Conventions::      Tips for writing a minor mode.
* Keymaps and Minor Modes::     How a minor mode can have its own keymap.
* Defining Minor Modes::        A convenient facility for defining minor modes.


File: elisp,  Node: Minor Mode Conventions,  Next: Keymaps and Minor Modes,  Up: Minor Modes

23.3.1 Conventions for Writing Minor Modes
------------------------------------------

There are conventions for writing minor modes just as there are for
major modes.  Several of the major mode conventions apply to minor
modes as well: those regarding the name of the mode initialization
function, the names of global symbols, the use of a hook at the end of
the initialization function, and the use of keymaps and other tables.

   In addition, there are several conventions that are specific to
minor modes.  (The easiest way to follow all the conventions is to use
the macro `define-minor-mode'; *Note Defining Minor Modes::.)

   * Make a variable whose name ends in `-mode' to control the minor
     mode.  We call this the "mode variable".  The minor mode command
     should set this variable (`nil' to disable; anything else to
     enable).

     If possible, implement the mode so that setting the variable
     automatically enables or disables the mode.  Then the minor mode
     command does not need to do anything except set the variable.

     This variable is used in conjunction with the `minor-mode-alist' to
     display the minor mode name in the mode line.  It can also enable
     or disable a minor mode keymap.  Individual commands or hooks can
     also check the variable's value.

     If you want the minor mode to be enabled separately in each buffer,
     make the variable buffer-local.

   * Define a command whose name is the same as the mode variable.  Its
     job is to enable and disable the mode by setting the variable.

     The command should accept one optional argument.  If the argument
     is `nil', it should toggle the mode (turn it on if it is off, and
     off if it is on).  It should turn the mode on if the argument is a
     positive integer, the symbol `t', or a list whose CAR is one of
     those.  It should turn the mode off if the argument is a negative
     integer or zero, the symbol `-', or a list whose CAR is a negative
     integer or zero.  The meaning of other arguments is not specified.

     Here is an example taken from the definition of
     `transient-mark-mode'.  It shows the use of `transient-mark-mode'
     as a variable that enables or disables the mode's behavior, and
     also shows the proper way to toggle, enable or disable the minor
     mode based on the raw prefix argument value.

          (setq transient-mark-mode
                (if (null arg) (not transient-mark-mode)
                  (> (prefix-numeric-value arg) 0)))

   * Add an element to `minor-mode-alist' for each minor mode (*note
     Definition of minor-mode-alist::), if you want to indicate the
     minor mode in the mode line.  This element should be a list of the
     following form:

          (MODE-VARIABLE STRING)

     Here MODE-VARIABLE is the variable that controls enabling of the
     minor mode, and STRING is a short string, starting with a space,
     to represent the mode in the mode line.  These strings must be
     short so that there is room for several of them at once.

     When you add an element to `minor-mode-alist', use `assq' to check
     for an existing element, to avoid duplication.  For example:

          (unless (assq 'leif-mode minor-mode-alist)
            (setq minor-mode-alist
                  (cons '(leif-mode " Leif") minor-mode-alist)))

     or like this, using `add-to-list' (*note List Variables::):

          (add-to-list 'minor-mode-alist '(leif-mode " Leif"))

   Global minor modes distributed with Emacs should if possible support
enabling and disabling via Custom (*note Customization::).  To do this,
the first step is to define the mode variable with `defcustom', and
specify `:type boolean'.

   If just setting the variable is not sufficient to enable the mode,
you should also specify a `:set' method which enables the mode by
invoking the mode command.  Note in the variable's documentation string
that setting the variable other than via Custom may not take effect.

   Also mark the definition with an autoload cookie (*note autoload
cookie::), and specify a `:require' so that customizing the variable
will load the library that defines the mode.  This will copy suitable
definitions into `loaddefs.el' so that users can use `customize-option'
to enable the mode.  For example:


     ;;;###autoload
     (defcustom msb-mode nil
       "Toggle msb-mode.
     Setting this variable directly does not take effect;
     use either \\[customize] or the function `msb-mode'."
       :set 'custom-set-minor-mode
       :initialize 'custom-initialize-default
       :version "20.4"
       :type    'boolean
       :group   'msb
       :require 'msb)


File: elisp,  Node: Keymaps and Minor Modes,  Next: Defining Minor Modes,  Prev: Minor Mode Conventions,  Up: Minor Modes

23.3.2 Keymaps and Minor Modes
------------------------------

Each minor mode can have its own keymap, which is active when the mode
is enabled.  To set up a keymap for a minor mode, add an element to the
alist `minor-mode-map-alist'.  *Note Definition of
minor-mode-map-alist::.

   One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert.  In general, this is the only way to do that, since the
facilities for customizing `self-insert-command' are limited to special
cases (designed for abbrevs and Auto Fill mode).  (Do not try
substituting your own definition of `self-insert-command' for the
standard one.  The editor command loop handles this function specially.)

   The key sequences bound in a minor mode should consist of `C-c'
followed by one of `.,/?`'"[]\|~!#$%^&*()-_+='.  (The other punctuation
characters are reserved for major modes.)


File: elisp,  Node: Defining Minor Modes,  Prev: Keymaps and Minor Modes,  Up: Minor Modes

23.3.3 Defining Minor Modes
---------------------------

The macro `define-minor-mode' offers a convenient way of implementing a
mode in one self-contained definition.

 -- Macro: define-minor-mode mode doc [init-value [lighter [keymap]]]
          keyword-args... body...
     This macro defines a new minor mode whose name is MODE (a symbol).
     It defines a command named MODE to toggle the minor mode, with
     DOC as its documentation string.  It also defines a variable named
     MODE, which is set to `t' or `nil' by enabling or disabling the
     mode.  The variable is initialized to INIT-VALUE.  Except in
     unusual circumstances (see below), this value must be `nil'.

     The string LIGHTER says what to display in the mode line when the
     mode is enabled; if it is `nil', the mode is not displayed in the
     mode line.

     The optional argument KEYMAP specifies the keymap for the minor
     mode.  It can be a variable name, whose value is the keymap, or it
     can be an alist specifying bindings in this form:

          (KEY-SEQUENCE . DEFINITION)

     The above three arguments INIT-VALUE, LIGHTER, and KEYMAP can be
     (partially) omitted when KEYWORD-ARGS are used.  The KEYWORD-ARGS
     consist of keywords followed by corresponding values.  A few
     keywords have special meanings:

    `:group GROUP'
          Custom group name to use in all generated `defcustom' forms.
          Defaults to MODE without the possible trailing `-mode'.
          *Warning:* don't use this default group name unless you have
          written a `defgroup' to define that group properly.  *Note
          Group Definitions::.

    `:global GLOBAL'
          If non-`nil', this specifies that the minor mode should be
          global rather than buffer-local.  It defaults to `nil'.

          One of the effects of making a minor mode global is that the
          MODE variable becomes a customization variable.  Toggling it
          through the Custom interface turns the mode on and off, and
          its value can be saved for future Emacs sessions (*note
          Saving Customizations: (emacs)Saving Customizations.  For the
          saved variable to work, you should ensure that the
          `define-minor-mode' form is evaluated each time Emacs starts;
          for packages that are not part of Emacs, the easiest way to
          do this is to specify a `:require' keyword.

    `:init-value INIT-VALUE'
          This is equivalent to specifying INIT-VALUE positionally.

    `:lighter LIGHTER'
          This is equivalent to specifying LIGHTER positionally.

    `:keymap KEYMAP'
          This is equivalent to specifying KEYMAP positionally.

     Any other keyword arguments are passed directly to the `defcustom'
     generated for the variable MODE.

     The command named MODE first performs the standard actions such as
     setting the variable named MODE and then executes the BODY forms,
     if any.  It finishes by running the mode hook variable `MODE-hook'.

   The initial value must be `nil' except in cases where (1) the mode
is preloaded in Emacs, or (2) it is painless for loading to enable the
mode even though the user did not request it.  For instance, if the
mode has no effect unless something else is enabled, and will always be
loaded by that time, enabling it by default is harmless.  But these are
unusual circumstances.  Normally, the initial value must be `nil'.

   The name `easy-mmode-define-minor-mode' is an alias for this macro.

   Here is an example of using `define-minor-mode':

     (define-minor-mode hungry-mode
       "Toggle Hungry mode.
     With no argument, this command toggles the mode.
     Non-null prefix argument turns on the mode.
     Null prefix argument turns off the mode.

     When Hungry mode is enabled, the control delete key
     gobbles all preceding whitespace except the last.
     See the command \\[hungry-electric-delete]."
      ;; The initial value.
      nil
      ;; The indicator for the mode line.
      " Hungry"
      ;; The minor mode bindings.
      '(("\C-\^?" . hungry-electric-delete))
      :group 'hunger)

This defines a minor mode named "Hungry mode," a command named
`hungry-mode' to toggle it, a variable named `hungry-mode' which
indicates whether the mode is enabled, and a variable named
`hungry-mode-map' which holds the keymap that is active when the mode
is enabled.  It initializes the keymap with a key binding for
`C-<DEL>'.  It puts the variable `hungry-mode' into custom group
`hunger'.  There are no BODY forms--many minor modes don't need any.

   Here's an equivalent way to write it:

     (define-minor-mode hungry-mode
       "Toggle Hungry mode.
     With no argument, this command toggles the mode.
     Non-null prefix argument turns on the mode.
     Null prefix argument turns off the mode.

     When Hungry mode is enabled, the control delete key
     gobbles all preceding whitespace except the last.
     See the command \\[hungry-electric-delete]."
      ;; The initial value.
      :init-value nil
      ;; The indicator for the mode line.
      :lighter " Hungry"
      ;; The minor mode bindings.
      :keymap
      '(("\C-\^?" . hungry-electric-delete)
        ("\C-\M-\^?"
         . (lambda ()
             (interactive)
             (hungry-electric-delete t))))
      :group 'hunger)

 -- Macro: define-globalized-minor-mode global-mode mode turn-on
          keyword-args...
     This defines a global toggle named GLOBAL-MODE whose meaning is to
     enable or disable the buffer-local minor mode MODE in all buffers.
     To turn on the minor mode in a buffer, it uses the function
     TURN-ON; to turn off the minor mode, it calls `mode' with -1 as
     argument.

     Globally enabling the mode also affects buffers subsequently
     created by visiting files, and buffers that use a major mode other
     than Fundamental mode; but it does not detect the creation of a
     new buffer in Fundamental mode.

     This defines the customization option GLOBAL-MODE (*note
     Customization::), which can be toggled in the Custom interface to
     turn the minor mode on and off.  As with `define-minor-mode', you
     should ensure that the `define-globalized-minor-mode' form is
     evaluated each time Emacs starts, for example by providing a
     `:require' keyword.

     Use `:group GROUP' in KEYWORD-ARGS to specify the custom group for
     the mode variable of the global minor mode.


File: elisp,  Node: Mode Line Format,  Next: Imenu,  Prev: Minor Modes,  Up: Modes

23.4 Mode-Line Format
=====================

Each Emacs window (aside from minibuffer windows) typically has a mode
line at the bottom, which displays status information about the buffer
displayed in the window.  The mode line contains information about the
buffer, such as its name, associated file, depth of recursive editing,
and major and minor modes.  A window can also have a "header line",
which is much like the mode line but appears at the top of the window.

   This section describes how to control the contents of the mode line
and header line.  We include it in this chapter because much of the
information displayed in the mode line relates to the enabled major and
minor modes.

* Menu:

* Base: Mode Line Basics. Basic ideas of mode line control.
* Data: Mode Line Data.   The data structure that controls the mode line.
* Top: Mode Line Top.     The top level variable, mode-line-format.
* Mode Line Variables::   Variables used in that data structure.
* %-Constructs::          Putting information into a mode line.
* Properties in Mode::    Using text properties in the mode line.
* Header Lines::          Like a mode line, but at the top.
* Emulating Mode Line::   Formatting text as the mode line would.


File: elisp,  Node: Mode Line Basics,  Next: Mode Line Data,  Up: Mode Line Format

23.4.1 Mode Line Basics
-----------------------

`mode-line-format' is a buffer-local variable that holds a "mode line
construct", a kind of template, which controls what is displayed on the
mode line of the current buffer.  The value of `header-line-format'
specifies the buffer's header line in the same way.  All windows for
the same buffer use the same `mode-line-format' and
`header-line-format'.

   For efficiency, Emacs does not continuously recompute the mode line
and header line of a window.  It does so when circumstances appear to
call for it--for instance, if you change the window configuration,
switch buffers, narrow or widen the buffer, scroll, or change the
buffer's modification status.  If you modify any of the variables
referenced by `mode-line-format' (*note Mode Line Variables::), or any
other variables and data structures that affect how text is displayed
(*note Display::), you may want to force an update of the mode line so
as to display the new information or display it in the new way.

 -- Function: force-mode-line-update &optional all
     Force redisplay of the current buffer's mode line and header line.
     The next redisplay will update the mode line and header line based
     on the latest values of all relevant variables.  With optional
     non-`nil' ALL, force redisplay of all mode lines and header lines.

     This function also forces recomputation of the menu bar menus and
     the frame title.

   The selected window's mode line is usually displayed in a different
color using the face `mode-line'.  Other windows' mode lines appear in
the face `mode-line-inactive' instead.  *Note Faces::.


File: elisp,  Node: Mode Line Data,  Next: Mode Line Top,  Prev: Mode Line Basics,  Up: Mode Line Format

23.4.2 The Data Structure of the Mode Line
------------------------------------------

The mode-line contents are controlled by a data structure called a
"mode-line construct", made up of lists, strings, symbols, and numbers
kept in buffer-local variables.  Each data type has a specific meaning
for the mode-line appearance, as described below.  The same data
structure is used for constructing frame titles (*note Frame Titles::)
and header lines (*note Header Lines::).

   A mode-line construct may be as simple as a fixed string of text,
but it usually specifies how to combine fixed strings with variables'
values to construct the text.  Many of these variables are themselves
defined to have mode-line constructs as their values.

   Here are the meanings of various data types as mode-line constructs:

`STRING'
     A string as a mode-line construct appears verbatim except for
     "`%'-constructs" in it.  These stand for substitution of other
     data; see *Note %-Constructs::.

     If parts of the string have `face' properties, they control
     display of the text just as they would text in the buffer.  Any
     characters which have no `face' properties are displayed, by
     default, in the face `mode-line' or `mode-line-inactive' (*note
     Standard Faces: (emacs)Standard Faces.).  The `help-echo' and
     `local-map' properties in STRING have special meanings.  *Note
     Properties in Mode::.

`SYMBOL'
     A symbol as a mode-line construct stands for its value.  The value
     of SYMBOL is used as a mode-line construct, in place of SYMBOL.
     However, the symbols `t' and `nil' are ignored, as is any symbol
     whose value is void.

     There is one exception: if the value of SYMBOL is a string, it is
     displayed verbatim: the `%'-constructs are not recognized.

     Unless SYMBOL is marked as "risky" (i.e., it has a non-`nil'
     `risky-local-variable' property), all text properties specified in
     SYMBOL's value are ignored.  This includes the text properties of
     strings in SYMBOL's value, as well as all `:eval' and
     `:propertize' forms in it.  (The reason for this is security:
     non-risky variables could be set automatically from file variables
     without prompting the user.)

`(STRING REST...)'
`(LIST REST...)'
     A list whose first element is a string or list means to process
     all the elements recursively and concatenate the results.  This is
     the most common form of mode-line construct.

`(:eval FORM)'
     A list whose first element is the symbol `:eval' says to evaluate
     FORM, and use the result as a string to display.  Make sure this
     evaluation cannot load any files, as doing so could cause infinite
     recursion.

`(:propertize ELT PROPS...)'
     A list whose first element is the symbol `:propertize' says to
     process the mode-line construct ELT recursively, then add the text
     properties specified by PROPS to the result.  The argument PROPS
     should consist of zero or more pairs TEXT-PROPERTY VALUE.  (This
     feature is new as of Emacs 22.1.)

`(SYMBOL THEN ELSE)'
     A list whose first element is a symbol that is not a keyword
     specifies a conditional.  Its meaning depends on the value of
     SYMBOL.  If SYMBOL has a non-`nil' value, the second element,
     THEN, is processed recursively as a mode-line element.  Otherwise,
     the third element, ELSE, is processed recursively.  You may omit
     ELSE; then the mode-line element displays nothing if the value of
     SYMBOL is `nil' or void.

`(WIDTH REST...)'
     A list whose first element is an integer specifies truncation or
     padding of the results of REST.  The remaining elements REST are
     processed recursively as mode-line constructs and concatenated
     together.  When WIDTH is positive, the result is space filled on
     the right if its width is less than WIDTH.  When WIDTH is
     negative, the result is truncated on the right to -WIDTH columns
     if its width exceeds -WIDTH.

     For example, the usual way to show what percentage of a buffer is
     above the top of the window is to use a list like this: `(-3
     "%p")'.


File: elisp,  Node: Mode Line Top,  Next: Mode Line Variables,  Prev: Mode Line Data,  Up: Mode Line Format

23.4.3 The Top Level of Mode Line Control
-----------------------------------------

The variable in overall control of the mode line is `mode-line-format'.

 -- Variable: mode-line-format
     The value of this variable is a mode-line construct that controls
     the contents of the mode-line.  It is always buffer-local in all
     buffers.

     If you set this variable to `nil' in a buffer, that buffer does
     not have a mode line.  (A window that is just one line tall never
     displays a mode line.)

   The default value of `mode-line-format' is designed to use the
values of other variables such as `mode-line-position' and
`mode-line-modes' (which in turn incorporates the values of the
variables `mode-name' and `minor-mode-alist').  Very few modes need to
alter `mode-line-format' itself.  For most purposes, it is sufficient
to alter some of the variables that `mode-line-format' either directly
or indirectly refers to.

   If you do alter `mode-line-format' itself, the new value should use
the same variables that appear in the default value (*note Mode Line
Variables::), rather than duplicating their contents or displaying the
information in another fashion.  This way, customizations made by the
user or by Lisp programs (such as `display-time' and major modes) via
changes to those variables remain effective.

   Here is an example of a `mode-line-format' that might be useful for
`shell-mode', since it contains the host name and default directory.

     (setq mode-line-format
       (list "-"
        'mode-line-mule-info
        'mode-line-modified
        'mode-line-frame-identification
        "%b--"
        ;; Note that this is evaluated while making the list.
        ;; It makes a mode-line construct which is just a string.
        (getenv "HOST")
        ":"
        'default-directory
        "   "
        'global-mode-string
        "   %[("
        '(:eval (mode-line-mode-name))
        'mode-line-process
        'minor-mode-alist
        "%n"
        ")%]--"
        '(which-func-mode ("" which-func-format "--"))
        '(line-number-mode "L%l--")
        '(column-number-mode "C%c--")
        '(-3 "%p")
        "-%-"))

(The variables `line-number-mode', `column-number-mode' and
`which-func-mode' enable particular minor modes; as usual, these
variable names are also the minor mode command names.)


File: elisp,  Node: Mode Line Variables,  Next: %-Constructs,  Prev: Mode Line Top,  Up: Mode Line Format

23.4.4 Variables Used in the Mode Line
--------------------------------------

This section describes variables incorporated by the standard value of
`mode-line-format' into the text of the mode line.  There is nothing
inherently special about these variables; any other variables could
have the same effects on the mode line if `mode-line-format''s value
were changed to use them.  However, various parts of Emacs set these
variables on the understanding that they will control parts of the mode
line; therefore, practically speaking, it is essential for the mode
line to use them.

 -- Variable: mode-line-mule-info
     This variable holds the value of the mode-line construct that
     displays information about the language environment, buffer coding
     system, and current input method.  *Note Non-ASCII Characters::.

 -- Variable: mode-line-modified
     This variable holds the value of the mode-line construct that
     displays whether the current buffer is modified.

     The default value of `mode-line-modified' is `("%1*%1+")'.  This
     means that the mode line displays `**' if the buffer is modified,
     `--' if the buffer is not modified, `%%' if the buffer is read
     only, and `%*' if the buffer is read only and modified.

     Changing this variable does not force an update of the mode line.

 -- Variable: mode-line-frame-identification
     This variable identifies the current frame.  The default value is
     `"  "' if you are using a window system which can show multiple
     frames, or `"-%F  "' on an ordinary terminal which shows only one
     frame at a time.

 -- Variable: mode-line-buffer-identification
     This variable identifies the buffer being displayed in the window.
     Its default value is `("%12b")', which displays the buffer name,
     padded with spaces to at least 12 columns.

 -- Variable: mode-line-position
     This variable indicates the position in the buffer.  Here is a
     simplified version of its default value.  The actual default value
     also specifies addition of the `help-echo' text property.

          ((-3 "%p")
           (size-indication-mode (8 " of %I"))
           (line-number-mode
            ((column-number-mode
              (10 " (%l,%c)")
              (6 " L%l")))
            ((column-number-mode
              (5 " C%c")))))

     This means that `mode-line-position' displays at least the buffer
     percentage and possibly the buffer size, the line number and the
     column number.

 -- Variable: vc-mode
     The variable `vc-mode', buffer-local in each buffer, records
     whether the buffer's visited file is maintained with version
     control, and, if so, which kind.  Its value is a string that
     appears in the mode line, or `nil' for no version control.

 -- Variable: mode-line-modes
     This variable displays the buffer's major and minor modes.  Here
     is a simplified version of its default value.  The real default
     value also specifies addition of text properties.

          ("%[(" mode-name
           mode-line-process minor-mode-alist
           "%n" ")%]--")

     So `mode-line-modes' normally also displays the recursive editing
     level, information on the process status and whether narrowing is
     in effect.

   The following three variables are used in `mode-line-modes':

 -- Variable: mode-name
     This buffer-local variable holds the "pretty" name of the current
     buffer's major mode.  Each major mode should set this variable so
     that the mode name will appear in the mode line.

 -- Variable: mode-line-process
     This buffer-local variable contains the mode-line information on
     process status in modes used for communicating with subprocesses.
     It is displayed immediately following the major mode name, with no
     intervening space.  For example, its value in the `*shell*' buffer
     is `(":%s")', which allows the shell to display its status along
     with the major mode as: `(Shell:run)'.  Normally this variable is
     `nil'.

 -- Variable: minor-mode-alist
     This variable holds an association list whose elements specify how
     the mode line should indicate that a minor mode is active.  Each
     element of the `minor-mode-alist' should be a two-element list:

          (MINOR-MODE-VARIABLE MODE-LINE-STRING)

     More generally, MODE-LINE-STRING can be any mode-line spec.  It
     appears in the mode line when the value of MINOR-MODE-VARIABLE is
     non-`nil', and not otherwise.  These strings should begin with
     spaces so that they don't run together.  Conventionally, the
     MINOR-MODE-VARIABLE for a specific mode is set to a non-`nil'
     value when that minor mode is activated.

     `minor-mode-alist' itself is not buffer-local.  Each variable
     mentioned in the alist should be buffer-local if its minor mode
     can be enabled separately in each buffer.

 -- Variable: global-mode-string
     This variable holds a mode-line spec that, by default, appears in
     the mode line just after the `which-func-mode' minor mode if set,
     else after `mode-line-modes'.  The command `display-time' sets
     `global-mode-string' to refer to the variable
     `display-time-string', which holds a string containing the time
     and load information.

     The `%M' construct substitutes the value of `global-mode-string',
     but that is obsolete, since the variable is included in the mode
     line from `mode-line-format'.

   The variable `default-mode-line-format' is where `mode-line-format'
usually gets its value:

 -- Variable: default-mode-line-format
     This variable holds the default `mode-line-format' for buffers
     that do not override it.  This is the same as `(default-value
     'mode-line-format)'.

     Here is a simplified version of the default value of
     `default-mode-line-format'.  The real default value also specifies
     addition of text properties.

          ("-"
           mode-line-mule-info
           mode-line-modified
           mode-line-frame-identification
           mode-line-buffer-identification
           "   "
           mode-line-position
           (vc-mode vc-mode)
           "   "
           mode-line-modes
           (which-func-mode ("" which-func-format "--"))
           (global-mode-string ("--" global-mode-string))
           "-%-")


File: elisp,  Node: %-Constructs,  Next: Properties in Mode,  Prev: Mode Line Variables,  Up: Mode Line Format

23.4.5 `%'-Constructs in the Mode Line
--------------------------------------

Strings used as mode-line constructs can use certain `%'-constructs to
substitute various kinds of data.  Here is a list of the defined
`%'-constructs, and what they mean.  In any construct except `%%', you
can add a decimal integer after the `%' to specify a minimum field
width.  If the width is less, the field is padded with spaces to the
right.

`%b'
     The current buffer name, obtained with the `buffer-name' function.
     *Note Buffer Names::.

`%c'
     The current column number of point.

`%e'
     When Emacs is nearly out of memory for Lisp objects, a brief
     message saying so.  Otherwise, this is empty.

`%f'
     The visited file name, obtained with the `buffer-file-name'
     function.  *Note Buffer File Name::.

`%F'
     The title (only on a window system) or the name of the selected
     frame.  *Note Basic Parameters::.

`%i'
     The size of the accessible part of the current buffer; basically
     `(- (point-max) (point-min))'.

`%I'
     Like `%i', but the size is printed in a more readable way by using
     `k' for 10^3, `M' for 10^6, `G' for 10^9, etc., to abbreviate.

`%l'
     The current line number of point, counting within the accessible
     portion of the buffer.

`%n'
     `Narrow' when narrowing is in effect; nothing otherwise (see
     `narrow-to-region' in *Note Narrowing::).

`%p'
     The percentage of the buffer text above the *top* of window, or
     `Top', `Bottom' or `All'.  Note that the default mode-line
     specification truncates this to three characters.

`%P'
     The percentage of the buffer text that is above the *bottom* of
     the window (which includes the text visible in the window, as well
     as the text above the top), plus `Top' if the top of the buffer is
     visible on screen; or `Bottom' or `All'.

`%s'
     The status of the subprocess belonging to the current buffer,
     obtained with `process-status'.  *Note Process Information::.

`%t'
     Whether the visited file is a text file or a binary file.  This is
     a meaningful distinction only on certain operating systems (*note
     MS-DOS File Types::).

`%z'
     The mnemonics of keyboard, terminal, and buffer coding systems.

`%Z'
     Like `%z', but including the end-of-line format.

`%*'
     `%' if the buffer is read only (see `buffer-read-only');
     `*' if the buffer is modified (see `buffer-modified-p');
     `-' otherwise.  *Note Buffer Modification::.

`%+'
     `*' if the buffer is modified (see `buffer-modified-p');
     `%' if the buffer is read only (see `buffer-read-only');
     `-' otherwise.  This differs from `%*' only for a modified
     read-only buffer.  *Note Buffer Modification::.

`%&'
     `*' if the buffer is modified, and `-' otherwise.

`%['
     An indication of the depth of recursive editing levels (not
     counting minibuffer levels): one `[' for each editing level.
     *Note Recursive Editing::.

`%]'
     One `]' for each recursive editing level (not counting minibuffer
     levels).

`%-'
     Dashes sufficient to fill the remainder of the mode line.

`%%'
     The character `%'--this is how to include a literal `%' in a
     string in which `%'-constructs are allowed.

   The following two `%'-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
`mode-name' and `global-mode-string'.

`%m'
     The value of `mode-name'.

`%M'
     The value of `global-mode-string'.


File: elisp,  Node: Properties in Mode,  Next: Header Lines,  Prev: %-Constructs,  Up: Mode Line Format

23.4.6 Properties in the Mode Line
----------------------------------

Certain text properties are meaningful in the mode line.  The `face'
property affects the appearance of text; the `help-echo' property
associates help strings with the text, and `local-map' can make the
text mouse-sensitive.

   There are four ways to specify text properties for text in the mode
line:

  1. Put a string with a text property directly into the mode-line data
     structure.

  2. Put a text property on a mode-line %-construct such as `%12b'; then
     the expansion of the %-construct will have that same text property.

  3. Use a `(:propertize ELT PROPS...)' construct to give ELT a text
     property specified by PROPS.

  4. Use a list containing `:eval FORM' in the mode-line data
     structure, and make FORM evaluate to a string that has a text
     property.

   You can use the `local-map' property to specify a keymap.  This
keymap only takes real effect for mouse clicks; binding character keys
and function keys to it has no effect, since it is impossible to move
point into the mode line.

   When the mode line refers to a variable which does not have a
non-`nil' `risky-local-variable' property, any text properties given or
specified within that variable's values are ignored.  This is because
such properties could otherwise specify functions to be called, and
those functions could come from file local variables.


File: elisp,  Node: Header Lines,  Next: Emulating Mode Line,  Prev: Properties in Mode,  Up: Mode Line Format

23.4.7 Window Header Lines
--------------------------

A window can have a "header line" at the top, just as it can have a
mode line at the bottom.  The header line feature works just like the
mode-line feature, except that it's controlled by different variables.

 -- Variable: header-line-format
     This variable, local in every buffer, specifies how to display the
     header line, for windows displaying the buffer.  The format of the
     value is the same as for `mode-line-format' (*note Mode Line
     Data::).

 -- Variable: default-header-line-format
     This variable holds the default `header-line-format' for buffers
     that do not override it.  This is the same as `(default-value
     'header-line-format)'.

     It is normally `nil', so that ordinary buffers have no header line.

   A window that is just one line tall never displays a header line.  A
window that is two lines tall cannot display both a mode line and a
header line at once; if it has a mode line, then it does not display a
header line.


File: elisp,  Node: Emulating Mode Line,  Prev: Header Lines,  Up: Mode Line Format

23.4.8 Emulating Mode-Line Formatting
-------------------------------------

You can use the function `format-mode-line' to compute the text that
would appear in a mode line or header line based on a certain mode-line
specification.

 -- Function: format-mode-line format &optional face window buffer
     This function formats a line of text according to FORMAT as if it
     were generating the mode line for WINDOW, but instead of
     displaying the text in the mode line or the header line, it returns
     the text as a string.  The argument WINDOW defaults to the
     selected window.  If BUFFER is non-`nil', all the information used
     is taken from BUFFER; by default, it comes from WINDOW's buffer.

     The value string normally has text properties that correspond to
     the faces, keymaps, etc., that the mode line would have.  And any
     character for which no `face' property is specified gets a default
     value which is usually FACE.  (If FACE is `t', that stands for
     either `mode-line' if WINDOW is selected, otherwise
     `mode-line-inactive'.  If FACE is `nil' or omitted, that stands
     for no face property.)

     However, if FACE is an integer, the value has no text properties.

     For example, `(format-mode-line header-line-format)' returns the
     text that would appear in the selected window's header line (`""'
     if it has no header line).  `(format-mode-line header-line-format
     'header-line)' returns the same text, with each character carrying
     the face that it will have in the header line itself.


File: elisp,  Node: Imenu,  Next: Font Lock Mode,  Prev: Mode Line Format,  Up: Modes

23.5 Imenu
==========

"Imenu" is a feature that lets users select a definition or section in
the buffer, from a menu which lists all of them, to go directly to that
location in the buffer.  Imenu works by constructing a buffer index
which lists the names and buffer positions of the definitions, or other
named portions of the buffer; then the user can choose one of them and
move point to it.  Major modes can add a menu bar item to use Imenu
using `imenu-add-to-menubar'.

 -- Function: imenu-add-to-menubar name
     This function defines a local menu bar item named NAME to run
     Imenu.

   The user-level commands for using Imenu are described in the Emacs
Manual (*note Imenu: (emacs)Imenu.).  This section explains how to
customize Imenu's method of finding definitions or buffer portions for
a particular major mode.

   The usual and simplest way is to set the variable
`imenu-generic-expression':

 -- Variable: imenu-generic-expression
     This variable, if non-`nil', is a list that specifies regular
     expressions for finding definitions for Imenu.  Simple elements of
     `imenu-generic-expression' look like this:

          (MENU-TITLE REGEXP INDEX)

     Here, if MENU-TITLE is non-`nil', it says that the matches for
     this element should go in a submenu of the buffer index;
     MENU-TITLE itself specifies the name for the submenu.  If
     MENU-TITLE is `nil', the matches for this element go directly in
     the top level of the buffer index.

     The second item in the list, REGEXP, is a regular expression
     (*note Regular Expressions::); anything in the buffer that it
     matches is considered a definition, something to mention in the
     buffer index.  The third item, INDEX, is a non-negative integer
     that indicates which subexpression in REGEXP matches the
     definition's name.

     An element can also look like this:

          (MENU-TITLE REGEXP INDEX FUNCTION ARGUMENTS...)

     Each match for this element creates an index item, and when the
     index item is selected by the user, it calls FUNCTION with
     arguments consisting of the item name, the buffer position, and
     ARGUMENTS.

     For Emacs Lisp mode, `imenu-generic-expression' could look like
     this:

          ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\
          \\s-+\\([-A-Za-z0-9+]+\\)" 2)
           ("*Vars*" "^\\s-*(def\\(var\\|const\\)\
          \\s-+\\([-A-Za-z0-9+]+\\)" 2)
           ("*Types*"
            "^\\s-*\
          (def\\(type\\|struct\\|class\\|ine-condition\\)\
          \\s-+\\([-A-Za-z0-9+]+\\)" 2))

     Setting this variable makes it buffer-local in the current buffer.

 -- Variable: imenu-case-fold-search
     This variable controls whether matching against the regular
     expressions in the value of `imenu-generic-expression' is
     case-sensitive: `t', the default, means matching should ignore
     case.

     Setting this variable makes it buffer-local in the current buffer.

 -- Variable: imenu-syntax-alist
     This variable is an alist of syntax table modifiers to use while
     processing `imenu-generic-expression', to override the syntax table
     of the current buffer.  Each element should have this form:

          (CHARACTERS . SYNTAX-DESCRIPTION)

     The CAR, CHARACTERS, can be either a character or a string.  The
     element says to give that character or characters the syntax
     specified by SYNTAX-DESCRIPTION, which is passed to
     `modify-syntax-entry' (*note Syntax Table Functions::).

     This feature is typically used to give word syntax to characters
     which normally have symbol syntax, and thus to simplify
     `imenu-generic-expression' and speed up matching.  For example,
     Fortran mode uses it this way:

          (setq imenu-syntax-alist '(("_$" . "w")))

     The `imenu-generic-expression' regular expressions can then use
     `\\sw+' instead of `\\(\\sw\\|\\s_\\)+'.  Note that this technique
     may be inconvenient when the mode needs to limit the initial
     character of a name to a smaller set of characters than are
     allowed in the rest of a name.

     Setting this variable makes it buffer-local in the current buffer.

   Another way to customize Imenu for a major mode is to set the
variables `imenu-prev-index-position-function' and
`imenu-extract-index-name-function':

 -- Variable: imenu-prev-index-position-function
     If this variable is non-`nil', its value should be a function that
     finds the next "definition" to put in the buffer index, scanning
     backward in the buffer from point.  It should return `nil' if it
     doesn't find another "definition" before point.  Otherwise it
     should leave point at the place it finds a "definition" and return
     any non-`nil' value.

     Setting this variable makes it buffer-local in the current buffer.

 -- Variable: imenu-extract-index-name-function
     If this variable is non-`nil', its value should be a function to
     return the name for a definition, assuming point is in that
     definition as the `imenu-prev-index-position-function' function
     would leave it.

     Setting this variable makes it buffer-local in the current buffer.

   The last way to customize Imenu for a major mode is to set the
variable `imenu-create-index-function':

 -- Variable: imenu-create-index-function
     This variable specifies the function to use for creating a buffer
     index.  The function should take no arguments, and return an index
     alist for the current buffer.  It is called within
     `save-excursion', so where it leaves point makes no difference.

     The index alist can have three types of elements.  Simple elements
     look like this:

          (INDEX-NAME . INDEX-POSITION)

     Selecting a simple element has the effect of moving to position
     INDEX-POSITION in the buffer.  Special elements look like this:

          (INDEX-NAME INDEX-POSITION FUNCTION ARGUMENTS...)

     Selecting a special element performs:

          (funcall FUNCTION
                   INDEX-NAME INDEX-POSITION ARGUMENTS...)

     A nested sub-alist element looks like this:

          (MENU-TITLE SUB-ALIST)

     It creates the submenu MENU-TITLE specified by SUB-ALIST.

     The default value of `imenu-create-index-function' is
     `imenu-default-create-index-function'.  This function calls the
     value of `imenu-prev-index-position-function' and the value of
     `imenu-extract-index-name-function' to produce the index alist.
     However, if either of these two variables is `nil', the default
     function uses `imenu-generic-expression' instead.

     Setting this variable makes it buffer-local in the current buffer.


File: elisp,  Node: Font Lock Mode,  Next: Desktop Save Mode,  Prev: Imenu,  Up: Modes

23.6 Font Lock Mode
===================

"Font Lock mode" is a feature that automatically attaches `face'
properties to certain parts of the buffer based on their syntactic
role.  How it parses the buffer depends on the major mode; most major
modes define syntactic criteria for which faces to use in which
contexts.  This section explains how to customize Font Lock for a
particular major mode.

   Font Lock mode finds text to highlight in two ways: through
syntactic parsing based on the syntax table, and through searching
(usually for regular expressions).  Syntactic fontification happens
first; it finds comments and string constants and highlights them.
Search-based fontification happens second.

* Menu:

* Font Lock Basics::            Overview of customizing Font Lock.
* Search-based Fontification::  Fontification based on regexps.
* Customizing Keywords::        Customizing search-based fontification.
* Other Font Lock Variables::   Additional customization facilities.
* Levels of Font Lock::         Each mode can define alternative levels
                                  so that the user can select more or less.
* Precalculated Fontification:: How Lisp programs that produce the buffer
                                  contents can also specify how to fontify it.
* Faces for Font Lock::         Special faces specifically for Font Lock.
* Syntactic Font Lock::         Fontification based on syntax tables.
* Setting Syntax Properties::   Defining character syntax based on context
                                  using the Font Lock mechanism.
* Multiline Font Lock::         How to coerce Font Lock into properly
                                  highlighting multiline constructs.


File: elisp,  Node: Font Lock Basics,  Next: Search-based Fontification,  Up: Font Lock Mode

23.6.1 Font Lock Basics
-----------------------

There are several variables that control how Font Lock mode highlights
text.  But major modes should not set any of these variables directly.
Instead, they should set `font-lock-defaults' as a buffer-local
variable.  The value assigned to this variable is used, if and when Font
Lock mode is enabled, to set all the other variables.

 -- Variable: font-lock-defaults
     This variable is set by major modes, as a buffer-local variable, to
     specify how to fontify text in that mode.  It automatically becomes
     buffer-local when you set it.  If its value is `nil', Font-Lock
     mode does no highlighting, and you can use the `Faces' menu (under
     `Edit' and then `Text Properties' in the menu bar) to assign faces
     explicitly to text in the buffer.

     If non-`nil', the value should look like this:

          (KEYWORDS [KEYWORDS-ONLY [CASE-FOLD
           [SYNTAX-ALIST [SYNTAX-BEGIN OTHER-VARS...]]]])

     The first element, KEYWORDS, indirectly specifies the value of
     `font-lock-keywords' which directs search-based fontification.  It
     can be a symbol, a variable or a function whose value is the list
     to use for `font-lock-keywords'.  It can also be a list of several
     such symbols, one for each possible level of fontification.  The
     first symbol specifies how to do level 1 fontification, the second
     symbol how to do level 2, and so on.  *Note Levels of Font Lock::.

     The second element, KEYWORDS-ONLY, specifies the value of the
     variable `font-lock-keywords-only'.  If this is omitted or `nil',
     syntactic fontification (of strings and comments) is also
     performed.  If this is non-`nil', such fontification is not
     performed.  *Note Syntactic Font Lock::.

     The third element, CASE-FOLD, specifies the value of
     `font-lock-keywords-case-fold-search'.  If it is non-`nil', Font
     Lock mode ignores case when searching as directed by
     `font-lock-keywords'.

     If the fourth element, SYNTAX-ALIST, is non-`nil', it should be a
     list of cons cells of the form `(CHAR-OR-STRING . STRING)'.  These
     are used to set up a syntax table for syntactic fontification
     (*note Syntax Table Functions::).  The resulting syntax table is
     stored in `font-lock-syntax-table'.

     The fifth element, SYNTAX-BEGIN, specifies the value of
     `font-lock-beginning-of-syntax-function'.  We recommend setting
     this variable to `nil' and using `syntax-begin-function' instead.

     All the remaining elements (if any) are collectively called
     OTHER-VARS.  Each of these elements should have the form
     `(VARIABLE . VALUE)'--which means, make VARIABLE buffer-local and
     then set it to VALUE.  You can use these OTHER-VARS to set other
     variables that affect fontification, aside from those you can
     control with the first five elements.  *Note Other Font Lock
     Variables::.

   If your mode fontifies text explicitly by adding `font-lock-face'
properties, it can specify `(nil t)' for `font-lock-defaults' to turn
off all automatic fontification.  However, this is not required; it is
possible to fontify some things using `font-lock-face' properties and
set up automatic fontification for other parts of the text.


File: elisp,  Node: Search-based Fontification,  Next: Customizing Keywords,  Prev: Font Lock Basics,  Up: Font Lock Mode

23.6.2 Search-based Fontification
---------------------------------

The most important variable for customizing Font Lock mode is
`font-lock-keywords'.  It specifies the search criteria for
search-based fontification.  You should specify the value of this
variable with KEYWORDS in `font-lock-defaults'.

 -- Variable: font-lock-keywords
     This variable's value is a list of the keywords to highlight.  Be
     careful when composing regular expressions for this list; a poorly
     written pattern can dramatically slow things down!

   Each element of `font-lock-keywords' specifies how to find certain
cases of text, and how to highlight those cases.  Font Lock mode
processes the elements of `font-lock-keywords' one by one, and for each
element, it finds and handles all matches.  Ordinarily, once part of
the text has been fontified already, this cannot be overridden by a
subsequent match in the same text; but you can specify different
behavior using the OVERRIDE element of a SUBEXP-HIGHLIGHTER.

   Each element of `font-lock-keywords' should have one of these forms:

`REGEXP'
     Highlight all matches for REGEXP using `font-lock-keyword-face'.
     For example,

          ;; Highlight occurrences of the word `foo'
          ;; using `font-lock-keyword-face'.
          "\\<foo\\>"

     The function `regexp-opt' (*note Regexp Functions::) is useful for
     calculating optimal regular expressions to match a number of
     different keywords.

`FUNCTION'
     Find text by calling FUNCTION, and highlight the matches it finds
     using `font-lock-keyword-face'.

     When FUNCTION is called, it receives one argument, the limit of
     the search; it should begin searching at point, and not search
     beyond the limit.  It should return non-`nil' if it succeeds, and
     set the match data to describe the match that was found.
     Returning `nil' indicates failure of the search.

     Fontification will call FUNCTION repeatedly with the same limit,
     and with point where the previous invocation left it, until
     FUNCTION fails.  On failure, FUNCTION need not reset point in any
     particular way.

`(MATCHER . SUBEXP)'
     In this kind of element, MATCHER is either a regular expression or
     a function, as described above.  The CDR, SUBEXP, specifies which
     subexpression of MATCHER should be highlighted (instead of the
     entire text that MATCHER matched).

          ;; Highlight the `bar' in each occurrence of `fubar',
          ;; using `font-lock-keyword-face'.
          ("fu\\(bar\\)" . 1)

     If you use `regexp-opt' to produce the regular expression MATCHER,
     you can use `regexp-opt-depth' (*note Regexp Functions::) to
     calculate the value for SUBEXP.

`(MATCHER . FACESPEC)'
     In this kind of element, FACESPEC is an expression whose value
     specifies the face to use for highlighting.  In the simplest case,
     FACESPEC is a Lisp variable (a symbol) whose value is a face name.

          ;; Highlight occurrences of `fubar',
          ;; using the face which is the value of `fubar-face'.
          ("fubar" . fubar-face)

     However, FACESPEC can also evaluate to a list of this form:

          (face FACE PROP1 VAL1 PROP2 VAL2...)

     to specify the face FACE and various additional text properties to
     put on the text that matches.  If you do this, be sure to add the
     other text property names that you set in this way to the value of
     `font-lock-extra-managed-props' so that the properties will also
     be cleared out when they are no longer appropriate.  Alternatively,
     you can set the variable `font-lock-unfontify-region-function' to
     a function that clears these properties.  *Note Other Font Lock
     Variables::.

`(MATCHER . SUBEXP-HIGHLIGHTER)'
     In this kind of element, SUBEXP-HIGHLIGHTER is a list which
     specifies how to highlight matches found by MATCHER.  It has the
     form:

          (SUBEXP FACESPEC [[OVERRIDE [LAXMATCH]])

     The CAR, SUBEXP, is an integer specifying which subexpression of
     the match to fontify (0 means the entire matching text).  The
     second subelement, FACESPEC, is an expression whose value
     specifies the face, as described above.

     The last two values in SUBEXP-HIGHLIGHTER, OVERRIDE and LAXMATCH,
     are optional flags.  If OVERRIDE is `t', this element can override
     existing fontification made by previous elements of
     `font-lock-keywords'.  If it is `keep', then each character is
     fontified if it has not been fontified already by some other
     element.  If it is `prepend', the face specified by FACESPEC is
     added to the beginning of the `font-lock-face' property.  If it is
     `append', the face is added to the end of the `font-lock-face'
     property.

     If LAXMATCH is non-`nil', it means there should be no error if
     there is no subexpression numbered SUBEXP in MATCHER.  Obviously,
     fontification of the subexpression numbered SUBEXP will not occur.
     However, fontification of other subexpressions (and other
     regexps) will continue.  If LAXMATCH is `nil', and the specified
     subexpression is missing, then an error is signaled which
     terminates search-based fontification.

     Here are some examples of elements of this kind, and what they do:

          ;; Highlight occurrences of either `foo' or `bar', using
          ;; `foo-bar-face', even if they have already been highlighted.
          ;; `foo-bar-face' should be a variable whose value is a face.
          ("foo\\|bar" 0 foo-bar-face t)

          ;; Highlight the first subexpression within each occurrence
          ;; that the function `fubar-match' finds,
          ;; using the face which is the value of `fubar-face'.
          (fubar-match 1 fubar-face)

`(MATCHER . ANCHORED-HIGHLIGHTER)'
     In this kind of element, ANCHORED-HIGHLIGHTER specifies how to
     highlight text that follows a match found by MATCHER.  So a match
     found by MATCHER acts as the anchor for further searches specified
     by ANCHORED-HIGHLIGHTER.  ANCHORED-HIGHLIGHTER is a list of the
     following form:

          (ANCHORED-MATCHER PRE-FORM POST-FORM
                                  SUBEXP-HIGHLIGHTERS...)

     Here, ANCHORED-MATCHER, like MATCHER, is either a regular
     expression or a function.  After a match of MATCHER is found,
     point is at the end of the match.  Now, Font Lock evaluates the
     form PRE-FORM.  Then it searches for matches of ANCHORED-MATCHER
     and uses SUBEXP-HIGHLIGHTERS to highlight these.  A
     SUBEXP-HIGHLIGHTER is as described above.  Finally, Font Lock
     evaluates POST-FORM.

     The forms PRE-FORM and POST-FORM can be used to initialize before,
     and cleanup after, ANCHORED-MATCHER is used.  Typically, PRE-FORM
     is used to move point to some position relative to the match of
     MATCHER, before starting with ANCHORED-MATCHER.  POST-FORM might
     be used to move back, before resuming with MATCHER.

     After Font Lock evaluates PRE-FORM, it does not search for
     ANCHORED-MATCHER beyond the end of the line.  However, if PRE-FORM
     returns a buffer position that is greater than the position of
     point after PRE-FORM is evaluated, then the position returned by
     PRE-FORM is used as the limit of the search instead.  It is
     generally a bad idea to return a position greater than the end of
     the line; in other words, the ANCHORED-MATCHER search should not
     span lines.

     For example,

          ;; Highlight occurrences of the word `item' following
          ;; an occurrence of the word `anchor' (on the same line)
          ;; in the value of `item-face'.
          ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face))

     Here, PRE-FORM and POST-FORM are `nil'.  Therefore searching for
     `item' starts at the end of the match of `anchor', and searching
     for subsequent instances of `anchor' resumes from where searching
     for `item' concluded.

`(MATCHER HIGHLIGHTERS...)'
     This sort of element specifies several HIGHLIGHTER lists for a
     single MATCHER.  A HIGHLIGHTER list can be of the type
     SUBEXP-HIGHLIGHTER or ANCHORED-HIGHLIGHTER as described above.

     For example,

          ;; Highlight occurrences of the word `anchor' in the value
          ;; of `anchor-face', and subsequent occurrences of the word
          ;; `item' (on the same line) in the value of `item-face'.
          ("\\<anchor\\>" (0 anchor-face)
                          ("\\<item\\>" nil nil (0 item-face)))

`(eval . FORM)'
     Here FORM is an expression to be evaluated the first time this
     value of `font-lock-keywords' is used in a buffer.  Its value
     should have one of the forms described in this table.

   *Warning:* Do not design an element of `font-lock-keywords' to match
text which spans lines; this does not work reliably.  For details, see
*Note Multiline Font Lock::.

   You can use CASE-FOLD in `font-lock-defaults' to specify the value
of `font-lock-keywords-case-fold-search' which says whether
search-based fontification should be case-insensitive.

 -- Variable: font-lock-keywords-case-fold-search
     Non-`nil' means that regular expression matching for the sake of
     `font-lock-keywords' should be case-insensitive.


File: elisp,  Node: Customizing Keywords,  Next: Other Font Lock Variables,  Prev: Search-based Fontification,  Up: Font Lock Mode

23.6.3 Customizing Search-Based Fontification
---------------------------------------------

You can use `font-lock-add-keywords' to add additional search-based
fontification rules to a major mode, and `font-lock-remove-keywords' to
removes rules.

 -- Function: font-lock-add-keywords mode keywords &optional how
     This function adds highlighting KEYWORDS, for the current buffer
     or for major mode MODE.  The argument KEYWORDS should be a list
     with the same format as the variable `font-lock-keywords'.

     If MODE is a symbol which is a major mode command name, such as
     `c-mode', the effect is that enabling Font Lock mode in MODE will
     add KEYWORDS to `font-lock-keywords'.  Calling with a non-`nil'
     value of MODE is correct only in your `~/.emacs' file.

     If MODE is `nil', this function adds KEYWORDS to
     `font-lock-keywords' in the current buffer.  This way of calling
     `font-lock-add-keywords' is usually used in mode hook functions.

     By default, KEYWORDS are added at the beginning of
     `font-lock-keywords'.  If the optional argument HOW is `set', they
     are used to replace the value of `font-lock-keywords'.  If HOW is
     any other non-`nil' value, they are added at the end of
     `font-lock-keywords'.

     Some modes provide specialized support you can use in additional
     highlighting patterns.  See the variables
     `c-font-lock-extra-types', `c++-font-lock-extra-types', and
     `java-font-lock-extra-types', for example.

     *Warning:* major mode functions must not call
     `font-lock-add-keywords' under any circumstances, either directly
     or indirectly, except through their mode hooks.  (Doing so would
     lead to incorrect behavior for some minor modes.)  They should set
     up their rules for search-based fontification by setting
     `font-lock-keywords'.

 -- Function: font-lock-remove-keywords mode keywords
     This function removes KEYWORDS from `font-lock-keywords' for the
     current buffer or for major mode MODE.  As in
     `font-lock-add-keywords', MODE should be a major mode command name
     or `nil'.  All the caveats and requirements for
     `font-lock-add-keywords' apply here too.

   For example, this code

     (font-lock-add-keywords 'c-mode
      '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
        ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face)))

adds two fontification patterns for C mode: one to fontify the word
`FIXME', even in comments, and another to fontify the words `and', `or'
and `not' as keywords.

That example affects only C mode proper.  To add the same patterns to C
mode _and_ all modes derived from it, do this instead:

     (add-hook 'c-mode-hook
      (lambda ()
       (font-lock-add-keywords nil
        '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
          ("\\<\\(and\\|or\\|not\\)\\>" .
           font-lock-keyword-face)))))


File: elisp,  Node: Other Font Lock Variables,  Next: Levels of Font Lock,  Prev: Customizing Keywords,  Up: Font Lock Mode

23.6.4 Other Font Lock Variables
--------------------------------

This section describes additional variables that a major mode can set
by means of OTHER-VARS in `font-lock-defaults' (*note Font Lock
Basics::).

 -- Variable: font-lock-mark-block-function
     If this variable is non-`nil', it should be a function that is
     called with no arguments, to choose an enclosing range of text for
     refontification for the command `M-o M-o'
     (`font-lock-fontify-block').

     The function should report its choice by placing the region around
     it.  A good choice is a range of text large enough to give proper
     results, but not too large so that refontification becomes slow.
     Typical values are `mark-defun' for programming modes or
     `mark-paragraph' for textual modes.

 -- Variable: font-lock-extra-managed-props
     This variable specifies additional properties (other than
     `font-lock-face') that are being managed by Font Lock mode.  It is
     used by `font-lock-default-unfontify-region', which normally only
     manages the `font-lock-face' property.  If you want Font Lock to
     manage other properties as well, you must specify them in a
     FACESPEC in `font-lock-keywords' as well as add them to this list.
     *Note Search-based Fontification::.

 -- Variable: font-lock-fontify-buffer-function
     Function to use for fontifying the buffer.  The default value is
     `font-lock-default-fontify-buffer'.

 -- Variable: font-lock-unfontify-buffer-function
     Function to use for unfontifying the buffer.  This is used when
     turning off Font Lock mode.  The default value is
     `font-lock-default-unfontify-buffer'.

 -- Variable: font-lock-fontify-region-function
     Function to use for fontifying a region.  It should take two
     arguments, the beginning and end of the region, and an optional
     third argument VERBOSE.  If VERBOSE is non-`nil', the function
     should print status messages.  The default value is
     `font-lock-default-fontify-region'.

 -- Variable: font-lock-unfontify-region-function
     Function to use for unfontifying a region.  It should take two
     arguments, the beginning and end of the region.  The default value
     is `font-lock-default-unfontify-region'.


File: elisp,  Node: Levels of Font Lock,  Next: Precalculated Fontification,  Prev: Other Font Lock Variables,  Up: Font Lock Mode

23.6.5 Levels of Font Lock
--------------------------

Many major modes offer three different levels of fontification.  You
can define multiple levels by using a list of symbols for KEYWORDS in
`font-lock-defaults'.  Each symbol specifies one level of
fontification; it is up to the user to choose one of these levels.  The
chosen level's symbol value is used to initialize `font-lock-keywords'.

   Here are the conventions for how to define the levels of
fontification:

   * Level 1: highlight function declarations, file directives (such as
     include or import directives), strings and comments.  The idea is
     speed, so only the most important and top-level components are
     fontified.

   * Level 2: in addition to level 1, highlight all language keywords,
     including type names that act like keywords, as well as named
     constant values.  The idea is that all keywords (either syntactic
     or semantic) should be fontified appropriately.

   * Level 3: in addition to level 2, highlight the symbols being
     defined in function and variable declarations, and all builtin
     function names, wherever they appear.


File: elisp,  Node: Precalculated Fontification,  Next: Faces for Font Lock,  Prev: Levels of Font Lock,  Up: Font Lock Mode

23.6.6 Precalculated Fontification
----------------------------------

In addition to using `font-lock-defaults' for search-based
fontification, you may use the special character property
`font-lock-face' (*note Special Properties::).  This property acts just
like the explicit `face' property, but its activation is toggled when
the user calls `M-x font-lock-mode'.  Using `font-lock-face' is
especially convenient for special modes which construct their text
programmatically, such as `list-buffers' and `occur'.

   If your mode does not use any of the other machinery of Font Lock
(i.e. it only uses the `font-lock-face' property), it should not set
the variable `font-lock-defaults'.


File: elisp,  Node: Faces for Font Lock,  Next: Syntactic Font Lock,  Prev: Precalculated Fontification,  Up: Font Lock Mode

23.6.7 Faces for Font Lock
--------------------------

You can make Font Lock mode use any face, but several faces are defined
specifically for Font Lock mode.  Each of these symbols is both a face
name, and a variable whose default value is the symbol itself.  Thus,
the default value of `font-lock-comment-face' is
`font-lock-comment-face'.  This means you can write
`font-lock-comment-face' in a context such as `font-lock-keywords'
where a face-name-valued expression is used.

`font-lock-comment-face'
     Used (typically) for comments.

`font-lock-comment-delimiter-face'
     Used (typically) for comments delimiters.

`font-lock-doc-face'
     Used (typically) for documentation strings in the code.

`font-lock-string-face'
     Used (typically) for string constants.

`font-lock-keyword-face'
     Used (typically) for keywords--names that have special syntactic
     significance, like `for' and `if' in C.

`font-lock-builtin-face'
     Used (typically) for built-in function names.

`font-lock-function-name-face'
     Used (typically) for the name of a function being defined or
     declared, in a function definition or declaration.

`font-lock-variable-name-face'
     Used (typically) for the name of a variable being defined or
     declared, in a variable definition or declaration.

`font-lock-type-face'
     Used (typically) for names of user-defined data types, where they
     are defined and where they are used.

`font-lock-constant-face'
     Used (typically) for constant names.

`font-lock-preprocessor-face'
     Used (typically) for preprocessor commands.

`font-lock-negation-char-face'
     Used (typically) for easily-overlooked negation characters.

`font-lock-warning-face'
     Used (typically) for constructs that are peculiar, or that greatly
     change the meaning of other text.  For example, this is used for
     `;;;###autoload' cookies in Emacs Lisp, and for `#error'
     directives in C.


File: elisp,  Node: Syntactic Font Lock,  Next: Setting Syntax Properties,  Prev: Faces for Font Lock,  Up: Font Lock Mode

23.6.8 Syntactic Font Lock
--------------------------

Syntactic fontification uses the syntax table to find comments and
string constants (*note Syntax Tables::).  It highlights them using
`font-lock-comment-face' and `font-lock-string-face' (*note Faces for
Font Lock::), or whatever `font-lock-syntactic-face-function' chooses.
There are several variables that affect syntactic fontification; you
should set them by means of `font-lock-defaults' (*note Font Lock
Basics::).

 -- Variable: font-lock-keywords-only
     Non-`nil' means Font Lock should not do syntactic fontification;
     it should only fontify based on `font-lock-keywords'.  The normal
     way for a mode to set this variable to `t' is with KEYWORDS-ONLY
     in `font-lock-defaults'.

 -- Variable: font-lock-syntax-table
     This variable holds the syntax table to use for fontification of
     comments and strings.  Specify it using SYNTAX-ALIST in
     `font-lock-defaults'.  If this is `nil', fontification uses the
     buffer's syntax table.

 -- Variable: font-lock-beginning-of-syntax-function
     If this variable is non-`nil', it should be a function to move
     point back to a position that is syntactically at "top level" and
     outside of strings or comments.  Font Lock uses this when necessary
     to get the right results for syntactic fontification.

     This function is called with no arguments.  It should leave point
     at the beginning of any enclosing syntactic block.  Typical values
     are `beginning-of-line' (used when the start of the line is known
     to be outside a syntactic block), or `beginning-of-defun' for
     programming modes, or `backward-paragraph' for textual modes.

     If the value is `nil', Font Lock uses `syntax-begin-function' to
     move back outside of any comment, string, or sexp.  This variable
     is semi-obsolete; we recommend setting `syntax-begin-function'
     instead.

     Specify this variable using SYNTAX-BEGIN in `font-lock-defaults'.

 -- Variable: font-lock-syntactic-face-function
     A function to determine which face to use for a given syntactic
     element (a string or a comment).  The function is called with one
     argument, the parse state at point returned by
     `parse-partial-sexp', and should return a face.  The default value
     returns `font-lock-comment-face' for comments and
     `font-lock-string-face' for strings.

     This can be used to highlighting different kinds of strings or
     comments differently.  It is also sometimes abused together with
     `font-lock-syntactic-keywords' to highlight constructs that span
     multiple lines, but this is too esoteric to document here.

     Specify this variable using OTHER-VARS in `font-lock-defaults'.


File: elisp,  Node: Setting Syntax Properties,  Next: Multiline Font Lock,  Prev: Syntactic Font Lock,  Up: Font Lock Mode

23.6.9 Setting Syntax Properties
--------------------------------

Font Lock mode can be used to update `syntax-table' properties
automatically (*note Syntax Properties::).  This is useful in languages
for which a single syntax table by itself is not sufficient.

 -- Variable: font-lock-syntactic-keywords
     This variable enables and controls updating `syntax-table'
     properties by Font Lock.  Its value should be a list of elements of
     this form:

          (MATCHER SUBEXP SYNTAX OVERRIDE LAXMATCH)

     The parts of this element have the same meanings as in the
     corresponding sort of element of `font-lock-keywords',

          (MATCHER SUBEXP FACESPEC OVERRIDE LAXMATCH)

     However, instead of specifying the value FACESPEC to use for the
     `face' property, it specifies the value SYNTAX to use for the
     `syntax-table' property.  Here, SYNTAX can be a string (as taken
     by `modify-syntax-entry'), a syntax table, a cons cell (as
     returned by `string-to-syntax'), or an expression whose value is
     one of those two types.  OVERRIDE cannot be `prepend' or `append'.

     For example, an element of the form:

          ("\\$\\(#\\)" 1 ".")

     highlights syntactically a hash character when following a dollar
     character, with a SYNTAX of `"."' (meaning punctuation syntax).
     Assuming that the buffer syntax table specifies hash characters to
     have comment start syntax, the element will only highlight hash
     characters that do not follow dollar characters as comments
     syntactically.

     An element of the form:

           ("\\('\\).\\('\\)"
            (1 "\"")
            (2 "\""))

     highlights syntactically both single quotes which surround a single
     character, with a SYNTAX of `"\""' (meaning string quote syntax).
     Assuming that the buffer syntax table does not specify single
     quotes to have quote syntax, the element will only highlight
     single quotes of the form `'C'' as strings syntactically.  Other
     forms, such as `foo'bar' or `'fubar'', will not be highlighted as
     strings.

     Major modes normally set this variable with OTHER-VARS in
     `font-lock-defaults'.


File: elisp,  Node: Multiline Font Lock,  Prev: Setting Syntax Properties,  Up: Font Lock Mode

23.6.10 Multiline Font Lock Constructs
--------------------------------------

Normally, elements of `font-lock-keywords' should not match across
multiple lines; that doesn't work reliably, because Font Lock usually
scans just part of the buffer, and it can miss a multi-line construct
that crosses the line boundary where the scan starts.  (The scan
normally starts at the beginning of a line.)

   Making elements that match multiline constructs work properly has
two aspects: correct _identification_ and correct _rehighlighting_.
The first means that Font Lock finds all multiline constructs.  The
second means that Font Lock will correctly rehighlight all the relevant
text when a multiline construct is changed--for example, if some of the
text that was previously part of a multiline construct ceases to be
part of it.  The two aspects are closely related, and often getting one
of them to work will appear to make the other also work.  However, for
reliable results you must attend explicitly to both aspects.

   There are three ways to ensure correct identification of multiline
constructs:

   * Add a function to `font-lock-extend-region-functions' that does
     the _identification_ and extends the scan so that the scanned text
     never starts or ends in the middle of a multiline construct.

   * Use the `font-lock-fontify-region-function' hook similarly to
     extend the scan so that the scanned text never starts or ends in
     the middle of a multiline construct.

   * Somehow identify the multiline construct right when it gets
     inserted into the buffer (or at any point after that but before
     font-lock tries to highlight it), and mark it with a
     `font-lock-multiline' which will instruct font-lock not to start
     or end the scan in the middle of the construct.

   There are three ways to do rehighlighting of multiline constructs:

   * Place a `font-lock-multiline' property on the construct.  This
     will rehighlight the whole construct if any part of it is changed.
     In some cases you can do this automatically by setting the
     `font-lock-multiline' variable, which see.

   * Make sure `jit-lock-contextually' is set and rely on it doing its
     job.  This will only rehighlight the part of the construct that
     follows the actual change, and will do it after a short delay.
     This only works if the highlighting of the various parts of your
     multiline construct never depends on text in subsequent lines.
     Since `jit-lock-contextually' is activated by default, this can be
     an attractive solution.

   * Place a `jit-lock-defer-multiline' property on the construct.
     This works only if `jit-lock-contextually' is used, and with the
     same delay before rehighlighting, but like `font-lock-multiline',
     it also handles the case where highlighting depends on subsequent
     lines.

* Menu:

* Font Lock Multiline::         Marking multiline chunks with a text property
* Region to Fontify::           Controlling which region gets refontified
                                  after a buffer change.


File: elisp,  Node: Font Lock Multiline,  Next: Region to Fontify,  Up: Multiline Font Lock

23.6.10.1 Font Lock Multiline
.............................

One way to ensure reliable rehighlighting of multiline Font Lock
constructs is to put on them the text property `font-lock-multiline'.
It should be present and non-`nil' for text that is part of a multiline
construct.

   When Font Lock is about to highlight a range of text, it first
extends the boundaries of the range as necessary so that they do not
fall within text marked with the `font-lock-multiline' property.  Then
it removes any `font-lock-multiline' properties from the range, and
highlights it.  The highlighting specification (mostly
`font-lock-keywords') must reinstall this property each time, whenever
it is appropriate.

   *Warning:* don't use the `font-lock-multiline' property on large
ranges of text, because that will make rehighlighting slow.

 -- Variable: font-lock-multiline
     If the `font-lock-multiline' variable is set to `t', Font Lock
     will try to add the `font-lock-multiline' property automatically
     on multiline constructs.  This is not a universal solution,
     however, since it slows down Font Lock somewhat.  It can miss some
     multiline constructs, or make the property larger or smaller than
     necessary.

     For elements whose MATCHER is a function, the function should
     ensure that submatch 0 covers the whole relevant multiline
     construct, even if only a small subpart will be highlighted.  It
     is often just as easy to add the `font-lock-multiline' property by
     hand.

   The `font-lock-multiline' property is meant to ensure proper
refontification; it does not automatically identify new multiline
constructs.  Identifying the requires that Font-Lock operate on large
enough chunks at a time.  This will happen by accident on many cases,
which may give the impression that multiline constructs magically work.
If you set the `font-lock-multiline' variable non-`nil', this
impression will be even stronger, since the highlighting of those
constructs which are found will be properly updated from then on.  But
that does not work reliably.

   To find multiline constructs reliably, you must either manually
place the `font-lock-multiline' property on the text before Font-Lock
looks at it, or use `font-lock-fontify-region-function'.


File: elisp,  Node: Region to Fontify,  Prev: Font Lock Multiline,  Up: Multiline Font Lock

23.6.10.2 Region to Fontify after a Buffer Change
.................................................

When a buffer is changed, the region that Font Lock refontifies is by
default the smallest sequence of whole lines that spans the change.
While this works well most of the time, sometimes it doesn't--for
example, when a change alters the syntactic meaning of text on an
earlier line.

   You can enlarge (or even reduce) the region to fontify by setting
one the following variables:

 -- Variable: font-lock-extend-after-change-region-function
     This buffer-local variable is either `nil' or a function for
     Font-Lock to call to determine the region to scan and fontify.

     The function is given three parameters, the standard BEG, END, and
     OLD-LEN from after-change-functions (*note Change Hooks::).  It
     should return either a cons of the beginning and end buffer
     positions (in that order) of the region to fontify, or `nil'
     (which means choose the region in the standard way).  This
     function needs to preserve point, the match-data, and the current
     restriction.  The region it returns may start or end in the middle
     of a line.

     Since this function is called after every buffer change, it should
     be reasonably fast.


File: elisp,  Node: Desktop Save Mode,  Prev: Font Lock Mode,  Up: Modes

23.7 Desktop Save Mode
======================

"Desktop Save Mode" is a feature to save the state of Emacs from one
session to another.  The user-level commands for using Desktop Save
Mode are described in the GNU Emacs Manual (*note Saving Emacs
Sessions: (emacs)Saving Emacs Sessions.).  Modes whose buffers visit a
file, don't have to do anything to use this feature.

   For buffers not visiting a file to have their state saved, the major
mode must bind the buffer local variable `desktop-save-buffer' to a
non-`nil' value.

 -- Variable: desktop-save-buffer
     If this buffer-local variable is non-`nil', the buffer will have
     its state saved in the desktop file at desktop save.  If the value
     is a function, it is called at desktop save with argument
     DESKTOP-DIRNAME, and its value is saved in the desktop file along
     with the state of the buffer for which it was called.  When file
     names are returned as part of the auxiliary information, they
     should be formatted using the call

          (desktop-file-name FILE-NAME DESKTOP-DIRNAME)


   For buffers not visiting a file to be restored, the major mode must
define a function to do the job, and that function must be listed in
the alist `desktop-buffer-mode-handlers'.

 -- Variable: desktop-buffer-mode-handlers
     Alist with elements

          (MAJOR-MODE . RESTORE-BUFFER-FUNCTION)

     The function RESTORE-BUFFER-FUNCTION will be called with argument
     list

          (BUFFER-FILE-NAME BUFFER-NAME DESKTOP-BUFFER-MISC)

     and it should return the restored buffer.  Here
     DESKTOP-BUFFER-MISC is the value returned by the function
     optionally bound to `desktop-save-buffer'.


File: elisp,  Node: Documentation,  Next: Files,  Prev: Modes,  Up: Top

24 Documentation
****************

GNU Emacs Lisp has convenient on-line help facilities, most of which
derive their information from the documentation strings associated with
functions and variables.  This chapter describes how to write good
documentation strings for your Lisp programs, as well as how to write
programs to access documentation.

   Note that the documentation strings for Emacs are not the same thing
as the Emacs manual.  Manuals have their own source files, written in
the Texinfo language; documentation strings are specified in the
definitions of the functions and variables they apply to.  A collection
of documentation strings is not sufficient as a manual because a good
manual is not organized in that fashion; it is organized in terms of
topics of discussion.

   For commands to display documentation strings, see *Note Help:
(emacs)Help.  For the conventions for writing documentation strings,
see *Note Documentation Tips::.

* Menu:

* Documentation Basics::      Good style for doc strings.
                                Where to put them.  How Emacs stores them.
* Accessing Documentation::   How Lisp programs can access doc strings.
* Keys in Documentation::     Substituting current key bindings.
* Describing Characters::     Making printable descriptions of
                                non-printing characters and key sequences.
* Help Functions::            Subroutines used by Emacs help facilities.


File: elisp,  Node: Documentation Basics,  Next: Accessing Documentation,  Up: Documentation

24.1 Documentation Basics
=========================

A documentation string is written using the Lisp syntax for strings,
with double-quote characters surrounding the text of the string.  This
is because it really is a Lisp string object.  The string serves as
documentation when it is written in the proper place in the definition
of a function or variable.  In a function definition, the documentation
string follows the argument list.  In a variable definition, the
documentation string follows the initial value of the variable.

   When you write a documentation string, make the first line a
complete sentence (or two complete sentences) since some commands, such
as `apropos', show only the first line of a multi-line documentation
string.  Also, you should not indent the second line of a documentation
string, if it has one, because that looks odd when you use `C-h f'
(`describe-function') or `C-h v' (`describe-variable') to view the
documentation string.  There are many other conventions for doc
strings; see *Note Documentation Tips::.

   Documentation strings can contain several special substrings, which
stand for key bindings to be looked up in the current keymaps when the
documentation is displayed.  This allows documentation strings to refer
to the keys for related commands and be accurate even when a user
rearranges the key bindings.  (*Note Keys in Documentation::.)

   Emacs Lisp mode fills documentation strings to the width specified
by `emacs-lisp-docstring-fill-column'.

   In Emacs Lisp, a documentation string is accessible through the
function or variable that it describes:

   * The documentation for a function is usually stored in the function
     definition itself (*note Lambda Expressions::).  The function
     `documentation' knows how to extract it.  You can also put
     function documentation in the `function-documentation' property of
     the function name.  That is useful with definitions such as
     keyboard macros that can't hold a documentation string.

   * The documentation for a variable is stored in the variable's
     property list under the property name `variable-documentation'.
     The function `documentation-property' knows how to retrieve it.

   To save space, the documentation for preloaded functions and
variables (including primitive functions and autoloaded functions) is
stored in the file `emacs/etc/DOC-VERSION'--not inside Emacs.  The
documentation strings for functions and variables loaded during the
Emacs session from byte-compiled files are stored in those files (*note
Docs and Compilation::).

   The data structure inside Emacs has an integer offset into the file,
or a list containing a file name and an integer, in place of the
documentation string.  The functions `documentation' and
`documentation-property' use that information to fetch the
documentation string from the appropriate file; this is transparent to
the user.

   The `emacs/lib-src' directory contains two utilities that you can
use to print nice-looking hardcopy for the file
`emacs/etc/DOC-VERSION'.  These are `sorted-doc' and `digest-doc'.


File: elisp,  Node: Accessing Documentation,  Next: Keys in Documentation,  Prev: Documentation Basics,  Up: Documentation

24.2 Access to Documentation Strings
====================================

 -- Function: documentation-property symbol property &optional verbatim
     This function returns the documentation string that is recorded in
     SYMBOL's property list under property PROPERTY.  It retrieves the
     text from a file if the value calls for that.  If the property
     value isn't `nil', isn't a string, and doesn't refer to text in a
     file, then it is evaluated to obtain a string.

     The last thing this function does is pass the string through
     `substitute-command-keys' to substitute actual key bindings,
     unless VERBATIM is non-`nil'.

          (documentation-property 'command-line-processed
             'variable-documentation)
               => "Non-nil once command line has been processed"
          (symbol-plist 'command-line-processed)
               => (variable-documentation 188902)
          (documentation-property 'emacs 'group-documentation)
               => "Customization of the One True Editor."

 -- Function: documentation function &optional verbatim
     This function returns the documentation string of FUNCTION.
     `documentation' handles macros, named keyboard macros, and special
     forms, as well as ordinary functions.

     If FUNCTION is a symbol, this function first looks for the
     `function-documentation' property of that symbol; if that has a
     non-`nil' value, the documentation comes from that value (if the
     value is not a string, it is evaluated).  If FUNCTION is not a
     symbol, or if it has no `function-documentation' property, then
     `documentation' extracts the documentation string from the actual
     function definition, reading it from a file if called for.

     Finally, unless VERBATIM is non-`nil', it calls
     `substitute-command-keys' so as to return a value containing the
     actual (current) key bindings.

     The function `documentation' signals a `void-function' error if
     FUNCTION has no function definition.  However, it is OK if the
     function definition has no documentation string.  In that case,
     `documentation' returns `nil'.

 -- Function: face-documentation face
     This function returns the documentation string of FACE as a face.

   Here is an example of using the two functions, `documentation' and
`documentation-property', to display the documentation strings for
several symbols in a `*Help*' buffer.

     (defun describe-symbols (pattern)
       "Describe the Emacs Lisp symbols matching PATTERN.
     All symbols that have PATTERN in their name are described
     in the `*Help*' buffer."
       (interactive "sDescribe symbols matching: ")
       (let ((describe-func
              (function
               (lambda (s)
                 ;; Print description of symbol.
                 (if (fboundp s)             ; It is a function.
                     (princ
                      (format "%s\t%s\n%s\n\n" s
                        (if (commandp s)
                            (let ((keys (where-is-internal s)))
                              (if keys
                                  (concat
                                   "Keys: "
                                   (mapconcat 'key-description
                                              keys " "))
                                "Keys: none"))
                          "Function")
                        (or (documentation s)
                            "not documented"))))

                 (if (boundp s)              ; It is a variable.
                     (princ
                      (format "%s\t%s\n%s\n\n" s
                        (if (user-variable-p s)
                            "Option " "Variable")
                        (or (documentation-property
                              s 'variable-documentation)
                            "not documented")))))))
             sym-list)

         ;; Build a list of symbols that match pattern.
         (mapatoms (function
                    (lambda (sym)
                      (if (string-match pattern (symbol-name sym))
                          (setq sym-list (cons sym sym-list))))))

         ;; Display the data.
         (with-output-to-temp-buffer "*Help*"
           (mapcar describe-func (sort sym-list 'string<))
           (print-help-return-message))))

   The `describe-symbols' function works like `apropos', but provides
more information.

     (describe-symbols "goal")

     ---------- Buffer: *Help* ----------
     goal-column     Option
     *Semipermanent goal column for vertical motion, as set by ...

     set-goal-column Keys: C-x C-n
     Set the current horizontal position as a goal for C-n and C-p.
     Those commands will move to this position in the line moved to
     rather than trying to keep the same horizontal position.
     With a non-nil argument, clears out the goal column
     so that C-n and C-p resume vertical motion.
     The goal column is stored in the variable `goal-column'.

     temporary-goal-column   Variable
     Current goal column for vertical motion.
     It is the column where point was
     at the start of current run of vertical motion commands.
     When the `track-eol' feature is doing its job, the value is 9999.
     ---------- Buffer: *Help* ----------

   The asterisk `*' as the first character of a variable's doc string,
as shown above for the `goal-column' variable, means that it is a user
option; see the description of `defvar' in *Note Defining Variables::.

 -- Function: Snarf-documentation filename
     This function is used only during Emacs initialization, just before
     the runnable Emacs is dumped.  It finds the file offsets of the
     documentation strings stored in the file FILENAME, and records
     them in the in-core function definitions and variable property
     lists in place of the actual strings.  *Note Building Emacs::.

     Emacs reads the file FILENAME from the `emacs/etc' directory.
     When the dumped Emacs is later executed, the same file will be
     looked for in the directory `doc-directory'.  Usually FILENAME is
     `"DOC-VERSION"'.

 -- Variable: doc-directory
     This variable holds the name of the directory which should contain
     the file `"DOC-VERSION"' that contains documentation strings for
     built-in and preloaded functions and variables.

     In most cases, this is the same as `data-directory'.  They may be
     different when you run Emacs from the directory where you built it,
     without actually installing it.  *Note Definition of
     data-directory::.

     In older Emacs versions, `exec-directory' was used for this.


File: elisp,  Node: Keys in Documentation,  Next: Describing Characters,  Prev: Accessing Documentation,  Up: Documentation

24.3 Substituting Key Bindings in Documentation
===============================================

When documentation strings refer to key sequences, they should use the
current, actual key bindings.  They can do so using certain special text
sequences described below.  Accessing documentation strings in the usual
way substitutes current key binding information for these special
sequences.  This works by calling `substitute-command-keys'.  You can
also call that function yourself.

   Here is a list of the special sequences and what they mean:

`\[COMMAND]'
     stands for a key sequence that will invoke COMMAND, or `M-x
     COMMAND' if COMMAND has no key bindings.

`\{MAPVAR}'
     stands for a summary of the keymap which is the value of the
     variable MAPVAR.  The summary is made using `describe-bindings'.

`\<MAPVAR>'
     stands for no text itself.  It is used only for a side effect: it
     specifies MAPVAR's value as the keymap for any following
     `\[COMMAND]' sequences in this documentation string.

`\='
     quotes the following character and is discarded; thus, `\=\[' puts
     `\[' into the output, and `\=\=' puts `\=' into the output.

   *Please note:* Each `\' must be doubled when written in a string in
Emacs Lisp.

 -- Function: substitute-command-keys string
     This function scans STRING for the above special sequences and
     replaces them by what they stand for, returning the result as a
     string.  This permits display of documentation that refers
     accurately to the user's own customized key bindings.

   Here are examples of the special sequences:

     (substitute-command-keys
        "To abort recursive edit, type: \\[abort-recursive-edit]")
     => "To abort recursive edit, type: C-]"

     (substitute-command-keys
        "The keys that are defined for the minibuffer here are:
       \\{minibuffer-local-must-match-map}")
     => "The keys that are defined for the minibuffer here are:

     ?               minibuffer-completion-help
     SPC             minibuffer-complete-word
     TAB             minibuffer-complete
     C-j             minibuffer-complete-and-exit
     RET             minibuffer-complete-and-exit
     C-g             abort-recursive-edit
     "

     (substitute-command-keys
        "To abort a recursive edit from the minibuffer, type\
     \\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
     => "To abort a recursive edit from the minibuffer, type C-g."

   There are other special conventions for the text in documentation
strings--for instance, you can refer to functions, variables, and
sections of this manual.  *Note Documentation Tips::, for details.


File: elisp,  Node: Describing Characters,  Next: Help Functions,  Prev: Keys in Documentation,  Up: Documentation

24.4 Describing Characters for Help Messages
============================================

These functions convert events, key sequences, or characters to textual
descriptions.  These descriptions are useful for including arbitrary
text characters or key sequences in messages, because they convert
non-printing and whitespace characters to sequences of printing
characters.  The description of a non-whitespace printing character is
the character itself.

 -- Function: key-description sequence &optional prefix
     This function returns a string containing the Emacs standard
     notation for the input events in SEQUENCE.  If PREFIX is
     non-`nil', it is a sequence of input events leading up to SEQUENCE
     and is included in the return value.  Both arguments may be
     strings, vectors or lists.  *Note Input Events::, for more
     information about valid events.

          (key-description [?\M-3 delete])
               => "M-3 <delete>"
          (key-description [delete] "\M-3")
               => "M-3 <delete>"

     See also the examples for `single-key-description', below.

 -- Function: single-key-description event &optional no-angles
     This function returns a string describing EVENT in the standard
     Emacs notation for keyboard input.  A normal printing character
     appears as itself, but a control character turns into a string
     starting with `C-', a meta character turns into a string starting
     with `M-', and space, tab, etc. appear as `SPC', `TAB', etc.  A
     function key symbol appears inside angle brackets `<...>'.  An
     event that is a list appears as the name of the symbol in the CAR
     of the list, inside angle brackets.

     If the optional argument NO-ANGLES is non-`nil', the angle
     brackets around function keys and event symbols are omitted; this
     is for compatibility with old versions of Emacs which didn't use
     the brackets.

          (single-key-description ?\C-x)
               => "C-x"
          (key-description "\C-x \M-y \n \t \r \f123")
               => "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3"
          (single-key-description 'delete)
               => "<delete>"
          (single-key-description 'C-mouse-1)
               => "<C-mouse-1>"
          (single-key-description 'C-mouse-1 t)
               => "C-mouse-1"

 -- Function: text-char-description character
     This function returns a string describing CHARACTER in the
     standard Emacs notation for characters that appear in text--like
     `single-key-description', except that control characters are
     represented with a leading caret (which is how control characters
     in Emacs buffers are usually displayed).  Another difference is
     that `text-char-description' recognizes the 2**7 bit as the Meta
     character, whereas `single-key-description' uses the 2**27 bit for
     Meta.

          (text-char-description ?\C-c)
               => "^C"
          (text-char-description ?\M-m)
               => "\xed"
          (text-char-description ?\C-\M-m)
               => "\x8d"
          (text-char-description (+ 128 ?m))
               => "M-m"
          (text-char-description (+ 128 ?\C-m))
               => "M-^M"

 -- Function: read-kbd-macro string &optional need-vector
     This function is used mainly for operating on keyboard macros, but
     it can also be used as a rough inverse for `key-description'.  You
     call it with a string containing key descriptions, separated by
     spaces; it returns a string or vector containing the corresponding
     events.  (This may or may not be a single valid key sequence,
     depending on what events you use; *note Key Sequences::.)  If
     NEED-VECTOR is non-`nil', the return value is always a vector.


File: elisp,  Node: Help Functions,  Prev: Describing Characters,  Up: Documentation

24.5 Help Functions
===================

Emacs provides a variety of on-line help functions, all accessible to
the user as subcommands of the prefix `C-h'.  For more information
about them, see *Note Help: (emacs)Help.  Here we describe some
program-level interfaces to the same information.

 -- Command: apropos pattern &optional do-all
     This function finds all "meaningful" symbols whose names contain a
     match for the apropos pattern PATTERN.  An apropos pattern is
     either a word to match, a space-separated list of words of which at
     least two must match, or a regular expression (if any special
     regular expression characters occur).  A symbol is "meaningful" if
     it has a definition as a function, variable, or face, or has
     properties.

     The function returns a list of elements that look like this:

          (SYMBOL SCORE FN-DOC VAR-DOC
           PLIST-DOC WIDGET-DOC FACE-DOC GROUP-DOC)

     Here, SCORE is an integer measure of how important the symbol
     seems to be as a match, and the remaining elements are
     documentation strings for SYMBOL's various roles (or `nil').

     It also displays the symbols in a buffer named `*Apropos*', each
     with a one-line description taken from the beginning of its
     documentation string.

     If DO-ALL is non-`nil', or if the user option `apropos-do-all' is
     non-`nil', then `apropos' also shows key bindings for the
     functions that are found; it also shows _all_ interned symbols,
     not just meaningful ones (and it lists them in the return value as
     well).

 -- Variable: help-map
     The value of this variable is a local keymap for characters
     following the Help key, `C-h'.

 -- Prefix Command: help-command
     This symbol is not a function; its function definition cell holds
     the keymap known as `help-map'.  It is defined in `help.el' as
     follows:

          (define-key global-map (char-to-string help-char) 'help-command)
          (fset 'help-command help-map)

 -- Function: print-help-return-message &optional function
     This function builds a string that explains how to restore the
     previous state of the windows after a help command.  After
     building the message, it applies FUNCTION to it if FUNCTION is
     non-`nil'.  Otherwise it calls `message' to display it in the echo
     area.

     This function expects to be called inside a
     `with-output-to-temp-buffer' special form, and expects
     `standard-output' to have the value bound by that special form.
     For an example of its use, see the long example in *Note Accessing
     Documentation::.

 -- Variable: help-char
     The value of this variable is the help character--the character
     that Emacs recognizes as meaning Help.  By default, its value is
     8, which stands for `C-h'.  When Emacs reads this character, if
     `help-form' is a non-`nil' Lisp expression, it evaluates that
     expression, and displays the result in a window if it is a string.

     Usually the value of `help-form' is `nil'.  Then the help
     character has no special meaning at the level of command input, and
     it becomes part of a key sequence in the normal way.  The standard
     key binding of `C-h' is a prefix key for several general-purpose
     help features.

     The help character is special after prefix keys, too.  If it has no
     binding as a subcommand of the prefix key, it runs
     `describe-prefix-bindings', which displays a list of all the
     subcommands of the prefix key.

 -- Variable: help-event-list
     The value of this variable is a list of event types that serve as
     alternative "help characters."  These events are handled just like
     the event specified by `help-char'.

 -- Variable: help-form
     If this variable is non-`nil', its value is a form to evaluate
     whenever the character `help-char' is read.  If evaluating the form
     produces a string, that string is displayed.

     A command that calls `read-event' or `read-char' probably should
     bind `help-form' to a non-`nil' expression while it does input.
     (The time when you should not do this is when `C-h' has some other
     meaning.)  Evaluating this expression should result in a string
     that explains what the input is for and how to enter it properly.

     Entry to the minibuffer binds this variable to the value of
     `minibuffer-help-form' (*note Definition of
     minibuffer-help-form::).

 -- Variable: prefix-help-command
     This variable holds a function to print help for a prefix key.  The
     function is called when the user types a prefix key followed by
     the help character, and the help character has no binding after
     that prefix.  The variable's default value is
     `describe-prefix-bindings'.

 -- Function: describe-prefix-bindings
     This function calls `describe-bindings' to display a list of all
     the subcommands of the prefix key of the most recent key sequence.
     The prefix described consists of all but the last event of that
     key sequence.  (The last event is, presumably, the help character.)

   The following two functions are meant for modes that want to provide
help without relinquishing control, such as the "electric" modes.
Their names begin with `Helper' to distinguish them from the ordinary
help functions.

 -- Command: Helper-describe-bindings
     This command pops up a window displaying a help buffer containing a
     listing of all of the key bindings from both the local and global
     keymaps.  It works by calling `describe-bindings'.

 -- Command: Helper-help
     This command provides help for the current mode.  It prompts the
     user in the minibuffer with the message `Help (Type ? for further
     options)', and then provides assistance in finding out what the key
     bindings are, and what the mode is intended for.  It returns `nil'.

     This can be customized by changing the map `Helper-help-map'.

 -- Variable: data-directory
     This variable holds the name of the directory in which Emacs finds
     certain documentation and text files that come with Emacs.  In
     older Emacs versions, `exec-directory' was used for this.

 -- Macro: make-help-screen fname help-line help-text help-map
     This macro defines a help command named FNAME that acts like a
     prefix key that shows a list of the subcommands it offers.

     When invoked, FNAME displays HELP-TEXT in a window, then reads and
     executes a key sequence according to HELP-MAP.  The string
     HELP-TEXT should describe the bindings available in HELP-MAP.

     The command FNAME is defined to handle a few events itself, by
     scrolling the display of HELP-TEXT.  When FNAME reads one of those
     special events, it does the scrolling and then reads another
     event.  When it reads an event that is not one of those few, and
     which has a binding in HELP-MAP, it executes that key's binding and
     then returns.

     The argument HELP-LINE should be a single-line summary of the
     alternatives in HELP-MAP.  In the current version of Emacs, this
     argument is used only if you set the option `three-step-help' to
     `t'.

     This macro is used in the command `help-for-help' which is the
     binding of `C-h C-h'.

 -- User Option: three-step-help
     If this variable is non-`nil', commands defined with
     `make-help-screen' display their HELP-LINE strings in the echo
     area at first, and display the longer HELP-TEXT strings only if
     the user types the help character again.


File: elisp,  Node: Files,  Next: Backups and Auto-Saving,  Prev: Documentation,  Up: Top

25 Files
********

In Emacs, you can find, create, view, save, and otherwise work with
files and file directories.  This chapter describes most of the
file-related functions of Emacs Lisp, but a few others are described in
*Note Buffers::, and those related to backups and auto-saving are
described in *Note Backups and Auto-Saving::.

   Many of the file functions take one or more arguments that are file
names.  A file name is actually a string.  Most of these functions
expand file name arguments by calling `expand-file-name', so that `~'
is handled correctly, as are relative file names (including `../').
These functions don't recognize environment variable substitutions such
as `$HOME'.  *Note File Name Expansion::.

   When file I/O functions signal Lisp errors, they usually use the
condition `file-error' (*note Handling Errors::).  The error message is
in most cases obtained from the operating system, according to locale
`system-message-locale', and decoded using coding system
`locale-coding-system' (*note Locales::).

* Menu:

* Visiting Files::           Reading files into Emacs buffers for editing.
* Saving Buffers::           Writing changed buffers back into files.
* Reading from Files::       Reading files into buffers without visiting.
* Writing to Files::         Writing new files from parts of buffers.
* File Locks::               Locking and unlocking files, to prevent
                               simultaneous editing by two people.
* Information about Files::  Testing existence, accessibility, size of files.
* Changing Files::           Renaming files, changing protection, etc.
* File Names::               Decomposing and expanding file names.
* Contents of Directories::  Getting a list of the files in a directory.
* Create/Delete Dirs::	     Creating and Deleting Directories.
* Magic File Names::	     Defining "magic" special handling
			       for certain file names.
* Format Conversion::        Conversion to and from various file formats.


File: elisp,  Node: Visiting Files,  Next: Saving Buffers,  Up: Files

25.1 Visiting Files
===================

Visiting a file means reading a file into a buffer.  Once this is done,
we say that the buffer is "visiting" that file, and call the file "the
visited file" of the buffer.

   A file and a buffer are two different things.  A file is information
recorded permanently in the computer (unless you delete it).  A buffer,
on the other hand, is information inside of Emacs that will vanish at
the end of the editing session (or when you kill the buffer).  Usually,
a buffer contains information that you have copied from a file; then we
say the buffer is visiting that file.  The copy in the buffer is what
you modify with editing commands.  Such changes to the buffer do not
change the file; therefore, to make the changes permanent, you must
"save" the buffer, which means copying the altered buffer contents back
into the file.

   In spite of the distinction between files and buffers, people often
refer to a file when they mean a buffer and vice-versa.  Indeed, we say,
"I am editing a file," rather than, "I am editing a buffer that I will
soon save as a file of the same name."  Humans do not usually need to
make the distinction explicit.  When dealing with a computer program,
however, it is good to keep the distinction in mind.

* Menu:

* Visiting Functions::         The usual interface functions for visiting.
* Subroutines of Visiting::    Lower-level subroutines that they use.


File: elisp,  Node: Visiting Functions,  Next: Subroutines of Visiting,  Up: Visiting Files

25.1.1 Functions for Visiting Files
-----------------------------------

This section describes the functions normally used to visit files.  For
historical reasons, these functions have names starting with `find-'
rather than `visit-'.  *Note Buffer File Name::, for functions and
variables that access the visited file name of a buffer or that find an
existing buffer by its visited file name.

   In a Lisp program, if you want to look at the contents of a file but
not alter it, the fastest way is to use `insert-file-contents' in a
temporary buffer.  Visiting the file is not necessary and takes longer.
*Note Reading from Files::.

 -- Command: find-file filename &optional wildcards
     This command selects a buffer visiting the file FILENAME, using an
     existing buffer if there is one, and otherwise creating a new
     buffer and reading the file into it.  It also returns that buffer.

     Aside from some technical details, the body of the `find-file'
     function is basically equivalent to:

          (switch-to-buffer (find-file-noselect filename nil nil wildcards))

     (See `switch-to-buffer' in *Note Displaying Buffers::.)

     If WILDCARDS is non-`nil', which is always true in an interactive
     call, then `find-file' expands wildcard characters in FILENAME and
     visits all the matching files.

     When `find-file' is called interactively, it prompts for FILENAME
     in the minibuffer.

 -- Function: find-file-noselect filename &optional nowarn rawfile
          wildcards
     This function is the guts of all the file-visiting functions.  It
     returns a buffer visiting the file FILENAME.  You may make the
     buffer current or display it in a window if you wish, but this
     function does not do so.

     The function returns an existing buffer if there is one; otherwise
     it creates a new buffer and reads the file into it.  When
     `find-file-noselect' uses an existing buffer, it first verifies
     that the file has not changed since it was last visited or saved in
     that buffer.  If the file has changed, this function asks the user
     whether to reread the changed file.  If the user says `yes', any
     edits previously made in the buffer are lost.

     Reading the file involves decoding the file's contents (*note
     Coding Systems::), including end-of-line conversion, and format
     conversion (*note Format Conversion::).  If WILDCARDS is non-`nil',
     then `find-file-noselect' expands wildcard characters in FILENAME
     and visits all the matching files.

     This function displays warning or advisory messages in various
     peculiar cases, unless the optional argument NOWARN is non-`nil'.
     For example, if it needs to create a buffer, and there is no file
     named FILENAME, it displays the message `(New file)' in the echo
     area, and leaves the buffer empty.

     The `find-file-noselect' function normally calls `after-find-file'
     after reading the file (*note Subroutines of Visiting::).  That
     function sets the buffer major mode, parses local variables, warns
     the user if there exists an auto-save file more recent than the
     file just visited, and finishes by running the functions in
     `find-file-hook'.

     If the optional argument RAWFILE is non-`nil', then
     `after-find-file' is not called, and the
     `find-file-not-found-functions' are not run in case of failure.
     What's more, a non-`nil' RAWFILE value suppresses coding system
     conversion and format conversion.

     The `find-file-noselect' function usually returns the buffer that
     is visiting the file FILENAME.  But, if wildcards are actually
     used and expanded, it returns a list of buffers that are visiting
     the various files.

          (find-file-noselect "/etc/fstab")
               => #<buffer fstab>

 -- Command: find-file-other-window filename &optional wildcards
     This command selects a buffer visiting the file FILENAME, but does
     so in a window other than the selected window.  It may use another
     existing window or split a window; see *Note Displaying Buffers::.

     When this command is called interactively, it prompts for FILENAME.

 -- Command: find-file-read-only filename &optional wildcards
     This command selects a buffer visiting the file FILENAME, like
     `find-file', but it marks the buffer as read-only.  *Note Read
     Only Buffers::, for related functions and variables.

     When this command is called interactively, it prompts for FILENAME.

 -- Command: view-file filename
     This command visits FILENAME using View mode, returning to the
     previous buffer when you exit View mode.  View mode is a minor
     mode that provides commands to skim rapidly through the file, but
     does not let you modify the text.  Entering View mode runs the
     normal hook `view-mode-hook'.  *Note Hooks::.

     When `view-file' is called interactively, it prompts for FILENAME.

 -- User Option: find-file-wildcards
     If this variable is non-`nil', then the various `find-file'
     commands check for wildcard characters and visit all the files that
     match them (when invoked interactively or when their WILDCARDS
     argument is non-`nil').  If this option is `nil', then the
     `find-file' commands ignore their WILDCARDS argument and never
     treat wildcard characters specially.

 -- Variable: find-file-hook
     The value of this variable is a list of functions to be called
     after a file is visited.  The file's local-variables specification
     (if any) will have been processed before the hooks are run.  The
     buffer visiting the file is current when the hook functions are
     run.

     This variable is a normal hook.  *Note Hooks::.

 -- Variable: find-file-not-found-functions
     The value of this variable is a list of functions to be called when
     `find-file' or `find-file-noselect' is passed a nonexistent file
     name.  `find-file-noselect' calls these functions as soon as it
     detects a nonexistent file.  It calls them in the order of the
     list, until one of them returns non-`nil'.  `buffer-file-name' is
     already set up.

     This is not a normal hook because the values of the functions are
     used, and in many cases only some of the functions are called.


File: elisp,  Node: Subroutines of Visiting,  Prev: Visiting Functions,  Up: Visiting Files

25.1.2 Subroutines of Visiting
------------------------------

The `find-file-noselect' function uses two important subroutines which
are sometimes useful in user Lisp code: `create-file-buffer' and
`after-find-file'.  This section explains how to use them.

 -- Function: create-file-buffer filename
     This function creates a suitably named buffer for visiting
     FILENAME, and returns it.  It uses FILENAME (sans directory) as
     the name if that name is free; otherwise, it appends a string such
     as `<2>' to get an unused name.  See also *Note Creating Buffers::.

     *Please note:* `create-file-buffer' does _not_ associate the new
     buffer with a file and does not select the buffer.  It also does
     not use the default major mode.

          (create-file-buffer "foo")
               => #<buffer foo>
          (create-file-buffer "foo")
               => #<buffer foo<2>>
          (create-file-buffer "foo")
               => #<buffer foo<3>>

     This function is used by `find-file-noselect'.  It uses
     `generate-new-buffer' (*note Creating Buffers::).

 -- Function: after-find-file &optional error warn noauto
          after-find-file-from-revert-buffer nomodes
     This function sets the buffer major mode, and parses local
     variables (*note Auto Major Mode::).  It is called by
     `find-file-noselect' and by the default revert function (*note
     Reverting::).

     If reading the file got an error because the file does not exist,
     but its directory does exist, the caller should pass a non-`nil'
     value for ERROR.  In that case, `after-find-file' issues a warning:
     `(New file)'.  For more serious errors, the caller should usually
     not call `after-find-file'.

     If WARN is non-`nil', then this function issues a warning if an
     auto-save file exists and is more recent than the visited file.

     If NOAUTO is non-`nil', that says not to enable or disable
     Auto-Save mode.  The mode remains enabled if it was enabled before.

     If AFTER-FIND-FILE-FROM-REVERT-BUFFER is non-`nil', that means
     this call was from `revert-buffer'.  This has no direct effect,
     but some mode functions and hook functions check the value of this
     variable.

     If NOMODES is non-`nil', that means don't alter the buffer's major
     mode, don't process local variables specifications in the file,
     and don't run `find-file-hook'.  This feature is used by
     `revert-buffer' in some cases.

     The last thing `after-find-file' does is call all the functions in
     the list `find-file-hook'.


File: elisp,  Node: Saving Buffers,  Next: Reading from Files,  Prev: Visiting Files,  Up: Files

25.2 Saving Buffers
===================

When you edit a file in Emacs, you are actually working on a buffer
that is visiting that file--that is, the contents of the file are
copied into the buffer and the copy is what you edit.  Changes to the
buffer do not change the file until you "save" the buffer, which means
copying the contents of the buffer into the file.

 -- Command: save-buffer &optional backup-option
     This function saves the contents of the current buffer in its
     visited file if the buffer has been modified since it was last
     visited or saved.  Otherwise it does nothing.

     `save-buffer' is responsible for making backup files.  Normally,
     BACKUP-OPTION is `nil', and `save-buffer' makes a backup file only
     if this is the first save since visiting the file.  Other values
     for BACKUP-OPTION request the making of backup files in other
     circumstances:

        * With an argument of 4 or 64, reflecting 1 or 3 `C-u''s, the
          `save-buffer' function marks this version of the file to be
          backed up when the buffer is next saved.

        * With an argument of 16 or 64, reflecting 2 or 3 `C-u''s, the
          `save-buffer' function unconditionally backs up the previous
          version of the file before saving it.

        * With an argument of 0, unconditionally do _not_ make any
          backup file.

 -- Command: save-some-buffers &optional save-silently-p pred
     This command saves some modified file-visiting buffers.  Normally
     it asks the user about each buffer.  But if SAVE-SILENTLY-P is
     non-`nil', it saves all the file-visiting buffers without querying
     the user.

     The optional PRED argument controls which buffers to ask about (or
     to save silently if SAVE-SILENTLY-P is non-`nil').  If it is
     `nil', that means to ask only about file-visiting buffers.  If it
     is `t', that means also offer to save certain other non-file
     buffers--those that have a non-`nil' buffer-local value of
     `buffer-offer-save' (*note Killing Buffers::).  A user who says
     `yes' to saving a non-file buffer is asked to specify the file
     name to use.  The `save-buffers-kill-emacs' function passes the
     value `t' for PRED.

     If PRED is neither `t' nor `nil', then it should be a function of
     no arguments.  It will be called in each buffer to decide whether
     to offer to save that buffer.  If it returns a non-`nil' value in
     a certain buffer, that means do offer to save that buffer.

 -- Command: write-file filename &optional confirm
     This function writes the current buffer into file FILENAME, makes
     the buffer visit that file, and marks it not modified.  Then it
     renames the buffer based on FILENAME, appending a string like `<2>'
     if necessary to make a unique buffer name.  It does most of this
     work by calling `set-visited-file-name' (*note Buffer File Name::)
     and `save-buffer'.

     If CONFIRM is non-`nil', that means to ask for confirmation before
     overwriting an existing file.  Interactively, confirmation is
     required, unless the user supplies a prefix argument.

     If FILENAME is an existing directory, or a symbolic link to one,
     `write-file' uses the name of the visited file, in directory
     FILENAME.  If the buffer is not visiting a file, it uses the
     buffer name instead.

   Saving a buffer runs several hooks.  It also performs format
conversion (*note Format Conversion::), and may save text properties in
"annotations" (*note Saving Properties::).

 -- Variable: write-file-functions
     The value of this variable is a list of functions to be called
     before writing out a buffer to its visited file.  If one of them
     returns non-`nil', the file is considered already written and the
     rest of the functions are not called, nor is the usual code for
     writing the file executed.

     If a function in `write-file-functions' returns non-`nil', it is
     responsible for making a backup file (if that is appropriate).  To
     do so, execute the following code:

          (or buffer-backed-up (backup-buffer))

     You might wish to save the file modes value returned by
     `backup-buffer' and use that (if non-`nil') to set the mode bits
     of the file that you write.  This is what `save-buffer' normally
     does. *Note Making Backup Files: Making Backups.

     The hook functions in `write-file-functions' are also responsible
     for encoding the data (if desired): they must choose a suitable
     coding system and end-of-line conversion (*note Lisp and Coding
     Systems::), perform the encoding (*note Explicit Encoding::), and
     set `last-coding-system-used' to the coding system that was used
     (*note Encoding and I/O::).

     If you set this hook locally in a buffer, it is assumed to be
     associated with the file or the way the contents of the buffer were
     obtained.  Thus the variable is marked as a permanent local, so
     that changing the major mode does not alter a buffer-local value.
     On the other hand, calling `set-visited-file-name' will reset it.
     If this is not what you want, you might like to use
     `write-contents-functions' instead.

     Even though this is not a normal hook, you can use `add-hook' and
     `remove-hook' to manipulate the list.  *Note Hooks::.

 -- Variable: write-contents-functions
     This works just like `write-file-functions', but it is intended
     for hooks that pertain to the buffer's contents, not to the
     particular visited file or its location.  Such hooks are usually
     set up by major modes, as buffer-local bindings for this variable.
     This variable automatically becomes buffer-local whenever it is
     set; switching to a new major mode always resets this variable,
     but calling `set-visited-file-name' does not.

     If any of the functions in this hook returns non-`nil', the file
     is considered already written and the rest are not called and
     neither are the functions in `write-file-functions'.

 -- User Option: before-save-hook
     This normal hook runs before a buffer is saved in its visited file,
     regardless of whether that is done normally or by one of the hooks
     described above.  For instance, the `copyright.el' program uses
     this hook to make sure the file you are saving has the current
     year in its copyright notice.

 -- User Option: after-save-hook
     This normal hook runs after a buffer has been saved in its visited
     file.  One use of this hook is in Fast Lock mode; it uses this
     hook to save the highlighting information in a cache file.

 -- User Option: file-precious-flag
     If this variable is non-`nil', then `save-buffer' protects against
     I/O errors while saving by writing the new file to a temporary
     name instead of the name it is supposed to have, and then renaming
     it to the intended name after it is clear there are no errors.
     This procedure prevents problems such as a lack of disk space from
     resulting in an invalid file.

     As a side effect, backups are necessarily made by copying.  *Note
     Rename or Copy::.  Yet, at the same time, saving a precious file
     always breaks all hard links between the file you save and other
     file names.

     Some modes give this variable a non-`nil' buffer-local value in
     particular buffers.

 -- User Option: require-final-newline
     This variable determines whether files may be written out that do
     _not_ end with a newline.  If the value of the variable is `t',
     then `save-buffer' silently adds a newline at the end of the file
     whenever the buffer being saved does not already end in one.  If
     the value of the variable is non-`nil', but not `t', then
     `save-buffer' asks the user whether to add a newline each time the
     case arises.

     If the value of the variable is `nil', then `save-buffer' doesn't
     add newlines at all.  `nil' is the default value, but a few major
     modes set it to `t' in particular buffers.

   See also the function `set-visited-file-name' (*note Buffer File
Name::).


File: elisp,  Node: Reading from Files,  Next: Writing to Files,  Prev: Saving Buffers,  Up: Files

25.3 Reading from Files
=======================

You can copy a file from the disk and insert it into a buffer using the
`insert-file-contents' function.  Don't use the user-level command
`insert-file' in a Lisp program, as that sets the mark.

 -- Function: insert-file-contents filename &optional visit beg end
          replace
     This function inserts the contents of file FILENAME into the
     current buffer after point.  It returns a list of the absolute
     file name and the length of the data inserted.  An error is
     signaled if FILENAME is not the name of a file that can be read.

     The function `insert-file-contents' checks the file contents
     against the defined file formats, and converts the file contents if
     appropriate.  *Note Format Conversion::.  It also calls the
     functions in the list `after-insert-file-functions'; see *Note
     Saving Properties::.  Normally, one of the functions in the
     `after-insert-file-functions' list determines the coding system
     (*note Coding Systems::) used for decoding the file's contents,
     including end-of-line conversion.

     If VISIT is non-`nil', this function additionally marks the buffer
     as unmodified and sets up various fields in the buffer so that it
     is visiting the file FILENAME: these include the buffer's visited
     file name and its last save file modtime.  This feature is used by
     `find-file-noselect' and you probably should not use it yourself.

     If BEG and END are non-`nil', they should be integers specifying
     the portion of the file to insert.  In this case, VISIT must be
     `nil'.  For example,

          (insert-file-contents filename nil 0 500)

     inserts the first 500 characters of a file.

     If the argument REPLACE is non-`nil', it means to replace the
     contents of the buffer (actually, just the accessible portion)
     with the contents of the file.  This is better than simply
     deleting the buffer contents and inserting the whole file, because
     (1) it preserves some marker positions and (2) it puts less data
     in the undo list.

     It is possible to read a special file (such as a FIFO or an I/O
     device) with `insert-file-contents', as long as REPLACE and VISIT
     are `nil'.

 -- Function: insert-file-contents-literally filename &optional visit
          beg end replace
     This function works like `insert-file-contents' except that it does
     not do format decoding (*note Format Conversion::), does not do
     character code conversion (*note Coding Systems::), does not run
     `find-file-hook', does not perform automatic uncompression, and so
     on.

   If you want to pass a file name to another process so that another
program can read the file, use the function `file-local-copy'; see
*Note Magic File Names::.


File: elisp,  Node: Writing to Files,  Next: File Locks,  Prev: Reading from Files,  Up: Files

25.4 Writing to Files
=====================

You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the `append-to-file' and `write-region'
functions.  Don't use these functions to write to files that are being
visited; that could cause confusion in the mechanisms for visiting.

 -- Command: append-to-file start end filename
     This function appends the contents of the region delimited by
     START and END in the current buffer to the end of file FILENAME.
     If that file does not exist, it is created.  This function returns
     `nil'.

     An error is signaled if FILENAME specifies a nonwritable file, or
     a nonexistent file in a directory where files cannot be created.

     When called from Lisp, this function is completely equivalent to:

          (write-region start end filename t)

 -- Command: write-region start end filename &optional append visit
          lockname mustbenew
     This function writes the region delimited by START and END in the
     current buffer into the file specified by FILENAME.

     If START is `nil', then the command writes the entire buffer
     contents (_not_ just the accessible portion) to the file and
     ignores END.

     If START is a string, then `write-region' writes or appends that
     string, rather than text from the buffer.  END is ignored in this
     case.

     If APPEND is non-`nil', then the specified text is appended to the
     existing file contents (if any).  If APPEND is an integer,
     `write-region' seeks to that byte offset from the start of the
     file and writes the data from there.

     If MUSTBENEW is non-`nil', then `write-region' asks for
     confirmation if FILENAME names an existing file.  If MUSTBENEW is
     the symbol `excl', then `write-region' does not ask for
     confirmation, but instead it signals an error
     `file-already-exists' if the file already exists.

     The test for an existing file, when MUSTBENEW is `excl', uses a
     special system feature.  At least for files on a local disk, there
     is no chance that some other program could create a file of the
     same name before Emacs does, without Emacs's noticing.

     If VISIT is `t', then Emacs establishes an association between the
     buffer and the file: the buffer is then visiting that file.  It
     also sets the last file modification time for the current buffer to
     FILENAME's modtime, and marks the buffer as not modified.  This
     feature is used by `save-buffer', but you probably should not use
     it yourself.

     If VISIT is a string, it specifies the file name to visit.  This
     way, you can write the data to one file (FILENAME) while recording
     the buffer as visiting another file (VISIT).  The argument VISIT
     is used in the echo area message and also for file locking; VISIT
     is stored in `buffer-file-name'.  This feature is used to
     implement `file-precious-flag'; don't use it yourself unless you
     really know what you're doing.

     The optional argument LOCKNAME, if non-`nil', specifies the file
     name to use for purposes of locking and unlocking, overriding
     FILENAME and VISIT for that purpose.

     The function `write-region' converts the data which it writes to
     the appropriate file formats specified by `buffer-file-format'.
     *Note Format Conversion::.  It also calls the functions in the list
     `write-region-annotate-functions'; see *Note Saving Properties::.

     Normally, `write-region' displays the message `Wrote FILENAME' in
     the echo area.  If VISIT is neither `t' nor `nil' nor a string,
     then this message is inhibited.  This feature is useful for
     programs that use files for internal purposes, files that the user
     does not need to know about.

 -- Macro: with-temp-file file body...
     The `with-temp-file' macro evaluates the BODY forms with a
     temporary buffer as the current buffer; then, at the end, it
     writes the buffer contents into file FILE.  It kills the temporary
     buffer when finished, restoring the buffer that was current before
     the `with-temp-file' form.  Then it returns the value of the last
     form in BODY.

     The current buffer is restored even in case of an abnormal exit via
     `throw' or error (*note Nonlocal Exits::).

     See also `with-temp-buffer' in *Note The Current Buffer:
     Definition of with-temp-buffer.


File: elisp,  Node: File Locks,  Next: Information about Files,  Prev: Writing to Files,  Up: Files

25.5 File Locks
===============

When two users edit the same file at the same time, they are likely to
interfere with each other.  Emacs tries to prevent this situation from
arising by recording a "file lock" when a file is being modified.
(File locks are not implemented on Microsoft systems.)  Emacs can then
detect the first attempt to modify a buffer visiting a file that is
locked by another Emacs job, and ask the user what to do.  The file
lock is really a file, a symbolic link with a special name, stored in
the same directory as the file you are editing.

   When you access files using NFS, there may be a small probability
that you and another user will both lock the same file "simultaneously."
If this happens, it is possible for the two users to make changes
simultaneously, but Emacs will still warn the user who saves second.
Also, the detection of modification of a buffer visiting a file changed
on disk catches some cases of simultaneous editing; see *Note
Modification Time::.

 -- Function: file-locked-p filename
     This function returns `nil' if the file FILENAME is not locked.
     It returns `t' if it is locked by this Emacs process, and it
     returns the name of the user who has locked it if it is locked by
     some other job.

          (file-locked-p "foo")
               => nil

 -- Function: lock-buffer &optional filename
     This function locks the file FILENAME, if the current buffer is
     modified.  The argument FILENAME defaults to the current buffer's
     visited file.  Nothing is done if the current buffer is not
     visiting a file, or is not modified, or if the system does not
     support locking.

 -- Function: unlock-buffer
     This function unlocks the file being visited in the current buffer,
     if the buffer is modified.  If the buffer is not modified, then
     the file should not be locked, so this function does nothing.  It
     also does nothing if the current buffer is not visiting a file, or
     if the system does not support locking.

   File locking is not supported on some systems.  On systems that do
not support it, the functions `lock-buffer', `unlock-buffer' and
`file-locked-p' do nothing and return `nil'.

 -- Function: ask-user-about-lock file other-user
     This function is called when the user tries to modify FILE, but it
     is locked by another user named OTHER-USER.  The default
     definition of this function asks the user to say what to do.  The
     value this function returns determines what Emacs does next:

        * A value of `t' says to grab the lock on the file.  Then this
          user may edit the file and OTHER-USER loses the lock.

        * A value of `nil' says to ignore the lock and let this user
          edit the file anyway.

        * This function may instead signal a `file-locked' error, in
          which case the change that the user was about to make does
          not take place.

          The error message for this error looks like this:

               error--> File is locked: FILE OTHER-USER

          where `file' is the name of the file and OTHER-USER is the
          name of the user who has locked the file.

     If you wish, you can replace the `ask-user-about-lock' function
     with your own version that makes the decision in another way.  The
     code for its usual definition is in `userlock.el'.


File: elisp,  Node: Information about Files,  Next: Changing Files,  Prev: File Locks,  Up: Files

25.6 Information about Files
============================

The functions described in this section all operate on strings that
designate file names.  With a few exceptions, all the functions have
names that begin with the word `file'.  These functions all return
information about actual files or directories, so their arguments must
all exist as actual files or directories unless otherwise noted.

* Menu:

* Testing Accessibility::   Is a given file readable?  Writable?
* Kinds of Files::          Is it a directory?  A symbolic link?
* Truenames::		    Eliminating symbolic links from a file name.
* File Attributes::         How large is it?  Any other names?  Etc.
* Locating Files::          How to find a file in standard places.


File: elisp,  Node: Testing Accessibility,  Next: Kinds of Files,  Up: Information about Files

25.6.1 Testing Accessibility
----------------------------

These functions test for permission to access a file in specific ways.
Unless explicitly stated otherwise, they recursively follow symbolic
links for their file name arguments, at all levels (at the level of the
file itself and at all levels of parent directories).

 -- Function: file-exists-p filename
     This function returns `t' if a file named FILENAME appears to
     exist.  This does not mean you can necessarily read the file, only
     that you can find out its attributes.  (On Unix and GNU/Linux,
     this is true if the file exists and you have execute permission on
     the containing directories, regardless of the protection of the
     file itself.)

     If the file does not exist, or if fascist access control policies
     prevent you from finding the attributes of the file, this function
     returns `nil'.

     Directories are files, so `file-exists-p' returns `t' when given a
     directory name.  However, symbolic links are treated specially;
     `file-exists-p' returns `t' for a symbolic link name only if the
     target file exists.

 -- Function: file-readable-p filename
     This function returns `t' if a file named FILENAME exists and you
     can read it.  It returns `nil' otherwise.

          (file-readable-p "files.texi")
               => t
          (file-exists-p "/usr/spool/mqueue")
               => t
          (file-readable-p "/usr/spool/mqueue")
               => nil

 -- Function: file-executable-p filename
     This function returns `t' if a file named FILENAME exists and you
     can execute it.  It returns `nil' otherwise.  On Unix and
     GNU/Linux, if the file is a directory, execute permission means
     you can check the existence and attributes of files inside the
     directory, and open those files if their modes permit.

 -- Function: file-writable-p filename
     This function returns `t' if the file FILENAME can be written or
     created by you, and `nil' otherwise.  A file is writable if the
     file exists and you can write it.  It is creatable if it does not
     exist, but the specified directory does exist and you can write in
     that directory.

     In the third example below, `foo' is not writable because the
     parent directory does not exist, even though the user could create
     such a directory.

          (file-writable-p "~/foo")
               => t
          (file-writable-p "/foo")
               => nil
          (file-writable-p "~/no-such-dir/foo")
               => nil

 -- Function: file-accessible-directory-p dirname
     This function returns `t' if you have permission to open existing
     files in the directory whose name as a file is DIRNAME; otherwise
     (or if there is no such directory), it returns `nil'.  The value
     of DIRNAME may be either a directory name (such as `/foo/') or the
     file name of a file which is a directory (such as `/foo', without
     the final slash).

     Example: after the following,

          (file-accessible-directory-p "/foo")
               => nil

     we can deduce that any attempt to read a file in `/foo/' will give
     an error.

 -- Function: access-file filename string
     This function opens file FILENAME for reading, then closes it and
     returns `nil'.  However, if the open fails, it signals an error
     using STRING as the error message text.

 -- Function: file-ownership-preserved-p filename
     This function returns `t' if deleting the file FILENAME and then
     creating it anew would keep the file's owner unchanged.  It also
     returns `t' for nonexistent files.

     If FILENAME is a symbolic link, then, unlike the other functions
     discussed here, `file-ownership-preserved-p' does _not_ replace
     FILENAME with its target.  However, it does recursively follow
     symbolic links at all levels of parent directories.

 -- Function: file-newer-than-file-p filename1 filename2
     This function returns `t' if the file FILENAME1 is newer than file
     FILENAME2.  If FILENAME1 does not exist, it returns `nil'.  If
     FILENAME1 does exist, but FILENAME2 does not, it returns `t'.

     In the following example, assume that the file `aug-19' was written
     on the 19th, `aug-20' was written on the 20th, and the file
     `no-file' doesn't exist at all.

          (file-newer-than-file-p "aug-19" "aug-20")
               => nil
          (file-newer-than-file-p "aug-20" "aug-19")
               => t
          (file-newer-than-file-p "aug-19" "no-file")
               => t
          (file-newer-than-file-p "no-file" "aug-19")
               => nil

     You can use `file-attributes' to get a file's last modification
     time as a list of two numbers.  *Note File Attributes::.


File: elisp,  Node: Kinds of Files,  Next: Truenames,  Prev: Testing Accessibility,  Up: Information about Files

25.6.2 Distinguishing Kinds of Files
------------------------------------

This section describes how to distinguish various kinds of files, such
as directories, symbolic links, and ordinary files.

 -- Function: file-symlink-p filename
     If the file FILENAME is a symbolic link, the `file-symlink-p'
     function returns the (non-recursive) link target as a string.
     (Determining the file name that the link points to from the target
     is nontrivial.)  First, this function recursively follows symbolic
     links at all levels of parent directories.

     If the file FILENAME is not a symbolic link (or there is no such
     file), `file-symlink-p' returns `nil'.

          (file-symlink-p "foo")
               => nil
          (file-symlink-p "sym-link")
               => "foo"
          (file-symlink-p "sym-link2")
               => "sym-link"
          (file-symlink-p "/bin")
               => "/pub/bin"


   The next two functions recursively follow symbolic links at all
levels for FILENAME.

 -- Function: file-directory-p filename
     This function returns `t' if FILENAME is the name of an existing
     directory, `nil' otherwise.

          (file-directory-p "~rms")
               => t
          (file-directory-p "~rms/lewis/files.texi")
               => nil
          (file-directory-p "~rms/lewis/no-such-file")
               => nil
          (file-directory-p "$HOME")
               => nil
          (file-directory-p
           (substitute-in-file-name "$HOME"))
               => t

 -- Function: file-regular-p filename
     This function returns `t' if the file FILENAME exists and is a
     regular file (not a directory, named pipe, terminal, or other I/O
     device).


File: elisp,  Node: Truenames,  Next: File Attributes,  Prev: Kinds of Files,  Up: Information about Files

25.6.3 Truenames
----------------

The "truename" of a file is the name that you get by following symbolic
links at all levels until none remain, then simplifying away `.' and
`..' appearing as name components.  This results in a sort of canonical
name for the file.  A file does not always have a unique truename; the
number of distinct truenames a file has is equal to the number of hard
links to the file.  However, truenames are useful because they
eliminate symbolic links as a cause of name variation.

 -- Function: file-truename filename
     The function `file-truename' returns the truename of the file
     FILENAME.  The argument must be an absolute file name.

     This function does not expand environment variables.  Only
     `substitute-in-file-name' does that.  *Note Definition of
     substitute-in-file-name::.

     If you may need to follow symbolic links preceding `..' appearing
     as a name component, you should make sure to call `file-truename'
     without prior direct or indirect calls to `expand-file-name', as
     otherwise the file name component immediately preceding `..' will
     be "simplified away" before `file-truename' is called.  To
     eliminate the need for a call to `expand-file-name',
     `file-truename' handles `~' in the same way that
     `expand-file-name' does.  *Note Functions that Expand Filenames:
     File Name Expansion.

 -- Function: file-chase-links filename &optional limit
     This function follows symbolic links, starting with FILENAME,
     until it finds a file name which is not the name of a symbolic
     link.  Then it returns that file name.  This function does _not_
     follow symbolic links at the level of parent directories.

     If you specify a number for LIMIT, then after chasing through that
     many links, the function just returns what it has even if that is
     still a symbolic link.

   To illustrate the difference between `file-chase-links' and
`file-truename', suppose that `/usr/foo' is a symbolic link to the
directory `/home/foo', and `/home/foo/hello' is an ordinary file (or at
least, not a symbolic link) or nonexistent.  Then we would have:

     (file-chase-links "/usr/foo/hello")
          ;; This does not follow the links in the parent directories.
          => "/usr/foo/hello"
     (file-truename "/usr/foo/hello")
          ;; Assuming that `/home' is not a symbolic link.
          => "/home/foo/hello"

   *Note Buffer File Name::, for related information.


File: elisp,  Node: File Attributes,  Next: Locating Files,  Prev: Truenames,  Up: Information about Files

25.6.4 Other Information about Files
------------------------------------

This section describes the functions for getting detailed information
about a file, other than its contents.  This information includes the
mode bits that control access permission, the owner and group numbers,
the number of names, the inode number, the size, and the times of access
and modification.

 -- Function: file-modes filename
     This function returns the mode bits of FILENAME, as an integer.
     The mode bits are also called the file permissions, and they
     specify access control in the usual Unix fashion.  If the
     low-order bit is 1, then the file is executable by all users, if
     the second-lowest-order bit is 1, then the file is writable by all
     users, etc.

     The highest value returnable is 4095 (7777 octal), meaning that
     everyone has read, write, and execute permission, that the SUID bit
     is set for both others and group, and that the sticky bit is set.

     If FILENAME does not exist, `file-modes' returns `nil'.

     This function recursively follows symbolic links at all levels.

          (file-modes "~/junk/diffs")
               => 492               ; Decimal integer.
          (format "%o" 492)
               => "754"             ; Convert to octal.

          (set-file-modes "~/junk/diffs" 438)
               => nil

          (format "%o" 438)
               => "666"             ; Convert to octal.

          % ls -l diffs
            -rw-rw-rw-  1 lewis 0 3063 Oct 30 16:00 diffs

   If the FILENAME argument to the next two functions is a symbolic
link, then these function do _not_ replace it with its target.
However, they both recursively follow symbolic links at all levels of
parent directories.

 -- Function: file-nlinks filename
     This functions returns the number of names (i.e., hard links) that
     file FILENAME has.  If the file does not exist, then this function
     returns `nil'.  Note that symbolic links have no effect on this
     function, because they are not considered to be names of the files
     they link to.

          % ls -l foo*
          -rw-rw-rw-  2 rms       4 Aug 19 01:27 foo
          -rw-rw-rw-  2 rms       4 Aug 19 01:27 foo1

          (file-nlinks "foo")
               => 2
          (file-nlinks "doesnt-exist")
               => nil

 -- Function: file-attributes filename &optional id-format
     This function returns a list of attributes of file FILENAME.  If
     the specified file cannot be opened, it returns `nil'.  The
     optional parameter ID-FORMAT specifies the preferred format of
     attributes UID and GID (see below)--the valid values are `'string'
     and `'integer'.  The latter is the default, but we plan to change
     that, so you should specify a non-`nil' value for ID-FORMAT if you
     use the returned UID or GID.

     The elements of the list, in order, are:

       0. `t' for a directory, a string for a symbolic link (the name
          linked to), or `nil' for a text file.

       1. The number of names the file has.  Alternate names, also
          known as hard links, can be created by using the
          `add-name-to-file' function (*note Changing Files::).

       2. The file's UID, normally as a string.  However, if it does
          not correspond to a named user, the value is an integer or a
          floating point number.

       3. The file's GID, likewise.

       4. The time of last access, as a list of two integers.  The
          first integer has the high-order 16 bits of time, the second
          has the low 16 bits.  (This is similar to the value of
          `current-time'; see *Note Time of Day::.)

       5. The time of last modification as a list of two integers (as
          above).  

       6. The time of last status change as a list of two integers (as
          above).

       7. The size of the file in bytes.  If the size is too large to
          fit in a Lisp integer, this is a floating point number.

       8. The file's modes, as a string of ten letters or dashes, as in
          `ls -l'.

       9. `t' if the file's GID would change if file were deleted and
          recreated; `nil' otherwise.

      10. The file's inode number.  If possible, this is an integer.
          If the inode number is too large to be represented as an
          integer in Emacs Lisp, then the value has the form `(HIGH .
          LOW)', where LOW holds the low 16 bits.

      11. The file system number of the file system that the file is in.
          Depending on the magnitude of the value, this can be either
          an integer or a cons cell, in the same manner as the inode
          number.  This element and the file's inode number together
          give enough information to distinguish any two files on the
          system--no two files can have the same values for both of
          these numbers.

     For example, here are the file attributes for `files.texi':

          (file-attributes "files.texi" 'string)
               =>  (nil 1 "lh" "users"
                    (8489 20284)
                    (8489 20284)
                    (8489 20285)
                    14906 "-rw-rw-rw-"
                    nil 129500 -32252)

     and here is how the result is interpreted:

    `nil'
          is neither a directory nor a symbolic link.

    `1'
          has only one name (the name `files.texi' in the current
          default directory).

    `"lh"'
          is owned by the user with name "lh".

    `"users"'
          is in the group with name "users".

    `(8489 20284)'
          was last accessed on Aug 19 00:09.

    `(8489 20284)'
          was last modified on Aug 19 00:09.

    `(8489 20285)'
          last had its inode changed on Aug 19 00:09.

    `14906'
          is 14906 bytes long.  (It may not contain 14906 characters,
          though, if some of the bytes belong to multibyte sequences.)

    `"-rw-rw-rw-"'
          has a mode of read and write access for the owner, group, and
          world.

    `nil'
          would retain the same GID if it were recreated.

    `129500'
          has an inode number of 129500.

    `-32252'
          is on file system number -32252.


File: elisp,  Node: Locating Files,  Prev: File Attributes,  Up: Information about Files

25.6.5 How to Locate Files in Standard Places
---------------------------------------------

This section explains how to search for a file in a list of directories
(a "path").  One example is when you need to look for a program's
executable file, e.g., to find out whether a given program is installed
on the user's system.  Another example is the search for Lisp libraries
(*note Library Search::).  Such searches generally need to try various
possible file name extensions, in addition to various possible
directories.  Emacs provides a function for such a generalized search
for a file.

 -- Function: locate-file filename path &optional suffixes predicate
     This function searches for a file whose name is FILENAME in a list
     of directories given by PATH, trying the suffixes in SUFFIXES.  If
     it finds such a file, it returns the full "absolute file name" of
     the file (*note Relative File Names::); otherwise it returns `nil'.

     The optional argument SUFFIXES gives the list of file-name
     suffixes to append to FILENAME when searching.  `locate-file'
     tries each possible directory with each of these suffixes.  If
     SUFFIXES is `nil', or `("")', then there are no suffixes, and
     FILENAME is used only as-is.  Typical values of SUFFIXES are
     `exec-suffixes' (*note exec-suffixes: Subprocess Creation.),
     `load-suffixes', `load-file-rep-suffixes' and the return value of
     the function `get-load-suffixes' (*note Load Suffixes::).

     Typical values for PATH are `exec-path' (*note exec-path:
     Subprocess Creation.) when looking for executable programs or
     `load-path' (*note load-path: Library Search.) when looking for
     Lisp files.  If FILENAME is absolute, PATH has no effect, but the
     suffixes in SUFFIXES are still tried.

     The optional argument PREDICATE, if non-`nil', specifies the
     predicate function to use for testing whether a candidate file is
     suitable.  The predicate function is passed the candidate file
     name as its single argument.  If PREDICATE is `nil' or unspecified,
     `locate-file' uses `file-readable-p' as the default predicate.
     Useful non-default predicates include `file-executable-p',
     `file-directory-p', and other predicates described in *Note Kinds
     of Files::.

     For compatibility, PREDICATE can also be one of the symbols
     `executable', `readable', `writable', `exists', or a list of one
     or more of these symbols.

 -- Function: executable-find program
     This function searches for the executable file of the named
     PROGRAM and returns the full absolute name of the executable,
     including its file-name extensions, if any.  It returns `nil' if
     the file is not found.  The functions searches in all the
     directories in `exec-path' and tries all the file-name extensions
     in `exec-suffixes'.


File: elisp,  Node: Changing Files,  Next: File Names,  Prev: Information about Files,  Up: Files

25.7 Changing File Names and Attributes
=======================================

The functions in this section rename, copy, delete, link, and set the
modes of files.

   In the functions that have an argument NEWNAME, if a file by the
name of NEWNAME already exists, the actions taken depend on the value
of the argument OK-IF-ALREADY-EXISTS:

   * Signal a `file-already-exists' error if OK-IF-ALREADY-EXISTS is
     `nil'.

   * Request confirmation if OK-IF-ALREADY-EXISTS is a number.

   * Replace the old file without confirmation if OK-IF-ALREADY-EXISTS
     is any other value.

   The next four commands all recursively follow symbolic links at all
levels of parent directories for their first argument, but, if that
argument is itself a symbolic link, then only `copy-file' replaces it
with its (recursive) target.

 -- Command: add-name-to-file oldname newname &optional
          ok-if-already-exists
     This function gives the file named OLDNAME the additional name
     NEWNAME.  This means that NEWNAME becomes a new "hard link" to
     OLDNAME.

     In the first part of the following example, we list two files,
     `foo' and `foo3'.

          % ls -li fo*
          81908 -rw-rw-rw-  1 rms       29 Aug 18 20:32 foo
          84302 -rw-rw-rw-  1 rms       24 Aug 18 20:31 foo3

     Now we create a hard link, by calling `add-name-to-file', then list
     the files again.  This shows two names for one file, `foo' and
     `foo2'.

          (add-name-to-file "foo" "foo2")
               => nil

          % ls -li fo*
          81908 -rw-rw-rw-  2 rms       29 Aug 18 20:32 foo
          81908 -rw-rw-rw-  2 rms       29 Aug 18 20:32 foo2
          84302 -rw-rw-rw-  1 rms       24 Aug 18 20:31 foo3

     Finally, we evaluate the following:

          (add-name-to-file "foo" "foo3" t)

     and list the files again.  Now there are three names for one file:
     `foo', `foo2', and `foo3'.  The old contents of `foo3' are lost.

          (add-name-to-file "foo1" "foo3")
               => nil

          % ls -li fo*
          81908 -rw-rw-rw-  3 rms       29 Aug 18 20:32 foo
          81908 -rw-rw-rw-  3 rms       29 Aug 18 20:32 foo2
          81908 -rw-rw-rw-  3 rms       29 Aug 18 20:32 foo3

     This function is meaningless on operating systems where multiple
     names for one file are not allowed.  Some systems implement
     multiple names by copying the file instead.

     See also `file-nlinks' in *Note File Attributes::.

 -- Command: rename-file filename newname &optional ok-if-already-exists
     This command renames the file FILENAME as NEWNAME.

     If FILENAME has additional names aside from FILENAME, it continues
     to have those names.  In fact, adding the name NEWNAME with
     `add-name-to-file' and then deleting FILENAME has the same effect
     as renaming, aside from momentary intermediate states.

 -- Command: copy-file oldname newname &optional ok-if-exists time
          preserve-uid-gid
     This command copies the file OLDNAME to NEWNAME.  An error is
     signaled if OLDNAME does not exist.  If NEWNAME names a directory,
     it copies OLDNAME into that directory, preserving its final name
     component.

     If TIME is non-`nil', then this function gives the new file the
     same last-modified time that the old one has.  (This works on only
     some operating systems.)  If setting the time gets an error,
     `copy-file' signals a `file-date-error' error.  In an interactive
     call, a prefix argument specifies a non-`nil' value for TIME.

     This function copies the file modes, too.

     If argument PRESERVE-UID-GID is `nil', we let the operating system
     decide the user and group ownership of the new file (this is
     usually set to the user running Emacs).  If PRESERVE-UID-GID is
     non-`nil', we attempt to copy the user and group ownership of the
     file.  This works only on some operating systems, and only if you
     have the correct permissions to do so.

 -- Command: make-symbolic-link filename newname &optional ok-if-exists
     This command makes a symbolic link to FILENAME, named NEWNAME.
     This is like the shell command `ln -s FILENAME NEWNAME'.

     This function is not available on systems that don't support
     symbolic links.

 -- Command: delete-file filename
     This command deletes the file FILENAME, like the shell command `rm
     FILENAME'.  If the file has multiple names, it continues to exist
     under the other names.

     A suitable kind of `file-error' error is signaled if the file does
     not exist, or is not deletable.  (On Unix and GNU/Linux, a file is
     deletable if its directory is writable.)

     If FILENAME is a symbolic link, `delete-file' does not replace it
     with its target, but it does follow symbolic links at all levels
     of parent directories.

     See also `delete-directory' in *Note Create/Delete Dirs::.

 -- Function: define-logical-name varname string
     This function defines the logical name VARNAME to have the value
     STRING.  It is available only on VMS.

 -- Function: set-file-modes filename mode
     This function sets mode bits of FILENAME to MODE (which must be an
     integer).  Only the low 12 bits of MODE are used.  This function
     recursively follows symbolic links at all levels for FILENAME.

 -- Function: set-default-file-modes mode
     This function sets the default file protection for new files
     created by Emacs and its subprocesses.  Every file created with
     Emacs initially has this protection, or a subset of it
     (`write-region' will not give a file execute permission even if
     the default file protection allows execute permission).  On Unix
     and GNU/Linux, the default protection is the bitwise complement of
     the "umask" value.

     The argument MODE must be an integer.  On most systems, only the
     low 9 bits of MODE are meaningful.  You can use the Lisp construct
     for octal character codes to enter MODE; for example,

          (set-default-file-modes ?\644)

     Saving a modified version of an existing file does not count as
     creating the file; it preserves the existing file's mode, whatever
     that is.  So the default file protection has no effect.

 -- Function: default-file-modes
     This function returns the current default protection value.

 -- Function: set-file-times filename &optional time
     This function sets the access and modification times of FILENAME
     to TIME.  The return value is `t' if the times are successfully
     set, otherwise it is `nil'.  TIME defaults to the current time and
     must be in the format returned by `current-time' (*note Time of
     Day::).

   On MS-DOS, there is no such thing as an "executable" file mode bit.
So Emacs considers a file executable if its name ends in one of the
standard executable extensions, such as `.com', `.bat', `.exe', and
some others.  Files that begin with the Unix-standard `#!' signature,
such as shell and Perl scripts, are also considered as executable
files.  This is reflected in the values returned by `file-modes' and
`file-attributes'.  Directories are also reported with executable bit
set, for compatibility with Unix.


File: elisp,  Node: File Names,  Next: Contents of Directories,  Prev: Changing Files,  Up: Files

25.8 File Names
===============

Files are generally referred to by their names, in Emacs as elsewhere.
File names in Emacs are represented as strings.  The functions that
operate on a file all expect a file name argument.

   In addition to operating on files themselves, Emacs Lisp programs
often need to operate on file names; i.e., to take them apart and to use
part of a name to construct related file names.  This section describes
how to manipulate file names.

   The functions in this section do not actually access files, so they
can operate on file names that do not refer to an existing file or
directory.

   On MS-DOS and MS-Windows, these functions (like the function that
actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
where backslashes separate the components, as well as Unix syntax; but
they always return Unix syntax.  On VMS, these functions (and the ones
that operate on files) understand both VMS file-name syntax and Unix
syntax.  This enables Lisp programs to specify file names in Unix syntax
and work properly on all systems without change.

* Menu:

* File Name Components::  The directory part of a file name, and the rest.
* Relative File Names::   Some file names are relative to a current directory.
* Directory Names::       A directory's name as a directory
                            is different from its name as a file.
* File Name Expansion::   Converting relative file names to absolute ones.
* Unique File Names::     Generating names for temporary files.
* File Name Completion::  Finding the completions for a given file name.
* Standard File Names::   If your package uses a fixed file name,
                            how to handle various operating systems simply.


File: elisp,  Node: File Name Components,  Next: Relative File Names,  Up: File Names

25.8.1 File Name Components
---------------------------

The operating system groups files into directories.  To specify a file,
you must specify the directory and the file's name within that
directory.  Therefore, Emacs considers a file name as having two main
parts: the "directory name" part, and the "nondirectory" part (or "file
name within the directory").  Either part may be empty.  Concatenating
these two parts reproduces the original file name.

   On most systems, the directory part is everything up to and including
the last slash (backslash is also allowed in input on MS-DOS or
MS-Windows); the nondirectory part is the rest.  The rules in VMS syntax
are complicated.

   For some purposes, the nondirectory part is further subdivided into
the name proper and the "version number".  On most systems, only backup
files have version numbers in their names.  On VMS, every file has a
version number, but most of the time the file name actually used in
Emacs omits the version number, so that version numbers in Emacs are
found mostly in directory lists.

 -- Function: file-name-directory filename
     This function returns the directory part of FILENAME, as a
     directory name (*note Directory Names::), or `nil' if FILENAME
     does not include a directory part.

     On GNU and Unix systems, a string returned by this function always
     ends in a slash.  On MS-DOS it can also end in a colon.  On VMS, it
     returns a string ending in one of the three characters `:', `]',
     or `>'.

          (file-name-directory "lewis/foo")  ; Unix example
               => "lewis/"
          (file-name-directory "foo")        ; Unix example
               => nil
          (file-name-directory "[X]FOO.TMP") ; VMS example
               => "[X]"

 -- Function: file-name-nondirectory filename
     This function returns the nondirectory part of FILENAME.

          (file-name-nondirectory "lewis/foo")
               => "foo"
          (file-name-nondirectory "foo")
               => "foo"
          (file-name-nondirectory "lewis/")
               => ""
          ;; The following example is accurate only on VMS.
          (file-name-nondirectory "[X]FOO.TMP")
               => "FOO.TMP"

 -- Function: file-name-sans-versions filename &optional
          keep-backup-version
     This function returns FILENAME with any file version numbers,
     backup version numbers, or trailing tildes discarded.

     If KEEP-BACKUP-VERSION is non-`nil', then true file version
     numbers understood as such by the file system are discarded from
     the return value, but backup version numbers are kept.

          (file-name-sans-versions "~rms/foo.~1~")
               => "~rms/foo"
          (file-name-sans-versions "~rms/foo~")
               => "~rms/foo"
          (file-name-sans-versions "~rms/foo")
               => "~rms/foo"
          ;; The following example applies to VMS only.
          (file-name-sans-versions "foo;23")
               => "foo"

 -- Function: file-name-extension filename &optional period
     This function returns FILENAME's final "extension," if any, after
     applying `file-name-sans-versions' to remove any version/backup
     part.  The extension, in a file name, is the part that starts with
     the last `.' in the last name component (minus any version/backup
     part).

     This function returns `nil' for extensionless file names such as
     `foo'.  It returns `""' for null extensions, as in `foo.'.  If the
     last component of a file name begins with a `.', that `.'  doesn't
     count as the beginning of an extension.  Thus, `.emacs''s
     "extension" is `nil', not `.emacs'.

     If PERIOD is non-`nil', then the returned value includes the
     period that delimits the extension, and if FILENAME has no
     extension, the value is `""'.

 -- Function: file-name-sans-extension filename
     This function returns FILENAME minus its extension, if any.  The
     version/backup part, if present, is only removed if the file has an
     extension.  For example,

          (file-name-sans-extension "foo.lose.c")
               => "foo.lose"
          (file-name-sans-extension "big.hack/foo")
               => "big.hack/foo"
          (file-name-sans-extension "/my/home/.emacs")
               => "/my/home/.emacs"
          (file-name-sans-extension "/my/home/.emacs.el")
               => "/my/home/.emacs"
          (file-name-sans-extension "~/foo.el.~3~")
               => "~/foo"
          (file-name-sans-extension "~/foo.~3~")
               => "~/foo.~3~"

     Note that the `.~3~' in the two last examples is the backup part,
     not an extension.


File: elisp,  Node: Relative File Names,  Next: Directory Names,  Prev: File Name Components,  Up: File Names

25.8.2 Absolute and Relative File Names
---------------------------------------

All the directories in the file system form a tree starting at the root
directory.  A file name can specify all the directory names starting
from the root of the tree; then it is called an "absolute" file name.
Or it can specify the position of the file in the tree relative to a
default directory; then it is called a "relative" file name.  On Unix
and GNU/Linux, an absolute file name starts with a slash or a tilde
(`~'), and a relative one does not.  On MS-DOS and MS-Windows, an
absolute file name starts with a slash or a backslash, or with a drive
specification `X:/', where X is the "drive letter".  The rules on VMS
are complicated.

 -- Function: file-name-absolute-p filename
     This function returns `t' if file FILENAME is an absolute file
     name, `nil' otherwise.  On VMS, this function understands both
     Unix syntax and VMS syntax.

          (file-name-absolute-p "~rms/foo")
               => t
          (file-name-absolute-p "rms/foo")
               => nil
          (file-name-absolute-p "/user/rms/foo")
               => t

   Given a possibly relative file name, you can convert it to an
absolute name using `expand-file-name' (*note File Name Expansion::).
This function converts absolute file names to relative names:

 -- Function: file-relative-name filename &optional directory
     This function tries to return a relative name that is equivalent to
     FILENAME, assuming the result will be interpreted relative to
     DIRECTORY (an absolute directory name or directory file name).  If
     DIRECTORY is omitted or `nil', it defaults to the current buffer's
     default directory.

     On some operating systems, an absolute file name begins with a
     device name.  On such systems, FILENAME has no relative equivalent
     based on DIRECTORY if they start with two different device names.
     In this case, `file-relative-name' returns FILENAME in absolute
     form.

          (file-relative-name "/foo/bar" "/foo/")
               => "bar"
          (file-relative-name "/foo/bar" "/hack/")
               => "../foo/bar"


File: elisp,  Node: Directory Names,  Next: File Name Expansion,  Prev: Relative File Names,  Up: File Names

25.8.3 Directory Names
----------------------

A "directory name" is the name of a directory.  A directory is actually
a kind of file, so it has a file name, which is related to the
directory name but not identical to it.  (This is not quite the same as
the usual Unix terminology.)  These two different names for the same
entity are related by a syntactic transformation.  On GNU and Unix
systems, this is simple: a directory name ends in a slash, whereas the
directory's name as a file lacks that slash.  On MS-DOS and VMS, the
relationship is more complicated.

   The difference between a directory name and its name as a file is
subtle but crucial.  When an Emacs variable or function argument is
described as being a directory name, a file name of a directory is not
acceptable.  When `file-name-directory' returns a string, that is
always a directory name.

   The following two functions convert between directory names and file
names.  They do nothing special with environment variable substitutions
such as `$HOME', and the constructs `~', `.' and `..'.

 -- Function: file-name-as-directory filename
     This function returns a string representing FILENAME in a form
     that the operating system will interpret as the name of a
     directory.  On most systems, this means appending a slash to the
     string (if it does not already end in one).  On VMS, the function
     converts a string of the form `[X]Y.DIR.1' to the form `[X.Y]'.

          (file-name-as-directory "~rms/lewis")
               => "~rms/lewis/"

 -- Function: directory-file-name dirname
     This function returns a string representing DIRNAME in a form that
     the operating system will interpret as the name of a file.  On most
     systems, this means removing the final slash (or backslash) from
     the string.  On VMS, the function converts a string of the form
     `[X.Y]' to `[X]Y.DIR.1'.

          (directory-file-name "~lewis/")
               => "~lewis"

   Given a directory name, you can combine it with a relative file name
using `concat':

     (concat DIRNAME RELFILE)

Be sure to verify that the file name is relative before doing that.  If
you use an absolute file name, the results could be syntactically
invalid or refer to the wrong file.

   If you want to use a directory file name in making such a
combination, you must first convert it to a directory name using
`file-name-as-directory':

     (concat (file-name-as-directory DIRFILE) RELFILE)

Don't try concatenating a slash by hand, as in

     ;;; Wrong!
     (concat DIRFILE "/" RELFILE)

because this is not portable.  Always use `file-name-as-directory'.

   Directory name abbreviations are useful for directories that are
normally accessed through symbolic links.  Sometimes the users recognize
primarily the link's name as "the name" of the directory, and find it
annoying to see the directory's "real" name.  If you define the link
name as an abbreviation for the "real" name, Emacs shows users the
abbreviation instead.

 -- Variable: directory-abbrev-alist
     The variable `directory-abbrev-alist' contains an alist of
     abbreviations to use for file directories.  Each element has the
     form `(FROM . TO)', and says to replace FROM with TO when it
     appears in a directory name.  The FROM string is actually a
     regular expression; it should always start with `^'.  The TO
     string should be an ordinary absolute directory name.  Do not use
     `~' to stand for a home directory in that string.  The function
     `abbreviate-file-name' performs these substitutions.

     You can set this variable in `site-init.el' to describe the
     abbreviations appropriate for your site.

     Here's an example, from a system on which file system `/home/fsf'
     and so on are normally accessed through symbolic links named `/fsf'
     and so on.

          (("^/home/fsf" . "/fsf")
           ("^/home/gp" . "/gp")
           ("^/home/gd" . "/gd"))

   To convert a directory name to its abbreviation, use this function:

 -- Function: abbreviate-file-name filename
     This function applies abbreviations from `directory-abbrev-alist'
     to its argument, and substitutes `~' for the user's home
     directory.  You can use it for directory names and for file names,
     because it recognizes abbreviations even as part of the name.


File: elisp,  Node: File Name Expansion,  Next: Unique File Names,  Prev: Directory Names,  Up: File Names

25.8.4 Functions that Expand Filenames
--------------------------------------

"Expansion" of a file name means converting a relative file name to an
absolute one.  Since this is done relative to a default directory, you
must specify the default directory name as well as the file name to be
expanded.  Expansion also simplifies file names by eliminating
redundancies such as `./' and `NAME/../'.

 -- Function: expand-file-name filename &optional directory
     This function converts FILENAME to an absolute file name.  If
     DIRECTORY is supplied, it is the default directory to start with
     if FILENAME is relative.  (The value of DIRECTORY should itself be
     an absolute directory name or directory file name; it may start
     with `~'.)  Otherwise, the current buffer's value of
     `default-directory' is used.  For example:

          (expand-file-name "foo")
               => "/xcssun/users/rms/lewis/foo"
          (expand-file-name "../foo")
               => "/xcssun/users/rms/foo"
          (expand-file-name "foo" "/usr/spool/")
               => "/usr/spool/foo"
          (expand-file-name "$HOME/foo")
               => "/xcssun/users/rms/lewis/$HOME/foo"

     If the part of the combined file name before the first slash is
     `~', it expands to the value of the `HOME' environment variable
     (usually your home directory).  If the part before the first slash
     is `~USER' and if USER is a valid login name, it expands to USER's
     home directory.

     Filenames containing `.' or `..' are simplified to their canonical
     form:

          (expand-file-name "bar/../foo")
               => "/xcssun/users/rms/lewis/foo"

     In some cases, a leading `..' component can remain in the output:

          (expand-file-name "../home" "/")
               => "/../home"

     This is for the sake of filesystems that have the concept of a
     "superroot" above the root directory `/'.  On other filesystems,
     `/../' is interpreted exactly the same as `/'.

     Note that `expand-file-name' does _not_ expand environment
     variables; only `substitute-in-file-name' does that.

     Note also that `expand-file-name' does not follow symbolic links
     at any level.  This results in a difference between the way
     `file-truename' and `expand-file-name' treat `..'.  Assuming that
     `/tmp/bar' is a symbolic link to the directory `/tmp/foo/bar' we
     get:

          (file-truename "/tmp/bar/../myfile")
               => "/tmp/foo/myfile"
          (expand-file-name "/tmp/bar/../myfile")
               => "/tmp/myfile"

     If you may need to follow symbolic links preceding `..', you
     should make sure to call `file-truename' without prior direct or
     indirect calls to `expand-file-name'.  *Note Truenames::.

 -- Variable: default-directory
     The value of this buffer-local variable is the default directory
     for the current buffer.  It should be an absolute directory name;
     it may start with `~'.  This variable is buffer-local in every
     buffer.

     `expand-file-name' uses the default directory when its second
     argument is `nil'.

     Aside from VMS, the value is always a string ending with a slash.

          default-directory
               => "/user/lewis/manual/"

 -- Function: substitute-in-file-name filename
     This function replaces environment variable references in FILENAME
     with the environment variable values.  Following standard Unix
     shell syntax, `$' is the prefix to substitute an environment
     variable value.  If the input contains `$$', that is converted to
     `$'; this gives the user a way to "quote" a `$'.

     The environment variable name is the series of alphanumeric
     characters (including underscores) that follow the `$'.  If the
     character following the `$' is a `{', then the variable name is
     everything up to the matching `}'.

     Calling `substitute-in-file-name' on output produced by
     `substitute-in-file-name' tends to give incorrect results.  For
     instance, use of `$$' to quote a single `$' won't work properly,
     and `$' in an environment variable's value could lead to repeated
     substitution.  Therefore, programs that call this function and put
     the output where it will be passed to this function need to double
     all `$' characters to prevent subsequent incorrect results.

     Here we assume that the environment variable `HOME', which holds
     the user's home directory name, has value `/xcssun/users/rms'.

          (substitute-in-file-name "$HOME/foo")
               => "/xcssun/users/rms/foo"

     After substitution, if a `~' or a `/' appears immediately after
     another `/', the function discards everything before it (up
     through the immediately preceding `/').

          (substitute-in-file-name "bar/~/foo")
               => "~/foo"
          (substitute-in-file-name "/usr/local/$HOME/foo")
               => "/xcssun/users/rms/foo"
               ;; `/usr/local/' has been discarded.

     On VMS, `$' substitution is not done, so this function does nothing
     on VMS except discard superfluous initial components as shown
     above.


File: elisp,  Node: Unique File Names,  Next: File Name Completion,  Prev: File Name Expansion,  Up: File Names

25.8.5 Generating Unique File Names
-----------------------------------

Some programs need to write temporary files.  Here is the usual way to
construct a name for such a file:

     (make-temp-file NAME-OF-APPLICATION)

The job of `make-temp-file' is to prevent two different users or two
different jobs from trying to use the exact same file name.

 -- Function: make-temp-file prefix &optional dir-flag suffix
     This function creates a temporary file and returns its name.  Emacs
     creates the temporary file's name by adding to PREFIX some random
     characters that are different in each Emacs job.  The result is
     guaranteed to be a newly created empty file.  On MS-DOS, this
     function can truncate the STRING prefix to fit into the 8+3
     file-name limits.  If PREFIX is a relative file name, it is
     expanded against `temporary-file-directory'.

          (make-temp-file "foo")
               => "/tmp/foo232J6v"

     When `make-temp-file' returns, the file has been created and is
     empty.  At that point, you should write the intended contents into
     the file.

     If DIR-FLAG is non-`nil', `make-temp-file' creates an empty
     directory instead of an empty file.  It returns the file name, not
     the directory name, of that directory.  *Note Directory Names::.

     If SUFFIX is non-`nil', `make-temp-file' adds it at the end of the
     file name.

     To prevent conflicts among different libraries running in the same
     Emacs, each Lisp program that uses `make-temp-file' should have its
     own PREFIX.  The number added to the end of PREFIX distinguishes
     between the same application running in different Emacs jobs.
     Additional added characters permit a large number of distinct
     names even in one Emacs job.

   The default directory for temporary files is controlled by the
variable `temporary-file-directory'.  This variable gives the user a
uniform way to specify the directory for all temporary files.  Some
programs use `small-temporary-file-directory' instead, if that is
non-`nil'.  To use it, you should expand the prefix against the proper
directory before calling `make-temp-file'.

   In older Emacs versions where `make-temp-file' does not exist, you
should use `make-temp-name' instead:

     (make-temp-name
      (expand-file-name NAME-OF-APPLICATION
                        temporary-file-directory))

 -- Function: make-temp-name string
     This function generates a string that can be used as a unique file
     name.  The name starts with STRING, and has several random
     characters appended to it, which are different in each Emacs job.
     It is like `make-temp-file' except that it just constructs a name,
     and does not create a file.  Another difference is that STRING
     should be an absolute file name.  On MS-DOS, this function can
     truncate the STRING prefix to fit into the 8+3 file-name limits.

 -- Variable: temporary-file-directory
     This variable specifies the directory name for creating temporary
     files.  Its value should be a directory name (*note Directory
     Names::), but it is good for Lisp programs to cope if the value is
     a directory's file name instead.  Using the value as the second
     argument to `expand-file-name' is a good way to achieve that.

     The default value is determined in a reasonable way for your
     operating system; it is based on the `TMPDIR', `TMP' and `TEMP'
     environment variables, with a fall-back to a system-dependent name
     if none of these variables is defined.

     Even if you do not use `make-temp-file' to create the temporary
     file, you should still use this variable to decide which directory
     to put the file in.  However, if you expect the file to be small,
     you should use `small-temporary-file-directory' first if that is
     non-`nil'.

 -- Variable: small-temporary-file-directory
     This variable specifies the directory name for creating certain
     temporary files, which are likely to be small.

     If you want to write a temporary file which is likely to be small,
     you should compute the directory like this:

          (make-temp-file
            (expand-file-name PREFIX
                              (or small-temporary-file-directory
                                  temporary-file-directory)))


File: elisp,  Node: File Name Completion,  Next: Standard File Names,  Prev: Unique File Names,  Up: File Names

25.8.6 File Name Completion
---------------------------

This section describes low-level subroutines for completing a file
name.  For higher level functions, see *Note Reading File Names::.

 -- Function: file-name-all-completions partial-filename directory
     This function returns a list of all possible completions for a file
     whose name starts with PARTIAL-FILENAME in directory DIRECTORY.
     The order of the completions is the order of the files in the
     directory, which is unpredictable and conveys no useful
     information.

     The argument PARTIAL-FILENAME must be a file name containing no
     directory part and no slash (or backslash on some systems).  The
     current buffer's default directory is prepended to DIRECTORY, if
     DIRECTORY is not absolute.

     In the following example, suppose that `~rms/lewis' is the current
     default directory, and has five files whose names begin with `f':
     `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.

          (file-name-all-completions "f" "")
               => ("foo" "file~" "file.c.~2~"
                          "file.c.~1~" "file.c")

          (file-name-all-completions "fo" "")
               => ("foo")

 -- Function: file-name-completion filename directory &optional
          predicate
     This function completes the file name FILENAME in directory
     DIRECTORY.  It returns the longest prefix common to all file names
     in directory DIRECTORY that start with FILENAME.  If PREDICATE is
     non-`nil' then it ignores possible completions that don't satisfy
     PREDICATE, after calling that function with one argument, the
     expanded absolute file name.

     If only one match exists and FILENAME matches it exactly, the
     function returns `t'.  The function returns `nil' if directory
     DIRECTORY contains no name starting with FILENAME.

     In the following example, suppose that the current default
     directory has five files whose names begin with `f': `foo',
     `file~', `file.c', `file.c.~1~', and `file.c.~2~'.

          (file-name-completion "fi" "")
               => "file"

          (file-name-completion "file.c.~1" "")
               => "file.c.~1~"

          (file-name-completion "file.c.~1~" "")
               => t

          (file-name-completion "file.c.~3" "")
               => nil

 -- User Option: completion-ignored-extensions
     `file-name-completion' usually ignores file names that end in any
     string in this list.  It does not ignore them when all the possible
     completions end in one of these suffixes.  This variable has no
     effect on `file-name-all-completions'.

     A typical value might look like this:

          completion-ignored-extensions
               => (".o" ".elc" "~" ".dvi")

     If an element of `completion-ignored-extensions' ends in a slash
     `/', it signals a directory.  The elements which do _not_ end in a
     slash will never match a directory; thus, the above value will not
     filter out a directory named `foo.elc'.


File: elisp,  Node: Standard File Names,  Prev: File Name Completion,  Up: File Names

25.8.7 Standard File Names
--------------------------

Most of the file names used in Lisp programs are entered by the user.
But occasionally a Lisp program needs to specify a standard file name
for a particular use--typically, to hold customization information
about each user.  For example, abbrev definitions are stored (by
default) in the file `~/.abbrev_defs'; the `completion' package stores
completions in the file `~/.completions'.  These are two of the many
standard file names used by parts of Emacs for certain purposes.

   Various operating systems have their own conventions for valid file
names and for which file names to use for user profile data.  A Lisp
program which reads a file using a standard file name ought to use, on
each type of system, a file name suitable for that system.  The function
`convert-standard-filename' makes this easy to do.

 -- Function: convert-standard-filename filename
     This function alters the file name FILENAME to fit the conventions
     of the operating system in use, and returns the result as a new
     string.

   The recommended way to specify a standard file name in a Lisp program
is to choose a name which fits the conventions of GNU and Unix systems,
usually with a nondirectory part that starts with a period, and pass it
to `convert-standard-filename' instead of using it directly.  Here is
an example from the `completion' package:

     (defvar save-completions-file-name
             (convert-standard-filename "~/.completions")
       "*The file name to save completions to.")

   On GNU and Unix systems, and on some other systems as well,
`convert-standard-filename' returns its argument unchanged.  On some
other systems, it alters the name to fit the system's conventions.

   For example, on MS-DOS the alterations made by this function include
converting a leading `.'  to `_', converting a `_' in the middle of the
name to `.' if there is no other `.', inserting a `.' after eight
characters if there is none, and truncating to three characters after
the `.'.  (It makes other changes as well.)  Thus, `.abbrev_defs'
becomes `_abbrev.def', and `.completions' becomes `_complet.ion'.


File: elisp,  Node: Contents of Directories,  Next: Create/Delete Dirs,  Prev: File Names,  Up: Files

25.9 Contents of Directories
============================

A directory is a kind of file that contains other files entered under
various names.  Directories are a feature of the file system.

   Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the `ls' shell command.  In the
latter case, it can optionally display information about each file,
depending on the options passed to the `ls' command.

 -- Function: directory-files directory &optional full-name
          match-regexp nosort
     This function returns a list of the names of the files in the
     directory DIRECTORY.  By default, the list is in alphabetical
     order.

     If FULL-NAME is non-`nil', the function returns the files'
     absolute file names.  Otherwise, it returns the names relative to
     the specified directory.

     If MATCH-REGEXP is non-`nil', this function returns only those
     file names that contain a match for that regular expression--the
     other file names are excluded from the list.  On case-insensitive
     filesystems, the regular expression matching is case-insensitive.

     If NOSORT is non-`nil', `directory-files' does not sort the list,
     so you get the file names in no particular order.  Use this if you
     want the utmost possible speed and don't care what order the files
     are processed in.  If the order of processing is visible to the
     user, then the user will probably be happier if you do sort the
     names.

          (directory-files "~lewis")
               => ("#foo#" "#foo.el#" "." ".."
                   "dired-mods.el" "files.texi"
                   "files.texi.~1~")

     An error is signaled if DIRECTORY is not the name of a directory
     that can be read.

 -- Function: directory-files-and-attributes directory &optional
          full-name match-regexp nosort id-format
     This is similar to `directory-files' in deciding which files to
     report on and how to report their names.  However, instead of
     returning a list of file names, it returns for each file a list
     `(FILENAME . ATTRIBUTES)', where ATTRIBUTES is what
     `file-attributes' would return for that file.  The optional
     argument ID-FORMAT has the same meaning as the corresponding
     argument to `file-attributes' (*note Definition of
     file-attributes::).

 -- Function: file-name-all-versions file dirname
     This function returns a list of all versions of the file named
     FILE in directory DIRNAME.  It is only available on VMS.

 -- Function: file-expand-wildcards pattern &optional full
     This function expands the wildcard pattern PATTERN, returning a
     list of file names that match it.

     If PATTERN is written as an absolute file name, the values are
     absolute also.

     If PATTERN is written as a relative file name, it is interpreted
     relative to the current default directory.  The file names
     returned are normally also relative to the current default
     directory.  However, if FULL is non-`nil', they are absolute.

 -- Function: insert-directory file switches &optional wildcard
          full-directory-p
     This function inserts (in the current buffer) a directory listing
     for directory FILE, formatted with `ls' according to SWITCHES.  It
     leaves point after the inserted text.  SWITCHES may be a string of
     options, or a list of strings representing individual options.

     The argument FILE may be either a directory name or a file
     specification including wildcard characters.  If WILDCARD is
     non-`nil', that means treat FILE as a file specification with
     wildcards.

     If FULL-DIRECTORY-P is non-`nil', that means the directory listing
     is expected to show the full contents of a directory.  You should
     specify `t' when FILE is a directory and switches do not contain
     `-d'.  (The `-d' option to `ls' says to describe a directory
     itself as a file, rather than showing its contents.)

     On most systems, this function works by running a directory listing
     program whose name is in the variable `insert-directory-program'.
     If WILDCARD is non-`nil', it also runs the shell specified by
     `shell-file-name', to expand the wildcards.

     MS-DOS and MS-Windows systems usually lack the standard Unix
     program `ls', so this function emulates the standard Unix program
     `ls' with Lisp code.

     As a technical detail, when SWITCHES contains the long `--dired'
     option, `insert-directory' treats it specially, for the sake of
     dired.  However, the normally equivalent short `-D' option is just
     passed on to `insert-directory-program', as any other option.

 -- Variable: insert-directory-program
     This variable's value is the program to run to generate a
     directory listing for the function `insert-directory'.  It is
     ignored on systems which generate the listing with Lisp code.


File: elisp,  Node: Create/Delete Dirs,  Next: Magic File Names,  Prev: Contents of Directories,  Up: Files

25.10 Creating and Deleting Directories
=======================================

Most Emacs Lisp file-manipulation functions get errors when used on
files that are directories.  For example, you cannot delete a directory
with `delete-file'.  These special functions exist to create and delete
directories.

 -- Function: make-directory dirname &optional parents
     This function creates a directory named DIRNAME.  If PARENTS is
     non-`nil', as is always the case in an interactive call, that
     means to create the parent directories first, if they don't
     already exist.

 -- Function: delete-directory dirname
     This function deletes the directory named DIRNAME.  The function
     `delete-file' does not work for files that are directories; you
     must use `delete-directory' for them.  If the directory contains
     any files, `delete-directory' signals an error.

     This function only follows symbolic links at the level of parent
     directories.


File: elisp,  Node: Magic File Names,  Next: Format Conversion,  Prev: Create/Delete Dirs,  Up: Files

25.11 Making Certain File Names "Magic"
=======================================

You can implement special handling for certain file names.  This is
called making those names "magic".  The principal use for this feature
is in implementing remote file names (*note Remote Files: (emacs)Remote
Files.).

   To define a kind of magic file name, you must supply a regular
expression to define the class of names (all those that match the
regular expression), plus a handler that implements all the primitive
Emacs file operations for file names that do match.

   The variable `file-name-handler-alist' holds a list of handlers,
together with regular expressions that determine when to apply each
handler.  Each element has this form:

     (REGEXP . HANDLER)

All the Emacs primitives for file access and file name transformation
check the given file name against `file-name-handler-alist'.  If the
file name matches REGEXP, the primitives handle that file by calling
HANDLER.

   The first argument given to HANDLER is the name of the primitive, as
a symbol; the remaining arguments are the arguments that were passed to
that primitive.  (The first of these arguments is most often the file
name itself.)  For example, if you do this:

     (file-exists-p FILENAME)

and FILENAME has handler HANDLER, then HANDLER is called like this:

     (funcall HANDLER 'file-exists-p FILENAME)

   When a function takes two or more arguments that must be file names,
it checks each of those names for a handler.  For example, if you do
this:

     (expand-file-name FILENAME DIRNAME)

then it checks for a handler for FILENAME and then for a handler for
DIRNAME.  In either case, the HANDLER is called like this:

     (funcall HANDLER 'expand-file-name FILENAME DIRNAME)

The HANDLER then needs to figure out whether to handle FILENAME or
DIRNAME.

   If the specified file name matches more than one handler, the one
whose match starts last in the file name gets precedence.  This rule is
chosen so that handlers for jobs such as uncompression are handled
first, before handlers for jobs such as remote file access.

   Here are the operations that a magic file name handler gets to
handle:

`access-file', `add-name-to-file', `byte-compiler-base-file-name',
`copy-file', `delete-directory', `delete-file',
`diff-latest-backup-file', `directory-file-name', `directory-files',
`directory-files-and-attributes', `dired-call-process',
`dired-compress-file', `dired-uncache',
`expand-file-name', `file-accessible-directory-p', `file-attributes',
`file-directory-p', `file-executable-p', `file-exists-p',
`file-local-copy', `file-remote-p', `file-modes',
`file-name-all-completions', `file-name-as-directory',
`file-name-completion', `file-name-directory', `file-name-nondirectory',
`file-name-sans-versions', `file-newer-than-file-p',
`file-ownership-preserved-p', `file-readable-p', `file-regular-p',
`file-symlink-p', `file-truename', `file-writable-p',
`find-backup-file-name', `find-file-noselect',
`get-file-buffer', `insert-directory', `insert-file-contents',
`load', `make-auto-save-file-name', `make-directory',
`make-directory-internal', `make-symbolic-link',
`rename-file', `set-file-modes', `set-file-times',
`set-visited-file-modtime', `shell-command', `substitute-in-file-name',
`unhandled-file-name-directory', `vc-registered',
`verify-visited-file-modtime',
`write-region'.

   Handlers for `insert-file-contents' typically need to clear the
buffer's modified flag, with `(set-buffer-modified-p nil)', if the
VISIT argument is non-`nil'.  This also has the effect of unlocking the
buffer if it is locked.

   The handler function must handle all of the above operations, and
possibly others to be added in the future.  It need not implement all
these operations itself--when it has nothing special to do for a
certain operation, it can reinvoke the primitive, to handle the
operation "in the usual way."  It should always reinvoke the primitive
for an operation it does not recognize.  Here's one way to do this:

     (defun my-file-handler (operation &rest args)
       ;; First check for the specific operations
       ;; that we have special handling for.
       (cond ((eq operation 'insert-file-contents) ...)
             ((eq operation 'write-region) ...)
             ...
             ;; Handle any operation we don't know about.
             (t (let ((inhibit-file-name-handlers
                       (cons 'my-file-handler
                             (and (eq inhibit-file-name-operation operation)
                                  inhibit-file-name-handlers)))
                      (inhibit-file-name-operation operation))
                  (apply operation args)))))

   When a handler function decides to call the ordinary Emacs primitive
for the operation at hand, it needs to prevent the primitive from
calling the same handler once again, thus leading to an infinite
recursion.  The example above shows how to do this, with the variables
`inhibit-file-name-handlers' and `inhibit-file-name-operation'.  Be
careful to use them exactly as shown above; the details are crucial for
proper behavior in the case of multiple handlers, and for operations
that have two file names that may each have handlers.

   Handlers that don't really do anything special for actual access to
the file--such as the ones that implement completion of host names for
remote file names--should have a non-`nil' `safe-magic' property.  For
instance, Emacs normally "protects" directory names it finds in `PATH'
from becoming magic, if they look like magic file names, by prefixing
them with `/:'.  But if the handler that would be used for them has a
non-`nil' `safe-magic' property, the `/:' is not added.

   A file name handler can have an `operations' property to declare
which operations it handles in a nontrivial way.  If this property has
a non-`nil' value, it should be a list of operations; then only those
operations will call the handler.  This avoids inefficiency, but its
main purpose is for autoloaded handler functions, so that they won't be
loaded except when they have real work to do.

   Simply deferring all operations to the usual primitives does not
work.  For instance, if the file name handler applies to
`file-exists-p', then it must handle `load' itself, because the usual
`load' code won't work properly in that case.  However, if the handler
uses the `operations' property to say it doesn't handle
`file-exists-p', then it need not handle `load' nontrivially.

 -- Variable: inhibit-file-name-handlers
     This variable holds a list of handlers whose use is presently
     inhibited for a certain operation.

 -- Variable: inhibit-file-name-operation
     The operation for which certain handlers are presently inhibited.

 -- Function: find-file-name-handler file operation
     This function returns the handler function for file name FILE, or
     `nil' if there is none.  The argument OPERATION should be the
     operation to be performed on the file--the value you will pass to
     the handler as its first argument when you call it.  If OPERATION
     equals `inhibit-file-name-operation', or if it is not found in the
     `operations' property of the handler, this function returns `nil'.

 -- Function: file-local-copy filename
     This function copies file FILENAME to an ordinary non-magic file
     on the local machine, if it isn't on the local machine already.
     Magic file names should handle the `file-local-copy' operation if
     they refer to files on other machines.  A magic file name that is
     used for other purposes than remote file access should not handle
     `file-local-copy'; then this function will treat the file as local.

     If FILENAME is local, whether magic or not, this function does
     nothing and returns `nil'.  Otherwise it returns the file name of
     the local copy file.

 -- Function: file-remote-p filename
     This function tests whether FILENAME is a remote file.  If
     FILENAME is local (not remote), the return value is `nil'.  If
     FILENAME is indeed remote, the return value is a string that
     identifies the remote system.

     This identifier string can include a host name and a user name, as
     well as characters designating the method used to access the remote
     system.  For example, the remote identifier string for the filename
     `/ssh:user@host:/some/file' is `/ssh:user@host:'.

     If `file-remote-p' returns the same identifier for two different
     filenames, that means they are stored on the same file system and
     can be accessed locally with respect to each other.  This means,
     for example, that it is possible to start a remote process
     accessing both files at the same time.  Implementors of file
     handlers need to ensure this principle is valid.

 -- Function: unhandled-file-name-directory filename
     This function returns the name of a directory that is not magic.
     It uses the directory part of FILENAME if that is not magic.  For a
     magic file name, it invokes the file name handler, which therefore
     decides what value to return.

     This is useful for running a subprocess; every subprocess must
     have a non-magic directory to serve as its current directory, and
     this function is a good way to come up with one.


File: elisp,  Node: Format Conversion,  Prev: Magic File Names,  Up: Files

25.12 File Format Conversion
============================

The variable `format-alist' defines a list of "file formats", which
describe textual representations used in files for the data (text,
text-properties, and possibly other information) in an Emacs buffer.
Emacs performs format conversion if appropriate when reading and writing
files.

 -- Variable: format-alist
     This list contains one format definition for each defined file
     format.

   Each format definition is a list of this form:

     (NAME DOC-STRING REGEXP FROM-FN TO-FN MODIFY MODE-FN)

   Here is what the elements in a format definition mean:

NAME
     The name of this format.

DOC-STRING
     A documentation string for the format.

REGEXP
     A regular expression which is used to recognize files represented
     in this format.

FROM-FN
     A shell command or function to decode data in this format (to
     convert file data into the usual Emacs data representation).

     A shell command is represented as a string; Emacs runs the command
     as a filter to perform the conversion.

     If FROM-FN is a function, it is called with two arguments, BEGIN
     and END, which specify the part of the buffer it should convert.
     It should convert the text by editing it in place.  Since this can
     change the length of the text, FROM-FN should return the modified
     end position.

     One responsibility of FROM-FN is to make sure that the beginning
     of the file no longer matches REGEXP.  Otherwise it is likely to
     get called again.

TO-FN
     A shell command or function to encode data in this format--that
     is, to convert the usual Emacs data representation into this
     format.

     If TO-FN is a string, it is a shell command; Emacs runs the
     command as a filter to perform the conversion.

     If TO-FN is a function, it is called with three arguments: BEGIN
     and END, which specify the part of the buffer it should convert,
     and BUFFER, which specifies which buffer.  There are two ways it
     can do the conversion:

        * By editing the buffer in place.  In this case, TO-FN should
          return the end-position of the range of text, as modified.

        * By returning a list of annotations.  This is a list of
          elements of the form `(POSITION . STRING)', where POSITION is
          an integer specifying the relative position in the text to be
          written, and STRING is the annotation to add there.  The list
          must be sorted in order of position when TO-FN returns it.

          When `write-region' actually writes the text from the buffer
          to the file, it intermixes the specified annotations at the
          corresponding positions.  All this takes place without
          modifying the buffer.

MODIFY
     A flag, `t' if the encoding function modifies the buffer, and
     `nil' if it works by returning a list of annotations.

MODE-FN
     A minor-mode function to call after visiting a file converted from
     this format.  The function is called with one argument, the
     integer 1; that tells a minor-mode function to enable the mode.

   The function `insert-file-contents' automatically recognizes file
formats when it reads the specified file.  It checks the text of the
beginning of the file against the regular expressions of the format
definitions, and if it finds a match, it calls the decoding function for
that format.  Then it checks all the known formats over again.  It
keeps checking them until none of them is applicable.

   Visiting a file, with `find-file-noselect' or the commands that use
it, performs conversion likewise (because it calls
`insert-file-contents'); it also calls the mode function for each
format that it decodes.  It stores a list of the format names in the
buffer-local variable `buffer-file-format'.

 -- Variable: buffer-file-format
     This variable states the format of the visited file.  More
     precisely, this is a list of the file format names that were
     decoded in the course of visiting the current buffer's file.  It
     is always buffer-local in all buffers.

   When `write-region' writes data into a file, it first calls the
encoding functions for the formats listed in `buffer-file-format', in
the order of appearance in the list.

 -- Command: format-write-file file format &optional confirm
     This command writes the current buffer contents into the file FILE
     in format FORMAT, and makes that format the default for future
     saves of the buffer.  The argument FORMAT is a list of format
     names.  Except for the FORMAT argument, this command is similar to
     `write-file'.  In particular, CONFIRM has the same meaning and
     interactive treatment as the corresponding argument to
     `write-file'.  *Note Definition of write-file::.

 -- Command: format-find-file file format
     This command finds the file FILE, converting it according to
     format FORMAT.  It also makes FORMAT the default if the buffer is
     saved later.

     The argument FORMAT is a list of format names.  If FORMAT is
     `nil', no conversion takes place.  Interactively, typing just
     <RET> for FORMAT specifies `nil'.

 -- Command: format-insert-file file format &optional beg end
     This command inserts the contents of file FILE, converting it
     according to format FORMAT.  If BEG and END are non-`nil', they
     specify which part of the file to read, as in
     `insert-file-contents' (*note Reading from Files::).

     The return value is like what `insert-file-contents' returns: a
     list of the absolute file name and the length of the data inserted
     (after conversion).

     The argument FORMAT is a list of format names.  If FORMAT is
     `nil', no conversion takes place.  Interactively, typing just
     <RET> for FORMAT specifies `nil'.

 -- Variable: buffer-auto-save-file-format
     This variable specifies the format to use for auto-saving.  Its
     value is a list of format names, just like the value of
     `buffer-file-format'; however, it is used instead of
     `buffer-file-format' for writing auto-save files.  If the value is
     `t', the default, auto-saving uses the same format as a regular
     save in the same buffer.  This variable is always buffer-local in
     all buffers.


File: elisp,  Node: Backups and Auto-Saving,  Next: Buffers,  Prev: Files,  Up: Top

26 Backups and Auto-Saving
**************************

Backup files and auto-save files are two methods by which Emacs tries
to protect the user from the consequences of crashes or of the user's
own errors.  Auto-saving preserves the text from earlier in the current
editing session; backup files preserve file contents prior to the
current session.

* Menu:

* Backup Files::   How backup files are made; how their names are chosen.
* Auto-Saving::    How auto-save files are made; how their names are chosen.
* Reverting::      `revert-buffer', and how to customize what it does.


File: elisp,  Node: Backup Files,  Next: Auto-Saving,  Up: Backups and Auto-Saving

26.1 Backup Files
=================

A "backup file" is a copy of the old contents of a file you are
editing.  Emacs makes a backup file the first time you save a buffer
into its visited file.  Thus, normally, the backup file contains the
contents of the file as it was before the current editing session.  The
contents of the backup file normally remain unchanged once it exists.

   Backups are usually made by renaming the visited file to a new name.
Optionally, you can specify that backup files should be made by copying
the visited file.  This choice makes a difference for files with
multiple names; it also can affect whether the edited file remains owned
by the original owner or becomes owned by the user editing it.

   By default, Emacs makes a single backup file for each file edited.
You can alternatively request numbered backups; then each new backup
file gets a new name.  You can delete old numbered backups when you
don't want them any more, or Emacs can delete them automatically.

* Menu:

* Making Backups::     How Emacs makes backup files, and when.
* Rename or Copy::     Two alternatives: renaming the old file or copying it.
* Numbered Backups::   Keeping multiple backups for each source file.
* Backup Names::       How backup file names are computed; customization.


File: elisp,  Node: Making Backups,  Next: Rename or Copy,  Up: Backup Files

26.1.1 Making Backup Files
--------------------------

 -- Function: backup-buffer
     This function makes a backup of the file visited by the current
     buffer, if appropriate.  It is called by `save-buffer' before
     saving the buffer the first time.

     If a backup was made by renaming, the return value is a cons cell
     of the form (MODES . BACKUPNAME), where MODES are the mode bits of
     the original file, as returned by `file-modes' (*note Other
     Information about Files: File Attributes.), and BACKUPNAME is the
     name of the backup.  In all other cases, that is, if a backup was
     made by copying or if no backup was made, this function returns
     `nil'.

 -- Variable: buffer-backed-up
     This buffer-local variable says whether this buffer's file has
     been backed up on account of this buffer.  If it is non-`nil', the
     backup file has been written.  Otherwise, the file should be backed
     up when it is next saved (if backups are enabled).  This is a
     permanent local; `kill-all-local-variables' does not alter it.

 -- User Option: make-backup-files
     This variable determines whether or not to make backup files.  If
     it is non-`nil', then Emacs creates a backup of each file when it
     is saved for the first time--provided that `backup-inhibited' is
     `nil' (see below).

     The following example shows how to change the `make-backup-files'
     variable only in the Rmail buffers and not elsewhere.  Setting it
     `nil' stops Emacs from making backups of these files, which may
     save disk space.  (You would put this code in your init file.)

          (add-hook 'rmail-mode-hook
                    (function (lambda ()
                                (make-local-variable
                                 'make-backup-files)
                                (setq make-backup-files nil))))

 -- Variable: backup-enable-predicate
     This variable's value is a function to be called on certain
     occasions to decide whether a file should have backup files.  The
     function receives one argument, an absolute file name to consider.
     If the function returns `nil', backups are disabled for that
     file.  Otherwise, the other variables in this section say whether
     and how to make backups.

     The default value is `normal-backup-enable-predicate', which checks
     for files in `temporary-file-directory' and
     `small-temporary-file-directory'.

 -- Variable: backup-inhibited
     If this variable is non-`nil', backups are inhibited.  It records
     the result of testing `backup-enable-predicate' on the visited file
     name.  It can also coherently be used by other mechanisms that
     inhibit backups based on which file is visited.  For example, VC
     sets this variable non-`nil' to prevent making backups for files
     managed with a version control system.

     This is a permanent local, so that changing the major mode does
     not lose its value.  Major modes should not set this
     variable--they should set `make-backup-files' instead.

 -- Variable: backup-directory-alist
     This variable's value is an alist of filename patterns and backup
     directory names.  Each element looks like
          (REGEXP . DIRECTORY)

     Backups of files with names matching REGEXP will be made in
     DIRECTORY.  DIRECTORY may be relative or absolute.  If it is
     absolute, so that all matching files are backed up into the same
     directory, the file names in this directory will be the full name
     of the file backed up with all directory separators changed to `!'
     to prevent clashes.  This will not work correctly if your
     filesystem truncates the resulting name.

     For the common case of all backups going into one directory, the
     alist should contain a single element pairing `"."' with the
     appropriate directory name.

     If this variable is `nil', or it fails to match a filename, the
     backup is made in the original file's directory.

     On MS-DOS filesystems without long names this variable is always
     ignored.

 -- Variable: make-backup-file-name-function
     This variable's value is a function to use for making backups
     instead of the default `make-backup-file-name'.  A value of `nil'
     gives the default `make-backup-file-name' behavior.  *Note Naming
     Backup Files: Backup Names.

     This could be buffer-local to do something special for specific
     files.  If you define it, you may need to change
     `backup-file-name-p' and `file-name-sans-versions' too.


File: elisp,  Node: Rename or Copy,  Next: Numbered Backups,  Prev: Making Backups,  Up: Backup Files

26.1.2 Backup by Renaming or by Copying?
----------------------------------------

There are two ways that Emacs can make a backup file:

   * Emacs can rename the original file so that it becomes a backup
     file, and then write the buffer being saved into a new file.
     After this procedure, any other names (i.e., hard links) of the
     original file now refer to the backup file.  The new file is owned
     by the user doing the editing, and its group is the default for
     new files written by the user in that directory.

   * Emacs can copy the original file into a backup file, and then
     overwrite the original file with new contents.  After this
     procedure, any other names (i.e., hard links) of the original file
     continue to refer to the current (updated) version of the file.
     The file's owner and group will be unchanged.

   The first method, renaming, is the default.

   The variable `backup-by-copying', if non-`nil', says to use the
second method, which is to copy the original file and overwrite it with
the new buffer contents.  The variable `file-precious-flag', if
non-`nil', also has this effect (as a sideline of its main
significance).  *Note Saving Buffers::.

 -- User Option: backup-by-copying
     If this variable is non-`nil', Emacs always makes backup files by
     copying.

   The following three variables, when non-`nil', cause the second
method to be used in certain special cases.  They have no effect on the
treatment of files that don't fall into the special cases.

 -- User Option: backup-by-copying-when-linked
     If this variable is non-`nil', Emacs makes backups by copying for
     files with multiple names (hard links).

     This variable is significant only if `backup-by-copying' is `nil',
     since copying is always used when that variable is non-`nil'.

 -- User Option: backup-by-copying-when-mismatch
     If this variable is non-`nil', Emacs makes backups by copying in
     cases where renaming would change either the owner or the group of
     the file.

     The value has no effect when renaming would not alter the owner or
     group of the file; that is, for files which are owned by the user
     and whose group matches the default for a new file created there
     by the user.

     This variable is significant only if `backup-by-copying' is `nil',
     since copying is always used when that variable is non-`nil'.

 -- User Option: backup-by-copying-when-privileged-mismatch
     This variable, if non-`nil', specifies the same behavior as
     `backup-by-copying-when-mismatch', but only for certain user-id
     values: namely, those less than or equal to a certain number.  You
     set this variable to that number.

     Thus, if you set `backup-by-copying-when-privileged-mismatch' to
     0, backup by copying is done for the superuser only, when
     necessary to prevent a change in the owner of the file.

     The default is 200.


File: elisp,  Node: Numbered Backups,  Next: Backup Names,  Prev: Rename or Copy,  Up: Backup Files

26.1.3 Making and Deleting Numbered Backup Files
------------------------------------------------

If a file's name is `foo', the names of its numbered backup versions
are `foo.~V~', for various integers V, like this: `foo.~1~', `foo.~2~',
`foo.~3~', ..., `foo.~259~', and so on.

 -- User Option: version-control
     This variable controls whether to make a single non-numbered backup
     file or multiple numbered backups.

    `nil'
          Make numbered backups if the visited file already has
          numbered backups; otherwise, do not.  This is the default.

    `never'
          Do not make numbered backups.

    ANYTHING ELSE
          Make numbered backups.

   The use of numbered backups ultimately leads to a large number of
backup versions, which must then be deleted.  Emacs can do this
automatically or it can ask the user whether to delete them.

 -- User Option: kept-new-versions
     The value of this variable is the number of newest versions to keep
     when a new numbered backup is made.  The newly made backup is
     included in the count.  The default value is 2.

 -- User Option: kept-old-versions
     The value of this variable is the number of oldest versions to keep
     when a new numbered backup is made.  The default value is 2.

   If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is excess.  The function `find-backup-file-name'
(*note Backup Names::) is responsible for determining which backup
versions to delete, but does not delete them itself.

 -- User Option: delete-old-versions
     If this variable is `t', then saving a file deletes excess backup
     versions silently.  If it is `nil', that means to ask for
     confirmation before deleting excess backups.  Otherwise, they are
     not deleted at all.

 -- User Option: dired-kept-versions
     This variable specifies how many of the newest backup versions to
     keep in the Dired command `.' (`dired-clean-directory').  That's
     the same thing `kept-new-versions' specifies when you make a new
     backup file.  The default is 2.


File: elisp,  Node: Backup Names,  Prev: Numbered Backups,  Up: Backup Files

26.1.4 Naming Backup Files
--------------------------

The functions in this section are documented mainly because you can
customize the naming conventions for backup files by redefining them.
If you change one, you probably need to change the rest.

 -- Function: backup-file-name-p filename
     This function returns a non-`nil' value if FILENAME is a possible
     name for a backup file.  It just checks the name, not whether a
     file with the name FILENAME exists.

          (backup-file-name-p "foo")
               => nil
          (backup-file-name-p "foo~")
               => 3

     The standard definition of this function is as follows:

          (defun backup-file-name-p (file)
            "Return non-nil if FILE is a backup file \
          name (numeric or not)..."
            (string-match "~\\'" file))

     Thus, the function returns a non-`nil' value if the file name ends
     with a `~'.  (We use a backslash to split the documentation
     string's first line into two lines in the text, but produce just
     one line in the string itself.)

     This simple expression is placed in a separate function to make it
     easy to redefine for customization.

 -- Function: make-backup-file-name filename
     This function returns a string that is the name to use for a
     non-numbered backup file for file FILENAME.  On Unix, this is just
     FILENAME with a tilde appended.

     The standard definition of this function, on most operating
     systems, is as follows:

          (defun make-backup-file-name (file)
            "Create the non-numeric backup file name for FILE..."
            (concat file "~"))

     You can change the backup-file naming convention by redefining this
     function.  The following example redefines `make-backup-file-name'
     to prepend a `.' in addition to appending a tilde:

          (defun make-backup-file-name (filename)
            (expand-file-name
              (concat "." (file-name-nondirectory filename) "~")
              (file-name-directory filename)))

          (make-backup-file-name "backups.texi")
               => ".backups.texi~"

     Some parts of Emacs, including some Dired commands, assume that
     backup file names end with `~'.  If you do not follow that
     convention, it will not cause serious problems, but these commands
     may give less-than-desirable results.

 -- Function: find-backup-file-name filename
     This function computes the file name for a new backup file for
     FILENAME.  It may also propose certain existing backup files for
     deletion.  `find-backup-file-name' returns a list whose CAR is the
     name for the new backup file and whose CDR is a list of backup
     files whose deletion is proposed.  The value can also be `nil',
     which means not to make a backup.

     Two variables, `kept-old-versions' and `kept-new-versions',
     determine which backup versions should be kept.  This function
     keeps those versions by excluding them from the CDR of the value.
     *Note Numbered Backups::.

     In this example, the value says that `~rms/foo.~5~' is the name to
     use for the new backup file, and `~rms/foo.~3~' is an "excess"
     version that the caller should consider deleting now.

          (find-backup-file-name "~rms/foo")
               => ("~rms/foo.~5~" "~rms/foo.~3~")

 -- Function: file-newest-backup filename
     This function returns the name of the most recent backup file for
     FILENAME, or `nil' if that file has no backup files.

     Some file comparison commands use this function so that they can
     automatically compare a file with its most recent backup.


File: elisp,  Node: Auto-Saving,  Next: Reverting,  Prev: Backup Files,  Up: Backups and Auto-Saving

26.2 Auto-Saving
================

Emacs periodically saves all files that you are visiting; this is
called "auto-saving".  Auto-saving prevents you from losing more than a
limited amount of work if the system crashes.  By default, auto-saves
happen every 300 keystrokes, or after around 30 seconds of idle time.
*Note Auto Save: (emacs)Auto Save, for information on auto-save for
users.  Here we describe the functions used to implement auto-saving
and the variables that control them.

 -- Variable: buffer-auto-save-file-name
     This buffer-local variable is the name of the file used for
     auto-saving the current buffer.  It is `nil' if the buffer should
     not be auto-saved.

          buffer-auto-save-file-name
               => "/xcssun/users/rms/lewis/#backups.texi#"

 -- Command: auto-save-mode arg
     When used interactively without an argument, this command is a
     toggle switch: it turns on auto-saving of the current buffer if it
     is off, and vice versa.  With an argument ARG, the command turns
     auto-saving on if the value of ARG is `t', a nonempty list, or a
     positive integer.  Otherwise, it turns auto-saving off.

 -- Function: auto-save-file-name-p filename
     This function returns a non-`nil' value if FILENAME is a string
     that could be the name of an auto-save file.  It assumes the usual
     naming convention for auto-save files: a name that begins and ends
     with hash marks (`#') is a possible auto-save file name.  The
     argument FILENAME should not contain a directory part.

          (make-auto-save-file-name)
               => "/xcssun/users/rms/lewis/#backups.texi#"
          (auto-save-file-name-p "#backups.texi#")
               => 0
          (auto-save-file-name-p "backups.texi")
               => nil

     The standard definition of this function is as follows:

          (defun auto-save-file-name-p (filename)
            "Return non-nil if FILENAME can be yielded by..."
            (string-match "^#.*#$" filename))

     This function exists so that you can customize it if you wish to
     change the naming convention for auto-save files.  If you redefine
     it, be sure to redefine the function `make-auto-save-file-name'
     correspondingly.

 -- Function: make-auto-save-file-name
     This function returns the file name to use for auto-saving the
     current buffer.  This is just the file name with hash marks (`#')
     prepended and appended to it.  This function does not look at the
     variable `auto-save-visited-file-name' (described below); callers
     of this function should check that variable first.

          (make-auto-save-file-name)
               => "/xcssun/users/rms/lewis/#backups.texi#"

     Here is a simplified version of the standard definition of this
     function:

          (defun make-auto-save-file-name ()
            "Return file name to use for auto-saves \
          of current buffer.."
            (if buffer-file-name
                (concat
                 (file-name-directory buffer-file-name)
                 "#"
                 (file-name-nondirectory buffer-file-name)
                 "#")
              (expand-file-name
               (concat "#%" (buffer-name) "#"))))

     This exists as a separate function so that you can redefine it to
     customize the naming convention for auto-save files.  Be sure to
     change `auto-save-file-name-p' in a corresponding way.

 -- User Option: auto-save-visited-file-name
     If this variable is non-`nil', Emacs auto-saves buffers in the
     files they are visiting.  That is, the auto-save is done in the
     same file that you are editing.  Normally, this variable is `nil',
     so auto-save files have distinct names that are created by
     `make-auto-save-file-name'.

     When you change the value of this variable, the new value does not
     take effect in an existing buffer until the next time auto-save
     mode is reenabled in it.  If auto-save mode is already enabled,
     auto-saves continue to go in the same file name until
     `auto-save-mode' is called again.

 -- Function: recent-auto-save-p
     This function returns `t' if the current buffer has been
     auto-saved since the last time it was read in or saved.

 -- Function: set-buffer-auto-saved
     This function marks the current buffer as auto-saved.  The buffer
     will not be auto-saved again until the buffer text is changed
     again.  The function returns `nil'.

 -- User Option: auto-save-interval
     The value of this variable specifies how often to do auto-saving,
     in terms of number of input events.  Each time this many
     additional input events are read, Emacs does auto-saving for all
     buffers in which that is enabled.  Setting this to zero disables
     autosaving based on the number of characters typed.

 -- User Option: auto-save-timeout
     The value of this variable is the number of seconds of idle time
     that should cause auto-saving.  Each time the user pauses for this
     long, Emacs does auto-saving for all buffers in which that is
     enabled.  (If the current buffer is large, the specified timeout
     is multiplied by a factor that increases as the size increases;
     for a million-byte buffer, the factor is almost 4.)

     If the value is zero or `nil', then auto-saving is not done as a
     result of idleness, only after a certain number of input events as
     specified by `auto-save-interval'.

 -- Variable: auto-save-hook
     This normal hook is run whenever an auto-save is about to happen.

 -- User Option: auto-save-default
     If this variable is non-`nil', buffers that are visiting files
     have auto-saving enabled by default.  Otherwise, they do not.

 -- Command: do-auto-save &optional no-message current-only
     This function auto-saves all buffers that need to be auto-saved.
     It saves all buffers for which auto-saving is enabled and that
     have been changed since the previous auto-save.

     If any buffers are auto-saved, `do-auto-save' normally displays a
     message saying `Auto-saving...' in the echo area while auto-saving
     is going on.  However, if NO-MESSAGE is non-`nil', the message is
     inhibited.

     If CURRENT-ONLY is non-`nil', only the current buffer is
     auto-saved.

 -- Function: delete-auto-save-file-if-necessary &optional force
     This function deletes the current buffer's auto-save file if
     `delete-auto-save-files' is non-`nil'.  It is called every time a
     buffer is saved.

     Unless FORCE is non-`nil', this function only deletes the file if
     it was written by the current Emacs session since the last true
     save.

 -- User Option: delete-auto-save-files
     This variable is used by the function
     `delete-auto-save-file-if-necessary'.  If it is non-`nil', Emacs
     deletes auto-save files when a true save is done (in the visited
     file).  This saves disk space and unclutters your directory.

 -- Function: rename-auto-save-file
     This function adjusts the current buffer's auto-save file name if
     the visited file name has changed.  It also renames an existing
     auto-save file, if it was made in the current Emacs session.  If
     the visited file name has not changed, this function does nothing.

 -- Variable: buffer-saved-size
     The value of this buffer-local variable is the length of the
     current buffer, when it was last read in, saved, or auto-saved.
     This is used to detect a substantial decrease in size, and turn
     off auto-saving in response.

     If it is -1, that means auto-saving is temporarily shut off in
     this buffer due to a substantial decrease in size.  Explicitly
     saving the buffer stores a positive value in this variable, thus
     reenabling auto-saving.  Turning auto-save mode off or on also
     updates this variable, so that the substantial decrease in size is
     forgotten.

 -- Variable: auto-save-list-file-name
     This variable (if non-`nil') specifies a file for recording the
     names of all the auto-save files.  Each time Emacs does
     auto-saving, it writes two lines into this file for each buffer
     that has auto-saving enabled.  The first line gives the name of
     the visited file (it's empty if the buffer has none), and the
     second gives the name of the auto-save file.

     When Emacs exits normally, it deletes this file; if Emacs crashes,
     you can look in the file to find all the auto-save files that
     might contain work that was otherwise lost.  The `recover-session'
     command uses this file to find them.

     The default name for this file specifies your home directory and
     starts with `.saves-'.  It also contains the Emacs process ID and
     the host name.

 -- Variable: auto-save-list-file-prefix
     After Emacs reads your init file, it initializes
     `auto-save-list-file-name' (if you have not already set it
     non-`nil') based on this prefix, adding the host name and process
     ID.  If you set this to `nil' in your init file, then Emacs does
     not initialize `auto-save-list-file-name'.


File: elisp,  Node: Reverting,  Prev: Auto-Saving,  Up: Backups and Auto-Saving

26.3 Reverting
==============

If you have made extensive changes to a file and then change your mind
about them, you can get rid of them by reading in the previous version
of the file with the `revert-buffer' command.  *Note Reverting a
Buffer: (emacs)Reverting.

 -- Command: revert-buffer &optional ignore-auto noconfirm
          preserve-modes
     This command replaces the buffer text with the text of the visited
     file on disk.  This action undoes all changes since the file was
     visited or saved.

     By default, if the latest auto-save file is more recent than the
     visited file, and the argument IGNORE-AUTO is `nil',
     `revert-buffer' asks the user whether to use that auto-save
     instead.  When you invoke this command interactively, IGNORE-AUTO
     is `t' if there is no numeric prefix argument; thus, the
     interactive default is not to check the auto-save file.

     Normally, `revert-buffer' asks for confirmation before it changes
     the buffer; but if the argument NOCONFIRM is non-`nil',
     `revert-buffer' does not ask for confirmation.

     Normally, this command reinitializes the buffer's major and minor
     modes using `normal-mode'.  But if PRESERVE-MODES is non-`nil',
     the modes remain unchanged.

     Reverting tries to preserve marker positions in the buffer by
     using the replacement feature of `insert-file-contents'.  If the
     buffer contents and the file contents are identical before the
     revert operation, reverting preserves all the markers.  If they
     are not identical, reverting does change the buffer; in that case,
     it preserves the markers in the unchanged text (if any) at the
     beginning and end of the buffer.  Preserving any additional
     markers would be problematical.

   You can customize how `revert-buffer' does its work by setting the
variables described in the rest of this section.

 -- User Option: revert-without-query
     This variable holds a list of files that should be reverted without
     query.  The value is a list of regular expressions.  If the
     visited file name matches one of these regular expressions, and
     the file has changed on disk but the buffer is not modified, then
     `revert-buffer' reverts the file without asking the user for
     confirmation.

   Some major modes customize `revert-buffer' by making buffer-local
bindings for these variables:

 -- Variable: revert-buffer-function
     The value of this variable is the function to use to revert this
     buffer.  If non-`nil', it should be a function with two optional
     arguments to do the work of reverting.  The two optional arguments,
     IGNORE-AUTO and NOCONFIRM, are the arguments that `revert-buffer'
     received.  If the value is `nil', reverting works the usual way.

     Modes such as Dired mode, in which the text being edited does not
     consist of a file's contents but can be regenerated in some other
     fashion, can give this variable a buffer-local value that is a
     function to regenerate the contents.

 -- Variable: revert-buffer-insert-file-contents-function
     The value of this variable, if non-`nil', specifies the function
     to use to insert the updated contents when reverting this buffer.
     The function receives two arguments: first the file name to use;
     second, `t' if the user has asked to read the auto-save file.

     The reason for a mode to set this variable instead of
     `revert-buffer-function' is to avoid duplicating or replacing the
     rest of what `revert-buffer' does: asking for confirmation,
     clearing the undo list, deciding the proper major mode, and
     running the hooks listed below.

 -- Variable: before-revert-hook
     This normal hook is run by `revert-buffer' before inserting the
     modified contents--but only if `revert-buffer-function' is `nil'.

 -- Variable: after-revert-hook
     This normal hook is run by `revert-buffer' after inserting the
     modified contents--but only if `revert-buffer-function' is `nil'.


File: elisp,  Node: Buffers,  Next: Windows,  Prev: Backups and Auto-Saving,  Up: Top

27 Buffers
**********

A "buffer" is a Lisp object containing text to be edited.  Buffers are
used to hold the contents of files that are being visited; there may
also be buffers that are not visiting files.  While several buffers may
exist at one time, only one buffer is designated the "current buffer"
at any time.  Most editing commands act on the contents of the current
buffer.  Each buffer, including the current buffer, may or may not be
displayed in any windows.

* Menu:

* Buffer Basics::       What is a buffer?
* Current Buffer::      Designating a buffer as current
                          so that primitives will access its contents.
* Buffer Names::        Accessing and changing buffer names.
* Buffer File Name::    The buffer file name indicates which file is visited.
* Buffer Modification:: A buffer is "modified" if it needs to be saved.
* Modification Time::   Determining whether the visited file was changed
                         ``behind Emacs's back''.
* Read Only Buffers::   Modifying text is not allowed in a read-only buffer.
* The Buffer List::     How to look at all the existing buffers.
* Creating Buffers::    Functions that create buffers.
* Killing Buffers::     Buffers exist until explicitly killed.
* Indirect Buffers::    An indirect buffer shares text with some other buffer.
* Buffer Gap::          The gap in the buffer.


File: elisp,  Node: Buffer Basics,  Next: Current Buffer,  Up: Buffers

27.1 Buffer Basics
==================

A "buffer" is a Lisp object containing text to be edited.  Buffers are
used to hold the contents of files that are being visited; there may
also be buffers that are not visiting files.  Although several buffers
normally exist, only one buffer is designated the "current buffer" at
any time.  Most editing commands act on the contents of the current
buffer.  Each buffer, including the current buffer, may or may not be
displayed in any windows.

Buffers in Emacs editing are objects that have distinct names and hold
text that can be edited.  Buffers appear to Lisp programs as a special
data type.  You can think of the contents of a buffer as a string that
you can extend; insertions and deletions may occur in any part of the
buffer.  *Note Text::.

   A Lisp buffer object contains numerous pieces of information.  Some
of this information is directly accessible to the programmer through
variables, while other information is accessible only through
special-purpose functions.  For example, the visited file name is
directly accessible through a variable, while the value of point is
accessible only through a primitive function.

   Buffer-specific information that is directly accessible is stored in
"buffer-local" variable bindings, which are variable values that are
effective only in a particular buffer.  This feature allows each buffer
to override the values of certain variables.  Most major modes override
variables such as `fill-column' or `comment-column' in this way.  For
more information about buffer-local variables and functions related to
them, see *Note Buffer-Local Variables::.

   For functions and variables related to visiting files in buffers, see
*Note Visiting Files:: and *Note Saving Buffers::.  For functions and
variables related to the display of buffers in windows, see *Note
Buffers and Windows::.

 -- Function: bufferp object
     This function returns `t' if OBJECT is a buffer, `nil' otherwise.


File: elisp,  Node: Current Buffer,  Next: Buffer Names,  Prev: Buffer Basics,  Up: Buffers

27.2 The Current Buffer
=======================

There are, in general, many buffers in an Emacs session.  At any time,
one of them is designated as the "current buffer".  This is the buffer
in which most editing takes place, because most of the primitives for
examining or changing text in a buffer operate implicitly on the
current buffer (*note Text::).  Normally the buffer that is displayed on
the screen in the selected window is the current buffer, but this is not
always so: a Lisp program can temporarily designate any buffer as
current in order to operate on its contents, without changing what is
displayed on the screen.

   The way to designate a current buffer in a Lisp program is by calling
`set-buffer'.  The specified buffer remains current until a new one is
designated.

   When an editing command returns to the editor command loop, the
command loop designates the buffer displayed in the selected window as
current, to prevent confusion: the buffer that the cursor is in when
Emacs reads a command is the buffer that the command will apply to.
(*Note Command Loop::.)  Therefore, `set-buffer' is not the way to
switch visibly to a different buffer so that the user can edit it.  For
that, you must use the functions described in *Note Displaying
Buffers::.

   *Warning:* Lisp functions that change to a different current buffer
should not depend on the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other programs
as well as from the command loop; it is convenient for the caller if
the subroutine does not change which buffer is current (unless, of
course, that is the subroutine's purpose).  Therefore, you should
normally use `set-buffer' within a `save-current-buffer' or
`save-excursion' (*note Excursions::) form that will restore the
current buffer when your function is done.  Here is an example, the
code for the command `append-to-buffer' (with the documentation string
abridged):

     (defun append-to-buffer (buffer start end)
       "Append to specified buffer the text of the region.
     ..."
       (interactive "BAppend to buffer: \nr")
       (let ((oldbuf (current-buffer)))
         (save-current-buffer
           (set-buffer (get-buffer-create buffer))
           (insert-buffer-substring oldbuf start end))))

This function binds a local variable to record the current buffer, and
then `save-current-buffer' arranges to make it current again.  Next,
`set-buffer' makes the specified buffer current.  Finally,
`insert-buffer-substring' copies the string from the original current
buffer to the specified (and now current) buffer.

   If the buffer appended to happens to be displayed in some window,
the next redisplay will show how its text has changed.  Otherwise, you
will not see the change immediately on the screen.  The buffer becomes
current temporarily during the execution of the command, but this does
not cause it to be displayed.

   If you make local bindings (with `let' or function arguments) for a
variable that may also have buffer-local bindings, make sure that the
same buffer is current at the beginning and at the end of the local
binding's scope.  Otherwise you might bind it in one buffer and unbind
it in another!  There are two ways to do this.  In simple cases, you may
see that nothing ever changes the current buffer within the scope of the
binding.  Otherwise, use `save-current-buffer' or `save-excursion' to
make sure that the buffer current at the beginning is current again
whenever the variable is unbound.

   Do not rely on using `set-buffer' to change the current buffer back,
because that won't do the job if a quit happens while the wrong buffer
is current.  Here is what _not_ to do:

     (let (buffer-read-only
           (obuf (current-buffer)))
       (set-buffer ...)
       ...
       (set-buffer obuf))

Using `save-current-buffer', as shown here, handles quitting, errors,
and `throw', as well as ordinary evaluation.

     (let (buffer-read-only)
       (save-current-buffer
         (set-buffer ...)
         ...))

 -- Function: current-buffer
     This function returns the current buffer.

          (current-buffer)
               => #<buffer buffers.texi>

 -- Function: set-buffer buffer-or-name
     This function makes BUFFER-OR-NAME the current buffer.  This does
     not display the buffer in any window, so the user cannot
     necessarily see the buffer.  But Lisp programs will now operate on
     it.

     This function returns the buffer identified by BUFFER-OR-NAME.  An
     error is signaled if BUFFER-OR-NAME does not identify an existing
     buffer.

 -- Special Form: save-current-buffer body...
     The `save-current-buffer' special form saves the identity of the
     current buffer, evaluates the BODY forms, and finally restores
     that buffer as current.  The return value is the value of the last
     form in BODY.  The current buffer is restored even in case of an
     abnormal exit via `throw' or error (*note Nonlocal Exits::).

     If the buffer that used to be current has been killed by the time
     of exit from `save-current-buffer', then it is not made current
     again, of course.  Instead, whichever buffer was current just
     before exit remains current.

 -- Macro: with-current-buffer buffer-or-name body...
     The `with-current-buffer' macro saves the identity of the current
     buffer, makes BUFFER-OR-NAME current, evaluates the BODY forms,
     and finally restores the buffer.  The return value is the value of
     the last form in BODY.  The current buffer is restored even in
     case of an abnormal exit via `throw' or error (*note Nonlocal
     Exits::).

     An error is signaled if BUFFER-OR-NAME does not identify an
     existing buffer.

 -- Macro: with-temp-buffer body...
     The `with-temp-buffer' macro evaluates the BODY forms with a
     temporary buffer as the current buffer.  It saves the identity of
     the current buffer, creates a temporary buffer and makes it
     current, evaluates the BODY forms, and finally restores the
     previous current buffer while killing the temporary buffer.  By
     default, undo information (*note Undo::) is not recorded in the
     buffer created by this macro (but BODY can enable that, if needed).

     The return value is the value of the last form in BODY.  You can
     return the contents of the temporary buffer by using
     `(buffer-string)' as the last form.

     The current buffer is restored even in case of an abnormal exit via
     `throw' or error (*note Nonlocal Exits::).

     See also `with-temp-file' in *Note Writing to Files: Definition of
     with-temp-file.


File: elisp,  Node: Buffer Names,  Next: Buffer File Name,  Prev: Current Buffer,  Up: Buffers

27.3 Buffer Names
=================

Each buffer has a unique name, which is a string.  Many of the
functions that work on buffers accept either a buffer or a buffer name
as an argument.  Any argument called BUFFER-OR-NAME is of this sort,
and an error is signaled if it is neither a string nor a buffer.  Any
argument called BUFFER must be an actual buffer object, not a name.

   Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, so that the `list-buffers' and
`buffer-menu' commands don't mention them (but if such a buffer visits
a file, it *is* mentioned).  A name starting with space also initially
disables recording undo information; see *Note Undo::.

 -- Function: buffer-name &optional buffer
     This function returns the name of BUFFER as a string.  If BUFFER
     is not supplied, it defaults to the current buffer.

     If `buffer-name' returns `nil', it means that BUFFER has been
     killed.  *Note Killing Buffers::.

          (buffer-name)
               => "buffers.texi"

          (setq foo (get-buffer "temp"))
               => #<buffer temp>
          (kill-buffer foo)
               => nil
          (buffer-name foo)
               => nil
          foo
               => #<killed buffer>

 -- Command: rename-buffer newname &optional unique
     This function renames the current buffer to NEWNAME.  An error is
     signaled if NEWNAME is not a string.

     Ordinarily, `rename-buffer' signals an error if NEWNAME is already
     in use.  However, if UNIQUE is non-`nil', it modifies NEWNAME to
     make a name that is not in use.  Interactively, you can make
     UNIQUE non-`nil' with a numeric prefix argument.  (This is how the
     command `rename-uniquely' is implemented.)

     This function returns the name actually given to the buffer.

 -- Function: get-buffer buffer-or-name
     This function returns the buffer specified by BUFFER-OR-NAME.  If
     BUFFER-OR-NAME is a string and there is no buffer with that name,
     the value is `nil'.  If BUFFER-OR-NAME is a buffer, it is returned
     as given; that is not very useful, so the argument is usually a
     name.  For example:

          (setq b (get-buffer "lewis"))
               => #<buffer lewis>
          (get-buffer b)
               => #<buffer lewis>
          (get-buffer "Frazzle-nots")
               => nil

     See also the function `get-buffer-create' in *Note Creating
     Buffers::.

 -- Function: generate-new-buffer-name starting-name &optional ignore
     This function returns a name that would be unique for a new
     buffer--but does not create the buffer.  It starts with
     STARTING-NAME, and produces a name not currently in use for any
     buffer by appending a number inside of `<...>'.  It starts at 2
     and keeps incrementing the number until it is not the name of an
     existing buffer.

     If the optional second argument IGNORE is non-`nil', it should be
     a string, a potential buffer name.  It means to consider that
     potential buffer acceptable, if it is tried, even it is the name
     of an existing buffer (which would normally be rejected).  Thus, if
     buffers named `foo', `foo<2>', `foo<3>' and `foo<4>' exist,

          (generate-new-buffer-name "foo")
               => "foo<5>"
          (generate-new-buffer-name "foo" "foo<3>")
               => "foo<3>"
          (generate-new-buffer-name "foo" "foo<6>")
               => "foo<5>"

     See the related function `generate-new-buffer' in *Note Creating
     Buffers::.


File: elisp,  Node: Buffer File Name,  Next: Buffer Modification,  Prev: Buffer Names,  Up: Buffers

27.4 Buffer File Name
=====================

The "buffer file name" is the name of the file that is visited in that
buffer.  When a buffer is not visiting a file, its buffer file name is
`nil'.  Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently.  *Note
Visiting Files::.

 -- Function: buffer-file-name &optional buffer
     This function returns the absolute file name of the file that
     BUFFER is visiting.  If BUFFER is not visiting any file,
     `buffer-file-name' returns `nil'.  If BUFFER is not supplied, it
     defaults to the current buffer.

          (buffer-file-name (other-buffer))
               => "/usr/user/lewis/manual/files.texi"

 -- Variable: buffer-file-name
     This buffer-local variable contains the name of the file being
     visited in the current buffer, or `nil' if it is not visiting a
     file.  It is a permanent local variable, unaffected by
     `kill-all-local-variables'.

          buffer-file-name
               => "/usr/user/lewis/manual/buffers.texi"

     It is risky to change this variable's value without doing various
     other things.  Normally it is better to use
     `set-visited-file-name' (see below); some of the things done
     there, such as changing the buffer name, are not strictly
     necessary, but others are essential to avoid confusing Emacs.

 -- Variable: buffer-file-truename
     This buffer-local variable holds the abbreviated truename of the
     file visited in the current buffer, or `nil' if no file is visited.
     It is a permanent local, unaffected by `kill-all-local-variables'.
     *Note Truenames::, and *Note Definition of abbreviate-file-name::.

 -- Variable: buffer-file-number
     This buffer-local variable holds the file number and directory
     device number of the file visited in the current buffer, or `nil'
     if no file or a nonexistent file is visited.  It is a permanent
     local, unaffected by `kill-all-local-variables'.

     The value is normally a list of the form `(FILENUM DEVNUM)'.  This
     pair of numbers uniquely identifies the file among all files
     accessible on the system.  See the function `file-attributes', in
     *Note File Attributes::, for more information about them.

     If `buffer-file-name' is the name of a symbolic link, then both
     numbers refer to the recursive target.

 -- Function: get-file-buffer filename
     This function returns the buffer visiting file FILENAME.  If there
     is no such buffer, it returns `nil'.  The argument FILENAME, which
     must be a string, is expanded (*note File Name Expansion::), then
     compared against the visited file names of all live buffers.  Note
     that the buffer's `buffer-file-name' must match the expansion of
     FILENAME exactly.  This function will not recognize other names
     for the same file.

          (get-file-buffer "buffers.texi")
              => #<buffer buffers.texi>

     In unusual circumstances, there can be more than one buffer
     visiting the same file name.  In such cases, this function returns
     the first such buffer in the buffer list.

 -- Function: find-buffer-visiting filename &optional predicate
     This is like `get-file-buffer', except that it can return any
     buffer visiting the file _possibly under a different name_.  That
     is, the buffer's `buffer-file-name' does not need to match the
     expansion of FILENAME exactly, it only needs to refer to the same
     file.  If PREDICATE is non-`nil', it should be a function of one
     argument, a buffer visiting FILENAME.  The buffer is only
     considered a suitable return value if PREDICATE returns non-`nil'.
     If it can not find a suitable buffer to return,
     `find-buffer-visiting' returns `nil'.

 -- Command: set-visited-file-name filename &optional no-query
          along-with-file
     If FILENAME is a non-empty string, this function changes the name
     of the file visited in the current buffer to FILENAME.  (If the
     buffer had no visited file, this gives it one.)  The _next time_
     the buffer is saved it will go in the newly-specified file.

     This command marks the buffer as modified, since it does not (as
     far as Emacs knows) match the contents of FILENAME, even if it
     matched the former visited file.  It also renames the buffer to
     correspond to the new file name, unless the new name is already in
     use.

     If FILENAME is `nil' or the empty string, that stands for "no
     visited file."  In this case, `set-visited-file-name' marks the
     buffer as having no visited file, without changing the buffer's
     modified flag.

     Normally, this function asks the user for confirmation if there
     already is a buffer visiting FILENAME.  If NO-QUERY is non-`nil',
     that prevents asking this question.  If there already is a buffer
     visiting FILENAME, and the user confirms or QUERY is non-`nil',
     this function makes the new buffer name unique by appending a
     number inside of `<...>' to FILENAME.

     If ALONG-WITH-FILE is non-`nil', that means to assume that the
     former visited file has been renamed to FILENAME.  In this case,
     the command does not change the buffer's modified flag, nor the
     buffer's recorded last file modification time as reported by
     `visited-file-modtime' (*note Modification Time::).  If
     ALONG-WITH-FILE is `nil', this function clears the recorded last
     file modification time, after which `visited-file-modtime' returns
     zero.

     When the function `set-visited-file-name' is called interactively,
     it prompts for FILENAME in the minibuffer.

 -- Variable: list-buffers-directory
     This buffer-local variable specifies a string to display in a
     buffer listing where the visited file name would go, for buffers
     that don't have a visited file name.  Dired buffers use this
     variable.


File: elisp,  Node: Buffer Modification,  Next: Modification Time,  Prev: Buffer File Name,  Up: Buffers

27.5 Buffer Modification
========================

Emacs keeps a flag called the "modified flag" for each buffer, to
record whether you have changed the text of the buffer.  This flag is
set to `t' whenever you alter the contents of the buffer, and cleared
to `nil' when you save it.  Thus, the flag shows whether there are
unsaved changes.  The flag value is normally shown in the mode line
(*note Mode Line Variables::), and controls saving (*note Saving
Buffers::) and auto-saving (*note Auto-Saving::).

   Some Lisp programs set the flag explicitly.  For example, the
function `set-visited-file-name' sets the flag to `t', because the text
does not match the newly-visited file, even if it is unchanged from the
file formerly visited.

   The functions that modify the contents of buffers are described in
*Note Text::.

 -- Function: buffer-modified-p &optional buffer
     This function returns `t' if the buffer BUFFER has been modified
     since it was last read in from a file or saved, or `nil'
     otherwise.  If BUFFER is not supplied, the current buffer is
     tested.

 -- Function: set-buffer-modified-p flag
     This function marks the current buffer as modified if FLAG is
     non-`nil', or as unmodified if the flag is `nil'.

     Another effect of calling this function is to cause unconditional
     redisplay of the mode line for the current buffer.  In fact, the
     function `force-mode-line-update' works by doing this:

          (set-buffer-modified-p (buffer-modified-p))

 -- Function: restore-buffer-modified-p flag
     Like `set-buffer-modified-p', but does not force redisplay of mode
     lines.

 -- Command: not-modified &optional arg
     This command marks the current buffer as unmodified, and not
     needing to be saved.  If ARG is non-`nil', it marks the buffer as
     modified, so that it will be saved at the next suitable occasion.
     Interactively, ARG is the prefix argument.

     Don't use this function in programs, since it prints a message in
     the echo area; use `set-buffer-modified-p' (above) instead.

 -- Function: buffer-modified-tick &optional buffer
     This function returns BUFFER's modification-count.  This is a
     counter that increments every time the buffer is modified.  If
     BUFFER is `nil' (or omitted), the current buffer is used.  The
     counter can wrap around occasionally.

 -- Function: buffer-chars-modified-tick &optional buffer
     This function returns BUFFER's character-change modification-count.
     Changes to text properties leave this counter unchanged; however,
     each time text is inserted or removed from the buffer, the counter
     is reset to the value that would be returned by
     `buffer-modified-tick'.  By comparing the values returned by two
     `buffer-chars-modified-tick' calls, you can tell whether a
     character change occurred in that buffer in between the calls.  If
     BUFFER is `nil' (or omitted), the current buffer is used.


File: elisp,  Node: Modification Time,  Next: Read Only Buffers,  Prev: Buffer Modification,  Up: Buffers

27.6 Buffer Modification Time
=============================

Suppose that you visit a file and make changes in its buffer, and
meanwhile the file itself is changed on disk.  At this point, saving the
buffer would overwrite the changes in the file.  Occasionally this may
be what you want, but usually it would lose valuable information.  Emacs
therefore checks the file's modification time using the functions
described below before saving the file.  (*Note File Attributes::, for
how to examine a file's modification time.)

 -- Function: verify-visited-file-modtime buffer
     This function compares what BUFFER has recorded for the
     modification time of its visited file against the actual
     modification time of the file as recorded by the operating system.
     The two should be the same unless some other process has written
     the file since Emacs visited or saved it.

     The function returns `t' if the last actual modification time and
     Emacs's recorded modification time are the same, `nil' otherwise.
     It also returns `t' if the buffer has no recorded last
     modification time, that is if `visited-file-modtime' would return
     zero.

     It always returns `t' for buffers that are not visiting a file,
     even if `visited-file-modtime' returns a non-zero value.  For
     instance, it always returns `t' for dired buffers.  It returns `t'
     for buffers that are visiting a file that does not exist and never
     existed, but `nil' for file-visiting buffers whose file has been
     deleted.

 -- Function: clear-visited-file-modtime
     This function clears out the record of the last modification time
     of the file being visited by the current buffer.  As a result, the
     next attempt to save this buffer will not complain of a
     discrepancy in file modification times.

     This function is called in `set-visited-file-name' and other
     exceptional places where the usual test to avoid overwriting a
     changed file should not be done.

 -- Function: visited-file-modtime
     This function returns the current buffer's recorded last file
     modification time, as a list of the form `(HIGH LOW)'.  (This is
     the same format that `file-attributes' uses to return time values;
     see *Note File Attributes::.)

     If the buffer has no recorded last modification time, this function
     returns zero.  This case occurs, for instance, if the buffer is not
     visiting a file or if the time has been explicitly cleared by
     `clear-visited-file-modtime'.  Note, however, that
     `visited-file-modtime' returns a list for some non-file buffers
     too.  For instance, in a Dired buffer listing a directory, it
     returns the last modification time of that directory, as recorded
     by Dired.

     For a new buffer visiting a not yet existing file, HIGH is -1 and
     LOW is 65535, that is, 2**16 - 1.

 -- Function: set-visited-file-modtime &optional time
     This function updates the buffer's record of the last modification
     time of the visited file, to the value specified by TIME if TIME
     is not `nil', and otherwise to the last modification time of the
     visited file.

     If TIME is neither `nil' nor zero, it should have the form `(HIGH
     . LOW)' or `(HIGH LOW)', in either case containing two integers,
     each of which holds 16 bits of the time.

     This function is useful if the buffer was not read from the file
     normally, or if the file itself has been changed for some known
     benign reason.

 -- Function: ask-user-about-supersession-threat filename
     This function is used to ask a user how to proceed after an
     attempt to modify an buffer visiting file FILENAME when the file
     is newer than the buffer text.  Emacs detects this because the
     modification time of the file on disk is newer than the last
     save-time of the buffer.  This means some other program has
     probably altered the file.

     Depending on the user's answer, the function may return normally,
     in which case the modification of the buffer proceeds, or it may
     signal a `file-supersession' error with data `(FILENAME)', in which
     case the proposed buffer modification is not allowed.

     This function is called automatically by Emacs on the proper
     occasions.  It exists so you can customize Emacs by redefining it.
     See the file `userlock.el' for the standard definition.

     See also the file locking mechanism in *Note File Locks::.


File: elisp,  Node: Read Only Buffers,  Next: The Buffer List,  Prev: Modification Time,  Up: Buffers

27.7 Read-Only Buffers
======================

If a buffer is "read-only", then you cannot change its contents,
although you may change your view of the contents by scrolling and
narrowing.

   Read-only buffers are used in two kinds of situations:

   * A buffer visiting a write-protected file is normally read-only.

     Here, the purpose is to inform the user that editing the buffer
     with the aim of saving it in the file may be futile or
     undesirable.  The user who wants to change the buffer text despite
     this can do so after clearing the read-only flag with `C-x C-q'.

   * Modes such as Dired and Rmail make buffers read-only when altering
     the contents with the usual editing commands would probably be a
     mistake.

     The special commands of these modes bind `buffer-read-only' to
     `nil' (with `let') or bind `inhibit-read-only' to `t' around the
     places where they themselves change the text.

 -- Variable: buffer-read-only
     This buffer-local variable specifies whether the buffer is
     read-only.  The buffer is read-only if this variable is non-`nil'.

 -- Variable: inhibit-read-only
     If this variable is non-`nil', then read-only buffers and,
     depending on the actual value, some or all read-only characters
     may be modified.  Read-only characters in a buffer are those that
     have non-`nil' `read-only' properties (either text properties or
     overlay properties).  *Note Special Properties::, for more
     information about text properties.  *Note Overlays::, for more
     information about overlays and their properties.

     If `inhibit-read-only' is `t', all `read-only' character
     properties have no effect.  If `inhibit-read-only' is a list, then
     `read-only' character properties have no effect if they are members
     of the list (comparison is done with `eq').

 -- Command: toggle-read-only &optional arg
     This command toggles whether the current buffer is read-only.  It
     is intended for interactive use; do not use it in programs.  At
     any given point in a program, you should know whether you want the
     read-only flag on or off; so you can set `buffer-read-only'
     explicitly to the proper value, `t' or `nil'.

     If ARG is non-`nil', it should be a raw prefix argument.
     `toggle-read-only' sets `buffer-read-only' to `t' if the numeric
     value of that prefix argument is positive and to `nil' otherwise.
     *Note Prefix Command Arguments::.

 -- Function: barf-if-buffer-read-only
     This function signals a `buffer-read-only' error if the current
     buffer is read-only.  *Note Using Interactive::, for another way to
     signal an error if the current buffer is read-only.


File: elisp,  Node: The Buffer List,  Next: Creating Buffers,  Prev: Read Only Buffers,  Up: Buffers

27.8 The Buffer List
====================

The "buffer list" is a list of all live buffers.  The order of the
buffers in the list is based primarily on how recently each buffer has
been displayed in a window.  Several functions, notably `other-buffer',
use this ordering.  A buffer list displayed for the user also follows
this order.

   Creating a buffer adds it to the end of the buffer list, and killing
a buffer removes it.  Buffers move to the front of the list when they
are selected for display in a window (*note Displaying Buffers::), and
to the end when they are buried (see `bury-buffer', below).  There are
no functions available to the Lisp programmer which directly manipulate
the buffer list.

   In addition to the fundamental Emacs buffer list, each frame has its
own version of the buffer list, in which the buffers that have been
selected in that frame come first, starting with the buffers most
recently selected _in that frame_.  (This order is recorded in FRAME's
`buffer-list' frame parameter; see *Note Buffer Parameters::.)  The
buffers that were never selected in FRAME come afterward, ordered
according to the fundamental Emacs buffer list.

 -- Function: buffer-list &optional frame
     This function returns the buffer list, including all buffers, even
     those whose names begin with a space.  The elements are actual
     buffers, not their names.

     If FRAME is a frame, this returns FRAME's buffer list.  If FRAME
     is `nil', the fundamental Emacs buffer list is used: all the
     buffers appear in order of most recent selection, regardless of
     which frames they were selected in.

          (buffer-list)
               => (#<buffer buffers.texi>
                   #<buffer  *Minibuf-1*> #<buffer buffer.c>
                   #<buffer *Help*> #<buffer TAGS>)

          ;; Note that the name of the minibuffer
          ;;   begins with a space!
          (mapcar (function buffer-name) (buffer-list))
              => ("buffers.texi" " *Minibuf-1*"
                  "buffer.c" "*Help*" "TAGS")

   The list that `buffer-list' returns is constructed specifically by
`buffer-list'; it is not an internal Emacs data structure, and
modifying it has no effect on the order of buffers.  If you want to
change the order of buffers in the frame-independent buffer list, here
is an easy way:

     (defun reorder-buffer-list (new-list)
       (while new-list
         (bury-buffer (car new-list))
         (setq new-list (cdr new-list))))

   With this method, you can specify any order for the list, but there
is no danger of losing a buffer or adding something that is not a valid
live buffer.

   To change the order or value of a frame's buffer list, set the
frame's `buffer-list' frame parameter with `modify-frame-parameters'
(*note Parameter Access::).

 -- Function: other-buffer &optional buffer visible-ok frame
     This function returns the first buffer in the buffer list other
     than BUFFER.  Usually this is the buffer selected most recently (in
     frame FRAME or else the currently selected frame, *note Input
     Focus::), aside from BUFFER.  Buffers whose names start with a
     space are not considered at all.

     If BUFFER is not supplied (or if it is not a buffer), then
     `other-buffer' returns the first buffer in the selected frame's
     buffer list that is not now visible in any window in a visible
     frame.

     If FRAME has a non-`nil' `buffer-predicate' parameter, then
     `other-buffer' uses that predicate to decide which buffers to
     consider.  It calls the predicate once for each buffer, and if the
     value is `nil', that buffer is ignored.  *Note Buffer Parameters::.

     If VISIBLE-OK is `nil', `other-buffer' avoids returning a buffer
     visible in any window on any visible frame, except as a last
     resort.   If VISIBLE-OK is non-`nil', then it does not matter
     whether a buffer is displayed somewhere or not.

     If no suitable buffer exists, the buffer `*scratch*' is returned
     (and created, if necessary).

 -- Command: bury-buffer &optional buffer-or-name
     This function puts BUFFER-OR-NAME at the end of the buffer list,
     without changing the order of any of the other buffers on the list.
     This buffer therefore becomes the least desirable candidate for
     `other-buffer' to return.  The argument can be either a buffer
     itself or the name of one.

     `bury-buffer' operates on each frame's `buffer-list' parameter as
     well as the frame-independent Emacs buffer list; therefore, the
     buffer that you bury will come last in the value of `(buffer-list
     FRAME)' and in the value of `(buffer-list nil)'.

     If BUFFER-OR-NAME is `nil' or omitted, this means to bury the
     current buffer.  In addition, if the buffer is displayed in the
     selected window, this switches to some other buffer (obtained using
     `other-buffer') in the selected window.  But if the buffer is
     displayed in some other window, it remains displayed there.

     To replace a buffer in all the windows that display it, use
     `replace-buffer-in-windows'.  *Note Buffers and Windows::.


File: elisp,  Node: Creating Buffers,  Next: Killing Buffers,  Prev: The Buffer List,  Up: Buffers

27.9 Creating Buffers
=====================

This section describes the two primitives for creating buffers.
`get-buffer-create' creates a buffer if it finds no existing buffer
with the specified name; `generate-new-buffer' always creates a new
buffer and gives it a unique name.

   Other functions you can use to create buffers include
`with-output-to-temp-buffer' (*note Temporary Displays::) and
`create-file-buffer' (*note Visiting Files::).  Starting a subprocess
can also create a buffer (*note Processes::).

 -- Function: get-buffer-create name
     This function returns a buffer named NAME.  It returns a live
     buffer with that name, if one exists; otherwise, it creates a new
     buffer.  The buffer does not become the current buffer--this
     function does not change which buffer is current.

     If NAME is a buffer instead of a string, it is returned, even if
     it is dead.  An error is signaled if NAME is neither a string nor
     a buffer.

          (get-buffer-create "foo")
               => #<buffer foo>

     The major mode for a newly created buffer is set to Fundamental
     mode.  (The variable `default-major-mode' is handled at a higher
     level; see *Note Auto Major Mode::.)  If the name begins with a
     space, the buffer initially disables undo information recording
     (*note Undo::).

 -- Function: generate-new-buffer name
     This function returns a newly created, empty buffer, but does not
     make it current.  If there is no buffer named NAME, then that is
     the name of the new buffer.  If that name is in use, this function
     adds suffixes of the form `<N>' to NAME, where N is an integer.
     It tries successive integers starting with 2 until it finds an
     available name.

     An error is signaled if NAME is not a string.

          (generate-new-buffer "bar")
               => #<buffer bar>
          (generate-new-buffer "bar")
               => #<buffer bar<2>>
          (generate-new-buffer "bar")
               => #<buffer bar<3>>

     The major mode for the new buffer is set to Fundamental mode.  The
     variable `default-major-mode' is handled at a higher level.  *Note
     Auto Major Mode::.

     See the related function `generate-new-buffer-name' in *Note
     Buffer Names::.


File: elisp,  Node: Killing Buffers,  Next: Indirect Buffers,  Prev: Creating Buffers,  Up: Buffers

27.10 Killing Buffers
=====================

"Killing a buffer" makes its name unknown to Emacs and makes the memory
space it occupied available for other use.

   The buffer object for the buffer that has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it.  Killed buffers retain
their identity, however; if you kill two distinct buffers, they remain
distinct according to `eq' although both are dead.

   If you kill a buffer that is current or displayed in a window, Emacs
automatically selects or displays some other buffer instead.  This means
that killing a buffer can in general change the current buffer.
Therefore, when you kill a buffer, you should also take the precautions
associated with changing the current buffer (unless you happen to know
that the buffer being killed isn't current).  *Note Current Buffer::.

   If you kill a buffer that is the base buffer of one or more indirect
buffers, the indirect buffers are automatically killed as well.

   The `buffer-name' of a killed buffer is `nil'.  You can use this
feature to test whether a buffer has been killed:

     (defun buffer-killed-p (buffer)
       "Return t if BUFFER is killed."
       (not (buffer-name buffer)))

 -- Command: kill-buffer buffer-or-name
     This function kills the buffer BUFFER-OR-NAME, freeing all its
     memory for other uses or to be returned to the operating system.
     If BUFFER-OR-NAME is `nil', it kills the current buffer.

     Any processes that have this buffer as the `process-buffer' are
     sent the `SIGHUP' signal, which normally causes them to terminate.
     (The basic meaning of `SIGHUP' is that a dialup line has been
     disconnected.)  *Note Signals to Processes::.

     If the buffer is visiting a file and contains unsaved changes,
     `kill-buffer' asks the user to confirm before the buffer is killed.
     It does this even if not called interactively.  To prevent the
     request for confirmation, clear the modified flag before calling
     `kill-buffer'.  *Note Buffer Modification::.

     Killing a buffer that is already dead has no effect.

     This function returns `t' if it actually killed the buffer.  It
     returns `nil' if the user refuses to confirm or if BUFFER-OR-NAME
     was already dead.

          (kill-buffer "foo.unchanged")
               => t
          (kill-buffer "foo.changed")

          ---------- Buffer: Minibuffer ----------
          Buffer foo.changed modified; kill anyway? (yes or no) yes
          ---------- Buffer: Minibuffer ----------

               => t

 -- Variable: kill-buffer-query-functions
     After confirming unsaved changes, `kill-buffer' calls the functions
     in the list `kill-buffer-query-functions', in order of appearance,
     with no arguments.  The buffer being killed is the current buffer
     when they are called.  The idea of this feature is that these
     functions will ask for confirmation from the user.  If any of them
     returns `nil', `kill-buffer' spares the buffer's life.

 -- Variable: kill-buffer-hook
     This is a normal hook run by `kill-buffer' after asking all the
     questions it is going to ask, just before actually killing the
     buffer.  The buffer to be killed is current when the hook
     functions run.  *Note Hooks::.  This variable is a permanent
     local, so its local binding is not cleared by changing major modes.

 -- Variable: buffer-offer-save
     This variable, if non-`nil' in a particular buffer, tells
     `save-buffers-kill-emacs' and `save-some-buffers' (if the second
     optional argument to that function is `t') to offer to save that
     buffer, just as they offer to save file-visiting buffers.  *Note
     Definition of save-some-buffers::.  The variable
     `buffer-offer-save' automatically becomes buffer-local when set
     for any reason.  *Note Buffer-Local Variables::.

 -- Variable: buffer-save-without-query
     This variable, if non-`nil' in a particular buffer, tells
     `save-buffers-kill-emacs' and `save-some-buffers' to save this
     buffer (if it's modified) without asking the user.  The variable
     automatically becomes buffer-local when set for any reason.

 -- Function: buffer-live-p object
     This function returns `t' if OBJECT is a buffer which has not been
     killed, `nil' otherwise.


File: elisp,  Node: Indirect Buffers,  Next: Buffer Gap,  Prev: Killing Buffers,  Up: Buffers

27.11 Indirect Buffers
======================

An "indirect buffer" shares the text of some other buffer, which is
called the "base buffer" of the indirect buffer.  In some ways it is
the analogue, for buffers, of a symbolic link among files.  The base
buffer may not itself be an indirect buffer.

   The text of the indirect buffer is always identical to the text of
its base buffer; changes made by editing either one are visible
immediately in the other.  This includes the text properties as well as
the characters themselves.

   In all other respects, the indirect buffer and its base buffer are
completely separate.  They have different names, independent values of
point, independent narrowing, independent markers and overlays (though
inserting or deleting text in either buffer relocates the markers and
overlays for both), independent major modes, and independent
buffer-local variable bindings.

   An indirect buffer cannot visit a file, but its base buffer can.  If
you try to save the indirect buffer, that actually saves the base
buffer.

   Killing an indirect buffer has no effect on its base buffer.  Killing
the base buffer effectively kills the indirect buffer in that it cannot
ever again be the current buffer.

 -- Command: make-indirect-buffer base-buffer name &optional clone
     This creates and returns an indirect buffer named NAME whose base
     buffer is BASE-BUFFER.  The argument BASE-BUFFER may be a live
     buffer or the name (a string) of an existing buffer.  If NAME is
     the name of an existing buffer, an error is signaled.

     If CLONE is non-`nil', then the indirect buffer originally shares
     the "state" of BASE-BUFFER such as major mode, minor modes, buffer
     local variables and so on.  If CLONE is omitted or `nil' the
     indirect buffer's state is set to the default state for new
     buffers.

     If BASE-BUFFER is an indirect buffer, its base buffer is used as
     the base for the new buffer.  If, in addition, CLONE is non-`nil',
     the initial state is copied from the actual base buffer, not from
     BASE-BUFFER.

 -- Function: clone-indirect-buffer newname display-flag &optional
          norecord
     This function creates and returns a new indirect buffer that shares
     the current buffer's base buffer and copies the rest of the current
     buffer's attributes.  (If the current buffer is not indirect, it is
     used as the base buffer.)

     If DISPLAY-FLAG is non-`nil', that means to display the new buffer
     by calling `pop-to-buffer'.  If NORECORD is non-`nil', that means
     not to put the new buffer to the front of the buffer list.

 -- Function: buffer-base-buffer &optional buffer
     This function returns the base buffer of BUFFER, which defaults to
     the current buffer.  If BUFFER is not indirect, the value is
     `nil'.  Otherwise, the value is another buffer, which is never an
     indirect buffer.


File: elisp,  Node: Buffer Gap,  Prev: Indirect Buffers,  Up: Buffers

27.12 The Buffer Gap
====================

Emacs buffers are implemented using an invisible "gap" to make
insertion and deletion faster.  Insertion works by filling in part of
the gap, and deletion adds to the gap.  Of course, this means that the
gap must first be moved to the locus of the insertion or deletion.
Emacs moves the gap only when you try to insert or delete.  This is why
your first editing command in one part of a large buffer, after
previously editing in another far-away part, sometimes involves a
noticeable delay.

   This mechanism works invisibly, and Lisp code should never be
affected by the gap's current location, but these functions are
available for getting information about the gap status.

 -- Function: gap-position
     This function returns the current gap position in the current
     buffer.

 -- Function: gap-size
     This function returns the current gap size of the current buffer.


File: elisp,  Node: Windows,  Next: Frames,  Prev: Buffers,  Up: Top

28 Windows
**********

This chapter describes most of the functions and variables related to
Emacs windows.  See *Note Display::, for information on how text is
displayed in windows.

* Menu:

* Basic Windows::           Basic information on using windows.
* Splitting Windows::       Splitting one window into two windows.
* Deleting Windows::        Deleting a window gives its space to other windows.
* Selecting Windows::       The selected window is the one that you edit in.
* Cyclic Window Ordering::  Moving around the existing windows.
* Buffers and Windows::     Each window displays the contents of a buffer.
* Displaying Buffers::      Higher-level functions for displaying a buffer
                              and choosing a window for it.
* Choosing Window::	    How to choose a window for displaying a buffer.
* Window Point::            Each window has its own location of point.
* Window Start::            The display-start position controls which text
                              is on-screen in the window.
* Textual Scrolling::       Moving text up and down through the window.
* Vertical Scrolling::      Moving the contents up and down on the window.
* Horizontal Scrolling::    Moving the contents sideways on the window.
* Size of Window::          Accessing the size of a window.
* Resizing Windows::        Changing the size of a window.
* Coordinates and Windows:: Converting coordinates to windows.
* Window Tree::             The layout and sizes of all windows in a frame.
* Window Configurations::   Saving and restoring the state of the screen.
* Window Hooks::            Hooks for scrolling, window size changes,
                              redisplay going past a certain point,
                              or window configuration changes.


File: elisp,  Node: Basic Windows,  Next: Splitting Windows,  Up: Windows

28.1 Basic Concepts of Emacs Windows
====================================

A "window" in Emacs is the physical area of the screen in which a
buffer is displayed.  The term is also used to refer to a Lisp object
that represents that screen area in Emacs Lisp.  It should be clear
from the context which is meant.

   Emacs groups windows into frames.  A frame represents an area of
screen available for Emacs to use.  Each frame always contains at least
one window, but you can subdivide it vertically or horizontally into
multiple nonoverlapping Emacs windows.

   In each frame, at any time, one and only one window is designated as
"selected within the frame".  The frame's cursor appears in that
window, but the other windows have "non-selected" cursors, normally
less visible.  (*note Cursor Parameters::, for customization of this.)
At any time, one frame is the selected frame; and the window selected
within that frame is "the selected window".  The selected window's
buffer is usually the current buffer (except when `set-buffer' has been
used).  *Note Current Buffer::.

   For practical purposes, a window exists only while it is displayed in
a frame.  Once removed from the frame, the window is effectively deleted
and should not be used, _even though there may still be references to
it_ from other Lisp objects.  Restoring a saved window configuration is
the only way for a window no longer on the screen to come back to life.
(*Note Deleting Windows::.)

   Each window has the following attributes:

   * containing frame

   * window height

   * window width

   * window edges with respect to the screen or frame

   * the buffer it displays

   * position within the buffer at the upper left of the window

   * amount of horizontal scrolling, in columns

   * point

   * the mark

   * how recently the window was selected

   * fringe settings

   * display margins

   * scroll-bar settings

   Users create multiple windows so they can look at several buffers at
once.  Lisp libraries use multiple windows for a variety of reasons, but
most often to display related information.  In Rmail, for example, you
can move through a summary buffer in one window while the other window
shows messages one at a time as they are reached.

   The meaning of "window" in Emacs is similar to what it means in the
context of general-purpose window systems such as X, but not identical.
The X Window System places X windows on the screen; Emacs uses one or
more X windows as frames, and subdivides them into Emacs windows.  When
you use Emacs on a character-only terminal, Emacs treats the whole
terminal screen as one frame.

   Most window systems support arbitrarily located overlapping windows.
In contrast, Emacs windows are "tiled"; they never overlap, and
together they fill the whole screen or frame.  Because of the way in
which Emacs creates new windows and resizes them, not all conceivable
tilings of windows on an Emacs frame are actually possible.  *Note
Splitting Windows::, and *Note Size of Window::.

   *Note Display::, for information on how the contents of the window's
buffer are displayed in the window.

 -- Function: windowp object
     This function returns `t' if OBJECT is a window.


File: elisp,  Node: Splitting Windows,  Next: Deleting Windows,  Prev: Basic Windows,  Up: Windows

28.2 Splitting Windows
======================

The functions described here are the primitives used to split a window
into two windows.  Two higher level functions sometimes split a window,
but not always: `pop-to-buffer' and `display-buffer' (*note Displaying
Buffers::).

   The functions described here do not accept a buffer as an argument.
The two "halves" of the split window initially display the same buffer
previously visible in the window that was split.

 -- Command: split-window &optional window size horizontal
     This function splits a new window out of WINDOW's screen area.  It
     returns the new window.

     If HORIZONTAL is non-`nil', then WINDOW splits into two side by
     side windows.  The original window WINDOW keeps the leftmost SIZE
     columns, and gives the rest of the columns to the new window.
     Otherwise, it splits into windows one above the other, and WINDOW
     keeps the upper SIZE lines and gives the rest of the lines to the
     new window.  The original window is therefore the left-hand or
     upper of the two, and the new window is the right-hand or lower.

     If WINDOW is omitted or `nil', that stands for the selected
     window.  When you split the selected window, it remains selected.

     If SIZE is omitted or `nil', then WINDOW is divided evenly into
     two parts.  (If there is an odd line, it is allocated to the new
     window.)  When `split-window' is called interactively, all its
     arguments are `nil'.

     If splitting would result in making a window that is smaller than
     `window-min-height' or `window-min-width', the function signals an
     error and does not split the window at all.

     The following example starts with one window on a screen that is 50
     lines high by 80 columns wide; then it splits the window.

          (setq w (selected-window))
               => #<window 8 on windows.texi>
          (window-edges)          ; Edges in order:
               => (0 0 80 50)     ;   left-top-right-bottom

          ;; Returns window created
          (setq w2 (split-window w 15))
               => #<window 28 on windows.texi>
          (window-edges w2)
               => (0 15 80 50)    ; Bottom window;
                                  ;   top is line 15
          (window-edges w)
               => (0 0 80 15)     ; Top window

     The screen looks like this:

                   __________
                  |          |  line 0
                  |    w     |
                  |__________|
                  |          |  line 15
                  |    w2    |
                  |__________|
                                line 50
           column 0   column 80

     Next, split the top window horizontally:

          (setq w3 (split-window w 35 t))
               => #<window 32 on windows.texi>
          (window-edges w3)
               => (35 0 80 15)  ; Left edge at column 35
          (window-edges w)
               => (0 0 35 15)   ; Right edge at column 35
          (window-edges w2)
               => (0 15 80 50)  ; Bottom window unchanged

     Now the screen looks like this:

               column 35
                   __________
                  |   |      |  line 0
                  | w |  w3  |
                  |___|______|
                  |          |  line 15
                  |    w2    |
                  |__________|
                                line 50
           column 0   column 80

     Normally, Emacs indicates the border between two side-by-side
     windows with a scroll bar (*note Scroll Bars: Layout Parameters.)
     or `|' characters.  The display table can specify alternative
     border characters; see *Note Display Tables::.

 -- Command: split-window-vertically &optional size
     This function splits the selected window into two windows, one
     above the other, leaving the upper of the two windows selected,
     with SIZE lines.  (If SIZE is negative, then the lower of the two
     windows gets - SIZE lines and the upper window gets the rest, but
     the upper window is still the one selected.)  However, if
     `split-window-keep-point' (see below) is `nil', then either window
     can be selected.

     In other respects, this function is similar to `split-window'.  In
     particular, the upper window is the original one and the return
     value is the new, lower window.

 -- User Option: split-window-keep-point
     If this variable is non-`nil' (the default), then
     `split-window-vertically' behaves as described above.

     If it is `nil', then `split-window-vertically' adjusts point in
     each of the two windows to avoid scrolling.  (This is useful on
     slow terminals.)  It selects whichever window contains the screen
     line that point was previously on.

     This variable only affects the behavior of
     `split-window-vertically'.  It has no effect on the other
     functions described here.

 -- Command: split-window-horizontally &optional size
     This function splits the selected window into two windows
     side-by-side, leaving the selected window on the left with SIZE
     columns.  If SIZE is negative, the rightmost window gets - SIZE
     columns, but the leftmost window still remains selected.

     This function is basically an interface to `split-window'.  You
     could define a simplified version of the function like this:

          (defun split-window-horizontally (&optional arg)
            "Split selected window into two windows, side by side..."
            (interactive "P")
            (let ((size (and arg (prefix-numeric-value arg))))
              (and size (< size 0)
          	 (setq size (+ (window-width) size)))
              (split-window nil size t)))

 -- Function: one-window-p &optional no-mini all-frames
     This function returns non-`nil' if there is only one window.  The
     argument NO-MINI, if non-`nil', means don't count the minibuffer
     even if it is active; otherwise, the minibuffer window is counted
     when it is active.

     The argument ALL-FRAMES specifies which frames to consider.  Here
     are the possible values and their meanings:

    `nil'
          Count the windows in the selected frame, plus the minibuffer
          used by that frame even if it lies in some other frame.

    `t'
          Count all windows in all existing frames.

    `visible'
          Count all windows in all visible frames.

    0
          Count all windows in all visible or iconified frames.

    anything else
          Count precisely the windows in the selected frame, and no
          others.


File: elisp,  Node: Deleting Windows,  Next: Selecting Windows,  Prev: Splitting Windows,  Up: Windows

28.3 Deleting Windows
=====================

A window remains visible on its frame unless you "delete" it by calling
certain functions that delete windows.  A deleted window cannot appear
on the screen, but continues to exist as a Lisp object until there are
no references to it.  There is no way to cancel the deletion of a
window aside from restoring a saved window configuration (*note Window
Configurations::).  Restoring a window configuration also deletes any
windows that aren't part of that configuration.

   When you delete a window, the space it took up is given to one
adjacent sibling.

 -- Function: window-live-p window
     This function returns `nil' if WINDOW is deleted, and `t'
     otherwise.

     *Warning:* Erroneous information or fatal errors may result from
     using a deleted window as if it were live.

 -- Command: delete-window &optional window
     This function removes WINDOW from display, and returns `nil'.  If
     WINDOW is omitted, then the selected window is deleted.  An error
     is signaled if there is only one window when `delete-window' is
     called.

 -- Command: delete-other-windows &optional window
     This function makes WINDOW the only window on its frame, by
     deleting the other windows in that frame.  If WINDOW is omitted or
     `nil', then the selected window is used by default.

     The return value is `nil'.

 -- Command: delete-windows-on buffer-or-name &optional frame
     This function deletes all windows showing BUFFER-OR-NAME.  If
     there are no windows showing BUFFER-OR-NAME, it does nothing.
     BUFFER-OR-NAME must be a buffer or the name of an existing buffer.

     `delete-windows-on' operates frame by frame.  If a frame has
     several windows showing different buffers, then those showing
     BUFFER-OR-NAME are removed, and the others expand to fill the
     space.  If all windows in some frame are showing BUFFER-OR-NAME
     (including the case where there is only one window), then the frame
     winds up with a single window showing another buffer chosen with
     `other-buffer'.  *Note The Buffer List::.

     The argument FRAME controls which frames to operate on.  This
     function does not use it in quite the same way as the other
     functions which scan all windows; specifically, the values `t' and
     `nil' have the opposite of their meanings in other functions.
     Here are the full details:

        * If it is `nil', operate on all frames.

        * If it is `t', operate on the selected frame.

        * If it is `visible', operate on all visible frames.

        * If it is 0, operate on all visible or iconified frames.

        * If it is a frame, operate on that frame.

     This function always returns `nil'.


File: elisp,  Node: Selecting Windows,  Next: Cyclic Window Ordering,  Prev: Deleting Windows,  Up: Windows

28.4 Selecting Windows
======================

When a window is selected, the buffer in the window becomes the current
buffer, and the cursor will appear in it.

 -- Function: selected-window
     This function returns the selected window.  This is the window in
     which the cursor appears and to which many commands apply.

 -- Function: select-window window &optional norecord
     This function makes WINDOW the selected window.  The cursor then
     appears in WINDOW (on redisplay).  Unless WINDOW was already
     selected, `select-window' makes WINDOW's buffer the current buffer.

     Normally WINDOW's selected buffer is moved to the front of the
     buffer list, but if NORECORD is non-`nil', the buffer list order
     is unchanged.

     The return value is WINDOW.

          (setq w (next-window))
          (select-window w)
               => #<window 65 on windows.texi>

 -- Macro: save-selected-window forms...
     This macro records the selected frame, as well as the selected
     window of each frame, executes FORMS in sequence, then restores the
     earlier selected frame and windows.  It also saves and restores the
     current buffer.  It returns the value of the last form in FORMS.

     This macro does not save or restore anything about the sizes,
     arrangement or contents of windows; therefore, if the FORMS change
     them, the change persists.  If the previously selected window of
     some frame is no longer live at the time of exit from FORMS, that
     frame's selected window is left alone.  If the previously selected
     window is no longer live, then whatever window is selected at the
     end of FORMS remains selected.

 -- Macro: with-selected-window window forms...
     This macro selects WINDOW (without changing the buffer list),
     executes FORMS in sequence, then restores the previously selected
     window and current buffer.  It is just like
     `save-selected-window', except that it explicitly selects WINDOW,
     also without altering the buffer list sequence.

   The following functions choose one of the windows on the screen,
offering various criteria for the choice.

 -- Function: get-lru-window &optional frame dedicated
     This function returns the window least recently "used" (that is,
     selected).  If any full-width windows are present, it only
     considers these.  The selected window is always the most recently
     used window.

     The selected window can be the least recently used window if it is
     the only window.  A newly created window becomes the least
     recently used window until it is selected.  A minibuffer window is
     never a candidate.  Dedicated windows are never candidates unless
     the DEDICATED argument is non-`nil', so if all existing windows
     are dedicated, the value is `nil'.

     The argument FRAME controls which windows are considered.

        * If it is `nil', consider windows on the selected frame.

        * If it is `t', consider windows on all frames.

        * If it is `visible', consider windows on all visible frames.

        * If it is 0, consider windows on all visible or iconified
          frames.

        * If it is a frame, consider windows on that frame.

 -- Function: get-largest-window &optional frame dedicated
     This function returns the window with the largest area (height
     times width).  If there are no side-by-side windows, then this is
     the window with the most lines.  A minibuffer window is never a
     candidate.  Dedicated windows are never candidates unless the
     DEDICATED argument is non-`nil', so if all existing windows are
     dedicated, the value is `nil'.

     If there are two candidate windows of the same size, this function
     prefers the one that comes first in the cyclic ordering of windows
     (see following section), starting from the selected window.

     The argument FRAME controls which set of windows to consider.  See
     `get-lru-window', above.

 -- Function: get-window-with-predicate predicate &optional minibuf
          all-frames default
     This function returns a window satisfying PREDICATE.  It cycles
     through all visible windows using `walk-windows' (*note Cyclic
     Window Ordering::), calling PREDICATE on each one of them with
     that window as its argument.  The function returns the first
     window for which PREDICATE returns a non-`nil' value; if that
     never happens, it returns DEFAULT.

     The optional arguments MINIBUF and ALL-FRAMES specify the set of
     windows to include in the scan.  See the description of
     `next-window' in *Note Cyclic Window Ordering::, for details.


File: elisp,  Node: Cyclic Window Ordering,  Next: Buffers and Windows,  Prev: Selecting Windows,  Up: Windows

28.5 Cyclic Ordering of Windows
===============================

When you use the command `C-x o' (`other-window') to select the next
window, it moves through all the windows on the screen in a specific
cyclic order.  For any given configuration of windows, this order never
varies.  It is called the "cyclic ordering of windows".

   This ordering generally goes from top to bottom, and from left to
right.  But it may go down first or go right first, depending on the
order in which the windows were split.

   If the first split was vertical (into windows one above each other),
and then the subwindows were split horizontally, then the ordering is
left to right in the top of the frame, and then left to right in the
next lower part of the frame, and so on.  If the first split was
horizontal, the ordering is top to bottom in the left part, and so on.
In general, within each set of siblings at any level in the window tree,
the order is left to right, or top to bottom.

 -- Function: next-window &optional window minibuf all-frames
     This function returns the window following WINDOW in the cyclic
     ordering of windows.  This is the window that `C-x o' would select
     if typed when WINDOW is selected.  If WINDOW is the only window
     visible, then this function returns WINDOW.  If omitted, WINDOW
     defaults to the selected window.

     The value of the argument MINIBUF determines whether the
     minibuffer is included in the window order.  Normally, when
     MINIBUF is `nil', the minibuffer is included if it is currently
     active; this is the behavior of `C-x o'.  (The minibuffer window
     is active while the minibuffer is in use.  *Note Minibuffers::.)

     If MINIBUF is `t', then the cyclic ordering includes the
     minibuffer window even if it is not active.

     If MINIBUF is neither `t' nor `nil', then the minibuffer window is
     not included even if it is active.

     The argument ALL-FRAMES specifies which frames to consider.  Here
     are the possible values and their meanings:

    `nil'
          Consider all the windows in WINDOW's frame, plus the
          minibuffer used by that frame even if it lies in some other
          frame.  If the minibuffer counts (as determined by MINIBUF),
          then all windows on all frames that share that minibuffer
          count too.

    `t'
          Consider all windows in all existing frames.

    `visible'
          Consider all windows in all visible frames.  (To get useful
          results, you must ensure WINDOW is in a visible frame.)

    0
          Consider all windows in all visible or iconified frames.

    a frame
          Consider all windows on that frame.

    anything else
          Consider precisely the windows in WINDOW's frame, and no
          others.

     This example assumes there are two windows, both displaying the
     buffer `windows.texi':

          (selected-window)
               => #<window 56 on windows.texi>
          (next-window (selected-window))
               => #<window 52 on windows.texi>
          (next-window (next-window (selected-window)))
               => #<window 56 on windows.texi>

 -- Function: previous-window &optional window minibuf all-frames
     This function returns the window preceding WINDOW in the cyclic
     ordering of windows.  The other arguments specify which windows to
     include in the cycle, as in `next-window'.

 -- Command: other-window count &optional all-frames
     This function selects the COUNTth following window in the cyclic
     order.  If count is negative, then it moves back -COUNT windows in
     the cycle, rather than forward.  It returns `nil'.

     The argument ALL-FRAMES has the same meaning as in `next-window',
     but the MINIBUF argument of `next-window' is always effectively
     `nil'.

     In an interactive call, COUNT is the numeric prefix argument.

 -- Function: walk-windows proc &optional minibuf all-frames
     This function cycles through all windows.  It calls the function
     `proc' once for each window, with the window as its sole argument.

     The optional arguments MINIBUF and ALL-FRAMES specify the set of
     windows to include in the scan.  See `next-window', above, for
     details.

 -- Function: window-list &optional frame minibuf window
     This function returns a list of the windows on FRAME, starting
     with WINDOW.  If FRAME is `nil' or omitted, `window-list' uses the
     selected frame instead; if WINDOW is `nil' or omitted, it uses the
     selected window.

     The value of MINIBUF determines if the minibuffer window is
     included in the result list.  If MINIBUF is `t', the result always
     includes the minibuffer window.  If MINIBUF is `nil' or omitted,
     that includes the minibuffer window if it is active.  If MINIBUF
     is neither `nil' nor `t', the result never includes the minibuffer
     window.


File: elisp,  Node: Buffers and Windows,  Next: Displaying Buffers,  Prev: Cyclic Window Ordering,  Up: Windows

28.6 Buffers and Windows
========================

This section describes low-level functions to examine windows or to
display buffers in windows in a precisely controlled fashion.  *Note
Displaying Buffers::, for related functions that find a window to use
and specify a buffer for it.  The functions described there are easier
to use than these, but they employ heuristics in choosing or creating a
window; use these functions when you need complete control.

 -- Function: set-window-buffer window buffer-or-name &optional
          keep-margins
     This function makes WINDOW display BUFFER-OR-NAME as its contents.
     It returns `nil'.  BUFFER-OR-NAME must be a buffer, or the name
     of an existing buffer.  This is the fundamental primitive for
     changing which buffer is displayed in a window, and all ways of
     doing that call this function.

          (set-window-buffer (selected-window) "foo")
               => nil

     Normally, displaying BUFFER in WINDOW resets the window's display
     margins, fringe widths, scroll bar settings, and position based on
     the local variables of BUFFER.  However, if KEEP-MARGINS is
     non-`nil', the display margins and fringe widths of WINDOW remain
     unchanged.  *Note Fringes::.

 -- Variable: buffer-display-count
     This buffer-local variable records the number of times a buffer is
     displayed in a window.  It is incremented each time
     `set-window-buffer' is called for the buffer.

 -- Function: window-buffer &optional window
     This function returns the buffer that WINDOW is displaying.  If
     WINDOW is omitted, this function returns the buffer for the
     selected window.

          (window-buffer)
               => #<buffer windows.texi>

 -- Function: get-buffer-window buffer-or-name &optional all-frames
     This function returns a window currently displaying
     BUFFER-OR-NAME, or `nil' if there is none.  If there are several
     such windows, then the function returns the first one in the
     cyclic ordering of windows, starting from the selected window.
     *Note Cyclic Window Ordering::.

     The argument ALL-FRAMES controls which windows to consider.

        * If it is `nil', consider windows on the selected frame.

        * If it is `t', consider windows on all frames.

        * If it is `visible', consider windows on all visible frames.

        * If it is 0, consider windows on all visible or iconified
          frames.

        * If it is a frame, consider windows on that frame.

 -- Function: get-buffer-window-list buffer-or-name &optional minibuf
          all-frames
     This function returns a list of all the windows currently
     displaying BUFFER-OR-NAME.

     The two optional arguments work like the optional arguments of
     `next-window' (*note Cyclic Window Ordering::); they are _not_
     like the single optional argument of `get-buffer-window'.  Perhaps
     we should change `get-buffer-window' in the future to make it
     compatible with the other functions.

 -- Variable: buffer-display-time
     This variable records the time at which a buffer was last made
     visible in a window.  It is always local in each buffer; each time
     `set-window-buffer' is called, it sets this variable to
     `(current-time)' in the specified buffer (*note Time of Day::).
     When a buffer is first created, `buffer-display-time' starts out
     with the value `nil'.


File: elisp,  Node: Displaying Buffers,  Next: Choosing Window,  Prev: Buffers and Windows,  Up: Windows

28.7 Displaying Buffers in Windows
==================================

In this section we describe convenient functions that choose a window
automatically and use it to display a specified buffer.  These functions
can also split an existing window in certain circumstances.  We also
describe variables that parameterize the heuristics used for choosing a
window.  *Note Buffers and Windows::, for low-level functions that give
you more precise control.  All of these functions work by calling
`set-window-buffer'.

   Do not use the functions in this section in order to make a buffer
current so that a Lisp program can access or modify it; they are too
drastic for that purpose, since they change the display of buffers in
windows, which would be gratuitous and surprise the user.  Instead, use
`set-buffer' and `save-current-buffer' (*note Current Buffer::), which
designate buffers as current for programmed access without affecting
the display of buffers in windows.

 -- Command: switch-to-buffer buffer-or-name &optional norecord
     This function makes BUFFER-OR-NAME the current buffer, and also
     displays the buffer in the selected window.  This means that a
     human can see the buffer and subsequent keyboard commands will
     apply to it.  Contrast this with `set-buffer', which makes
     BUFFER-OR-NAME the current buffer but does not display it in the
     selected window.  *Note Current Buffer::.

     If BUFFER-OR-NAME does not identify an existing buffer, then a new
     buffer by that name is created.  The major mode for the new buffer
     is set according to the variable `default-major-mode'.  *Note Auto
     Major Mode::.  If BUFFER-OR-NAME is `nil', `switch-to-buffer'
     chooses a buffer using `other-buffer'.

     Normally the specified buffer is put at the front of the buffer
     list (both the selected frame's buffer list and the
     frame-independent buffer list).  This affects the operation of
     `other-buffer'.  However, if NORECORD is non-`nil', this is not
     done.  *Note The Buffer List::.

     The `switch-to-buffer' function is often used interactively, as
     the binding of `C-x b'.  It is also used frequently in programs.
     It returns the buffer that it switched to.

   The next two functions are similar to `switch-to-buffer', except for
the described features.

 -- Command: switch-to-buffer-other-window buffer-or-name &optional
          norecord
     This function makes BUFFER-OR-NAME the current buffer and displays
     it in a window not currently selected.  It then selects that
     window.  The handling of the buffer is the same as in
     `switch-to-buffer'.

     The currently selected window is absolutely never used to do the
     job.  If it is the only window, then it is split to make a
     distinct window for this purpose.  If the selected window is
     already displaying the buffer, then it continues to do so, but
     another window is nonetheless found to display it in as well.

     This function updates the buffer list just like `switch-to-buffer'
     unless NORECORD is non-`nil'.

 -- Function: pop-to-buffer buffer-or-name &optional other-window
          norecord
     This function makes BUFFER-OR-NAME the current buffer and switches
     to it in some window, preferably not the window previously
     selected.  The "popped-to" window becomes the selected window
     within its frame.  The return value is the buffer that was
     switched to.  If BUFFER-OR-NAME is `nil', that means to choose some
     other buffer, but you don't specify which.

     If the variable `pop-up-frames' is non-`nil', `pop-to-buffer'
     looks for a window in any visible frame already displaying the
     buffer; if there is one, it returns that window and makes it be
     selected within its frame.  If there is none, it creates a new
     frame and displays the buffer in it.

     If `pop-up-frames' is `nil', then `pop-to-buffer' operates
     entirely within the selected frame.  (If the selected frame has
     just a minibuffer, `pop-to-buffer' operates within the most
     recently selected frame that was not just a minibuffer.)

     If the variable `pop-up-windows' is non-`nil', windows may be
     split to create a new window that is different from the original
     window.  For details, see *Note Choosing Window::.

     If OTHER-WINDOW is non-`nil', `pop-to-buffer' finds or creates
     another window even if BUFFER-OR-NAME is already visible in the
     selected window.  Thus BUFFER-OR-NAME could end up displayed in
     two windows.  On the other hand, if BUFFER-OR-NAME is already
     displayed in the selected window and OTHER-WINDOW is `nil', then
     the selected window is considered sufficient display for
     BUFFER-OR-NAME, so that nothing needs to be done.

     All the variables that affect `display-buffer' affect
     `pop-to-buffer' as well.  *Note Choosing Window::.

     If BUFFER-OR-NAME is a string that does not name an existing
     buffer, a buffer by that name is created.  The major mode for the
     new buffer is set according to the variable `default-major-mode'.
     *Note Auto Major Mode::.

     This function updates the buffer list just like `switch-to-buffer'
     unless NORECORD is non-`nil'.

 -- Command: replace-buffer-in-windows buffer-or-name
     This function replaces BUFFER-OR-NAME with some other buffer in all
     windows displaying it.  It chooses the other buffer with
     `other-buffer'.  In the usual applications of this function, you
     don't care which other buffer is used; you just want to make sure
     that BUFFER-OR-NAME is no longer displayed.

     This function returns `nil'.


File: elisp,  Node: Choosing Window,  Next: Window Point,  Prev: Displaying Buffers,  Up: Windows

28.8 Choosing a Window for Display
==================================

This section describes the basic facility that chooses a window to
display a buffer in--`display-buffer'.  All the higher-level functions
and commands use this subroutine.  Here we describe how to use
`display-buffer' and how to customize it.

 -- Command: display-buffer buffer-or-name &optional not-this-window
          frame
     This command makes BUFFER-OR-NAME appear in some window, like
     `pop-to-buffer', but it does not select that window and does not
     make the buffer current.  The identity of the selected window is
     unaltered by this function.  BUFFER-OR-NAME must be a buffer, or
     the name of an existing buffer.

     If NOT-THIS-WINDOW is non-`nil', it means to display the specified
     buffer in a window other than the selected one, even if it is
     already on display in the selected window.  This can cause the
     buffer to appear in two windows at once.  Otherwise, if
     BUFFER-OR-NAME is already being displayed in any window, that is
     good enough, so this function does nothing.

     `display-buffer' returns the window chosen to display
     BUFFER-OR-NAME.

     If the argument FRAME is non-`nil', it specifies which frames to
     check when deciding whether the buffer is already displayed.  If
     the buffer is already displayed in some window on one of these
     frames, `display-buffer' simply returns that window.  Here are the
     possible values of FRAME:

        * If it is `nil', consider windows on the selected frame.
          (Actually, the last non-minibuffer frame.)

        * If it is `t', consider windows on all frames.

        * If it is `visible', consider windows on all visible frames.

        * If it is 0, consider windows on all visible or iconified
          frames.

        * If it is a frame, consider windows on that frame.

     Precisely how `display-buffer' finds or creates a window depends on
     the variables described below.

 -- User Option: display-buffer-reuse-frames
     If this variable is non-`nil', `display-buffer' searches existing
     frames for a window displaying the buffer.  If the buffer is
     already displayed in a window in some frame, `display-buffer' makes
     the frame visible and raises it, to use that window.  If the
     buffer is not already displayed, or if
     `display-buffer-reuse-frames' is `nil', `display-buffer''s
     behavior is determined by other variables, described below.

 -- User Option: pop-up-windows
     This variable controls whether `display-buffer' makes new windows.
     If it is non-`nil' and there is only one window, then that window
     is split.  If it is `nil', then `display-buffer' does not split
     the single window, but uses it whole.

 -- User Option: split-height-threshold
     This variable determines when `display-buffer' may split a window,
     if there are multiple windows.  `display-buffer' always splits the
     largest window if it has at least this many lines.  If the largest
     window is not this tall, it is split only if it is the sole window
     and `pop-up-windows' is non-`nil'.

 -- User Option: even-window-heights
     This variable determines if `display-buffer' should even out window
     heights if the buffer gets displayed in an existing window, above
     or beneath another existing window.  If `even-window-heights' is
     `t', the default, window heights will be evened out.  If
     `even-window-heights' is `nil', the original window heights will
     be left alone.

 -- User Option: pop-up-frames
     This variable controls whether `display-buffer' makes new frames.
     If it is non-`nil', `display-buffer' looks for an existing window
     already displaying the desired buffer, on any visible frame.  If
     it finds one, it returns that window.  Otherwise it makes a new
     frame.  The variables `pop-up-windows' and
     `split-height-threshold' do not matter if `pop-up-frames' is
     non-`nil'.

     If `pop-up-frames' is `nil', then `display-buffer' either splits a
     window or reuses one.

     *Note Frames::, for more information.

 -- User Option: pop-up-frame-function
     This variable specifies how to make a new frame if `pop-up-frames'
     is non-`nil'.

     Its value should be a function of no arguments.  When
     `display-buffer' makes a new frame, it does so by calling that
     function, which should return a frame.  The default value of the
     variable is a function that creates a frame using parameters from
     `pop-up-frame-alist'.

 -- User Option: pop-up-frame-alist
     This variable holds an alist specifying frame parameters used when
     `display-buffer' makes a new frame.  *Note Frame Parameters::, for
     more information about frame parameters.

 -- User Option: special-display-buffer-names
     A list of buffer names for buffers that should be displayed
     specially.  If the buffer's name is in this list, `display-buffer'
     handles the buffer specially.

     By default, special display means to give the buffer a dedicated
     frame.

     If an element is a list, instead of a string, then the CAR of the
     list is the buffer name, and the rest of the list says how to
     create the frame.  There are two possibilities for the rest of the
     list (its CDR).  It can be an alist, specifying frame parameters,
     or it can contain a function and arguments to give to it.  (The
     function's first argument is always the buffer to be displayed;
     the arguments from the list come after that.)

     For example:

          (("myfile" (minibuffer) (menu-bar-lines . 0)))

     specifies to display a buffer named `myfile' in a dedicated frame
     with specified `minibuffer' and `menu-bar-lines' parameters.

     The list of frame parameters can also use the phony frame
     parameters `same-frame' and `same-window'.  If the specified frame
     parameters include `(same-window . VALUE)' and VALUE is non-`nil',
     that means to display the buffer in the current selected window.
     Otherwise, if they include `(same-frame .  VALUE)' and VALUE is
     non-`nil', that means to display the buffer in a new window in the
     currently selected frame.

 -- User Option: special-display-regexps
     A list of regular expressions that specify buffers that should be
     displayed specially.  If the buffer's name matches any of the
     regular expressions in this list, `display-buffer' handles the
     buffer specially.

     By default, special display means to give the buffer a dedicated
     frame.

     If an element is a list, instead of a string, then the CAR of the
     list is the regular expression, and the rest of the list says how
     to create the frame.  See above, under
     `special-display-buffer-names'.

 -- Function: special-display-p buffer-name
     This function returns non-`nil' if displaying a buffer named
     BUFFER-NAME with `display-buffer' would create a special frame.
     The value is `t' if it would use the default frame parameters, or
     else the specified list of frame parameters.

 -- Variable: special-display-function
     This variable holds the function to call to display a buffer
     specially.  It receives the buffer as an argument, and should
     return the window in which it is displayed.

     The default value of this variable is
     `special-display-popup-frame'.

 -- Function: special-display-popup-frame buffer &optional args
     This function makes BUFFER visible in a frame of its own.  If
     BUFFER is already displayed in a window in some frame, it makes
     the frame visible and raises it, to use that window.  Otherwise, it
     creates a frame that will be dedicated to BUFFER.  This function
     returns the window it used.

     If ARGS is an alist, it specifies frame parameters for the new
     frame.

     If ARGS is a list whose CAR is a symbol, then `(car ARGS)' is
     called as a function to actually create and set up the frame; it
     is called with BUFFER as first argument, and `(cdr ARGS)' as
     additional arguments.

     This function always uses an existing window displaying BUFFER,
     whether or not it is in a frame of its own; but if you set up the
     above variables in your init file, before BUFFER was created, then
     presumably the window was previously made by this function.

 -- User Option: special-display-frame-alist
     This variable holds frame parameters for
     `special-display-popup-frame' to use when it creates a frame.

 -- User Option: same-window-buffer-names
     A list of buffer names for buffers that should be displayed in the
     selected window.  If the buffer's name is in this list,
     `display-buffer' handles the buffer by switching to it in the
     selected window.

 -- User Option: same-window-regexps
     A list of regular expressions that specify buffers that should be
     displayed in the selected window.  If the buffer's name matches
     any of the regular expressions in this list, `display-buffer'
     handles the buffer by switching to it in the selected window.

 -- Function: same-window-p buffer-name
     This function returns `t' if displaying a buffer named BUFFER-NAME
     with `display-buffer' would put it in the selected window.

 -- Variable: display-buffer-function
     This variable is the most flexible way to customize the behavior of
     `display-buffer'.  If it is non-`nil', it should be a function
     that `display-buffer' calls to do the work.  The function should
     accept two arguments, the first two arguments that `display-buffer'
     received.  It should choose or create a window, display the
     specified buffer in it, and then return the window.

     This hook takes precedence over all the other options and hooks
     described above.

   A window can be marked as "dedicated" to its buffer.  Then
`display-buffer' will not try to use that window to display any other
buffer.

 -- Function: window-dedicated-p window
     This function returns non-`nil' if WINDOW is marked as dedicated;
     otherwise `nil'.

 -- Function: set-window-dedicated-p window flag
     This function marks WINDOW as dedicated if FLAG is non-`nil', and
     nondedicated otherwise.


File: elisp,  Node: Window Point,  Next: Window Start,  Prev: Choosing Window,  Up: Windows

28.9 Windows and Point
======================

Each window has its own value of point, independent of the value of
point in other windows displaying the same buffer.  This makes it useful
to have multiple windows showing one buffer.

   * The window point is established when a window is first created; it
     is initialized from the buffer's point, or from the window point
     of another window opened on the buffer if such a window exists.

   * Selecting a window sets the value of point in its buffer from the
     window's value of point.  Conversely, deselecting a window sets the
     window's value of point from that of the buffer.  Thus, when you
     switch between windows that display a given buffer, the point
     value for the selected window is in effect in the buffer, while
     the point values for the other windows are stored in those windows.

   * As long as the selected window displays the current buffer, the
     window's point and the buffer's point always move together; they
     remain equal.

*Note Positions::, for more details on buffer positions.

   As far as the user is concerned, point is where the cursor is, and
when the user switches to another buffer, the cursor jumps to the
position of point in that buffer.

 -- Function: window-point &optional window
     This function returns the current position of point in WINDOW.
     For a nonselected window, this is the value point would have (in
     that window's buffer) if that window were selected.  If WINDOW is
     `nil', the selected window is used.

     When WINDOW is the selected window and its buffer is also the
     current buffer, the value returned is the same as point in that
     buffer.

     Strictly speaking, it would be more correct to return the
     "top-level" value of point, outside of any `save-excursion' forms.
     But that value is hard to find.

 -- Function: set-window-point window position
     This function positions point in WINDOW at position POSITION in
     WINDOW's buffer.  It returns POSITION.

     If WINDOW is selected, and its buffer is current, this simply does
     `goto-char'.


File: elisp,  Node: Window Start,  Next: Textual Scrolling,  Prev: Window Point,  Up: Windows

28.10 The Window Start Position
===============================

Each window contains a marker used to keep track of a buffer position
that specifies where in the buffer display should start.  This position
is called the "display-start" position of the window (or just the
"start").  The character after this position is the one that appears at
the upper left corner of the window.  It is usually, but not
inevitably, at the beginning of a text line.

   After switching windows or buffers, and in some other cases, if the
window start is in the middle of a line, Emacs adjusts the window start
to the start of a line.  This prevents certain operations from leaving
the window start at a meaningless point within a line.  This feature
may interfere with testing some Lisp code by executing it using the
commands of Lisp mode, because they trigger this readjustment.  To test
such code, put it into a command and bind the command to a key.

 -- Function: window-start &optional window
     This function returns the display-start position of window WINDOW.
     If WINDOW is `nil', the selected window is used.  For example,

          (window-start)
               => 7058

     When you create a window, or display a different buffer in it, the
     display-start position is set to a display-start position recently
     used for the same buffer, or 1 if the buffer doesn't have any.

     Redisplay updates the window-start position (if you have not
     specified it explicitly since the previous redisplay)--for
     example, to make sure point appears on the screen.  Nothing except
     redisplay automatically changes the window-start position; if you
     move point, do not expect the window-start position to change in
     response until after the next redisplay.

     For a realistic example of using `window-start', see the
     description of `count-lines'.  *Note Definition of count-lines::.

 -- Function: window-end &optional window update
     This function returns the position of the end of the display in
     window WINDOW.  If WINDOW is `nil', the selected window is used.

     Simply changing the buffer text or moving point does not update the
     value that `window-end' returns.  The value is updated only when
     Emacs redisplays and redisplay completes without being preempted.

     If the last redisplay of WINDOW was preempted, and did not finish,
     Emacs does not know the position of the end of display in that
     window.  In that case, this function returns `nil'.

     If UPDATE is non-`nil', `window-end' always returns an up-to-date
     value for where the window ends, based on the current
     `window-start' value.  If the saved value is valid, `window-end'
     returns that; otherwise it computes the correct value by scanning
     the buffer text.

     Even if UPDATE is non-`nil', `window-end' does not attempt to
     scroll the display if point has moved off the screen, the way real
     redisplay would do.  It does not alter the `window-start' value.
     In effect, it reports where the displayed text will end if
     scrolling is not required.

 -- Function: set-window-start window position &optional noforce
     This function sets the display-start position of WINDOW to
     POSITION in WINDOW's buffer.  It returns POSITION.

     The display routines insist that the position of point be visible
     when a buffer is displayed.  Normally, they change the
     display-start position (that is, scroll the window) whenever
     necessary to make point visible.  However, if you specify the
     start position with this function using `nil' for NOFORCE, it
     means you want display to start at POSITION even if that would put
     the location of point off the screen.  If this does place point
     off screen, the display routines move point to the left margin on
     the middle line in the window.

     For example, if point is 1 and you set the start of the window
     to 37, the start of the next line, point will be "above" the top
     of the window.  The display routines will automatically move point
     if it is still 1 when redisplay occurs.  Here is an example:

          ;; Here is what `foo' looks like before executing
          ;;   the `set-window-start' expression.

          ---------- Buffer: foo ----------
          -!-This is the contents of buffer foo.
          2
          3
          4
          5
          6
          ---------- Buffer: foo ----------

          (set-window-start
           (selected-window)
           (save-excursion
             (goto-char 1)
             (forward-line 1)
             (point)))
          => 37

          ;; Here is what `foo' looks like after executing
          ;;   the `set-window-start' expression.
          ---------- Buffer: foo ----------
          2
          3
          -!-4
          5
          6
          ---------- Buffer: foo ----------

     If NOFORCE is non-`nil', and POSITION would place point off screen
     at the next redisplay, then redisplay computes a new window-start
     position that works well with point, and thus POSITION is not used.

 -- Function: pos-visible-in-window-p &optional position window
          partially
     This function returns non-`nil' if POSITION is within the range of
     text currently visible on the screen in WINDOW.  It returns `nil'
     if POSITION is scrolled vertically out of view.  Locations that
     are partially obscured are not considered visible unless PARTIALLY
     is non-`nil'.  The argument POSITION defaults to the current
     position of point in WINDOW; WINDOW, to the selected window.

     If POSITION is `t', that means to check the last visible position
     in WINDOW.

     The `pos-visible-in-window-p' function considers only vertical
     scrolling.  If POSITION is out of view only because WINDOW has
     been scrolled horizontally, `pos-visible-in-window-p' returns
     non-`nil' anyway.  *Note Horizontal Scrolling::.

     If POSITION is visible, `pos-visible-in-window-p' returns `t' if
     PARTIALLY is `nil'; if PARTIALLY is non-`nil', and the character
     after POSITION is fully visible, it returns a list of the form `(X
     Y)', where X and Y are the pixel coordinates relative to the top
     left corner of the window; otherwise it returns an extended list
     of the form `(X Y RTOP RBOT ROWH VPOS)', where the RTOP and RBOT
     specify the number of off-window pixels at the top and bottom of
     the row at POSITION, ROWH specifies the visible height of that row,
     and VPOS specifies the vertical position (zero-based row number)
     of that row.

     Here is an example:

          ;; If point is off the screen now, recenter it now.
          (or (pos-visible-in-window-p
               (point) (selected-window))
              (recenter 0))

 -- Function: window-line-height &optional line window
     This function returns information about text line LINE in WINDOW.
     If LINE is one of `header-line' or `mode-line',
     `window-line-height' returns information about the corresponding
     line of the window.  Otherwise, LINE is a text line number
     starting from 0.  A negative number counts from the end of the
     window.  The argument LINE defaults to the current line in WINDOW;
     WINDOW, to the selected window.

     If the display is not up to date, `window-line-height' returns
     `nil'.  In that case, `pos-visible-in-window-p' may be used to
     obtain related information.

     If there is no line corresponding to the specified LINE,
     `window-line-height' returns `nil'.  Otherwise, it returns a list
     `(HEIGHT VPOS YPOS OFFBOT)', where HEIGHT is the height in pixels
     of the visible part of the line, VPOS and YPOS are the vertical
     position in lines and pixels of the line relative to the top of
     the first text line, and OFFBOT is the number of off-window pixels
     at the bottom of the text line.  If there are off-window pixels at
     the top of the (first) text line, YPOS is negative.


File: elisp,  Node: Textual Scrolling,  Next: Vertical Scrolling,  Prev: Window Start,  Up: Windows

28.11 Textual Scrolling
=======================

"Textual scrolling" means moving the text up or down through a window.
It works by changing the value of the window's display-start location.
It may also change the value of `window-point' to keep point on the
screen.

   Textual scrolling was formerly called "vertical scrolling," but we
changed its name to distinguish it from the new vertical fractional
scrolling feature (*note Vertical Scrolling::).

   In the commands `scroll-up' and `scroll-down', the directions "up"
and "down" refer to the motion of the text in the buffer at which you
are looking through the window.  Imagine that the text is written on a
long roll of paper and that the scrolling commands move the paper up
and down.  Thus, if you are looking at text in the middle of a buffer
and repeatedly call `scroll-down', you will eventually see the
beginning of the buffer.

   Some people have urged that the opposite convention be used: they
imagine that the window moves over text that remains in place.  Then
"down" commands would take you to the end of the buffer.  This view is
more consistent with the actual relationship between windows and the
text in the buffer, but it is less like what the user sees.  The
position of a window on the terminal does not move, and short scrolling
commands clearly move the text up or down on the screen.  We have chosen
names that fit the user's point of view.

   The textual scrolling functions (aside from `scroll-other-window')
have unpredictable results if the current buffer is different from the
buffer that is displayed in the selected window.  *Note Current
Buffer::.

   If the window contains a row which is taller than the height of the
window (for example in the presence of a large image), the scroll
functions will adjust the window vscroll to scroll the partially
visible row.  To disable this feature, Lisp code may bind the variable
`auto-window-vscroll' to `nil' (*note Vertical Scrolling::).

 -- Command: scroll-up &optional count
     This function scrolls the text in the selected window upward COUNT
     lines.  If COUNT is negative, scrolling is actually downward.

     If COUNT is `nil' (or omitted), then the length of scroll is
     `next-screen-context-lines' lines less than the usable height of
     the window (not counting its mode line).

     `scroll-up' returns `nil', unless it gets an error because it
     can't scroll any further.

 -- Command: scroll-down &optional count
     This function scrolls the text in the selected window downward
     COUNT lines.  If COUNT is negative, scrolling is actually upward.

     If COUNT is omitted or `nil', then the length of the scroll is
     `next-screen-context-lines' lines less than the usable height of
     the window (not counting its mode line).

     `scroll-down' returns `nil', unless it gets an error because it
     can't scroll any further.

 -- Command: scroll-other-window &optional count
     This function scrolls the text in another window upward COUNT
     lines.  Negative values of COUNT, or `nil', are handled as in
     `scroll-up'.

     You can specify which buffer to scroll by setting the variable
     `other-window-scroll-buffer' to a buffer.  If that buffer isn't
     already displayed, `scroll-other-window' displays it in some
     window.

     When the selected window is the minibuffer, the next window is
     normally the one at the top left corner.  You can specify a
     different window to scroll, when the minibuffer is selected, by
     setting the variable `minibuffer-scroll-window'.  This variable
     has no effect when any other window is selected.  When it is
     non-`nil' and the minibuffer is selected, it takes precedence over
     `other-window-scroll-buffer'.  *Note Definition of
     minibuffer-scroll-window::.

     When the minibuffer is active, it is the next window if the
     selected window is the one at the bottom right corner.  In this
     case, `scroll-other-window' attempts to scroll the minibuffer.  If
     the minibuffer contains just one line, it has nowhere to scroll
     to, so the line reappears after the echo area momentarily displays
     the message `Beginning of buffer'.

 -- Variable: other-window-scroll-buffer
     If this variable is non-`nil', it tells `scroll-other-window'
     which buffer to scroll.

 -- User Option: scroll-margin
     This option specifies the size of the scroll margin--a minimum
     number of lines between point and the top or bottom of a window.
     Whenever point gets within this many lines of the top or bottom of
     the window, redisplay scrolls the text automatically (if possible)
     to move point out of the margin, closer to the center of the
     window.

 -- User Option: scroll-conservatively
     This variable controls how scrolling is done automatically when
     point moves off the screen (or into the scroll margin).  If the
     value is a positive integer N, then redisplay scrolls the text up
     to N lines in either direction, if that will bring point back into
     proper view.  This action is called "conservative scrolling".
     Otherwise, scrolling happens in the usual way, under the control of
     other variables such as `scroll-up-aggressively' and
     `scroll-down-aggressively'.

     The default value is zero, which means that conservative scrolling
     never happens.

 -- User Option: scroll-down-aggressively
     The value of this variable should be either `nil' or a fraction F
     between 0 and 1.  If it is a fraction, that specifies where on the
     screen to put point when scrolling down.  More precisely, when a
     window scrolls down because point is above the window start, the
     new start position is chosen to put point F part of the window
     height from the top.  The larger F, the more aggressive the
     scrolling.

     A value of `nil' is equivalent to .5, since its effect is to center
     point.  This variable automatically becomes buffer-local when set
     in any fashion.

 -- User Option: scroll-up-aggressively
     Likewise, for scrolling up.  The value, F, specifies how far point
     should be placed from the bottom of the window; thus, as with
     `scroll-up-aggressively', a larger value scrolls more aggressively.

 -- User Option: scroll-step
     This variable is an older variant of `scroll-conservatively'.  The
     difference is that it if its value is N, that permits scrolling
     only by precisely N lines, not a smaller number.  This feature
     does not work with `scroll-margin'.  The default value is zero.

 -- User Option: scroll-preserve-screen-position
     If this option is `t', scrolling which would move the current
     point position out of the window chooses the new position of point
     so that the vertical position of the cursor is unchanged, if
     possible.

     If it is non-`nil' and not `t', then the scrolling functions
     always preserve the vertical position of point, if possible.

 -- User Option: next-screen-context-lines
     The value of this variable is the number of lines of continuity to
     retain when scrolling by full screens.  For example, `scroll-up'
     with an argument of `nil' scrolls so that this many lines at the
     bottom of the window appear instead at the top.  The default value
     is `2'.

 -- Command: recenter &optional count
     This function scrolls the text in the selected window so that
     point is displayed at a specified vertical position within the
     window.  It does not "move point" with respect to the text.

     If COUNT is a nonnegative number, that puts the line containing
     point COUNT lines down from the top of the window.  If COUNT is a
     negative number, then it counts upward from the bottom of the
     window, so that -1 stands for the last usable line in the window.
     If COUNT is a non-`nil' list, then it stands for the line in the
     middle of the window.

     If COUNT is `nil', `recenter' puts the line containing point in
     the middle of the window, then clears and redisplays the entire
     selected frame.

     When `recenter' is called interactively, COUNT is the raw prefix
     argument.  Thus, typing `C-u' as the prefix sets the COUNT to a
     non-`nil' list, while typing `C-u 4' sets COUNT to 4, which
     positions the current line four lines from the top.

     With an argument of zero, `recenter' positions the current line at
     the top of the window.  This action is so handy that some people
     make a separate key binding to do this.  For example,

          (defun line-to-top-of-window ()
            "Scroll current line to top of window.
          Replaces three keystroke sequence C-u 0 C-l."
            (interactive)
            (recenter 0))

          (global-set-key [kp-multiply] 'line-to-top-of-window)


File: elisp,  Node: Vertical Scrolling,  Next: Horizontal Scrolling,  Prev: Textual Scrolling,  Up: Windows

28.12 Vertical Fractional Scrolling
===================================

"Vertical fractional scrolling" means shifting the image in the window
up or down by a specified multiple or fraction of a line.  Each window
has a "vertical scroll position", which is a number, never less than
zero.  It specifies how far to raise the contents of the window.
Raising the window contents generally makes all or part of some lines
disappear off the top, and all or part of some other lines appear at
the bottom.  The usual value is zero.

   The vertical scroll position is measured in units of the normal line
height, which is the height of the default font.  Thus, if the value is
.5, that means the window contents are scrolled up half the normal line
height.  If it is 3.3, that means the window contents are scrolled up
somewhat over three times the normal line height.

   What fraction of a line the vertical scrolling covers, or how many
lines, depends on what the lines contain.  A value of .5 could scroll a
line whose height is very short off the screen, while a value of 3.3
could scroll just part of the way through a tall line or an image.

 -- Function: window-vscroll &optional window pixels-p
     This function returns the current vertical scroll position of
     WINDOW.  If WINDOW is `nil', the selected window is used.  If
     PIXELS-P is non-`nil', the return value is measured in pixels,
     rather than in units of the normal line height.

          (window-vscroll)
               => 0

 -- Function: set-window-vscroll window lines &optional pixels-p
     This function sets WINDOW's vertical scroll position to LINES.
     The argument LINES should be zero or positive; if not, it is taken
     as zero.

     If WINDOW is `nil', the selected window is used.

     The actual vertical scroll position must always correspond to an
     integral number of pixels, so the value you specify is rounded
     accordingly.

     The return value is the result of this rounding.

          (set-window-vscroll (selected-window) 1.2)
               => 1.13

     If PIXELS-P is non-`nil', LINES specifies a number of pixels.  In
     this case, the return value is LINES.

 -- Variable: auto-window-vscroll
     If this variable is non-`nil', the line-move, scroll-up, and
     scroll-down functions will automatically modify the window vscroll
     to scroll through display rows that are taller that the height of
     the window, for example in the presence of large images.


File: elisp,  Node: Horizontal Scrolling,  Next: Size of Window,  Prev: Vertical Scrolling,  Up: Windows

28.13 Horizontal Scrolling
==========================

"Horizontal scrolling" means shifting the image in the window left or
right by a specified multiple of the normal character width.  Each
window has a "horizontal scroll position", which is a number, never
less than zero.  It specifies how far to shift the contents left.
Shifting the window contents left generally makes all or part of some
characters disappear off the left, and all or part of some other
characters appear at the right.  The usual value is zero.

   The horizontal scroll position is measured in units of the normal
character width, which is the width of space in the default font.  Thus,
if the value is 5, that means the window contents are scrolled left by 5
times the normal character width.  How many characters actually
disappear off to the left depends on their width, and could vary from
line to line.

   Because we read from side to side in the "inner loop," and from top
to bottom in the "outer loop," the effect of horizontal scrolling is
not like that of textual or vertical scrolling.  Textual scrolling
involves selection of a portion of text to display, and vertical
scrolling moves the window contents contiguously; but horizontal
scrolling causes part of _each line_ to go off screen.

   Usually, no horizontal scrolling is in effect; then the leftmost
column is at the left edge of the window.  In this state, scrolling to
the right is meaningless, since there is no data to the left of the edge
to be revealed by it; so this is not allowed.  Scrolling to the left is
allowed; it scrolls the first columns of text off the edge of the window
and can reveal additional columns on the right that were truncated
before.  Once a window has a nonzero amount of leftward horizontal
scrolling, you can scroll it back to the right, but only so far as to
reduce the net horizontal scroll to zero.  There is no limit to how far
left you can scroll, but eventually all the text will disappear off the
left edge.

   If `auto-hscroll-mode' is set, redisplay automatically alters the
horizontal scrolling of a window as necessary to ensure that point is
always visible.  However, you can still set the horizontal scrolling
value explicitly.  The value you specify serves as a lower bound for
automatic scrolling, i.e. automatic scrolling will not scroll a window
to a column less than the specified one.

 -- Command: scroll-left &optional count set-minimum
     This function scrolls the selected window COUNT columns to the
     left (or to the right if COUNT is negative).  The default for
     COUNT is the window width, minus 2.

     The return value is the total amount of leftward horizontal
     scrolling in effect after the change--just like the value returned
     by `window-hscroll' (below).

     Once you scroll a window as far right as it can go, back to its
     normal position where the total leftward scrolling is zero,
     attempts to scroll any farther right have no effect.

     If SET-MINIMUM is non-`nil', the new scroll amount becomes the
     lower bound for automatic scrolling; that is, automatic scrolling
     will not scroll a window to a column less than the value returned
     by this function.  Interactive calls pass non-`nil' for
     SET-MINIMUM.

 -- Command: scroll-right &optional count set-minimum
     This function scrolls the selected window COUNT columns to the
     right (or to the left if COUNT is negative).  The default for
     COUNT is the window width, minus 2.  Aside from the direction of
     scrolling, this works just like `scroll-left'.

 -- Function: window-hscroll &optional window
     This function returns the total leftward horizontal scrolling of
     WINDOW--the number of columns by which the text in WINDOW is
     scrolled left past the left margin.

     The value is never negative.  It is zero when no horizontal
     scrolling has been done in WINDOW (which is usually the case).

     If WINDOW is `nil', the selected window is used.

          (window-hscroll)
               => 0
          (scroll-left 5)
               => 5
          (window-hscroll)
               => 5

 -- Function: set-window-hscroll window columns
     This function sets horizontal scrolling of WINDOW.  The value of
     COLUMNS specifies the amount of scrolling, in terms of columns
     from the left margin.  The argument COLUMNS should be zero or
     positive; if not, it is taken as zero.  Fractional values of
     COLUMNS are not supported at present.

     Note that `set-window-hscroll' may appear not to work if you test
     it by evaluating a call with `M-:' in a simple way.  What happens
     is that the function sets the horizontal scroll value and returns,
     but then redisplay adjusts the horizontal scrolling to make point
     visible, and this overrides what the function did.  You can
     observe the function's effect if you call it while point is
     sufficiently far from the left margin that it will remain visible.

     The value returned is COLUMNS.

          (set-window-hscroll (selected-window) 10)
               => 10

   Here is how you can determine whether a given position POSITION is
off the screen due to horizontal scrolling:

     (defun hscroll-on-screen (window position)
       (save-excursion
         (goto-char position)
         (and
          (>= (- (current-column) (window-hscroll window)) 0)
          (< (- (current-column) (window-hscroll window))
             (window-width window)))))


File: elisp,  Node: Size of Window,  Next: Resizing Windows,  Prev: Horizontal Scrolling,  Up: Windows

28.14 The Size of a Window
==========================

An Emacs window is rectangular, and its size information consists of
the height (the number of lines) and the width (the number of character
positions in each line).  The mode line is included in the height.  But
the width does not count the scroll bar or the column of `|' characters
that separates side-by-side windows.

   The following three functions return size information about a window:

 -- Function: window-height &optional window
     This function returns the number of lines in WINDOW, including its
     mode line and header line, if any.  If WINDOW fills its entire
     frame except for the echo area, this is typically one less than
     the value of `frame-height' on that frame.

     If WINDOW is `nil', the function uses the selected window.

          (window-height)
               => 23
          (split-window-vertically)
               => #<window 4 on windows.texi>
          (window-height)
               => 11

 -- Function: window-body-height &optional window
     Like `window-height' but the value does not include the mode line
     (if any) or the header line (if any).

 -- Function: window-width &optional window
     This function returns the number of columns in WINDOW.  If WINDOW
     fills its entire frame, this is the same as the value of
     `frame-width' on that frame.  The width does not include the
     window's scroll bar or the column of `|' characters that separates
     side-by-side windows.

     If WINDOW is `nil', the function uses the selected window.

          (window-width)
               => 80

 -- Function: window-full-width-p &optional window
     This function returns non-`nil' if WINDOW is as wide as the frame
     that contains it; otherwise `nil'.  If WINDOW is `nil', the
     function uses the selected window.

 -- Function: window-edges &optional window
     This function returns a list of the edge coordinates of WINDOW.
     If WINDOW is `nil', the selected window is used.

     The order of the list is `(LEFT TOP RIGHT BOTTOM)', all elements
     relative to 0, 0 at the top left corner of the frame.  The element
     RIGHT of the value is one more than the rightmost column used by
     WINDOW, and BOTTOM is one more than the bottommost row used by
     WINDOW and its mode-line.

     The edges include the space used by the window's scroll bar,
     display margins, fringes, header line, and mode line, if it has
     them.  Also, if the window has a neighbor on the right, its right
     edge value includes the width of the separator line between the
     window and that neighbor.  Since the width of the window does not
     include this separator, the width does not usually equal the
     difference between the right and left edges.

 -- Function: window-inside-edges &optional window
     This is similar to `window-edges', but the edge values it returns
     include only the text area of the window.  They do not include the
     header line, mode line, scroll bar or vertical separator, fringes,
     or display margins.

   Here are the results obtained on a typical 24-line terminal with just
one window, with menu bar enabled:

     (window-edges (selected-window))
          => (0 1 80 23)
     (window-inside-edges (selected-window))
          => (0 1 80 22)

The bottom edge is at line 23 because the last line is the echo area.
The bottom inside edge is at line 22, which is the window's mode line.

   If WINDOW is at the upper left corner of its frame, and there is no
menu bar, then BOTTOM returned by `window-edges' is the same as the
value of `(window-height)', RIGHT is almost the same as the value of
`(window-width)', and TOP and LEFT are zero.  For example, the edges of
the following window are `0 0 8 5'.  Assuming that the frame has more
than 8 columns, the last column of the window (column 7) holds a border
rather than text.  The last row (row 4) holds the mode line, shown here
with `xxxxxxxxx'.

                0
                _______
             0 |       |
               |       |
               |       |
               |       |
               xxxxxxxxx  4

                       7

   In the following example, let's suppose that the frame is 7 columns
wide.  Then the edges of the left window are `0 0 4 3' and the edges of
the right window are `4 0 7 3'.  The inside edges of the left window
are `0 0 3 2', and the inside edges of the right window are `4 0 7 2',

                ___ ___
               |   |   |
               |   |   |
               xxxxxxxxx

                0  34  7

 -- Function: window-pixel-edges &optional window
     This function is like `window-edges' except that, on a graphical
     display, the edge values are measured in pixels instead of in
     character lines and columns.

 -- Function: window-inside-pixel-edges &optional window
     This function is like `window-inside-edges' except that, on a
     graphical display, the edge values are measured in pixels instead
     of in character lines and columns.


File: elisp,  Node: Resizing Windows,  Next: Coordinates and Windows,  Prev: Size of Window,  Up: Windows

28.15 Changing the Size of a Window
===================================

The window size functions fall into two classes: high-level commands
that change the size of windows and low-level functions that access
window size.  Emacs does not permit overlapping windows or gaps between
windows, so resizing one window affects other windows.

 -- Command: enlarge-window size &optional horizontal
     This function makes the selected window SIZE lines taller,
     stealing lines from neighboring windows.  It takes the lines from
     one window at a time until that window is used up, then takes from
     another.  If a window from which lines are stolen shrinks below
     `window-min-height' lines, that window disappears.

     If HORIZONTAL is non-`nil', this function makes WINDOW wider by
     SIZE columns, stealing columns instead of lines.  If a window from
     which columns are stolen shrinks below `window-min-width' columns,
     that window disappears.

     If the requested size would exceed that of the window's frame,
     then the function makes the window occupy the entire height (or
     width) of the frame.

     If there are various other windows from which lines or columns can
     be stolen, and some of them specify fixed size (using
     `window-size-fixed', see below), they are left untouched while
     other windows are "robbed."  If it would be necessary to alter the
     size of a fixed-size window, `enlarge-window' gets an error
     instead.

     If SIZE is negative, this function shrinks the window by -SIZE
     lines or columns.  If that makes the window smaller than the
     minimum size (`window-min-height' and `window-min-width'),
     `enlarge-window' deletes the window.

     `enlarge-window' returns `nil'.

 -- Command: enlarge-window-horizontally columns
     This function makes the selected window COLUMNS wider.  It could
     be defined as follows:

          (defun enlarge-window-horizontally (columns)
            (interactive "p")
            (enlarge-window columns t))

 -- Command: shrink-window size &optional horizontal
     This function is like `enlarge-window' but negates the argument
     SIZE, making the selected window smaller by giving lines (or
     columns) to the other windows.  If the window shrinks below
     `window-min-height' or `window-min-width', then it disappears.

     If SIZE is negative, the window is enlarged by -SIZE lines or
     columns.

 -- Command: shrink-window-horizontally columns
     This function makes the selected window COLUMNS narrower.  It
     could be defined as follows:

          (defun shrink-window-horizontally (columns)
            (interactive "p")
            (shrink-window columns t))

 -- Function: adjust-window-trailing-edge window delta horizontal
     This function makes the selected window DELTA lines taller or
     DELTA columns wider, by moving the bottom or right edge.  This
     function does not delete other windows; if it cannot make the
     requested size adjustment, it signals an error.  On success, this
     function returns `nil'.

 -- Function: fit-window-to-buffer &optional window max-height
          min-height
     This function makes WINDOW the right height to display its
     contents exactly.  If WINDOW is omitted or `nil', it uses the
     selected window.

     The argument MAX-HEIGHT specifies the maximum height the window is
     allowed to be; `nil' means use the frame height.  The argument
     MIN-HEIGHT specifies the minimum height for the window; `nil'
     means use `window-min-height'.  All these height values include
     the mode-line and/or header-line.

 -- Command: shrink-window-if-larger-than-buffer &optional window
     This command shrinks WINDOW vertically to be as small as possible
     while still showing the full contents of its buffer--but not less
     than `window-min-height' lines.  If WINDOW is not given, it
     defaults to the selected window.

     However, the command does nothing if the window is already too
     small to display the whole text of the buffer, or if part of the
     contents are currently scrolled off screen, or if the window is
     not the full width of its frame, or if the window is the only
     window in its frame.

     This command returns non-`nil' if it actually shrank the window
     and `nil' otherwise.

 -- Variable: window-size-fixed
     If this variable is non-`nil', in any given buffer, then the size
     of any window displaying the buffer remains fixed unless you
     explicitly change it or Emacs has no other choice.

     If the value is `height', then only the window's height is fixed;
     if the value is `width', then only the window's width is fixed.
     Any other non-`nil' value fixes both the width and the height.

     This variable automatically becomes buffer-local when set.

     Explicit size-change functions such as `enlarge-window' get an
     error if they would have to change a window size which is fixed.
     Therefore, when you want to change the size of such a window, you
     should bind `window-size-fixed' to `nil', like this:

          (let ((window-size-fixed nil))
             (enlarge-window 10))

     Note that changing the frame size will change the size of a
     fixed-size window, if there is no other alternative.

   The following two variables constrain the window-structure-changing
functions to a minimum height and width.

 -- User Option: window-min-height
     The value of this variable determines how short a window may become
     before it is automatically deleted.  Making a window smaller than
     `window-min-height' automatically deletes it, and no window may be
     created shorter than this.  The default value is 4.

     The absolute minimum window height is one; actions that change
     window sizes reset this variable to one if it is less than one.

 -- User Option: window-min-width
     The value of this variable determines how narrow a window may
     become before it is automatically deleted.  Making a window
     smaller than `window-min-width' automatically deletes it, and no
     window may be created narrower than this.  The default value is 10.

     The absolute minimum window width is two; actions that change
     window sizes reset this variable to two if it is less than two.


File: elisp,  Node: Coordinates and Windows,  Next: Window Tree,  Prev: Resizing Windows,  Up: Windows

28.16 Coordinates and Windows
=============================

This section describes how to relate screen coordinates to windows.

 -- Function: window-at x y &optional frame
     This function returns the window containing the specified cursor
     position in the frame FRAME.  The coordinates X and Y are measured
     in characters and count from the top left corner of the frame.  If
     they are out of range, `window-at' returns `nil'.

     If you omit FRAME, the selected frame is used.

 -- Function: coordinates-in-window-p coordinates window
     This function checks whether a particular frame position falls
     within the window WINDOW.

     The argument COORDINATES is a cons cell of the form `(X . Y)'.
     The coordinates X and Y are measured in characters, and count from
     the top left corner of the screen or frame.

     The value returned by `coordinates-in-window-p' is non-`nil' if
     the coordinates are inside WINDOW.  The value also indicates what
     part of the window the position is in, as follows:

    `(RELX . RELY)'
          The coordinates are inside WINDOW.  The numbers RELX and RELY
          are the equivalent window-relative coordinates for the
          specified position, counting from 0 at the top left corner of
          the window.

    `mode-line'
          The coordinates are in the mode line of WINDOW.

    `header-line'
          The coordinates are in the header line of WINDOW.

    `vertical-line'
          The coordinates are in the vertical line between WINDOW and
          its neighbor to the right.  This value occurs only if the
          window doesn't have a scroll bar; positions in a scroll bar
          are considered outside the window for these purposes.

    `left-fringe'
    `right-fringe'
          The coordinates are in the left or right fringe of the window.

    `left-margin'
    `right-margin'
          The coordinates are in the left or right margin of the window.

    `nil'
          The coordinates are not in any part of WINDOW.

     The function `coordinates-in-window-p' does not require a frame as
     argument because it always uses the frame that WINDOW is on.


File: elisp,  Node: Window Tree,  Next: Window Configurations,  Prev: Coordinates and Windows,  Up: Windows

28.17 The Window Tree
=====================

A "window tree" specifies the layout, size, and relationship between
all windows in one frame.

 -- Function: window-tree &optional frame
     This function returns the window tree for frame FRAME.  If FRAME
     is omitted, the selected frame is used.

     The return value is a list of the form `(ROOT MINI)', where ROOT
     represents the window tree of the frame's root window, and MINI is
     the frame's minibuffer window.

     If the root window is not split, ROOT is the root window itself.
     Otherwise, ROOT is a list `(DIR EDGES W1 W2 ...)' where DIR is
     `nil' for a horizontal split, and `t' for a vertical split, EDGES
     gives the combined size and position of the subwindows in the
     split, and the rest of the elements are the subwindows in the
     split.  Each of the subwindows may again be a window or a list
     representing a window split, and so on.  The EDGES element is a
     list `(LEFT TOP RIGHT BOTTOM)' similar to the value returned by
     `window-edges'.


File: elisp,  Node: Window Configurations,  Next: Window Hooks,  Prev: Window Tree,  Up: Windows

28.18 Window Configurations
===========================

A "window configuration" records the entire layout of one frame--all
windows, their sizes, which buffers they contain, how those buffers are
scrolled, and their values of point and the mark; also their fringes,
margins, and scroll bar settings.  It also includes the values of
`window-min-height', `window-min-width' and `minibuffer-scroll-window'.
As a special exception, the window configuration does not record the
value of point in the selected window for the current buffer.

   You can bring back an entire previous layout by restoring a window
configuration previously saved.  If you want to record all frames
instead of just one, use a frame configuration instead of a window
configuration.  *Note Frame Configurations::.

 -- Function: current-window-configuration &optional frame
     This function returns a new object representing FRAME's current
     window configuration.  If FRAME is omitted, the selected frame is
     used.

 -- Function: set-window-configuration configuration
     This function restores the configuration of windows and buffers as
     specified by CONFIGURATION, for the frame that CONFIGURATION was
     created for.

     The argument CONFIGURATION must be a value that was previously
     returned by `current-window-configuration'.  This configuration is
     restored in the frame from which CONFIGURATION was made, whether
     that frame is selected or not.  This always counts as a window size
     change and triggers execution of the `window-size-change-functions'
     (*note Window Hooks::), because `set-window-configuration' doesn't
     know how to tell whether the new configuration actually differs
     from the old one.

     If the frame which CONFIGURATION was saved from is dead, all this
     function does is restore the three variables `window-min-height',
     `window-min-width' and `minibuffer-scroll-window'. In this case,
     the function returns `nil'.  Otherwise, it returns `t'.

     Here is a way of using this function to get the same effect as
     `save-window-excursion':

          (let ((config (current-window-configuration)))
            (unwind-protect
                (progn (split-window-vertically nil)
                       ...)
              (set-window-configuration config)))

 -- Special Form: save-window-excursion forms...
     This special form records the window configuration, executes FORMS
     in sequence, then restores the earlier window configuration.  The
     window configuration includes, for each window, the value of point
     and the portion of the buffer that is visible.  It also includes
     the choice of selected window.  However, it does not include the
     value of point in the current buffer; use `save-excursion' also,
     if you wish to preserve that.

     Don't use this construct when `save-selected-window' is sufficient.

     Exit from `save-window-excursion' always triggers execution of the
     `window-size-change-functions'.  (It doesn't know how to tell
     whether the restored configuration actually differs from the one in
     effect at the end of the FORMS.)

     The return value is the value of the final form in FORMS.  For
     example:

          (split-window)
               => #<window 25 on control.texi>
          (setq w (selected-window))
               => #<window 19 on control.texi>
          (save-window-excursion
            (delete-other-windows w)
            (switch-to-buffer "foo")
            'do-something)
               => do-something
               ;; The screen is now split again.

 -- Function: window-configuration-p object
     This function returns `t' if OBJECT is a window configuration.

 -- Function: compare-window-configurations config1 config2
     This function compares two window configurations as regards the
     structure of windows, but ignores the values of point and mark and
     the saved scrolling positions--it can return `t' even if those
     aspects differ.

     The function `equal' can also compare two window configurations; it
     regards configurations as unequal if they differ in any respect,
     even a saved point or mark.

 -- Function: window-configuration-frame config
     This function returns the frame for which the window configuration
     CONFIG was made.

   Other primitives to look inside of window configurations would make
sense, but are not implemented because we did not need them.  See the
file `winner.el' for some more operations on windows configurations.


File: elisp,  Node: Window Hooks,  Prev: Window Configurations,  Up: Windows

28.19 Hooks for Window Scrolling and Changes
============================================

This section describes how a Lisp program can take action whenever a
window displays a different part of its buffer or a different buffer.
There are three actions that can change this: scrolling the window,
switching buffers in the window, and changing the size of the window.
The first two actions run `window-scroll-functions'; the last runs
`window-size-change-functions'.

 -- Variable: window-scroll-functions
     This variable holds a list of functions that Emacs should call
     before redisplaying a window with scrolling.  It is not a normal
     hook, because each function is called with two arguments: the
     window, and its new display-start position.

     Displaying a different buffer in the window also runs these
     functions.

     These functions must be careful in using `window-end' (*note
     Window Start::); if you need an up-to-date value, you must use the
     UPDATE argument to ensure you get it.

     *Warning:* don't use this feature to alter the way the window is
     scrolled.  It's not designed for that, and such use probably won't
     work.

 -- Variable: window-size-change-functions
     This variable holds a list of functions to be called if the size
     of any window changes for any reason.  The functions are called
     just once per redisplay, and just once for each frame on which
     size changes have occurred.

     Each function receives the frame as its sole argument.  There is no
     direct way to find out which windows on that frame have changed
     size, or precisely how.  However, if a size-change function
     records, at each call, the existing windows and their sizes, it
     can also compare the present sizes and the previous sizes.

     Creating or deleting windows counts as a size change, and therefore
     causes these functions to be called.  Changing the frame size also
     counts, because it changes the sizes of the existing windows.

     It is not a good idea to use `save-window-excursion' (*note Window
     Configurations::) in these functions, because that always counts
     as a size change, and it would cause these functions to be called
     over and over.  In most cases, `save-selected-window' (*note
     Selecting Windows::) is what you need here.

 -- Variable: redisplay-end-trigger-functions
     This abnormal hook is run whenever redisplay in a window uses text
     that extends past a specified end trigger position.  You set the
     end trigger position with the function
     `set-window-redisplay-end-trigger'.  The functions are called with
     two arguments: the window, and the end trigger position.  Storing
     `nil' for the end trigger position turns off the feature, and the
     trigger value is automatically reset to `nil' just after the hook
     is run.

 -- Function: set-window-redisplay-end-trigger window position
     This function sets WINDOW's end trigger position at POSITION.

 -- Function: window-redisplay-end-trigger &optional window
     This function returns WINDOW's current end trigger position.  If
     WINDOW is `nil' or omitted, it uses the selected window.

 -- Variable: window-configuration-change-hook
     A normal hook that is run every time you change the window
     configuration of an existing frame.  This includes splitting or
     deleting windows, changing the sizes of windows, or displaying a
     different buffer in a window.  The frame whose window
     configuration has changed is the selected frame when this hook
     runs.


File: elisp,  Node: Frames,  Next: Positions,  Prev: Windows,  Up: Top

29 Frames
*********

In Emacs editing, A "frame" is a screen object that contains one or
more Emacs windows.  It's the kind of object that is called a "window"
in the terminology of graphical environments; but we can't call it a
"window" here, because Emacs uses that word in a different way.

   A frame initially contains a single main window and/or a minibuffer
window; you can subdivide the main window vertically or horizontally
into smaller windows.  In Emacs Lisp, a "frame object" is a Lisp object
that represents a frame on the screen.

   When Emacs runs on a text-only terminal, it starts with one
"terminal frame".  If you create additional ones, Emacs displays one
and only one at any given time--on the terminal screen, of course.

   When Emacs communicates directly with a supported window system, such
as X, it does not have a terminal frame; instead, it starts with a
single "window frame", but you can create more, and Emacs can display
several such frames at once as is usual for window systems.

 -- Function: framep object
     This predicate returns a non-`nil' value if OBJECT is a frame, and
     `nil' otherwise.  For a frame, the value indicates which kind of
     display the frame uses:

    `x'
          The frame is displayed in an X window.

    `t'
          A terminal frame on a character display.

    `mac'
          The frame is displayed on a Macintosh.

    `w32'
          The frame is displayed on MS-Windows 9X/NT.

    `pc'
          The frame is displayed on an MS-DOS terminal.

* Menu:

* Creating Frames::		Creating additional frames.
* Multiple Displays::           Creating frames on other displays.
* Frame Parameters::		Controlling frame size, position, font, etc.
* Frame Titles::                Automatic updating of frame titles.
* Deleting Frames::		Frames last until explicitly deleted.
* Finding All Frames::		How to examine all existing frames.
* Frames and Windows::		A frame contains windows;
				  display of text always works through windows.
* Minibuffers and Frames::	How a frame finds the minibuffer to use.
* Input Focus::			Specifying the selected frame.
* Visibility of Frames::	Frames may be visible or invisible, or icons.
* Raising and Lowering::	Raising a frame makes it hide other windows;
				  lowering it makes the others hide it.
* Frame Configurations::	Saving the state of all frames.
* Mouse Tracking::		Getting events that say when the mouse moves.
* Mouse Position::		Asking where the mouse is, or moving it.
* Pop-Up Menus::		Displaying a menu for the user to select from.
* Dialog Boxes::                Displaying a box to ask yes or no.
* Pointer Shape::               Specifying the shape of the mouse pointer.
* Window System Selections::    Transferring text to and from other X clients.
* Drag and Drop::               Internals of Drag-and-Drop implementation.
* Color Names::	                Getting the definitions of color names.
* Text Terminal Colors::        Defining colors for text-only terminals.
* Resources::		        Getting resource values from the server.
* Display Feature Testing::     Determining the features of a terminal.

   *Note Display::, for information about the related topic of
controlling Emacs redisplay.


File: elisp,  Node: Creating Frames,  Next: Multiple Displays,  Up: Frames

29.1 Creating Frames
====================

To create a new frame, call the function `make-frame'.

 -- Function: make-frame &optional alist
     This function creates and returns a new frame, displaying the
     current buffer.  If you are using a supported window system, it
     makes a window frame; otherwise, it makes a terminal frame.

     The argument is an alist specifying frame parameters.  Any
     parameters not mentioned in ALIST default according to the value
     of the variable `default-frame-alist'; parameters not specified
     even there default from the standard X resources or whatever is
     used instead on your system.

     The set of possible parameters depends in principle on what kind of
     window system Emacs uses to display its frames.  *Note Window
     Frame Parameters::, for documentation of individual parameters you
     can specify.

     This function itself does not make the new frame the selected
     frame.  *Note Input Focus::.  The previously selected frame
     remains selected.  However, the window system may select the new
     frame for its own reasons, for instance if the frame appears under
     the mouse pointer and your setup is for focus to follow the
     pointer.

 -- Variable: before-make-frame-hook
     A normal hook run by `make-frame' before it actually creates the
     frame.

 -- Variable: after-make-frame-functions
     An abnormal hook run by `make-frame' after it creates the frame.
     Each function in `after-make-frame-functions' receives one
     argument, the frame just created.


File: elisp,  Node: Multiple Displays,  Next: Frame Parameters,  Prev: Creating Frames,  Up: Frames

29.2 Multiple Displays
======================

A single Emacs can talk to more than one X display.  Initially, Emacs
uses just one display--the one chosen with the `DISPLAY' environment
variable or with the `--display' option (*note Initial Options:
(emacs)Initial Options.).  To connect to another display, use the
command `make-frame-on-display' or specify the `display' frame
parameter when you create the frame.

   Emacs treats each X server as a separate terminal, giving each one
its own selected frame and its own minibuffer windows.  However, only
one of those frames is "_the_ selected frame" at any given moment, see
*Note Input Focus::.

   A few Lisp variables are "terminal-local"; that is, they have a
separate binding for each terminal.  The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to.  These variables include `default-minibuffer-frame',
`defining-kbd-macro', `last-kbd-macro', and `system-key-alist'.  They
are always terminal-local, and can never be buffer-local (*note
Buffer-Local Variables::).

   A single X server can handle more than one screen.  A display name
`HOST:SERVER.SCREEN' has three parts; the last part specifies the
screen number for a given server.  When you use two screens belonging
to one server, Emacs knows by the similarity in their names that they
share a single keyboard, and it treats them as a single terminal.

   Note that some graphical terminals can output to more than a one
monitor (or other output device) at the same time.  On these
"multi-monitor" setups, a single DISPLAY value controls the output to
all the physical monitors.  In this situation, there is currently no
platform-independent way for Emacs to distinguish between the different
physical monitors.

 -- Command: make-frame-on-display display &optional parameters
     This creates and returns a new frame on display DISPLAY, taking
     the other frame parameters from PARAMETERS.  Aside from the
     DISPLAY argument, it is like `make-frame' (*note Creating
     Frames::).

 -- Function: x-display-list
     This returns a list that indicates which X displays Emacs has a
     connection to.  The elements of the list are strings, and each one
     is a display name.

 -- Function: x-open-connection display &optional xrm-string
          must-succeed
     This function opens a connection to the X display DISPLAY.  It
     does not create a frame on that display, but it permits you to
     check that communication can be established with that display.

     The optional argument XRM-STRING, if not `nil', is a string of
     resource names and values, in the same format used in the
     `.Xresources' file.  The values you specify override the resource
     values recorded in the X server itself; they apply to all Emacs
     frames created on this display.  Here's an example of what this
     string might look like:

          "*BorderWidth: 3\n*InternalBorder: 2\n"

     *Note X Resources: (emacs)X Resources.

     If MUST-SUCCEED is non-`nil', failure to open the connection
     terminates Emacs.  Otherwise, it is an ordinary Lisp error.

 -- Function: x-close-connection display
     This function closes the connection to display DISPLAY.  Before
     you can do this, you must first delete all the frames that were
     open on that display (*note Deleting Frames::).


File: elisp,  Node: Frame Parameters,  Next: Frame Titles,  Prev: Multiple Displays,  Up: Frames

29.3 Frame Parameters
=====================

A frame has many parameters that control its appearance and behavior.
Just what parameters a frame has depends on what display mechanism it
uses.

   Frame parameters exist mostly for the sake of window systems.  A
terminal frame has a few parameters, mostly for compatibility's sake;
only the `height', `width', `name', `title', `menu-bar-lines',
`buffer-list' and `buffer-predicate' parameters do something special.
If the terminal supports colors, the parameters `foreground-color',
`background-color', `background-mode' and `display-type' are also
meaningful.

* Menu:

* Parameter Access::       How to change a frame's parameters.
* Initial Parameters::	   Specifying frame parameters when you make a frame.
* Window Frame Parameters:: List of frame parameters for window systems.
* Size and Position::      Changing the size and position of a frame.
* Geometry::               Parsing geometry specifications.


File: elisp,  Node: Parameter Access,  Next: Initial Parameters,  Up: Frame Parameters

29.3.1 Access to Frame Parameters
---------------------------------

These functions let you read and change the parameter values of a frame.

 -- Function: frame-parameter frame parameter
     This function returns the value of the parameter PARAMETER (a
     symbol) of FRAME.  If FRAME is `nil', it returns the selected
     frame's parameter.  If FRAME has no setting for PARAMETER, this
     function returns `nil'.

 -- Function: frame-parameters &optional frame
     The function `frame-parameters' returns an alist listing all the
     parameters of FRAME and their values.  If FRAME is `nil' or
     omitted, this returns the selected frame's parameters

 -- Function: modify-frame-parameters frame alist
     This function alters the parameters of frame FRAME based on the
     elements of ALIST.  Each element of ALIST has the form `(PARM .
     VALUE)', where PARM is a symbol naming a parameter.  If you don't
     mention a parameter in ALIST, its value doesn't change.  If FRAME
     is `nil', it defaults to the selected frame.

 -- Function: modify-all-frames-parameters alist
     This function alters the frame parameters of all existing frames
     according to ALIST, then modifies `default-frame-alist' (and, if
     necessary, `initial-frame-alist') to apply the same parameter
     values to frames that will be created henceforth.


File: elisp,  Node: Initial Parameters,  Next: Window Frame Parameters,  Prev: Parameter Access,  Up: Frame Parameters

29.3.2 Initial Frame Parameters
-------------------------------

You can specify the parameters for the initial startup frame by setting
`initial-frame-alist' in your init file (*note Init File::).

 -- Variable: initial-frame-alist
     This variable's value is an alist of parameter values used when
     creating the initial window frame.  You can set this variable to
     specify the appearance of the initial frame without altering
     subsequent frames.  Each element has the form:

          (PARAMETER . VALUE)

     Emacs creates the initial frame before it reads your init file.
     After reading that file, Emacs checks `initial-frame-alist', and
     applies the parameter settings in the altered value to the already
     created initial frame.

     If these settings affect the frame geometry and appearance, you'll
     see the frame appear with the wrong ones and then change to the
     specified ones.  If that bothers you, you can specify the same
     geometry and appearance with X resources; those do take effect
     before the frame is created.  *Note X Resources: (emacs)X
     Resources.

     X resource settings typically apply to all frames.  If you want to
     specify some X resources solely for the sake of the initial frame,
     and you don't want them to apply to subsequent frames, here's how
     to achieve this.  Specify parameters in `default-frame-alist' to
     override the X resources for subsequent frames; then, to prevent
     these from affecting the initial frame, specify the same
     parameters in `initial-frame-alist' with values that match the X
     resources.

   If these parameters specify a separate minibuffer-only frame with
`(minibuffer . nil)', and you have not created one, Emacs creates one
for you.

 -- Variable: minibuffer-frame-alist
     This variable's value is an alist of parameter values used when
     creating an initial minibuffer-only frame--if such a frame is
     needed, according to the parameters for the main initial frame.

 -- Variable: default-frame-alist
     This is an alist specifying default values of frame parameters for
     all Emacs frames--the first frame, and subsequent frames.  When
     using the X Window System, you can get the same results by means
     of X resources in many cases.

     Setting this variable does not affect existing frames.

   See also `special-display-frame-alist'.  *Note Definition of
special-display-frame-alist::.

   If you use options that specify window appearance when you invoke
Emacs, they take effect by adding elements to `default-frame-alist'.
One exception is `-geometry', which adds the specified position to
`initial-frame-alist' instead.  *Note Command Line Arguments for Emacs
Invocation: (emacs)Emacs Invocation.


File: elisp,  Node: Window Frame Parameters,  Next: Size and Position,  Prev: Initial Parameters,  Up: Frame Parameters

29.3.3 Window Frame Parameters
------------------------------

Just what parameters a frame has depends on what display mechanism it
uses.  This section describes the parameters that have special meanings
on some or all kinds of terminals.  Of these, `name', `title',
`height', `width', `buffer-list' and `buffer-predicate' provide
meaningful information in terminal frames, and `tty-color-mode' is
meaningful _only_ in terminal frames.

* Menu:

* Basic Parameters::            Parameters that are fundamental.
* Position Parameters::         The position of the frame on the screen.
* Size Parameters::             Frame's size.
* Layout Parameters::           Size of parts of the frame, and
                                  enabling or disabling some parts.
* Buffer Parameters::           Which buffers have been or should be shown.
* Management Parameters::       Communicating with the window manager.
* Cursor Parameters::           Controlling the cursor appearance.
* Color Parameters::            Colors of various parts of the frame.


File: elisp,  Node: Basic Parameters,  Next: Position Parameters,  Up: Window Frame Parameters

29.3.3.1 Basic Parameters
.........................

These frame parameters give the most basic information about the frame.
`title' and `name' are meaningful on all terminals.

`display'
     The display on which to open this frame.  It should be a string of
     the form `"HOST:DPY.SCREEN"', just like the `DISPLAY' environment
     variable.

`display-type'
     This parameter describes the range of possible colors that can be
     used in this frame.  Its value is `color', `grayscale' or `mono'.

`title'
     If a frame has a non-`nil' title, it appears in the window
     system's title bar at the top of the frame, and also in the mode
     line of windows in that frame if `mode-line-frame-identification'
     uses `%F' (*note %-Constructs::).  This is normally the case when
     Emacs is not using a window system, and can only display one frame
     at a time.  *Note Frame Titles::.

`name'
     The name of the frame.  The frame name serves as a default for the
     frame title, if the `title' parameter is unspecified or `nil'.  If
     you don't specify a name, Emacs sets the frame name automatically
     (*note Frame Titles::).

     If you specify the frame name explicitly when you create the
     frame, the name is also used (instead of the name of the Emacs
     executable) when looking up X resources for the frame.


File: elisp,  Node: Position Parameters,  Next: Size Parameters,  Prev: Basic Parameters,  Up: Window Frame Parameters

29.3.3.2 Position Parameters
............................

Position parameters' values are normally measured in pixels, but on
text-only terminals they count characters or lines instead.

`left'
     The screen position of the left edge, in pixels, with respect to
     the left edge of the screen.  The value may be a positive number
     POS, or a list of the form `(+ POS)' which permits specifying a
     negative POS value.

     A negative number -POS, or a list of the form `(- POS)', actually
     specifies the position of the right edge of the window with
     respect to the right edge of the screen.  A positive value of POS
     counts toward the left.  *Reminder:* if the parameter is a
     negative integer -POS, then POS is positive.

     Some window managers ignore program-specified positions.  If you
     want to be sure the position you specify is not ignored, specify a
     non-`nil' value for the `user-position' parameter as well.

`top'
     The screen position of the top edge, in pixels, with respect to the
     top edge of the screen.  It works just like `left', except
     vertically instead of horizontally.

`icon-left'
     The screen position of the left edge _of the frame's icon_, in
     pixels, counting from the left edge of the screen.  This takes
     effect if and when the frame is iconified.

     If you specify a value for this parameter, then you must also
     specify a value for `icon-top' and vice versa.  The window manager
     may ignore these two parameters.

`icon-top'
     The screen position of the top edge _of the frame's icon_, in
     pixels, counting from the top edge of the screen.  This takes
     effect if and when the frame is iconified.

`user-position'
     When you create a frame and specify its screen position with the
     `left' and `top' parameters, use this parameter to say whether the
     specified position was user-specified (explicitly requested in some
     way by a human user) or merely program-specified (chosen by a
     program).  A non-`nil' value says the position was user-specified.

     Window managers generally heed user-specified positions, and some
     heed program-specified positions too.  But many ignore
     program-specified positions, placing the window in a default
     fashion or letting the user place it with the mouse.  Some window
     managers, including `twm', let the user specify whether to obey
     program-specified positions or ignore them.

     When you call `make-frame', you should specify a non-`nil' value
     for this parameter if the values of the `left' and `top'
     parameters represent the user's stated preference; otherwise, use
     `nil'.


File: elisp,  Node: Size Parameters,  Next: Layout Parameters,  Prev: Position Parameters,  Up: Window Frame Parameters

29.3.3.3 Size Parameters
........................

Size parameters' values are normally measured in pixels, but on
text-only terminals they count characters or lines instead.

`height'
     The height of the frame contents, in characters.  (To get the
     height in pixels, call `frame-pixel-height'; see *Note Size and
     Position::.)

`width'
     The width of the frame contents, in characters.  (To get the width
     in pixels, call `frame-pixel-width'; see *Note Size and
     Position::.)

`user-size'
     This does for the size parameters `height' and `width' what the
     `user-position' parameter (see above) does for the position
     parameters `top' and `left'.

`fullscreen'
     Specify that width, height or both shall be set to the size of the
     screen.  The value `fullwidth' specifies that width shall be the
     size of the screen.  The value `fullheight' specifies that height
     shall be the size of the screen.  The value `fullboth' specifies
     that both the width and the height shall be set to the size of the
     screen.


File: elisp,  Node: Layout Parameters,  Next: Buffer Parameters,  Prev: Size Parameters,  Up: Window Frame Parameters

29.3.3.4 Layout Parameters
..........................

These frame parameters enable or disable various parts of the frame, or
control their sizes.

`border-width'
     The width in pixels of the frame's border.

`internal-border-width'
     The distance in pixels between text (or fringe) and the frame's
     border.

`vertical-scroll-bars'
     Whether the frame has scroll bars for vertical scrolling, and
     which side of the frame they should be on.  The possible values
     are `left', `right', and `nil' for no scroll bars.

`scroll-bar-width'
     The width of vertical scroll bars, in pixels, or `nil' meaning to
     use the default width.

`left-fringe'
`right-fringe'
     The default width of the left and right fringes of windows in this
     frame (*note Fringes::).  If either of these is zero, that
     effectively removes the corresponding fringe.  A value of `nil'
     stands for the standard fringe width, which is the width needed to
     display the fringe bitmaps.

     The combined fringe widths must add up to an integral number of
     columns, so the actual default fringe widths for the frame may be
     larger than the specified values.  The extra width needed to reach
     an acceptable total is distributed evenly between the left and
     right fringe.  However, you can force one fringe or the other to a
     precise width by specifying that width as a negative integer.  If
     both widths are negative, only the left fringe gets the specified
     width.

`menu-bar-lines'
     The number of lines to allocate at the top of the frame for a menu
     bar.  The default is 1.  A value of `nil' means don't display a
     menu bar.  *Note Menu Bar::.  (The X toolkit and GTK allow at most
     one menu bar line; they treat larger values as 1.)

`tool-bar-lines'
     The number of lines to use for the tool bar.  A value of `nil'
     means don't display a tool bar.  (GTK allows at most one tool bar
     line; it treats larger values as 1.)

`line-spacing'
     Additional space to leave below each text line, in pixels (a
     positive integer).  *Note Line Height::, for more information.


File: elisp,  Node: Buffer Parameters,  Next: Management Parameters,  Prev: Layout Parameters,  Up: Window Frame Parameters

29.3.3.5 Buffer Parameters
..........................

These frame parameters, meaningful on all kinds of terminals, deal with
which buffers have been, or should, be displayed in the frame.

`minibuffer'
     Whether this frame has its own minibuffer.  The value `t' means
     yes, `nil' means no, `only' means this frame is just a minibuffer.
     If the value is a minibuffer window (in some other frame), the
     new frame uses that minibuffer.

`buffer-predicate'
     The buffer-predicate function for this frame.  The function
     `other-buffer' uses this predicate (from the selected frame) to
     decide which buffers it should consider, if the predicate is not
     `nil'.  It calls the predicate with one argument, a buffer, once
     for each buffer; if the predicate returns a non-`nil' value, it
     considers that buffer.

`buffer-list'
     A list of buffers that have been selected in this frame, ordered
     most-recently-selected first.

`unsplittable'
     If non-`nil', this frame's window is never split automatically.


File: elisp,  Node: Management Parameters,  Next: Cursor Parameters,  Prev: Buffer Parameters,  Up: Window Frame Parameters

29.3.3.6 Window Management Parameters
.....................................

These frame parameters, meaningful only on window system displays,
interact with the window manager.

`visibility'
     The state of visibility of the frame.  There are three
     possibilities: `nil' for invisible, `t' for visible, and `icon' for
     iconified.  *Note Visibility of Frames::.

`auto-raise'
     Whether selecting the frame raises it (non-`nil' means yes).

`auto-lower'
     Whether deselecting the frame lowers it (non-`nil' means yes).

`icon-type'
     The type of icon to use for this frame when it is iconified.  If
     the value is a string, that specifies a file containing a bitmap
     to use.  Any other non-`nil' value specifies the default bitmap
     icon (a picture of a gnu); `nil' specifies a text icon.

`icon-name'
     The name to use in the icon for this frame, when and if the icon
     appears.  If this is `nil', the frame's title is used.

`window-id'
     The number of the window-system window used by the frame to
     contain the actual Emacs windows.

`outer-window-id'
     The number of the outermost window-system window used for the
     whole frame.

`wait-for-wm'
     If non-`nil', tell Xt to wait for the window manager to confirm
     geometry changes.  Some window managers, including versions of
     Fvwm2 and KDE, fail to confirm, so Xt hangs.  Set this to `nil' to
     prevent hanging with those window managers.



File: elisp,  Node: Cursor Parameters,  Next: Color Parameters,  Prev: Management Parameters,  Up: Window Frame Parameters

29.3.3.7 Cursor Parameters
..........................

This frame parameter controls the way the cursor looks.

`cursor-type'
     How to display the cursor.  Legitimate values are:

    `box'
          Display a filled box.  (This is the default.)

    `hollow'
          Display a hollow box.

    `nil'
          Don't display a cursor.

    `bar'
          Display a vertical bar between characters.

    `(bar . WIDTH)'
          Display a vertical bar WIDTH pixels wide between characters.

    `hbar'
          Display a horizontal bar.

    `(hbar . HEIGHT)'
          Display a horizontal bar HEIGHT pixels high.

   The buffer-local variable `cursor-type' overrides the value of the
`cursor-type' frame parameter, but if it is `t', that means to use the
cursor specified for the frame.

 -- Variable: blink-cursor-alist
     This variable specifies how to blink the cursor.  Each element has
     the form `(ON-STATE . OFF-STATE)'.  Whenever the cursor type
     equals ON-STATE (comparing using `equal'), the corresponding
     OFF-STATE specifies what the cursor looks like when it blinks
     "off."  Both ON-STATE and OFF-STATE should be suitable values for
     the `cursor-type' frame parameter.

     There are various defaults for how to blink each type of cursor, if
     the type is not mentioned as an ON-STATE here.  Changes in this
     variable do not take effect immediately, only when you specify the
     `cursor-type' frame parameter.

 -- Variable: cursor-in-non-selected-windows
     This variable controls how the cursor looks in a window that is not
     selected.  It supports the same values as the `cursor-type' frame
     parameter; also, `nil' means don't display a cursor in nonselected
     windows, and `t' (the default) means use a standard modificatoin
     of the usual cursor type (solid box becomes hollow box, and bar
     becomes a narrower bar).


File: elisp,  Node: Color Parameters,  Prev: Cursor Parameters,  Up: Window Frame Parameters

29.3.3.8 Color Parameters
.........................

These frame parameters control the use of colors.

`background-mode'
     This parameter is either `dark' or `light', according to whether
     the background color is a light one or a dark one.

`tty-color-mode'
     This parameter overrides the terminal's color support as given by
     the system's terminal capabilities database in that this
     parameter's value specifies the color mode to use in terminal
     frames.  The value can be either a symbol or a number.  A number
     specifies the number of colors to use (and, indirectly, what
     commands to issue to produce each color).  For example,
     `(tty-color-mode . 8)' specifies use of the ANSI escape sequences
     for 8 standard text colors.  A value of -1 turns off color support.

     If the parameter's value is a symbol, it specifies a number through
     the value of `tty-color-mode-alist', and the associated number is
     used instead.

`screen-gamma'
     If this is a number, Emacs performs "gamma correction" which
     adjusts the brightness of all colors.  The value should be the
     screen gamma of your display, a floating point number.

     Usual PC monitors have a screen gamma of 2.2, so color values in
     Emacs, and in X windows generally, are calibrated to display
     properly on a monitor with that gamma value.  If you specify 2.2
     for `screen-gamma', that means no correction is needed.  Other
     values request correction, designed to make the corrected colors
     appear on your screen the way they would have appeared without
     correction on an ordinary monitor with a gamma value of 2.2.

     If your monitor displays colors too light, you should specify a
     `screen-gamma' value smaller than 2.2.  This requests correction
     that makes colors darker.  A screen gamma value of 1.5 may give
     good results for LCD color displays.

   These frame parameters are semi-obsolete in that they are
automatically equivalent to particular face attributes of particular
faces.  *Note Standard Faces: (emacs)Standard Faces.

`font'
     The name of the font for displaying text in the frame.  This is a
     string, either a valid font name for your system or the name of an
     Emacs fontset (*note Fontsets::).  It is equivalent to the `font'
     attribute of the `default' face.

`foreground-color'
     The color to use for the image of a character.  It is equivalent to
     the `:foreground' attribute of the `default' face.

`background-color'
     The color to use for the background of characters.  It is
     equivalent to the `:background' attribute of the `default' face.

`mouse-color'
     The color for the mouse pointer.  It is equivalent to the
     `:background' attribute of the `mouse' face.

`cursor-color'
     The color for the cursor that shows point.  It is equivalent to the
     `:background' attribute of the `cursor' face.

`border-color'
     The color for the border of the frame.  It is equivalent to the
     `:background' attribute of the `border' face.

`scroll-bar-foreground'
     If non-`nil', the color for the foreground of scroll bars.  It is
     equivalent to the `:foreground' attribute of the `scroll-bar' face.

`scroll-bar-background'
     If non-`nil', the color for the background of scroll bars.  It is
     equivalent to the `:background' attribute of the `scroll-bar' face.


File: elisp,  Node: Size and Position,  Next: Geometry,  Prev: Window Frame Parameters,  Up: Frame Parameters

29.3.4 Frame Size And Position
------------------------------

You can read or change the size and position of a frame using the frame
parameters `left', `top', `height', and `width'.  Whatever geometry
parameters you don't specify are chosen by the window manager in its
usual fashion.

   Here are some special features for working with sizes and positions.
(For the precise meaning of "selected frame" used by these functions,
see *Note Input Focus::.)

 -- Function: set-frame-position frame left top
     This function sets the position of the top left corner of FRAME to
     LEFT and TOP.  These arguments are measured in pixels, and
     normally count from the top left corner of the screen.

     Negative parameter values position the bottom edge of the window
     up from the bottom edge of the screen, or the right window edge to
     the left of the right edge of the screen.  It would probably be
     better if the values were always counted from the left and top, so
     that negative arguments would position the frame partly off the
     top or left edge of the screen, but it seems inadvisable to change
     that now.

 -- Function: frame-height &optional frame
 -- Function: frame-width &optional frame
     These functions return the height and width of FRAME, measured in
     lines and columns.  If you don't supply FRAME, they use the
     selected frame.

 -- Function: screen-height
 -- Function: screen-width
     These functions are old aliases for `frame-height' and
     `frame-width'.  When you are using a non-window terminal, the size
     of the frame is normally the same as the size of the terminal
     screen.

 -- Function: frame-pixel-height &optional frame
 -- Function: frame-pixel-width &optional frame
     These functions return the height and width of the main display
     area of FRAME, measured in pixels.  If you don't supply FRAME,
     they use the selected frame.

     These values include the internal borders, and windows' scroll bars
     and fringes (which belong to individual windows, not to the frame
     itself), but do not include menu bars or tool bars (except when
     using X without an X toolkit).

 -- Function: frame-char-height &optional frame
 -- Function: frame-char-width &optional frame
     These functions return the height and width of a character in
     FRAME, measured in pixels.  The values depend on the choice of
     font.  If you don't supply FRAME, these functions use the selected
     frame.

 -- Function: set-frame-size frame cols rows
     This function sets the size of FRAME, measured in characters; COLS
     and ROWS specify the new width and height.

     To set the size based on values measured in pixels, use
     `frame-char-height' and `frame-char-width' to convert them to
     units of characters.

 -- Function: set-frame-height frame lines &optional pretend
     This function resizes FRAME to a height of LINES lines.  The sizes
     of existing windows in FRAME are altered proportionally to fit.

     If PRETEND is non-`nil', then Emacs displays LINES lines of output
     in FRAME, but does not change its value for the actual height of
     the frame.  This is only useful for a terminal frame.  Using a
     smaller height than the terminal actually implements may be useful
     to reproduce behavior observed on a smaller screen, or if the
     terminal malfunctions when using its whole screen.  Setting the
     frame height "for real" does not always work, because knowing the
     correct actual size may be necessary for correct cursor
     positioning on a terminal frame.

 -- Function: set-frame-width frame width &optional pretend
     This function sets the width of FRAME, measured in characters.
     The argument PRETEND has the same meaning as in `set-frame-height'.

   The older functions `set-screen-height' and `set-screen-width' were
used to specify the height and width of the screen, in Emacs versions
that did not support multiple frames.  They are semi-obsolete, but
still work; they apply to the selected frame.


File: elisp,  Node: Geometry,  Prev: Size and Position,  Up: Frame Parameters

29.3.5 Geometry
---------------

Here's how to examine the data in an X-style window geometry
specification:

 -- Function: x-parse-geometry geom
     The function `x-parse-geometry' converts a standard X window
     geometry string to an alist that you can use as part of the
     argument to `make-frame'.

     The alist describes which parameters were specified in GEOM, and
     gives the values specified for them.  Each element looks like
     `(PARAMETER . VALUE)'.  The possible PARAMETER values are `left',
     `top', `width', and `height'.

     For the size parameters, the value must be an integer.  The
     position parameter names `left' and `top' are not totally accurate,
     because some values indicate the position of the right or bottom
     edges instead.  These are the VALUE possibilities for the position
     parameters:

    an integer
          A positive integer relates the left edge or top edge of the
          window to the left or top edge of the screen.  A negative
          integer relates the right or bottom edge of the window to the
          right or bottom edge of the screen.

    `(+ POSITION)'
          This specifies the position of the left or top edge of the
          window relative to the left or top edge of the screen.  The
          integer POSITION may be positive or negative; a negative
          value specifies a position outside the screen.

    `(- POSITION)'
          This specifies the position of the right or bottom edge of
          the window relative to the right or bottom edge of the
          screen.  The integer POSITION may be positive or negative; a
          negative value specifies a position outside the screen.

     Here is an example:

          (x-parse-geometry "35x70+0-0")
               => ((height . 70) (width . 35)
                   (top - 0) (left . 0))


File: elisp,  Node: Frame Titles,  Next: Deleting Frames,  Prev: Frame Parameters,  Up: Frames

29.4 Frame Titles
=================

Every frame has a `name' parameter; this serves as the default for the
frame title which window systems typically display at the top of the
frame.  You can specify a name explicitly by setting the `name' frame
property.

   Normally you don't specify the name explicitly, and Emacs computes
the frame name automatically based on a template stored in the variable
`frame-title-format'.  Emacs recomputes the name each time the frame is
redisplayed.

 -- Variable: frame-title-format
     This variable specifies how to compute a name for a frame when you
     have not explicitly specified one.  The variable's value is
     actually a mode line construct, just like `mode-line-format',
     except that the `%c' and `%l' constructs are ignored.  *Note Mode
     Line Data::.

 -- Variable: icon-title-format
     This variable specifies how to compute the name for an iconified
     frame, when you have not explicitly specified the frame title.
     This title appears in the icon itself.

 -- Variable: multiple-frames
     This variable is set automatically by Emacs.  Its value is `t' when
     there are two or more frames (not counting minibuffer-only frames
     or invisible frames).  The default value of `frame-title-format'
     uses `multiple-frames' so as to put the buffer name in the frame
     title only when there is more than one frame.

     The value of this variable is not guaranteed to be accurate except
     while processing `frame-title-format' or `icon-title-format'.


File: elisp,  Node: Deleting Frames,  Next: Finding All Frames,  Prev: Frame Titles,  Up: Frames

29.5 Deleting Frames
====================

Frames remain potentially visible until you explicitly "delete" them.
A deleted frame cannot appear on the screen, but continues to exist as
a Lisp object until there are no references to it.

 -- Command: delete-frame &optional frame force
     This function deletes the frame FRAME.  Unless FRAME is a tooltip,
     it first runs the hook `delete-frame-functions' (each function
     gets one argument, FRAME).  By default, FRAME is the selected
     frame.

     A frame cannot be deleted if its minibuffer is used by other
     frames.  Normally, you cannot delete a frame if all other frames
     are invisible, but if the FORCE is non-`nil', then you are allowed
     to do so.

 -- Function: frame-live-p frame
     The function `frame-live-p' returns non-`nil' if the frame FRAME
     has not been deleted.  The possible non-`nil' return values are
     like those of `framep'.  *Note Frames::.

   Some window managers provide a command to delete a window.  These
work by sending a special message to the program that operates the
window.  When Emacs gets one of these commands, it generates a
`delete-frame' event, whose normal definition is a command that calls
the function `delete-frame'.  *Note Misc Events::.


File: elisp,  Node: Finding All Frames,  Next: Frames and Windows,  Prev: Deleting Frames,  Up: Frames

29.6 Finding All Frames
=======================

 -- Function: frame-list
     The function `frame-list' returns a list of all the frames that
     have not been deleted.  It is analogous to `buffer-list' for
     buffers, and includes frames on all terminals.  The list that you
     get is newly created, so modifying the list doesn't have any
     effect on the internals of Emacs.

 -- Function: visible-frame-list
     This function returns a list of just the currently visible frames.
     *Note Visibility of Frames::.  (Terminal frames always count as
     "visible," even though only the selected one is actually
     displayed.)

 -- Function: next-frame &optional frame minibuf
     The function `next-frame' lets you cycle conveniently through all
     the frames on the current display from an arbitrary starting
     point.  It returns the "next" frame after FRAME in the cycle.  If
     FRAME is omitted or `nil', it defaults to the selected frame
     (*note Input Focus::).

     The second argument, MINIBUF, says which frames to consider:

    `nil'
          Exclude minibuffer-only frames.

    `visible'
          Consider all visible frames.

    0
          Consider all visible or iconified frames.

    a window
          Consider only the frames using that particular window as their
          minibuffer.

    anything else
          Consider all frames.

 -- Function: previous-frame &optional frame minibuf
     Like `next-frame', but cycles through all frames in the opposite
     direction.

   See also `next-window' and `previous-window', in *Note Cyclic Window
Ordering::.


File: elisp,  Node: Frames and Windows,  Next: Minibuffers and Frames,  Prev: Finding All Frames,  Up: Frames

29.7 Frames and Windows
=======================

Each window is part of one and only one frame; you can get the frame
with `window-frame'.

 -- Function: window-frame window
     This function returns the frame that WINDOW is on.

   All the non-minibuffer windows in a frame are arranged in a cyclic
order.  The order runs from the frame's top window, which is at the
upper left corner, down and to the right, until it reaches the window at
the lower right corner (always the minibuffer window, if the frame has
one), and then it moves back to the top.  *Note Cyclic Window
Ordering::.

 -- Function: frame-first-window &optional frame
     This returns the topmost, leftmost window of frame FRAME.  If
     omitted or `nil', FRAME defaults to the selected frame.

   At any time, exactly one window on any frame is "selected within the
frame".  The significance of this designation is that selecting the
frame also selects this window.  You can get the frame's current
selected window with `frame-selected-window'.

 -- Function: frame-selected-window &optional frame
     This function returns the window on FRAME that is selected within
     FRAME.  If omitted or `nil', FRAME defaults to the selected frame.

 -- Function: set-frame-selected-window frame window
     This sets the selected window of frame FRAME to WINDOW.  If FRAME
     is `nil', it operates on the selected frame.  If FRAME is the
     selected frame, this makes WINDOW the selected window.  This
     function returns WINDOW.

   Conversely, selecting a window for Emacs with `select-window' also
makes that window selected within its frame.  *Note Selecting Windows::.

   Another function that (usually) returns one of the windows in a given
frame is `minibuffer-window'.  *Note Definition of minibuffer-window::.


File: elisp,  Node: Minibuffers and Frames,  Next: Input Focus,  Prev: Frames and Windows,  Up: Frames

29.8 Minibuffers and Frames
===========================

Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected.  If the frame has a minibuffer,
you can get it with `minibuffer-window' (*note Definition of
minibuffer-window::).

   However, you can also create a frame with no minibuffer.  Such a
frame must use the minibuffer window of some other frame.  When you
create the frame, you can specify explicitly the minibuffer window to
use (in some other frame).  If you don't, then the minibuffer is found
in the frame which is the value of the variable
`default-minibuffer-frame'.  Its value should be a frame that does have
a minibuffer.

   If you use a minibuffer-only frame, you might want that frame to
raise when you enter the minibuffer.  If so, set the variable
`minibuffer-auto-raise' to `t'.  *Note Raising and Lowering::.

 -- Variable: default-minibuffer-frame
     This variable specifies the frame to use for the minibuffer
     window, by default.  It does not affect existing frames.  It is
     always local to the current terminal and cannot be buffer-local.
     *Note Multiple Displays::.


File: elisp,  Node: Input Focus,  Next: Visibility of Frames,  Prev: Minibuffers and Frames,  Up: Frames

29.9 Input Focus
================

At any time, one frame in Emacs is the "selected frame".  The selected
window always resides on the selected frame.

   When Emacs displays its frames on several terminals (*note Multiple
Displays::), each terminal has its own selected frame.  But only one of
these is "_the_ selected frame": it's the frame that belongs to the
terminal from which the most recent input came.  That is, when Emacs
runs a command that came from a certain terminal, the selected frame is
the one of that terminal.  Since Emacs runs only a single command at any
given time, it needs to consider only one selected frame at a time; this
frame is what we call "the selected frame" in this manual.  The display
on which the selected frame is displayed is the "selected frame's
display".

 -- Function: selected-frame
     This function returns the selected frame.

   Some window systems and window managers direct keyboard input to the
window object that the mouse is in; others require explicit clicks or
commands to "shift the focus" to various window objects.  Either way,
Emacs automatically keeps track of which frame has the focus.  To
switch to a different frame from a Lisp function, call
`select-frame-set-input-focus'.

   Lisp programs can also switch frames "temporarily" by calling the
function `select-frame'.  This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.

   When using a text-only terminal, only one frame can be displayed at a
time on the terminal, so after a call to `select-frame', the next
redisplay actually displays the newly selected frame.  This frame
remains selected until a subsequent call to `select-frame' or
`select-frame-set-input-focus'.  Each terminal frame has a number which
appears in the mode line before the buffer name (*note Mode Line
Variables::).

 -- Function: select-frame-set-input-focus frame
     This function makes FRAME the selected frame, raises it (should it
     happen to be obscured by other frames) and tries to give it the X
     server's focus.  On a text-only terminal, the next redisplay
     displays the new frame on the entire terminal screen.  The return
     value of this function is not significant.

 -- Function: select-frame frame
     This function selects frame FRAME, temporarily disregarding the
     focus of the X server if any.  The selection of FRAME lasts until
     the next time the user does something to select a different frame,
     or until the next time this function is called.  (If you are using
     a window system, the previously selected frame may be restored as
     the selected frame after return to the command loop, because it
     still may have the window system's input focus.)  The specified
     FRAME becomes the selected frame, as explained above, and the
     terminal that FRAME is on becomes the selected terminal.  This
     function returns FRAME, or `nil' if FRAME has been deleted.

     In general, you should never use `select-frame' in a way that could
     switch to a different terminal without switching back when you're
     done.

   Emacs cooperates with the window system by arranging to select
frames as the server and window manager request.  It does so by
generating a special kind of input event, called a "focus" event, when
appropriate.  The command loop handles a focus event by calling
`handle-switch-frame'.  *Note Focus Events::.

 -- Command: handle-switch-frame frame
     This function handles a focus event by selecting frame FRAME.

     Focus events normally do their job by invoking this command.
     Don't call it for any other reason.

 -- Function: redirect-frame-focus frame &optional focus-frame
     This function redirects focus from FRAME to FOCUS-FRAME.  This
     means that FOCUS-FRAME will receive subsequent keystrokes and
     events intended for FRAME.  After such an event, the value of
     `last-event-frame' will be FOCUS-FRAME.  Also, switch-frame events
     specifying FRAME will instead select FOCUS-FRAME.

     If FOCUS-FRAME is omitted or `nil', that cancels any existing
     redirection for FRAME, which therefore once again receives its own
     events.

     One use of focus redirection is for frames that don't have
     minibuffers.  These frames use minibuffers on other frames.
     Activating a minibuffer on another frame redirects focus to that
     frame.  This puts the focus on the minibuffer's frame, where it
     belongs, even though the mouse remains in the frame that activated
     the minibuffer.

     Selecting a frame can also change focus redirections.  Selecting
     frame `bar', when `foo' had been selected, changes any redirections
     pointing to `foo' so that they point to `bar' instead.  This
     allows focus redirection to work properly when the user switches
     from one frame to another using `select-window'.

     This means that a frame whose focus is redirected to itself is
     treated differently from a frame whose focus is not redirected.
     `select-frame' affects the former but not the latter.

     The redirection lasts until `redirect-frame-focus' is called to
     change it.

 -- User Option: focus-follows-mouse
     This option is how you inform Emacs whether the window manager
     transfers focus when the user moves the mouse.  Non-`nil' says
     that it does.  When this is so, the command `other-frame' moves
     the mouse to a position consistent with the new selected frame.
     (This option has no effect on MS-Windows, where the mouse pointer
     is always automatically moved by the OS to the selected frame.)


File: elisp,  Node: Visibility of Frames,  Next: Raising and Lowering,  Prev: Input Focus,  Up: Frames

29.10 Visibility of Frames
==========================

A window frame may be "visible", "invisible", or "iconified".  If it is
visible, you can see its contents, unless other windows cover it.  If
it is iconified, the frame's contents do not appear on the screen, but
an icon does.  If the frame is invisible, it doesn't show on the
screen, not even as an icon.

   Visibility is meaningless for terminal frames, since only the
selected one is actually displayed in any case.

 -- Command: make-frame-visible &optional frame
     This function makes frame FRAME visible.  If you omit FRAME, it
     makes the selected frame visible.  This does not raise the frame,
     but you can do that with `raise-frame' if you wish (*note Raising
     and Lowering::).

 -- Command: make-frame-invisible &optional frame force
     This function makes frame FRAME invisible.  If you omit FRAME, it
     makes the selected frame invisible.

     Unless FORCE is non-`nil', this function refuses to make FRAME
     invisible if all other frames are invisible..

 -- Command: iconify-frame &optional frame
     This function iconifies frame FRAME.  If you omit FRAME, it
     iconifies the selected frame.

 -- Function: frame-visible-p frame
     This returns the visibility status of frame FRAME.  The value is
     `t' if FRAME is visible, `nil' if it is invisible, and `icon' if
     it is iconified.

     On a text-only terminal, all frames are considered visible, whether
     they are currently being displayed or not, and this function
     returns `t' for all frames.

   The visibility status of a frame is also available as a frame
parameter.  You can read or change it as such.  *Note Management
Parameters::.

   The user can iconify and deiconify frames with the window manager.
This happens below the level at which Emacs can exert any control, but
Emacs does provide events that you can use to keep track of such
changes.  *Note Misc Events::.


File: elisp,  Node: Raising and Lowering,  Next: Frame Configurations,  Prev: Visibility of Frames,  Up: Frames

29.11 Raising and Lowering Frames
=================================

Most window systems use a desktop metaphor.  Part of this metaphor is
the idea that windows are stacked in a notional third dimension
perpendicular to the screen surface, and thus ordered from "highest" to
"lowest."  Where two windows overlap, the one higher up covers the one
underneath.  Even a window at the bottom of the stack can be seen if no
other window overlaps it.

   A window's place in this ordering is not fixed; in fact, users tend
to change the order frequently.  "Raising" a window means moving it
"up," to the top of the stack.  "Lowering" a window means moving it to
the bottom of the stack.  This motion is in the notional third
dimension only, and does not change the position of the window on the
screen.

   You can raise and lower Emacs frame Windows with these functions:

 -- Command: raise-frame &optional frame
     This function raises frame FRAME (default, the selected frame).
     If FRAME is invisible or iconified, this makes it visible.

 -- Command: lower-frame &optional frame
     This function lowers frame FRAME (default, the selected frame).

 -- User Option: minibuffer-auto-raise
     If this is non-`nil', activation of the minibuffer raises the frame
     that the minibuffer window is in.

   You can also enable auto-raise (raising automatically when a frame is
selected) or auto-lower (lowering automatically when it is deselected)
for any frame using frame parameters.  *Note Management Parameters::.


File: elisp,  Node: Frame Configurations,  Next: Mouse Tracking,  Prev: Raising and Lowering,  Up: Frames

29.12 Frame Configurations
==========================

A "frame configuration" records the current arrangement of frames, all
their properties, and the window configuration of each one.  (*Note
Window Configurations::.)

 -- Function: current-frame-configuration
     This function returns a frame configuration list that describes
     the current arrangement of frames and their contents.

 -- Function: set-frame-configuration configuration &optional nodelete
     This function restores the state of frames described in
     CONFIGURATION.  However, this function does not restore deleted
     frames.

     Ordinarily, this function deletes all existing frames not listed in
     CONFIGURATION.  But if NODELETE is non-`nil', the unwanted frames
     are iconified instead.


File: elisp,  Node: Mouse Tracking,  Next: Mouse Position,  Prev: Frame Configurations,  Up: Frames

29.13 Mouse Tracking
====================

Sometimes it is useful to "track" the mouse, which means to display
something to indicate where the mouse is and move the indicator as the
mouse moves.  For efficient mouse tracking, you need a way to wait until
the mouse actually moves.

   The convenient way to track the mouse is to ask for events to
represent mouse motion.  Then you can wait for motion by waiting for an
event.  In addition, you can easily handle any other sorts of events
that may occur.  That is useful, because normally you don't want to
track the mouse forever--only until some other event, such as the
release of a button.

 -- Special Form: track-mouse body...
     This special form executes BODY, with generation of mouse motion
     events enabled.  Typically BODY would use `read-event' to read the
     motion events and modify the display accordingly.  *Note Motion
     Events::, for the format of mouse motion events.

     The value of `track-mouse' is that of the last form in BODY.  You
     should design BODY to return when it sees the up-event that
     indicates the release of the button, or whatever kind of event
     means it is time to stop tracking.

   The usual purpose of tracking mouse motion is to indicate on the
screen the consequences of pushing or releasing a button at the current
position.

   In many cases, you can avoid the need to track the mouse by using
the `mouse-face' text property (*note Special Properties::).  That
works at a much lower level and runs more smoothly than Lisp-level
mouse tracking.


File: elisp,  Node: Mouse Position,  Next: Pop-Up Menus,  Prev: Mouse Tracking,  Up: Frames

29.14 Mouse Position
====================

The functions `mouse-position' and `set-mouse-position' give access to
the current position of the mouse.

 -- Function: mouse-position
     This function returns a description of the position of the mouse.
     The value looks like `(FRAME X . Y)', where X and Y are integers
     giving the position in characters relative to the top left corner
     of the inside of FRAME.

 -- Variable: mouse-position-function
     If non-`nil', the value of this variable is a function for
     `mouse-position' to call.  `mouse-position' calls this function
     just before returning, with its normal return value as the sole
     argument, and it returns whatever this function returns to it.

     This abnormal hook exists for the benefit of packages like
     `xt-mouse.el' that need to do mouse handling at the Lisp level.

 -- Function: set-mouse-position frame x y
     This function "warps the mouse" to position X, Y in frame FRAME.
     The arguments X and Y are integers, giving the position in
     characters relative to the top left corner of the inside of FRAME.
     If FRAME is not visible, this function does nothing.  The return
     value is not significant.

 -- Function: mouse-pixel-position
     This function is like `mouse-position' except that it returns
     coordinates in units of pixels rather than units of characters.

 -- Function: set-mouse-pixel-position frame x y
     This function warps the mouse like `set-mouse-position' except that
     X and Y are in units of pixels rather than units of characters.
     These coordinates are not required to be within the frame.

     If FRAME is not visible, this function does nothing.  The return
     value is not significant.


File: elisp,  Node: Pop-Up Menus,  Next: Dialog Boxes,  Prev: Mouse Position,  Up: Frames

29.15 Pop-Up Menus
==================

When using a window system, a Lisp program can pop up a menu so that
the user can choose an alternative with the mouse.

 -- Function: x-popup-menu position menu
     This function displays a pop-up menu and returns an indication of
     what selection the user makes.

     The argument POSITION specifies where on the screen to put the top
     left corner of the menu.  It can be either a mouse button event
     (which says to put the menu where the user actuated the button) or
     a list of this form:

          ((XOFFSET YOFFSET) WINDOW)

     where XOFFSET and YOFFSET are coordinates, measured in pixels,
     counting from the top left corner of WINDOW.  WINDOW may be a
     window or a frame.

     If POSITION is `t', it means to use the current mouse position.
     If POSITION is `nil', it means to precompute the key binding
     equivalents for the keymaps specified in MENU, without actually
     displaying or popping up the menu.

     The argument MENU says what to display in the menu.  It can be a
     keymap or a list of keymaps (*note Menu Keymaps::).  In this case,
     the return value is the list of events corresponding to the user's
     choice.  (This list has more than one element if the choice
     occurred in a submenu.)  Note that `x-popup-menu' does not
     actually execute the command bound to that sequence of events.

     Alternatively, MENU can have the following form:

          (TITLE PANE1 PANE2...)

     where each pane is a list of form

          (TITLE ITEM1 ITEM2...)

     Each item should normally be a cons cell `(LINE . VALUE)', where
     LINE is a string, and VALUE is the value to return if that LINE is
     chosen.  An item can also be a string; this makes a non-selectable
     line in the menu.

     If the user gets rid of the menu without making a valid choice, for
     instance by clicking the mouse away from a valid choice or by
     typing keyboard input, then this normally results in a quit and
     `x-popup-menu' does not return.  But if POSITION is a mouse button
     event (indicating that the user invoked the menu with the mouse)
     then no quit occurs and `x-popup-menu' returns `nil'.

   *Usage note:* Don't use `x-popup-menu' to display a menu if you
could do the job with a prefix key defined with a menu keymap.  If you
use a menu keymap to implement a menu, `C-h c' and `C-h a' can see the
individual items in that menu and provide help for them.  If instead
you implement the menu by defining a command that calls `x-popup-menu',
the help facilities cannot know what happens inside that command, so
they cannot give any help for the menu's items.

   The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls `x-popup-menu'.  Therefore, if you try to implement a
submenu using `x-popup-menu', it cannot work with the menu bar in an
integrated fashion.  This is why all menu bar submenus are implemented
with menu keymaps within the parent menu, and never with
`x-popup-menu'.  *Note Menu Bar::.

   If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it.  To make the contents vary, add
a hook function to `menu-bar-update-hook' to update the contents of the
menu keymap as necessary.


File: elisp,  Node: Dialog Boxes,  Next: Pointer Shape,  Prev: Pop-Up Menus,  Up: Frames

29.16 Dialog Boxes
==================

A dialog box is a variant of a pop-up menu--it looks a little
different, it always appears in the center of a frame, and it has just
one level and one or more buttons.  The main use of dialog boxes is for
asking questions that the user can answer with "yes," "no," and a few
other alternatives.  With a single button, they can also force the user
to acknowledge important information.  The functions `y-or-n-p' and
`yes-or-no-p' use dialog boxes instead of the keyboard, when called
from commands invoked by mouse clicks.

 -- Function: x-popup-dialog position contents &optional header
     This function displays a pop-up dialog box and returns an
     indication of what selection the user makes.  The argument
     CONTENTS specifies the alternatives to offer; it has this format:

          (TITLE (STRING . VALUE)...)

     which looks like the list that specifies a single pane for
     `x-popup-menu'.

     The return value is VALUE from the chosen alternative.

     As for `x-popup-menu', an element of the list may be just a string
     instead of a cons cell `(STRING . VALUE)'.  That makes a box that
     cannot be selected.

     If `nil' appears in the list, it separates the left-hand items from
     the right-hand items; items that precede the `nil' appear on the
     left, and items that follow the `nil' appear on the right.  If you
     don't include a `nil' in the list, then approximately half the
     items appear on each side.

     Dialog boxes always appear in the center of a frame; the argument
     POSITION specifies which frame.  The possible values are as in
     `x-popup-menu', but the precise coordinates or the individual
     window don't matter; only the frame matters.

     If HEADER is non-`nil', the frame title for the box is
     `Information', otherwise it is `Question'.  The former is used for
     `message-box' (*note message-box::).

     In some configurations, Emacs cannot display a real dialog box; so
     instead it displays the same items in a pop-up menu in the center
     of the frame.

     If the user gets rid of the dialog box without making a valid
     choice, for instance using the window manager, then this produces
     a quit and `x-popup-dialog' does not return.


File: elisp,  Node: Pointer Shape,  Next: Window System Selections,  Prev: Dialog Boxes,  Up: Frames

29.17 Pointer Shape
===================

You can specify the mouse pointer style for particular text or images
using the `pointer' text property, and for images with the `:pointer'
and `:map' image properties.  The values you can use in these
properties are `text' (or `nil'), `arrow', `hand', `vdrag', `hdrag',
`modeline', and `hourglass'.  `text' stands for the usual mouse pointer
style used over text.

   Over void parts of the window (parts that do not correspond to any
of the buffer contents), the mouse pointer usually uses the `arrow'
style, but you can specify a different style (one of those above) by
setting `void-text-area-pointer'.

 -- Variable: void-text-area-pointer
     This variable specifies the mouse pointer style for void text
     areas.  These include the areas after the end of a line or below
     the last line in the buffer.  The default is to use the `arrow'
     (non-text) pointer style.

   You can specify what the `text' pointer style really looks like by
setting the variable `x-pointer-shape'.

 -- Variable: x-pointer-shape
     This variable specifies the pointer shape to use ordinarily in the
     Emacs frame, for the `text' pointer style.

 -- Variable: x-sensitive-text-pointer-shape
     This variable specifies the pointer shape to use when the mouse is
     over mouse-sensitive text.

   These variables affect newly created frames.  They do not normally
affect existing frames; however, if you set the mouse color of a frame,
that also installs the current value of those two variables.  *Note
Color Parameters::.

   The values you can use, to specify either of these pointer shapes,
are defined in the file `lisp/term/x-win.el'.  Use `M-x apropos <RET>
x-pointer <RET>' to see a list of them.


File: elisp,  Node: Window System Selections,  Next: Drag and Drop,  Prev: Pointer Shape,  Up: Frames

29.18 Window System Selections
==============================

The X server records a set of "selections" which permit transfer of
data between application programs.  The various selections are
distinguished by "selection types", represented in Emacs by symbols.  X
clients including Emacs can read or set the selection for any given
type.

 -- Command: x-set-selection type data
     This function sets a "selection" in the X server.  It takes two
     arguments: a selection type TYPE, and the value to assign to it,
     DATA.  If DATA is `nil', it means to clear out the selection.
     Otherwise, DATA may be a string, a symbol, an integer (or a cons
     of two integers or list of two integers), an overlay, or a cons of
     two markers pointing to the same buffer.  An overlay or a pair of
     markers stands for text in the overlay or between the markers.

     The argument DATA may also be a vector of valid non-vector
     selection values.

     Each possible TYPE has its own selection value, which changes
     independently.  The usual values of TYPE are `PRIMARY',
     `SECONDARY' and `CLIPBOARD'; these are symbols with upper-case
     names, in accord with X Window System conventions.  If TYPE is
     `nil', that stands for `PRIMARY'.

     This function returns DATA.

 -- Function: x-get-selection &optional type data-type
     This function accesses selections set up by Emacs or by other X
     clients.  It takes two optional arguments, TYPE and DATA-TYPE.
     The default for TYPE, the selection type, is `PRIMARY'.

     The DATA-TYPE argument specifies the form of data conversion to
     use, to convert the raw data obtained from another X client into
     Lisp data.  Meaningful values include `TEXT', `STRING',
     `UTF8_STRING', `TARGETS', `LENGTH', `DELETE', `FILE_NAME',
     `CHARACTER_POSITION', `NAME', `LINE_NUMBER', `COLUMN_NUMBER',
     `OWNER_OS', `HOST_NAME', `USER', `CLASS', `ATOM', and `INTEGER'.
     (These are symbols with upper-case names in accord with X
     conventions.)  The default for DATA-TYPE is `STRING'.

   The X server also has a set of eight numbered "cut buffers" which can
store text or other data being moved between applications.  Cut buffers
are considered obsolete, but Emacs supports them for the sake of X
clients that still use them.  Cut buffers are numbered from 0 to 7.

 -- Function: x-get-cut-buffer &optional n
     This function returns the contents of cut buffer number N.  If
     omitted N defaults to 0.

 -- Function: x-set-cut-buffer string &optional push
     This function stores STRING into the first cut buffer (cut buffer
     0).  If PUSH is `nil', only the first cut buffer is changed.  If
     PUSH is non-`nil', that says to move the values down through the
     series of cut buffers, much like the way successive kills in Emacs
     move down the kill ring.  In other words, the previous value of
     the first cut buffer moves into the second cut buffer, and the
     second to the third, and so on through all eight cut buffers.

 -- Variable: selection-coding-system
     This variable specifies the coding system to use when reading and
     writing selections or the clipboard.  *Note Coding Systems::.  The
     default is `compound-text-with-extensions', which converts to the
     text representation that X11 normally uses.

   When Emacs runs on MS-Windows, it does not implement X selections in
general, but it does support the clipboard.  `x-get-selection' and
`x-set-selection' on MS-Windows support the text data type only; if the
clipboard holds other types of data, Emacs treats the clipboard as
empty.

   On Mac OS, selection-like data transfer between applications is
performed through a mechanism called "scraps".  The clipboard is a
particular scrap named `com.apple.scrap.clipboard'.  Types of scrap
data are called "scrap flavor types", which are identified by four-char
codes such as `TEXT'.  Emacs associates a selection with a scrap, and a
selection type with a scrap flavor type via `mac-scrap-name' and
`mac-ostype' properties, respectively.

     (get 'CLIPBOARD 'mac-scrap-name)
          => "com.apple.scrap.clipboard"
     (get 'com.apple.traditional-mac-plain-text 'mac-ostype)
          => "TEXT"

   Conventionally, selection types for scrap flavor types on Mac OS have
the form of UTI (Uniform Type Identifier) such as
`com.apple.traditional-mac-plain-text', `public.utf16-plain-text', and
`public.file-url'.

 -- User Option: x-select-enable-clipboard
     If this is non-`nil', the Emacs yank functions consult the
     clipboard before the primary selection, and the kill functions
     store in the clipboard as well as the primary selection.
     Otherwise they do not access the clipboard at all.  The default is
     `nil' on most systems, but `t' on MS-Windows and Mac.


File: elisp,  Node: Drag and Drop,  Next: Color Names,  Prev: Window System Selections,  Up: Frames

29.19 Drag and Drop
===================

When a user drags something from another application over Emacs, that
other application expects Emacs to tell it if Emacs can handle the data
that is dragged.  The variable `x-dnd-test-function' is used by Emacs
to determine what to reply.  The default value is
`x-dnd-default-test-function' which accepts drops if the type of the
data to be dropped is present in `x-dnd-known-types'.  You can
customize `x-dnd-test-function' and/or `x-dnd-known-types' if you want
Emacs to accept or reject drops based on some other criteria.

   If you want to change the way Emacs handles drop of different types
or add a new type, customize `x-dnd-types-alist'.  This requires
detailed knowledge of what types other applications use for drag and
drop.

   When an URL is dropped on Emacs it may be a file, but it may also be
another URL type (ftp, http, etc.).  Emacs first checks
`dnd-protocol-alist' to determine what to do with the URL.  If there is
no match there and if `browse-url-browser-function' is an alist, Emacs
looks for a match there.  If no match is found the text for the URL is
inserted.  If you want to alter Emacs behavior, you can customize these
variables.


File: elisp,  Node: Color Names,  Next: Text Terminal Colors,  Prev: Drag and Drop,  Up: Frames

29.20 Color Names
=================

A color name is text (usually in a string) that specifies a color.
Symbolic names such as `black', `white', `red', etc., are allowed; use
`M-x list-colors-display' to see a list of defined names.  You can also
specify colors numerically in forms such as `#RGB' and `RGB:R/G/B',
where R specifies the red level, G specifies the green level, and B
specifies the blue level.  You can use either one, two, three, or four
hex digits for R; then you must use the same number of hex digits for
all G and B as well, making either 3, 6, 9 or 12 hex digits in all.
(See the documentation of the X Window System for more details about
numerical RGB specification of colors.)

   These functions provide a way to determine which color names are
valid, and what they look like.  In some cases, the value depends on the
"selected frame", as described below; see *Note Input Focus::, for the
meaning of the term "selected frame."

 -- Function: color-defined-p color &optional frame
     This function reports whether a color name is meaningful.  It
     returns `t' if so; otherwise, `nil'.  The argument FRAME says
     which frame's display to ask about; if FRAME is omitted or `nil',
     the selected frame is used.

     Note that this does not tell you whether the display you are using
     really supports that color.  When using X, you can ask for any
     defined color on any kind of display, and you will get some
     result--typically, the closest it can do.  To determine whether a
     frame can really display a certain color, use `color-supported-p'
     (see below).

     This function used to be called `x-color-defined-p', and that name
     is still supported as an alias.

 -- Function: defined-colors &optional frame
     This function returns a list of the color names that are defined
     and supported on frame FRAME (default, the selected frame).  If
     FRAME does not support colors, the value is `nil'.

     This function used to be called `x-defined-colors', and that name
     is still supported as an alias.

 -- Function: color-supported-p color &optional frame background-p
     This returns `t' if FRAME can really display the color COLOR (or
     at least something close to it).  If FRAME is omitted or `nil',
     the question applies to the selected frame.

     Some terminals support a different set of colors for foreground and
     background.  If BACKGROUND-P is non-`nil', that means you are
     asking whether COLOR can be used as a background; otherwise you
     are asking whether it can be used as a foreground.

     The argument COLOR must be a valid color name.

 -- Function: color-gray-p color &optional frame
     This returns `t' if COLOR is a shade of gray, as defined on
     FRAME's display.  If FRAME is omitted or `nil', the question
     applies to the selected frame.  If COLOR is not a valid color
     name, this function returns `nil'.

 -- Function: color-values color &optional frame
     This function returns a value that describes what COLOR should
     ideally look like on FRAME.  If COLOR is defined, the value is a
     list of three integers, which give the amount of red, the amount
     of green, and the amount of blue.  Each integer ranges in
     principle from 0 to 65535, but some displays may not use the full
     range.  This three-element list is called the "rgb values" of the
     color.

     If COLOR is not defined, the value is `nil'.

          (color-values "black")
               => (0 0 0)
          (color-values "white")
               => (65280 65280 65280)
          (color-values "red")
               => (65280 0 0)
          (color-values "pink")
               => (65280 49152 51968)
          (color-values "hungry")
               => nil

     The color values are returned for FRAME's display.  If FRAME is
     omitted or `nil', the information is returned for the selected
     frame's display.  If the frame cannot display colors, the value is
     `nil'.

     This function used to be called `x-color-values', and that name is
     still supported as an alias.


File: elisp,  Node: Text Terminal Colors,  Next: Resources,  Prev: Color Names,  Up: Frames

29.21 Text Terminal Colors
==========================

Text-only terminals usually support only a small number of colors, and
the computer uses small integers to select colors on the terminal.
This means that the computer cannot reliably tell what the selected
color looks like; instead, you have to inform your application which
small integers correspond to which colors.  However, Emacs does know
the standard set of colors and will try to use them automatically.

   The functions described in this section control how terminal colors
are used by Emacs.

   Several of these functions use or return "rgb values", described in
*Note Color Names::.

   These functions accept a display (either a frame or the name of a
terminal) as an optional argument.  We hope in the future to make Emacs
support more than one text-only terminal at one time; then this argument
will specify which terminal to operate on (the default being the
selected frame's terminal; *note Input Focus::).  At present, though,
the FRAME argument has no effect.

 -- Function: tty-color-define name number &optional rgb frame
     This function associates the color name NAME with color number
     NUMBER on the terminal.

     The optional argument RGB, if specified, is an rgb value, a list
     of three numbers that specify what the color actually looks like.
     If you do not specify RGB, then this color cannot be used by
     `tty-color-approximate' to approximate other colors, because Emacs
     will not know what it looks like.

 -- Function: tty-color-clear &optional frame
     This function clears the table of defined colors for a text-only
     terminal.

 -- Function: tty-color-alist &optional frame
     This function returns an alist recording the known colors
     supported by a text-only terminal.

     Each element has the form `(NAME NUMBER . RGB)' or `(NAME
     NUMBER)'.  Here, NAME is the color name, NUMBER is the number used
     to specify it to the terminal.  If present, RGB is a list of three
     color values (for red, green, and blue) that says what the color
     actually looks like.

 -- Function: tty-color-approximate rgb &optional frame
     This function finds the closest color, among the known colors
     supported for DISPLAY, to that described by the rgb value RGB (a
     list of color values).  The return value is an element of
     `tty-color-alist'.

 -- Function: tty-color-translate color &optional frame
     This function finds the closest color to COLOR among the known
     colors supported for DISPLAY and returns its index (an integer).
     If the name COLOR is not defined, the value is `nil'.


File: elisp,  Node: Resources,  Next: Display Feature Testing,  Prev: Text Terminal Colors,  Up: Frames

29.22 X Resources
=================

 -- Function: x-get-resource attribute class &optional component
          subclass
     The function `x-get-resource' retrieves a resource value from the X
     Window defaults database.

     Resources are indexed by a combination of a "key" and a "class".
     This function searches using a key of the form
     `INSTANCE.ATTRIBUTE' (where INSTANCE is the name under which Emacs
     was invoked), and using `Emacs.CLASS' as the class.

     The optional arguments COMPONENT and SUBCLASS add to the key and
     the class, respectively.  You must specify both of them or neither.
     If you specify them, the key is `INSTANCE.COMPONENT.ATTRIBUTE',
     and the class is `Emacs.CLASS.SUBCLASS'.

 -- Variable: x-resource-class
     This variable specifies the application name that `x-get-resource'
     should look up.  The default value is `"Emacs"'.  You can examine X
     resources for application names other than "Emacs" by binding this
     variable to some other string, around a call to `x-get-resource'.

 -- Variable: x-resource-name
     This variable specifies the instance name that `x-get-resource'
     should look up.  The default value is the name Emacs was invoked
     with, or the value specified with the `-name' or `-rn' switches.

   To illustrate some of the above, suppose that you have the line:

     xterm.vt100.background: yellow

in your X resources file (whose name is usually `~/.Xdefaults' or
`~/.Xresources').  Then:

     (let ((x-resource-class "XTerm") (x-resource-name "xterm"))
       (x-get-resource "vt100.background" "VT100.Background"))
          => "yellow"
     (let ((x-resource-class "XTerm") (x-resource-name "xterm"))
       (x-get-resource "background" "VT100" "vt100" "Background"))
          => "yellow"

   *Note X Resources: (emacs)X Resources.


File: elisp,  Node: Display Feature Testing,  Prev: Resources,  Up: Frames

29.23 Display Feature Testing
=============================

The functions in this section describe the basic capabilities of a
particular display.  Lisp programs can use them to adapt their behavior
to what the display can do.  For example, a program that ordinarily uses
a popup menu could use the minibuffer if popup menus are not supported.

   The optional argument DISPLAY in these functions specifies which
display to ask the question about.  It can be a display name, a frame
(which designates the display that frame is on), or `nil' (which refers
to the selected frame's display, *note Input Focus::).

   *Note Color Names::, *Note Text Terminal Colors::, for other
functions to obtain information about displays.

 -- Function: display-popup-menus-p &optional display
     This function returns `t' if popup menus are supported on DISPLAY,
     `nil' if not.  Support for popup menus requires that the mouse be
     available, since the user cannot choose menu items without a mouse.

 -- Function: display-graphic-p &optional display
     This function returns `t' if DISPLAY is a graphic display capable
     of displaying several frames and several different fonts at once.
     This is true for displays that use a window system such as X, and
     false for text-only terminals.

 -- Function: display-mouse-p &optional display
     This function returns `t' if DISPLAY has a mouse available, `nil'
     if not.

 -- Function: display-color-p &optional display
     This function returns `t' if the screen is a color screen.  It
     used to be called `x-display-color-p', and that name is still
     supported as an alias.

 -- Function: display-grayscale-p &optional display
     This function returns `t' if the screen can display shades of gray.
     (All color displays can do this.)

 -- Function: display-supports-face-attributes-p attributes &optional
          display
     This function returns non-`nil' if all the face attributes in
     ATTRIBUTES are supported (*note Face Attributes::).

     The definition of `supported' is somewhat heuristic, but basically
     means that a face containing all the attributes in ATTRIBUTES,
     when merged with the default face for display, can be represented
     in a way that's

       1. different in appearance than the default face, and

       2. `close in spirit' to what the attributes specify, if not
          exact.

     Point (2) implies that a `:weight black' attribute will be
     satisfied by any display that can display bold, as will
     `:foreground "yellow"' as long as some yellowish color can be
     displayed, but `:slant italic' will _not_ be satisfied by the tty
     display code's automatic substitution of a `dim' face for italic.

 -- Function: display-selections-p &optional display
     This function returns `t' if DISPLAY supports selections.
     Windowed displays normally support selections, but they may also be
     supported in some other cases.

 -- Function: display-images-p &optional display
     This function returns `t' if DISPLAY can display images.  Windowed
     displays ought in principle to handle images, but some systems
     lack the support for that.  On a display that does not support
     images, Emacs cannot display a tool bar.

 -- Function: display-screens &optional display
     This function returns the number of screens associated with the
     display.

 -- Function: display-pixel-height &optional display
     This function returns the height of the screen in pixels.  On a
     character terminal, it gives the height in characters.

     For graphical terminals, note that on "multi-monitor" setups this
     refers to the pixel width for all physical monitors associated with
     DISPLAY.  *Note Multiple Displays::.

 -- Function: display-pixel-width &optional display
     This function returns the width of the screen in pixels.  On a
     character terminal, it gives the width in characters.

     For graphical terminals, note that on "multi-monitor" setups this
     refers to the pixel width for all physical monitors associated with
     DISPLAY.  *Note Multiple Displays::.

 -- Function: display-mm-height &optional display
     This function returns the height of the screen in millimeters, or
     `nil' if Emacs cannot get that information.

 -- Function: display-mm-width &optional display
     This function returns the width of the screen in millimeters, or
     `nil' if Emacs cannot get that information.

 -- Variable: display-mm-dimensions-alist
     This variable allows the user to specify the dimensions of
     graphical displays returned by `display-mm-height' and
     `display-mm-width' in case the system provides incorrect values.

 -- Function: display-backing-store &optional display
     This function returns the backing store capability of the display.
     Backing store means recording the pixels of windows (and parts of
     windows) that are not exposed, so that when exposed they can be
     displayed very quickly.

     Values can be the symbols `always', `when-mapped', or
     `not-useful'.  The function can also return `nil' when the
     question is inapplicable to a certain kind of display.

 -- Function: display-save-under &optional display
     This function returns non-`nil' if the display supports the
     SaveUnder feature.  That feature is used by pop-up windows to save
     the pixels they obscure, so that they can pop down quickly.

 -- Function: display-planes &optional display
     This function returns the number of planes the display supports.
     This is typically the number of bits per pixel.  For a tty
     display, it is log to base two of the number of colors supported.

 -- Function: display-visual-class &optional display
     This function returns the visual class for the screen.  The value
     is one of the symbols `static-gray', `gray-scale', `static-color',
     `pseudo-color', `true-color', and `direct-color'.

 -- Function: display-color-cells &optional display
     This function returns the number of color cells the screen
     supports.

   These functions obtain additional information specifically about X
displays.

 -- Function: x-server-version &optional display
     This function returns the list of version numbers of the X server
     running the display.  The value is a list of three integers: the
     major and minor version numbers of the X protocol, and the
     distributor-specific release number of the X server software
     itself.

 -- Function: x-server-vendor &optional display
     This function returns the "vendor" that provided the X server
     software (as a string).  Really this means whoever distributes the
     X server.

     When the developers of X labelled software distributors as
     "vendors," they showed their false assumption that no system could
     ever be developed and distributed noncommercially.


File: elisp,  Node: Positions,  Next: Markers,  Prev: Frames,  Up: Top

30 Positions
************

A "position" is the index of a character in the text of a buffer.  More
precisely, a position identifies the place between two characters (or
before the first character, or after the last character), so we can
speak of the character before or after a given position.  However, we
often speak of the character "at" a position, meaning the character
after that position.

   Positions are usually represented as integers starting from 1, but
can also be represented as "markers"--special objects that relocate
automatically when text is inserted or deleted so they stay with the
surrounding characters.  Functions that expect an argument to be a
position (an integer), but accept a marker as a substitute, normally
ignore which buffer the marker points into; they convert the marker to
an integer, and use that integer, exactly as if you had passed the
integer as the argument, even if the marker points to the "wrong"
buffer.  A marker that points nowhere cannot convert to an integer;
using it instead of an integer causes an error.  *Note Markers::.

   See also the "field" feature (*note Fields::), which provides
functions that are used by many cursor-motion commands.

* Menu:

* Point::         The special position where editing takes place.
* Motion::        Changing point.
* Excursions::    Temporary motion and buffer changes.
* Narrowing::     Restricting editing to a portion of the buffer.


File: elisp,  Node: Point,  Next: Motion,  Up: Positions

30.1 Point
==========

"Point" is a special buffer position used by many editing commands,
including the self-inserting typed characters and text insertion
functions.  Other commands move point through the text to allow editing
and insertion at different places.

   Like other positions, point designates a place between two characters
(or before the first character, or after the last character), rather
than a particular character.  Usually terminals display the cursor over
the character that immediately follows point; point is actually before
the character on which the cursor sits.

   The value of point is a number no less than 1, and no greater than
the buffer size plus 1.  If narrowing is in effect (*note Narrowing::),
then point is constrained to fall within the accessible portion of the
buffer (possibly at one end of it).

   Each buffer has its own value of point, which is independent of the
value of point in other buffers.  Each window also has a value of point,
which is independent of the value of point in other windows on the same
buffer.  This is why point can have different values in various windows
that display the same buffer.  When a buffer appears in only one window,
the buffer's point and the window's point normally have the same value,
so the distinction is rarely important.  *Note Window Point::, for more
details.

 -- Function: point
     This function returns the value of point in the current buffer, as
     an integer.

          (point)
               => 175

 -- Function: point-min
     This function returns the minimum accessible value of point in the
     current buffer.  This is normally 1, but if narrowing is in
     effect, it is the position of the start of the region that you
     narrowed to.  (*Note Narrowing::.)

 -- Function: point-max
     This function returns the maximum accessible value of point in the
     current buffer.  This is `(1+ (buffer-size))', unless narrowing is
     in effect, in which case it is the position of the end of the
     region that you narrowed to.  (*Note Narrowing::.)

 -- Function: buffer-end flag
     This function returns `(point-max)' if FLAG is greater than 0,
     `(point-min)' otherwise.  The argument FLAG must be a number.

 -- Function: buffer-size &optional buffer
     This function returns the total number of characters in the current
     buffer.  In the absence of any narrowing (*note Narrowing::),
     `point-max' returns a value one larger than this.

     If you specify a buffer, BUFFER, then the value is the size of
     BUFFER.

          (buffer-size)
               => 35
          (point-max)
               => 36


File: elisp,  Node: Motion,  Next: Excursions,  Prev: Point,  Up: Positions

30.2 Motion
===========

Motion functions change the value of point, either relative to the
current value of point, relative to the beginning or end of the buffer,
or relative to the edges of the selected window.  *Note Point::.

* Menu:

* Character Motion::       Moving in terms of characters.
* Word Motion::            Moving in terms of words.
* Buffer End Motion::      Moving to the beginning or end of the buffer.
* Text Lines::             Moving in terms of lines of text.
* Screen Lines::           Moving in terms of lines as displayed.
* List Motion::            Moving by parsing lists and sexps.
* Skipping Characters::    Skipping characters belonging to a certain set.


File: elisp,  Node: Character Motion,  Next: Word Motion,  Up: Motion

30.2.1 Motion by Characters
---------------------------

These functions move point based on a count of characters.  `goto-char'
is the fundamental primitive; the other functions use that.

 -- Command: goto-char position
     This function sets point in the current buffer to the value
     POSITION.  If POSITION is less than 1, it moves point to the
     beginning of the buffer.  If POSITION is greater than the length
     of the buffer, it moves point to the end.

     If narrowing is in effect, POSITION still counts from the
     beginning of the buffer, but point cannot go outside the accessible
     portion.  If POSITION is out of range, `goto-char' moves point to
     the beginning or the end of the accessible portion.

     When this function is called interactively, POSITION is the
     numeric prefix argument, if provided; otherwise it is read from the
     minibuffer.

     `goto-char' returns POSITION.

 -- Command: forward-char &optional count
     This function moves point COUNT characters forward, towards the
     end of the buffer (or backward, towards the beginning of the
     buffer, if COUNT is negative).  If COUNT is `nil', the default is
     1.

     If this attempts to move past the beginning or end of the buffer
     (or the limits of the accessible portion, when narrowing is in
     effect), it signals an error with error symbol
     `beginning-of-buffer' or `end-of-buffer'.

     In an interactive call, COUNT is the numeric prefix argument.

 -- Command: backward-char &optional count
     This is just like `forward-char' except that it moves in the
     opposite direction.


File: elisp,  Node: Word Motion,  Next: Buffer End Motion,  Prev: Character Motion,  Up: Motion

30.2.2 Motion by Words
----------------------

These functions for parsing words use the syntax table to decide
whether a given character is part of a word.  *Note Syntax Tables::.

 -- Command: forward-word &optional count
     This function moves point forward COUNT words (or backward if
     COUNT is negative).  If COUNT is `nil', it moves forward one word.

     "Moving one word" means moving until point crosses a
     word-constituent character and then encounters a word-separator
     character.  However, this function cannot move point past the
     boundary of the accessible portion of the buffer, or across a
     field boundary (*note Fields::).  The most common case of a field
     boundary is the end of the prompt in the minibuffer.

     If it is possible to move COUNT words, without being stopped
     prematurely by the buffer boundary or a field boundary, the value
     is `t'.  Otherwise, the return value is `nil' and point stops at
     the buffer boundary or field boundary.

     If `inhibit-field-text-motion' is non-`nil', this function ignores
     field boundaries.

     In an interactive call, COUNT is specified by the numeric prefix
     argument.  If COUNT is omitted or `nil', it defaults to 1.

 -- Command: backward-word &optional count
     This function is just like `forward-word', except that it moves
     backward until encountering the front of a word, rather than
     forward.

 -- Variable: words-include-escapes
     This variable affects the behavior of `forward-word' and everything
     that uses it.  If it is non-`nil', then characters in the "escape"
     and "character quote" syntax classes count as part of words.
     Otherwise, they do not.

 -- Variable: inhibit-field-text-motion
     If this variable is non-`nil', certain motion functions including
     `forward-word', `forward-sentence', and `forward-paragraph' ignore
     field boundaries.


File: elisp,  Node: Buffer End Motion,  Next: Text Lines,  Prev: Word Motion,  Up: Motion

30.2.3 Motion to an End of the Buffer
-------------------------------------

To move point to the beginning of the buffer, write:

     (goto-char (point-min))

Likewise, to move to the end of the buffer, use:

     (goto-char (point-max))

   Here are two commands that users use to do these things.  They are
documented here to warn you not to use them in Lisp programs, because
they set the mark and display messages in the echo area.

 -- Command: beginning-of-buffer &optional n
     This function moves point to the beginning of the buffer (or the
     limits of the accessible portion, when narrowing is in effect),
     setting the mark at the previous position (except in Transient
     Mark mode, if the mark is already active, it does not set the
     mark.)

     If N is non-`nil', then it puts point N tenths of the way from the
     beginning of the accessible portion of the buffer.  In an
     interactive call, N is the numeric prefix argument, if provided;
     otherwise N defaults to `nil'.

     *Warning:* Don't use this function in Lisp programs!

 -- Command: end-of-buffer &optional n
     This function moves point to the end of the buffer (or the limits
     of the accessible portion, when narrowing is in effect), setting
     the mark at the previous position (except in Transient Mark mode
     when the mark is already active).  If N is non-`nil', then it puts
     point N tenths of the way from the end of the accessible portion of
     the buffer.

     In an interactive call, N is the numeric prefix argument, if
     provided; otherwise N defaults to `nil'.

     *Warning:* Don't use this function in Lisp programs!


File: elisp,  Node: Text Lines,  Next: Screen Lines,  Prev: Buffer End Motion,  Up: Motion

30.2.4 Motion by Text Lines
---------------------------

Text lines are portions of the buffer delimited by newline characters,
which are regarded as part of the previous line.  The first text line
begins at the beginning of the buffer, and the last text line ends at
the end of the buffer whether or not the last character is a newline.
The division of the buffer into text lines is not affected by the width
of the window, by line continuation in display, or by how tabs and
control characters are displayed.

 -- Command: goto-line line
     This function moves point to the front of the LINEth line,
     counting from line 1 at beginning of the buffer.  If LINE is less
     than 1, it moves point to the beginning of the buffer.  If LINE is
     greater than the number of lines in the buffer, it moves point to
     the end of the buffer--that is, the _end of the last line_ of the
     buffer.  This is the only case in which `goto-line' does not
     necessarily move to the beginning of a line.

     If narrowing is in effect, then LINE still counts from the
     beginning of the buffer, but point cannot go outside the accessible
     portion.  So `goto-line' moves point to the beginning or end of the
     accessible portion, if the line number specifies an inaccessible
     position.

     The return value of `goto-line' is the difference between LINE and
     the line number of the line to which point actually was able to
     move (in the full buffer, before taking account of narrowing).
     Thus, the value is positive if the scan encounters the real end of
     the buffer before finding the specified line.  The value is zero
     if scan encounters the end of the accessible portion but not the
     real end of the buffer.

     In an interactive call, LINE is the numeric prefix argument if one
     has been provided.  Otherwise LINE is read in the minibuffer.

 -- Command: beginning-of-line &optional count
     This function moves point to the beginning of the current line.
     With an argument COUNT not `nil' or 1, it moves forward COUNT-1
     lines and then to the beginning of the line.

     This function does not move point across a field boundary (*note
     Fields::) unless doing so would move beyond there to a different
     line; therefore, if COUNT is `nil' or 1, and point starts at a
     field boundary, point does not move.  To ignore field boundaries,
     either bind `inhibit-field-text-motion' to `t', or use the
     `forward-line' function instead.  For instance, `(forward-line 0)'
     does the same thing as `(beginning-of-line)', except that it
     ignores field boundaries.

     If this function reaches the end of the buffer (or of the
     accessible portion, if narrowing is in effect), it positions point
     there.  No error is signaled.

 -- Function: line-beginning-position &optional count
     Return the position that `(beginning-of-line COUNT)' would move to.

 -- Command: end-of-line &optional count
     This function moves point to the end of the current line.  With an
     argument COUNT not `nil' or 1, it moves forward COUNT-1 lines and
     then to the end of the line.

     This function does not move point across a field boundary (*note
     Fields::) unless doing so would move beyond there to a different
     line; therefore, if COUNT is `nil' or 1, and point starts at a
     field boundary, point does not move.  To ignore field boundaries,
     bind `inhibit-field-text-motion' to `t'.

     If this function reaches the end of the buffer (or of the
     accessible portion, if narrowing is in effect), it positions point
     there.  No error is signaled.

 -- Function: line-end-position &optional count
     Return the position that `(end-of-line COUNT)' would move to.

 -- Command: forward-line &optional count
     This function moves point forward COUNT lines, to the beginning of
     the line.  If COUNT is negative, it moves point -COUNT lines
     backward, to the beginning of a line.  If COUNT is zero, it moves
     point to the beginning of the current line.  If COUNT is `nil',
     that means 1.

     If `forward-line' encounters the beginning or end of the buffer (or
     of the accessible portion) before finding that many lines, it sets
     point there.  No error is signaled.

     `forward-line' returns the difference between COUNT and the number
     of lines actually moved.  If you attempt to move down five lines
     from the beginning of a buffer that has only three lines, point
     stops at the end of the last line, and the value will be 2.

     In an interactive call, COUNT is the numeric prefix argument.

 -- Function: count-lines start end
     This function returns the number of lines between the positions
     START and END in the current buffer.  If START and END are equal,
     then it returns 0.  Otherwise it returns at least 1, even if START
     and END are on the same line.  This is because the text between
     them, considered in isolation, must contain at least one line
     unless it is empty.

     Here is an example of using `count-lines':

          (defun current-line ()
            "Return the vertical position of point..."
            (+ (count-lines (window-start) (point))
               (if (= (current-column) 0) 1 0)))

 -- Function: line-number-at-pos &optional pos
     This function returns the line number in the current buffer
     corresponding to the buffer position POS.  If POS is `nil' or
     omitted, the current buffer position is used.

   Also see the functions `bolp' and `eolp' in *Note Near Point::.
These functions do not move point, but test whether it is already at the
beginning or end of a line.


File: elisp,  Node: Screen Lines,  Next: List Motion,  Prev: Text Lines,  Up: Motion

30.2.5 Motion by Screen Lines
-----------------------------

The line functions in the previous section count text lines, delimited
only by newline characters.  By contrast, these functions count screen
lines, which are defined by the way the text appears on the screen.  A
text line is a single screen line if it is short enough to fit the width
of the selected window, but otherwise it may occupy several screen
lines.

   In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines.  In these cases,
`vertical-motion' moves point much like `forward-line'.  *Note
Truncation::.

   Because the width of a given string depends on the flags that control
the appearance of certain characters, `vertical-motion' behaves
differently, for a given piece of text, depending on the buffer it is
in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows).  *Note Usual
Display::.

   These functions scan text to determine where screen lines break, and
thus take time proportional to the distance scanned.  If you intend to
use them heavily, Emacs provides caches which may improve the
performance of your code.  *Note cache-long-line-scans: Truncation.

 -- Function: vertical-motion count &optional window
     This function moves point to the start of the screen line COUNT
     screen lines down from the screen line containing point.  If COUNT
     is negative, it moves up instead.

     `vertical-motion' returns the number of screen lines over which it
     moved point.  The value may be less in absolute value than COUNT
     if the beginning or end of the buffer was reached.

     The window WINDOW is used for obtaining parameters such as the
     width, the horizontal scrolling, and the display table.  But
     `vertical-motion' always operates on the current buffer, even if
     WINDOW currently displays some other buffer.

 -- Function: count-screen-lines &optional beg end count-final-newline
          window
     This function returns the number of screen lines in the text from
     BEG to END.  The number of screen lines may be different from the
     number of actual lines, due to line continuation, the display
     table, etc.  If BEG and END are `nil' or omitted, they default to
     the beginning and end of the accessible portion of the buffer.

     If the region ends with a newline, that is ignored unless the
     optional third argument COUNT-FINAL-NEWLINE is non-`nil'.

     The optional fourth argument WINDOW specifies the window for
     obtaining parameters such as width, horizontal scrolling, and so
     on.  The default is to use the selected window's parameters.

     Like `vertical-motion', `count-screen-lines' always uses the
     current buffer, regardless of which buffer is displayed in WINDOW.
     This makes possible to use `count-screen-lines' in any buffer,
     whether or not it is currently displayed in some window.

 -- Command: move-to-window-line count
     This function moves point with respect to the text currently
     displayed in the selected window.  It moves point to the beginning
     of the screen line COUNT screen lines from the top of the window.
     If COUNT is negative, that specifies a position -COUNT lines from
     the bottom (or the last line of the buffer, if the buffer ends
     above the specified screen position).

     If COUNT is `nil', then point moves to the beginning of the line
     in the middle of the window.  If the absolute value of COUNT is
     greater than the size of the window, then point moves to the place
     that would appear on that screen line if the window were tall
     enough.  This will probably cause the next redisplay to scroll to
     bring that location onto the screen.

     In an interactive call, COUNT is the numeric prefix argument.

     The value returned is the window line number point has moved to,
     with the top line in the window numbered 0.

 -- Function: compute-motion from frompos to topos width offsets window
     This function scans the current buffer, calculating screen
     positions.  It scans the buffer forward from position FROM,
     assuming that is at screen coordinates FROMPOS, to position TO or
     coordinates TOPOS, whichever comes first.  It returns the ending
     buffer position and screen coordinates.

     The coordinate arguments FROMPOS and TOPOS are cons cells of the
     form `(HPOS . VPOS)'.

     The argument WIDTH is the number of columns available to display
     text; this affects handling of continuation lines.  `nil' means
     the actual number of usable text columns in the window, which is
     equivalent to the value returned by `(window-width window)'.

     The argument OFFSETS is either `nil' or a cons cell of the form
     `(HSCROLL . TAB-OFFSET)'.  Here HSCROLL is the number of columns
     not being displayed at the left margin; most callers get this by
     calling `window-hscroll'.  Meanwhile, TAB-OFFSET is the offset
     between column numbers on the screen and column numbers in the
     buffer.  This can be nonzero in a continuation line, when the
     previous screen lines' widths do not add up to a multiple of
     `tab-width'.  It is always zero in a non-continuation line.

     The window WINDOW serves only to specify which display table to
     use.  `compute-motion' always operates on the current buffer,
     regardless of what buffer is displayed in WINDOW.

     The return value is a list of five elements:

          (POS HPOS VPOS PREVHPOS CONTIN)

     Here POS is the buffer position where the scan stopped, VPOS is
     the vertical screen position, and HPOS is the horizontal screen
     position.

     The result PREVHPOS is the horizontal position one character back
     from POS.  The result CONTIN is `t' if the last line was continued
     after (or within) the previous character.

     For example, to find the buffer position of column COL of screen
     line LINE of a certain window, pass the window's display start
     location as FROM and the window's upper-left coordinates as
     FROMPOS.  Pass the buffer's `(point-max)' as TO, to limit the scan
     to the end of the accessible portion of the buffer, and pass LINE
     and COL as TOPOS.  Here's a function that does this:

          (defun coordinates-of-position (col line)
            (car (compute-motion (window-start)
                                 '(0 . 0)
                                 (point-max)
                                 (cons col line)
                                 (window-width)
                                 (cons (window-hscroll) 0)
                                 (selected-window))))

     When you use `compute-motion' for the minibuffer, you need to use
     `minibuffer-prompt-width' to get the horizontal position of the
     beginning of the first screen line.  *Note Minibuffer Contents::.


File: elisp,  Node: List Motion,  Next: Skipping Characters,  Prev: Screen Lines,  Up: Motion

30.2.6 Moving over Balanced Expressions
---------------------------------------

Here are several functions concerned with balanced-parenthesis
expressions (also called "sexps" in connection with moving across them
in Emacs).  The syntax table controls how these functions interpret
various characters; see *Note Syntax Tables::.  *Note Parsing
Expressions::, for lower-level primitives for scanning sexps or parts of
sexps.  For user-level commands, see *Note Commands for Editing with
Parentheses: (emacs)Parentheses.

 -- Command: forward-list &optional arg
     This function moves forward across ARG (default 1) balanced groups
     of parentheses.  (Other syntactic entities such as words or paired
     string quotes are ignored.)

 -- Command: backward-list &optional arg
     This function moves backward across ARG (default 1) balanced
     groups of parentheses.  (Other syntactic entities such as words or
     paired string quotes are ignored.)

 -- Command: up-list &optional arg
     This function moves forward out of ARG (default 1) levels of
     parentheses.  A negative argument means move backward but still to
     a less deep spot.

 -- Command: down-list &optional arg
     This function moves forward into ARG (default 1) levels of
     parentheses.  A negative argument means move backward but still go
     deeper in parentheses (-ARG levels).

 -- Command: forward-sexp &optional arg
     This function moves forward across ARG (default 1) balanced
     expressions.  Balanced expressions include both those delimited by
     parentheses and other kinds, such as words and string constants.
     *Note Parsing Expressions::.  For example,

          ---------- Buffer: foo ----------
          (concat-!- "foo " (car x) y z)
          ---------- Buffer: foo ----------

          (forward-sexp 3)
               => nil

          ---------- Buffer: foo ----------
          (concat "foo " (car x) y-!- z)
          ---------- Buffer: foo ----------

 -- Command: backward-sexp &optional arg
     This function moves backward across ARG (default 1) balanced
     expressions.

 -- Command: beginning-of-defun &optional arg
     This function moves back to the ARGth beginning of a defun.  If
     ARG is negative, this actually moves forward, but it still moves
     to the beginning of a defun, not to the end of one.  ARG defaults
     to 1.

 -- Command: end-of-defun &optional arg
     This function moves forward to the ARGth end of a defun.  If ARG
     is negative, this actually moves backward, but it still moves to
     the end of a defun, not to the beginning of one.  ARG defaults to
     1.

 -- User Option: defun-prompt-regexp
     If non-`nil', this buffer-local variable holds a regular
     expression that specifies what text can appear before the
     open-parenthesis that starts a defun.  That is to say, a defun
     begins on a line that starts with a match for this regular
     expression, followed by a character with open-parenthesis syntax.

 -- User Option: open-paren-in-column-0-is-defun-start
     If this variable's value is non-`nil', an open parenthesis in
     column 0 is considered to be the start of a defun.  If it is
     `nil', an open parenthesis in column 0 has no special meaning.
     The default is `t'.

 -- Variable: beginning-of-defun-function
     If non-`nil', this variable holds a function for finding the
     beginning of a defun.  The function `beginning-of-defun' calls
     this function instead of using its normal method.

 -- Variable: end-of-defun-function
     If non-`nil', this variable holds a function for finding the end of
     a defun.  The function `end-of-defun' calls this function instead
     of using its normal method.


File: elisp,  Node: Skipping Characters,  Prev: List Motion,  Up: Motion

30.2.7 Skipping Characters
--------------------------

The following two functions move point over a specified set of
characters.  For example, they are often used to skip whitespace.  For
related functions, see *Note Motion and Syntax::.

   These functions convert the set string to multibyte if the buffer is
multibyte, and they convert it to unibyte if the buffer is unibyte, as
the search functions do (*note Searching and Matching::).

 -- Function: skip-chars-forward character-set &optional limit
     This function moves point in the current buffer forward, skipping
     over a given set of characters.  It examines the character
     following point, then advances point if the character matches
     CHARACTER-SET.  This continues until it reaches a character that
     does not match.  The function returns the number of characters
     moved over.

     The argument CHARACTER-SET is a string, like the inside of a
     `[...]' in a regular expression except that `]' does not terminate
     it, and `\' quotes `^', `-' or `\'.  Thus, `"a-zA-Z"' skips over
     all letters, stopping before the first nonletter, and `"^a-zA-Z"'
     skips nonletters stopping before the first letter.  See *Note
     Regular Expressions::.  Character classes can also be used, e.g.
     `"[:alnum:]"'.  See *note Char Classes::.

     If LIMIT is supplied (it must be a number or a marker), it
     specifies the maximum position in the buffer that point can be
     skipped to.  Point will stop at or before LIMIT.

     In the following example, point is initially located directly
     before the `T'.  After the form is evaluated, point is located at
     the end of that line (between the `t' of `hat' and the newline).
     The function skips all letters and spaces, but not newlines.

          ---------- Buffer: foo ----------
          I read "-!-The cat in the hat
          comes back" twice.
          ---------- Buffer: foo ----------

          (skip-chars-forward "a-zA-Z ")
               => nil

          ---------- Buffer: foo ----------
          I read "The cat in the hat-!-
          comes back" twice.
          ---------- Buffer: foo ----------

 -- Function: skip-chars-backward character-set &optional limit
     This function moves point backward, skipping characters that match
     CHARACTER-SET, until LIMIT.  It is just like `skip-chars-forward'
     except for the direction of motion.

     The return value indicates the distance traveled.  It is an
     integer that is zero or less.


File: elisp,  Node: Excursions,  Next: Narrowing,  Prev: Motion,  Up: Positions

30.3 Excursions
===============

It is often useful to move point "temporarily" within a localized
portion of the program, or to switch buffers temporarily.  This is
called an "excursion", and it is done with the `save-excursion' special
form.  This construct initially remembers the identity of the current
buffer, and its values of point and the mark, and restores them after
the completion of the excursion.

   The forms for saving and restoring the configuration of windows are
described elsewhere (see *Note Window Configurations::, and *note Frame
Configurations::).

 -- Special Form: save-excursion body...
     The `save-excursion' special form saves the identity of the current
     buffer and the values of point and the mark in it, evaluates BODY,
     and finally restores the buffer and its saved values of point and
     the mark.  All three saved values are restored even in case of an
     abnormal exit via `throw' or error (*note Nonlocal Exits::).

     The `save-excursion' special form is the standard way to switch
     buffers or move point within one part of a program and avoid
     affecting the rest of the program.  It is used more than 4000
     times in the Lisp sources of Emacs.

     `save-excursion' does not save the values of point and the mark for
     other buffers, so changes in other buffers remain in effect after
     `save-excursion' exits.

     Likewise, `save-excursion' does not restore window-buffer
     correspondences altered by functions such as `switch-to-buffer'.
     One way to restore these correspondences, and the selected window,
     is to use `save-window-excursion' inside `save-excursion' (*note
     Window Configurations::).

     The value returned by `save-excursion' is the result of the last
     form in BODY, or `nil' if no body forms were given.

          (save-excursion FORMS)
          ==
          (let ((old-buf (current-buffer))
                (old-pnt (point-marker))
                (old-mark (copy-marker (mark-marker))))
            (unwind-protect
                (progn FORMS)
              (set-buffer old-buf)
              (goto-char old-pnt)
              (set-marker (mark-marker) old-mark)))

   *Warning:* Ordinary insertion of text adjacent to the saved point
value relocates the saved value, just as it relocates all markers.
More precisely, the saved value is a marker with insertion type `nil'.
*Note Marker Insertion Types::.  Therefore, when the saved point value
is restored, it normally comes before the inserted text.

   Although `save-excursion' saves the location of the mark, it does
not prevent functions which modify the buffer from setting
`deactivate-mark', and thus causing the deactivation of the mark after
the command finishes.  *Note The Mark::.


File: elisp,  Node: Narrowing,  Prev: Excursions,  Up: Positions

30.4 Narrowing
==============

"Narrowing" means limiting the text addressable by Emacs editing
commands to a limited range of characters in a buffer.  The text that
remains addressable is called the "accessible portion" of the buffer.

   Narrowing is specified with two buffer positions which become the
beginning and end of the accessible portion.  For most editing commands
and most Emacs primitives, these positions replace the values of the
beginning and end of the buffer.  While narrowing is in effect, no text
outside the accessible portion is displayed, and point cannot move
outside the accessible portion.

   Values such as positions or line numbers, which usually count from
the beginning of the buffer, do so despite narrowing, but the functions
which use them refuse to operate on text that is inaccessible.

   The commands for saving buffers are unaffected by narrowing; they
save the entire buffer regardless of any narrowing.

 -- Command: narrow-to-region start end
     This function sets the accessible portion of the current buffer to
     start at START and end at END.  Both arguments should be character
     positions.

     In an interactive call, START and END are set to the bounds of the
     current region (point and the mark, with the smallest first).

 -- Command: narrow-to-page &optional move-count
     This function sets the accessible portion of the current buffer to
     include just the current page.  An optional first argument
     MOVE-COUNT non-`nil' means to move forward or backward by
     MOVE-COUNT pages and then narrow to one page.  The variable
     `page-delimiter' specifies where pages start and end (*note
     Standard Regexps::).

     In an interactive call, MOVE-COUNT is set to the numeric prefix
     argument.

 -- Command: widen
     This function cancels any narrowing in the current buffer, so that
     the entire contents are accessible.  This is called "widening".
     It is equivalent to the following expression:

          (narrow-to-region 1 (1+ (buffer-size)))

 -- Special Form: save-restriction body...
     This special form saves the current bounds of the accessible
     portion, evaluates the BODY forms, and finally restores the saved
     bounds, thus restoring the same state of narrowing (or absence
     thereof) formerly in effect.  The state of narrowing is restored
     even in the event of an abnormal exit via `throw' or error (*note
     Nonlocal Exits::).  Therefore, this construct is a clean way to
     narrow a buffer temporarily.

     The value returned by `save-restriction' is that returned by the
     last form in BODY, or `nil' if no body forms were given.

     *Caution:* it is easy to make a mistake when using the
     `save-restriction' construct.  Read the entire description here
     before you try it.

     If BODY changes the current buffer, `save-restriction' still
     restores the restrictions on the original buffer (the buffer whose
     restrictions it saved from), but it does not restore the identity
     of the current buffer.

     `save-restriction' does _not_ restore point and the mark; use
     `save-excursion' for that.  If you use both `save-restriction' and
     `save-excursion' together, `save-excursion' should come first (on
     the outside).  Otherwise, the old point value would be restored
     with temporary narrowing still in effect.  If the old point value
     were outside the limits of the temporary narrowing, this would
     fail to restore it accurately.

     Here is a simple example of correct use of `save-restriction':

          ---------- Buffer: foo ----------
          This is the contents of foo
          This is the contents of foo
          This is the contents of foo-!-
          ---------- Buffer: foo ----------

          (save-excursion
            (save-restriction
              (goto-char 1)
              (forward-line 2)
              (narrow-to-region 1 (point))
              (goto-char (point-min))
              (replace-string "foo" "bar")))

          ---------- Buffer: foo ----------
          This is the contents of bar
          This is the contents of bar
          This is the contents of foo-!-
          ---------- Buffer: foo ----------


File: elisp,  Node: Markers,  Next: Text,  Prev: Positions,  Up: Top

31 Markers
**********

A "marker" is a Lisp object used to specify a position in a buffer
relative to the surrounding text.  A marker changes its offset from the
beginning of the buffer automatically whenever text is inserted or
deleted, so that it stays with the two characters on either side of it.

* Menu:

* Overview of Markers::      The components of a marker, and how it relocates.
* Predicates on Markers::    Testing whether an object is a marker.
* Creating Markers::         Making empty markers or markers at certain places.
* Information from Markers:: Finding the marker's buffer or character position.
* Marker Insertion Types::   Two ways a marker can relocate when you
                               insert where it points.
* Moving Markers::           Moving the marker to a new buffer or position.
* The Mark::                 How "the mark" is implemented with a marker.
* The Region::               How to access "the region".


File: elisp,  Node: Overview of Markers,  Next: Predicates on Markers,  Up: Markers

31.1 Overview of Markers
========================

A marker specifies a buffer and a position in that buffer.  The marker
can be used to represent a position in the functions that require one,
just as an integer could be used.  In that case, the marker's buffer is
normally ignored.  Of course, a marker used in this way usually points
to a position in the buffer that the function operates on, but that is
entirely the programmer's responsibility.  *Note Positions::, for a
complete description of positions.

   A marker has three attributes: the marker position, the marker
buffer, and the insertion type.  The marker position is an integer that
is equivalent (at a given time) to the marker as a position in that
buffer.  But the marker's position value can change often during the
life of the marker.  Insertion and deletion of text in the buffer
relocate the marker.  The idea is that a marker positioned between two
characters remains between those two characters despite insertion and
deletion elsewhere in the buffer.  Relocation changes the integer
equivalent of the marker.

   Deleting text around a marker's position leaves the marker between
the characters immediately before and after the deleted text.  Inserting
text at the position of a marker normally leaves the marker either in
front of or after the new text, depending on the marker's "insertion
type" (*note Marker Insertion Types::)--unless the insertion is done
with `insert-before-markers' (*note Insertion::).

   Insertion and deletion in a buffer must check all the markers and
relocate them if necessary.  This slows processing in a buffer with a
large number of markers.  For this reason, it is a good idea to make a
marker point nowhere if you are sure you don't need it any more.
Unreferenced markers are garbage collected eventually, but until then
will continue to use time if they do point somewhere.

   Because it is common to perform arithmetic operations on a marker
position, most of the arithmetic operations (including `+' and `-')
accept markers as arguments.  In such cases, the marker stands for its
current position.

   Here are examples of creating markers, setting markers, and moving
point to markers:

     ;; Make a new marker that initially does not point anywhere:
     (setq m1 (make-marker))
          => #<marker in no buffer>

     ;; Set `m1' to point between the 99th and 100th characters
     ;;   in the current buffer:
     (set-marker m1 100)
          => #<marker at 100 in markers.texi>

     ;; Now insert one character at the beginning of the buffer:
     (goto-char (point-min))
          => 1
     (insert "Q")
          => nil

     ;; `m1' is updated appropriately.
     m1
          => #<marker at 101 in markers.texi>

     ;; Two markers that point to the same position
     ;;   are not `eq', but they are `equal'.
     (setq m2 (copy-marker m1))
          => #<marker at 101 in markers.texi>
     (eq m1 m2)
          => nil
     (equal m1 m2)
          => t

     ;; When you are finished using a marker, make it point nowhere.
     (set-marker m1 nil)
          => #<marker in no buffer>


File: elisp,  Node: Predicates on Markers,  Next: Creating Markers,  Prev: Overview of Markers,  Up: Markers

31.2 Predicates on Markers
==========================

You can test an object to see whether it is a marker, or whether it is
either an integer or a marker.  The latter test is useful in connection
with the arithmetic functions that work with both markers and integers.

 -- Function: markerp object
     This function returns `t' if OBJECT is a marker, `nil' otherwise.
     Note that integers are not markers, even though many functions
     will accept either a marker or an integer.

 -- Function: integer-or-marker-p object
     This function returns `t' if OBJECT is an integer or a marker,
     `nil' otherwise.

 -- Function: number-or-marker-p object
     This function returns `t' if OBJECT is a number (either integer or
     floating point) or a marker, `nil' otherwise.


File: elisp,  Node: Creating Markers,  Next: Information from Markers,  Prev: Predicates on Markers,  Up: Markers

31.3 Functions that Create Markers
==================================

When you create a new marker, you can make it point nowhere, or point
to the present position of point, or to the beginning or end of the
accessible portion of the buffer, or to the same place as another given
marker.

   The next four functions all return markers with insertion type
`nil'.  *Note Marker Insertion Types::.

 -- Function: make-marker
     This function returns a newly created marker that does not point
     anywhere.

          (make-marker)
               => #<marker in no buffer>

 -- Function: point-marker
     This function returns a new marker that points to the present
     position of point in the current buffer.  *Note Point::.  For an
     example, see `copy-marker', below.

 -- Function: point-min-marker
     This function returns a new marker that points to the beginning of
     the accessible portion of the buffer.  This will be the beginning
     of the buffer unless narrowing is in effect.  *Note Narrowing::.

 -- Function: point-max-marker
     This function returns a new marker that points to the end of the
     accessible portion of the buffer.  This will be the end of the
     buffer unless narrowing is in effect.  *Note Narrowing::.

     Here are examples of this function and `point-min-marker', shown in
     a buffer containing a version of the source file for the text of
     this chapter.

          (point-min-marker)
               => #<marker at 1 in markers.texi>
          (point-max-marker)
               => #<marker at 15573 in markers.texi>

          (narrow-to-region 100 200)
               => nil
          (point-min-marker)
               => #<marker at 100 in markers.texi>
          (point-max-marker)
               => #<marker at 200 in markers.texi>

 -- Function: copy-marker marker-or-integer &optional insertion-type
     If passed a marker as its argument, `copy-marker' returns a new
     marker that points to the same place and the same buffer as does
     MARKER-OR-INTEGER.  If passed an integer as its argument,
     `copy-marker' returns a new marker that points to position
     MARKER-OR-INTEGER in the current buffer.

     The new marker's insertion type is specified by the argument
     INSERTION-TYPE.  *Note Marker Insertion Types::.

     If passed an integer argument less than 1, `copy-marker' returns a
     new marker that points to the beginning of the current buffer.  If
     passed an integer argument greater than the length of the buffer,
     `copy-marker' returns a new marker that points to the end of the
     buffer.

          (copy-marker 0)
               => #<marker at 1 in markers.texi>

          (copy-marker 20000)
               => #<marker at 7572 in markers.texi>

     An error is signaled if MARKER is neither a marker nor an integer.

   Two distinct markers are considered `equal' (even though not `eq')
to each other if they have the same position and buffer, or if they
both point nowhere.

     (setq p (point-marker))
          => #<marker at 2139 in markers.texi>

     (setq q (copy-marker p))
          => #<marker at 2139 in markers.texi>

     (eq p q)
          => nil

     (equal p q)
          => t


File: elisp,  Node: Information from Markers,  Next: Marker Insertion Types,  Prev: Creating Markers,  Up: Markers

31.4 Information from Markers
=============================

This section describes the functions for accessing the components of a
marker object.

 -- Function: marker-position marker
     This function returns the position that MARKER points to, or `nil'
     if it points nowhere.

 -- Function: marker-buffer marker
     This function returns the buffer that MARKER points into, or `nil'
     if it points nowhere.

          (setq m (make-marker))
               => #<marker in no buffer>
          (marker-position m)
               => nil
          (marker-buffer m)
               => nil

          (set-marker m 3770 (current-buffer))
               => #<marker at 3770 in markers.texi>
          (marker-buffer m)
               => #<buffer markers.texi>
          (marker-position m)
               => 3770

 -- Function: buffer-has-markers-at position
     This function returns `t' if one or more markers point at position
     POSITION in the current buffer.


File: elisp,  Node: Marker Insertion Types,  Next: Moving Markers,  Prev: Information from Markers,  Up: Markers

31.5 Marker Insertion Types
===========================

When you insert text directly at the place where a marker points, there
are two possible ways to relocate that marker: it can point before the
inserted text, or point after it.  You can specify which one a given
marker should do by setting its "insertion type".  Note that use of
`insert-before-markers' ignores markers' insertion types, always
relocating a marker to point after the inserted text.

 -- Function: set-marker-insertion-type marker type
     This function sets the insertion type of marker MARKER to TYPE.
     If TYPE is `t', MARKER will advance when text is inserted at its
     position.  If TYPE is `nil', MARKER does not advance when text is
     inserted there.

 -- Function: marker-insertion-type marker
     This function reports the current insertion type of MARKER.

   Most functions that create markers, without an argument allowing to
specify the insertion type, create them with insertion type `nil'.
Also, the mark has, by default, insertion type `nil'.


File: elisp,  Node: Moving Markers,  Next: The Mark,  Prev: Marker Insertion Types,  Up: Markers

31.6 Moving Marker Positions
============================

This section describes how to change the position of an existing
marker.  When you do this, be sure you know whether the marker is used
outside of your program, and, if so, what effects will result from
moving it--otherwise, confusing things may happen in other parts of
Emacs.

 -- Function: set-marker marker position &optional buffer
     This function moves MARKER to POSITION in BUFFER.  If BUFFER is
     not provided, it defaults to the current buffer.

     If POSITION is less than 1, `set-marker' moves MARKER to the
     beginning of the buffer.  If POSITION is greater than the size of
     the buffer, `set-marker' moves marker to the end of the buffer.
     If POSITION is `nil' or a marker that points nowhere, then MARKER
     is set to point nowhere.

     The value returned is MARKER.

          (setq m (point-marker))
               => #<marker at 4714 in markers.texi>
          (set-marker m 55)
               => #<marker at 55 in markers.texi>
          (setq b (get-buffer "foo"))
               => #<buffer foo>
          (set-marker m 0 b)
               => #<marker at 1 in foo>

 -- Function: move-marker marker position &optional buffer
     This is another name for `set-marker'.


File: elisp,  Node: The Mark,  Next: The Region,  Prev: Moving Markers,  Up: Markers

31.7 The Mark
=============

One special marker in each buffer is designated "the mark".  It
specifies a position to bound a range of text for commands such as
`kill-region' and `indent-rigidly'.  Lisp programs should set the mark
only to values that have a potential use to the user, and never for
their own internal purposes.  For example, the `replace-regexp' command
sets the mark to the value of point before doing any replacements,
because this enables the user to move back there conveniently after the
replace is finished.

   Many commands are designed to operate on the text between point and
the mark when called interactively.  If you are writing such a command,
don't examine the mark directly; instead, use `interactive' with the
`r' specification.  This provides the values of point and the mark as
arguments to the command in an interactive call, but permits other Lisp
programs to specify arguments explicitly.  *Note Interactive Codes::.

   Each buffer has a marker which represents the value of the mark in
that buffer, independent of any other buffer.  When a buffer is newly
created, this marker exists but does not point anywhere.  That means
the mark "doesn't exist" in that buffer as yet.

   Once the mark "exists" in a buffer, it normally never ceases to
exist.  However, it may become "inactive", if Transient Mark mode is
enabled.  The variable `mark-active', which is always buffer-local in
all buffers, indicates whether the mark is active: non-`nil' means yes.
A command can request deactivation of the mark upon return to the
editor command loop by setting `deactivate-mark' to a non-`nil' value
(but this causes deactivation only if Transient Mark mode is enabled).

   The main motivation for using Transient Mark mode is that this mode
also enables highlighting of the region when the mark is active.  *Note
Display::.

   In addition to the mark, each buffer has a "mark ring" which is a
list of markers containing previous values of the mark.  When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring.  The variable `mark-ring-max' specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.

   There is also a separate global mark ring, but that is used only in a
few particular user-level commands, and is not relevant to Lisp
programming.  So we do not describe it here.

 -- Function: mark &optional force
     This function returns the current buffer's mark position as an
     integer, or `nil' if no mark has ever been set in this buffer.

     If Transient Mark mode is enabled, and `mark-even-if-inactive' is
     `nil', `mark' signals an error if the mark is inactive.  However,
     if FORCE is non-`nil', then `mark' disregards inactivity of the
     mark, and returns the mark position anyway (or `nil').

 -- Function: mark-marker
     This function returns the marker that represents the current
     buffer's mark.  It is not a copy, it is the marker used
     internally.  Therefore, changing this marker's position will
     directly affect the buffer's mark.  Don't do that unless that is
     the effect you want.

          (setq m (mark-marker))
               => #<marker at 3420 in markers.texi>
          (set-marker m 100)
               => #<marker at 100 in markers.texi>
          (mark-marker)
               => #<marker at 100 in markers.texi>

     Like any marker, this marker can be set to point at any buffer you
     like.  If you make it point at any buffer other than the one of
     which it is the mark, it will yield perfectly consistent, but
     rather odd, results.  We recommend that you not do it!

 -- Function: set-mark position
     This function sets the mark to POSITION, and activates the mark.
     The old value of the mark is _not_ pushed onto the mark ring.

     *Please note:* Use this function only if you want the user to see
     that the mark has moved, and you want the previous mark position to
     be lost.  Normally, when a new mark is set, the old one should go
     on the `mark-ring'.  For this reason, most applications should use
     `push-mark' and `pop-mark', not `set-mark'.

     Novice Emacs Lisp programmers often try to use the mark for the
     wrong purposes.  The mark saves a location for the user's
     convenience.  An editing command should not alter the mark unless
     altering the mark is part of the user-level functionality of the
     command.  (And, in that case, this effect should be documented.)
     To remember a location for internal use in the Lisp program, store
     it in a Lisp variable.  For example:

          (let ((beg (point)))
            (forward-line 1)
            (delete-region beg (point))).

 -- Function: push-mark &optional position nomsg activate
     This function sets the current buffer's mark to POSITION, and
     pushes a copy of the previous mark onto `mark-ring'.  If POSITION
     is `nil', then the value of point is used.  `push-mark' returns
     `nil'.

     The function `push-mark' normally _does not_ activate the mark.
     To do that, specify `t' for the argument ACTIVATE.

     A `Mark set' message is displayed unless NOMSG is non-`nil'.

 -- Function: pop-mark
     This function pops off the top element of `mark-ring' and makes
     that mark become the buffer's actual mark.  This does not move
     point in the buffer, and it does nothing if `mark-ring' is empty.
     It deactivates the mark.

     The return value is not meaningful.

 -- User Option: transient-mark-mode
     This variable if non-`nil' enables Transient Mark mode, in which
     every buffer-modifying primitive sets `deactivate-mark'.  The
     consequence of this is that commands that modify the buffer
     normally make the mark inactive.

     Lisp programs can set `transient-mark-mode' to `only' to enable
     Transient Mark mode for the following command only.  During that
     following command, the value of `transient-mark-mode' is
     `identity'.  If it is still `identity' at the end of the command,
     it changes to `nil'.

 -- User Option: mark-even-if-inactive
     If this is non-`nil', Lisp programs and the Emacs user can use the
     mark even when it is inactive.  This option affects the behavior of
     Transient Mark mode.  When the option is non-`nil', deactivation of
     the mark turns off region highlighting, but commands that use the
     mark behave as if the mark were still active.

 -- Variable: deactivate-mark
     If an editor command sets this variable non-`nil', then the editor
     command loop deactivates the mark after the command returns (if
     Transient Mark mode is enabled).  All the primitives that change
     the buffer set `deactivate-mark', to deactivate the mark when the
     command is finished.

     To write Lisp code that modifies the buffer without causing
     deactivation of the mark at the end of the command, bind
     `deactivate-mark' to `nil' around the code that does the
     modification.  For example:

          (let (deactivate-mark)
            (insert " "))

 -- Function: deactivate-mark
     This function deactivates the mark, if Transient Mark mode is
     enabled.  Otherwise it does nothing.

 -- Variable: mark-active
     The mark is active when this variable is non-`nil'.  This variable
     is always buffer-local in each buffer.

 -- Variable: activate-mark-hook
 -- Variable: deactivate-mark-hook
     These normal hooks are run, respectively, when the mark becomes
     active and when it becomes inactive.  The hook
     `activate-mark-hook' is also run at the end of a command if the
     mark is active and it is possible that the region may have changed.

 -- Variable: mark-ring
     The value of this buffer-local variable is the list of saved former
     marks of the current buffer, most recent first.

          mark-ring
          => (#<marker at 11050 in markers.texi>
              #<marker at 10832 in markers.texi>
              ...)

 -- User Option: mark-ring-max
     The value of this variable is the maximum size of `mark-ring'.  If
     more marks than this are pushed onto the `mark-ring', `push-mark'
     discards an old mark when it adds a new one.


File: elisp,  Node: The Region,  Prev: The Mark,  Up: Markers

31.8 The Region
===============

The text between point and the mark is known as "the region".  Various
functions operate on text delimited by point and the mark, but only
those functions specifically related to the region itself are described
here.

   The next two functions signal an error if the mark does not point
anywhere.  If Transient Mark mode is enabled and
`mark-even-if-inactive' is `nil', they also signal an error if the mark
is inactive.

 -- Function: region-beginning
     This function returns the position of the beginning of the region
     (as an integer).  This is the position of either point or the mark,
     whichever is smaller.

 -- Function: region-end
     This function returns the position of the end of the region (as an
     integer).  This is the position of either point or the mark,
     whichever is larger.

   Few programs need to use the `region-beginning' and `region-end'
functions.  A command designed to operate on a region should normally
use `interactive' with the `r' specification to find the beginning and
end of the region.  This lets other Lisp programs specify the bounds
explicitly as arguments.  (*Note Interactive Codes::.)


File: elisp,  Node: Text,  Next: Non-ASCII Characters,  Prev: Markers,  Up: Top

32 Text
*******

This chapter describes the functions that deal with the text in a
buffer.  Most examine, insert, or delete text in the current buffer,
often operating at point or on text adjacent to point.  Many are
interactive.  All the functions that change the text provide for undoing
the changes (*note Undo::).

   Many text-related functions operate on a region of text defined by
two buffer positions passed in arguments named START and END.  These
arguments should be either markers (*note Markers::) or numeric
character positions (*note Positions::).  The order of these arguments
does not matter; it is all right for START to be the end of the region
and END the beginning.  For example, `(delete-region 1 10)' and
`(delete-region 10 1)' are equivalent.  An `args-out-of-range' error is
signaled if either START or END is outside the accessible portion of
the buffer.  In an interactive call, point and the mark are used for
these arguments.

   Throughout this chapter, "text" refers to the characters in the
buffer, together with their properties (when relevant).  Keep in mind
that point is always between two characters, and the cursor appears on
the character after point.

* Menu:

* Near Point::       Examining text in the vicinity of point.
* Buffer Contents::  Examining text in a general fashion.
* Comparing Text::   Comparing substrings of buffers.
* Insertion::        Adding new text to a buffer.
* Commands for Insertion::  User-level commands to insert text.
* Deletion::         Removing text from a buffer.
* User-Level Deletion::     User-level commands to delete text.
* The Kill Ring::    Where removed text sometimes is saved for later use.
* Undo::             Undoing changes to the text of a buffer.
* Maintaining Undo:: How to enable and disable undo information.
			How to control how much information is kept.
* Filling::          Functions for explicit filling.
* Margins::          How to specify margins for filling commands.
* Adaptive Fill::    Adaptive Fill mode chooses a fill prefix from context.
* Auto Filling::     How auto-fill mode is implemented to break lines.
* Sorting::          Functions for sorting parts of the buffer.
* Columns::          Computing horizontal positions, and using them.
* Indentation::      Functions to insert or adjust indentation.
* Case Changes::     Case conversion of parts of the buffer.
* Text Properties::  Assigning Lisp property lists to text characters.
* Substitution::     Replacing a given character wherever it appears.
* Transposition::    Swapping two portions of a buffer.
* Registers::        How registers are implemented.  Accessing the text or
                       position stored in a register.
* Base 64::          Conversion to or from base 64 encoding.
* MD5 Checksum::     Compute the MD5 "message digest"/"checksum".
* Atomic Changes::   Installing several buffer changes "atomically".
* Change Hooks::     Supplying functions to be run when text is changed.


File: elisp,  Node: Near Point,  Next: Buffer Contents,  Up: Text

32.1 Examining Text Near Point
==============================

Many functions are provided to look at the characters around point.
Several simple functions are described here.  See also `looking-at' in
*Note Regexp Search::.

   In the following four functions, "beginning" or "end" of buffer
refers to the beginning or end of the accessible portion.

 -- Function: char-after &optional position
     This function returns the character in the current buffer at (i.e.,
     immediately after) position POSITION.  If POSITION is out of range
     for this purpose, either before the beginning of the buffer, or at
     or beyond the end, then the value is `nil'.  The default for
     POSITION is point.

     In the following example, assume that the first character in the
     buffer is `@':

          (char-to-string (char-after 1))
               => "@"

 -- Function: char-before &optional position
     This function returns the character in the current buffer
     immediately before position POSITION.  If POSITION is out of range
     for this purpose, either at or before the beginning of the buffer,
     or beyond the end, then the value is `nil'.  The default for
     POSITION is point.

 -- Function: following-char
     This function returns the character following point in the current
     buffer.  This is similar to `(char-after (point))'.  However, if
     point is at the end of the buffer, then `following-char' returns 0.

     Remember that point is always between characters, and the cursor
     normally appears over the character following point.  Therefore,
     the character returned by `following-char' is the character the
     cursor is over.

     In this example, point is between the `a' and the `c'.

          ---------- Buffer: foo ----------
          Gentlemen may cry ``Pea-!-ce! Peace!,''
          but there is no peace.
          ---------- Buffer: foo ----------

          (char-to-string (preceding-char))
               => "a"
          (char-to-string (following-char))
               => "c"

 -- Function: preceding-char
     This function returns the character preceding point in the current
     buffer.  See above, under `following-char', for an example.  If
     point is at the beginning of the buffer, `preceding-char' returns
     0.

 -- Function: bobp
     This function returns `t' if point is at the beginning of the
     buffer.  If narrowing is in effect, this means the beginning of the
     accessible portion of the text.  See also `point-min' in *Note
     Point::.

 -- Function: eobp
     This function returns `t' if point is at the end of the buffer.
     If narrowing is in effect, this means the end of accessible
     portion of the text.  See also `point-max' in *Note Point::.

 -- Function: bolp
     This function returns `t' if point is at the beginning of a line.
     *Note Text Lines::.  The beginning of the buffer (or of its
     accessible portion) always counts as the beginning of a line.

 -- Function: eolp
     This function returns `t' if point is at the end of a line.  The
     end of the buffer (or of its accessible portion) is always
     considered the end of a line.


File: elisp,  Node: Buffer Contents,  Next: Comparing Text,  Prev: Near Point,  Up: Text

32.2 Examining Buffer Contents
==============================

This section describes functions that allow a Lisp program to convert
any portion of the text in the buffer into a string.

 -- Function: buffer-substring start end
     This function returns a string containing a copy of the text of the
     region defined by positions START and END in the current buffer.
     If the arguments are not positions in the accessible portion of
     the buffer, `buffer-substring' signals an `args-out-of-range'
     error.

     It is not necessary for START to be less than END; the arguments
     can be given in either order.  But most often the smaller argument
     is written first.

     Here's an example which assumes Font-Lock mode is not enabled:

          ---------- Buffer: foo ----------
          This is the contents of buffer foo

          ---------- Buffer: foo ----------

          (buffer-substring 1 10)
               => "This is t"
          (buffer-substring (point-max) 10)
               => "he contents of buffer foo\n"

     If the text being copied has any text properties, these are copied
     into the string along with the characters they belong to.  *Note
     Text Properties::.  However, overlays (*note Overlays::) in the
     buffer and their properties are ignored, not copied.

     For example, if Font-Lock mode is enabled, you might get results
     like these:

          (buffer-substring 1 10)
               => #("This is t" 0 1 (fontified t) 1 9 (fontified t))

 -- Function: buffer-substring-no-properties start end
     This is like `buffer-substring', except that it does not copy text
     properties, just the characters themselves.  *Note Text
     Properties::.

 -- Function: filter-buffer-substring start end &optional delete noprops
     This function passes the buffer text between START and END through
     the filter functions specified by the variable
     `buffer-substring-filters', and returns the value from the last
     filter function.  If `buffer-substring-filters' is `nil', the
     value is the unaltered text from the buffer, what
     `buffer-substring' would return.

     If DELETE is non-`nil', this function deletes the text between
     START and END after copying it, like `delete-and-extract-region'.

     If NOPROPS is non-`nil', the final string returned does not
     include text properties, while the string passed through the
     filters still includes text properties from the buffer text.

     Lisp code should use this function instead of `buffer-substring',
     `buffer-substring-no-properties', or `delete-and-extract-region'
     when copying into user-accessible data structures such as the
     kill-ring, X clipboard, and registers.  Major and minor modes can
     add functions to `buffer-substring-filters' to alter such text as
     it is copied out of the buffer.

 -- Variable: buffer-substring-filters
     This variable should be a list of functions that accept a single
     argument, a string, and return a string.
     `filter-buffer-substring' passes the buffer substring to the first
     function in this list, and the return value of each function is
     passed to the next function.  The return value of the last
     function is used as the return value of `filter-buffer-substring'.

     As a special convention, point is set to the start of the buffer
     text being operated on (i.e., the START argument for
     `filter-buffer-substring') before these functions are called.

     If this variable is `nil', no filtering is performed.

 -- Function: buffer-string
     This function returns the contents of the entire accessible
     portion of the current buffer as a string.  It is equivalent to

          (buffer-substring (point-min) (point-max))

          ---------- Buffer: foo ----------
          This is the contents of buffer foo

          ---------- Buffer: foo ----------

          (buffer-string)
               => "This is the contents of buffer foo\n"

 -- Function: current-word &optional strict really-word
     This function returns the symbol (or word) at or near point, as a
     string.  The return value includes no text properties.

     If the optional argument REALLY-WORD is non-`nil', it finds a
     word; otherwise, it finds a symbol (which includes both word
     characters and symbol constituent characters).

     If the optional argument STRICT is non-`nil', then point must be
     in or next to the symbol or word--if no symbol or word is there,
     the function returns `nil'.  Otherwise, a nearby symbol or word on
     the same line is acceptable.

 -- Function: thing-at-point thing
     Return the THING around or next to point, as a string.

     The argument THING is a symbol which specifies a kind of syntactic
     entity.  Possibilities include `symbol', `list', `sexp', `defun',
     `filename', `url', `word', `sentence', `whitespace', `line',
     `page', and others.

          ---------- Buffer: foo ----------
          Gentlemen may cry ``Pea-!-ce! Peace!,''
          but there is no peace.
          ---------- Buffer: foo ----------

          (thing-at-point 'word)
               => "Peace"
          (thing-at-point 'line)
               => "Gentlemen may cry ``Peace! Peace!,''\n"
          (thing-at-point 'whitespace)
               => nil


File: elisp,  Node: Comparing Text,  Next: Insertion,  Prev: Buffer Contents,  Up: Text

32.3 Comparing Text
===================

This function lets you compare portions of the text in a buffer, without
copying them into strings first.

 -- Function: compare-buffer-substrings buffer1 start1 end1 buffer2
          start2 end2
     This function lets you compare two substrings of the same buffer
     or two different buffers.  The first three arguments specify one
     substring, giving a buffer (or a buffer name) and two positions
     within the buffer.  The last three arguments specify the other
     substring in the same way.  You can use `nil' for BUFFER1,
     BUFFER2, or both to stand for the current buffer.

     The value is negative if the first substring is less, positive if
     the first is greater, and zero if they are equal.  The absolute
     value of the result is one plus the index of the first differing
     characters within the substrings.

     This function ignores case when comparing characters if
     `case-fold-search' is non-`nil'.  It always ignores text
     properties.

     Suppose the current buffer contains the text `foobarbar
     haha!rara!'; then in this example the two substrings are `rbar '
     and `rara!'.  The value is 2 because the first substring is greater
     at the second character.

          (compare-buffer-substrings nil 6 11 nil 16 21)
               => 2


File: elisp,  Node: Insertion,  Next: Commands for Insertion,  Prev: Comparing Text,  Up: Text

32.4 Inserting Text
===================

"Insertion" means adding new text to a buffer.  The inserted text goes
at point--between the character before point and the character after
point.  Some insertion functions leave point before the inserted text,
while other functions leave it after.  We call the former insertion
"after point" and the latter insertion "before point".

   Insertion relocates markers that point at positions after the
insertion point, so that they stay with the surrounding text (*note
Markers::).  When a marker points at the place of insertion, insertion
may or may not relocate the marker, depending on the marker's insertion
type (*note Marker Insertion Types::).  Certain special functions such
as `insert-before-markers' relocate all such markers to point after the
inserted text, regardless of the markers' insertion type.

   Insertion functions signal an error if the current buffer is
read-only or if they insert within read-only text.

   These functions copy text characters from strings and buffers along
with their properties.  The inserted characters have exactly the same
properties as the characters they were copied from.  By contrast,
characters specified as separate arguments, not part of a string or
buffer, inherit their text properties from the neighboring text.

   The insertion functions convert text from unibyte to multibyte in
order to insert in a multibyte buffer, and vice versa--if the text
comes from a string or from a buffer.  However, they do not convert
unibyte character codes 128 through 255 to multibyte characters, not
even if the current buffer is a multibyte buffer.  *Note Converting
Representations::.

 -- Function: insert &rest args
     This function inserts the strings and/or characters ARGS into the
     current buffer, at point, moving point forward.  In other words, it
     inserts the text before point.  An error is signaled unless all
     ARGS are either strings or characters.  The value is `nil'.

 -- Function: insert-before-markers &rest args
     This function inserts the strings and/or characters ARGS into the
     current buffer, at point, moving point forward.  An error is
     signaled unless all ARGS are either strings or characters.  The
     value is `nil'.

     This function is unlike the other insertion functions in that it
     relocates markers initially pointing at the insertion point, to
     point after the inserted text.  If an overlay begins at the
     insertion point, the inserted text falls outside the overlay; if a
     nonempty overlay ends at the insertion point, the inserted text
     falls inside that overlay.

 -- Function: insert-char character count &optional inherit
     This function inserts COUNT instances of CHARACTER into the
     current buffer before point.  The argument COUNT should be an
     integer, and CHARACTER must be a character.  The value is `nil'.

     This function does not convert unibyte character codes 128 through
     255 to multibyte characters, not even if the current buffer is a
     multibyte buffer.  *Note Converting Representations::.

     If INHERIT is non-`nil', then the inserted characters inherit
     sticky text properties from the two characters before and after the
     insertion point.  *Note Sticky Properties::.

 -- Function: insert-buffer-substring from-buffer-or-name &optional
          start end
     This function inserts a portion of buffer FROM-BUFFER-OR-NAME
     (which must already exist) into the current buffer before point.
     The text inserted is the region between START and END.  (These
     arguments default to the beginning and end of the accessible
     portion of that buffer.)  This function returns `nil'.

     In this example, the form is executed with buffer `bar' as the
     current buffer.  We assume that buffer `bar' is initially empty.

          ---------- Buffer: foo ----------
          We hold these truths to be self-evident, that all
          ---------- Buffer: foo ----------

          (insert-buffer-substring "foo" 1 20)
               => nil

          ---------- Buffer: bar ----------
          We hold these truth-!-
          ---------- Buffer: bar ----------

 -- Function: insert-buffer-substring-no-properties from-buffer-or-name
          &optional start end
     This is like `insert-buffer-substring' except that it does not
     copy any text properties.

   *Note Sticky Properties::, for other insertion functions that inherit
text properties from the nearby text in addition to inserting it.
Whitespace inserted by indentation functions also inherits text
properties.


File: elisp,  Node: Commands for Insertion,  Next: Deletion,  Prev: Insertion,  Up: Text

32.5 User-Level Insertion Commands
==================================

This section describes higher-level commands for inserting text,
commands intended primarily for the user but useful also in Lisp
programs.

 -- Command: insert-buffer from-buffer-or-name
     This command inserts the entire accessible contents of
     FROM-BUFFER-OR-NAME (which must exist) into the current buffer
     after point.  It leaves the mark after the inserted text.  The
     value is `nil'.

 -- Command: self-insert-command count
     This command inserts the last character typed; it does so COUNT
     times, before point, and returns `nil'.  Most printing characters
     are bound to this command.  In routine use, `self-insert-command'
     is the most frequently called function in Emacs, but programs
     rarely use it except to install it on a keymap.

     In an interactive call, COUNT is the numeric prefix argument.

     Self-insertion translates the input character through
     `translation-table-for-input'.  *Note Translation of Characters::.

     This command calls `auto-fill-function' whenever that is non-`nil'
     and the character inserted is in the table `auto-fill-chars'
     (*note Auto Filling::).

     This command performs abbrev expansion if Abbrev mode is enabled
     and the inserted character does not have word-constituent syntax.
     (*Note Abbrevs::, and *Note Syntax Class Table::.)  It is also
     responsible for calling `blink-paren-function' when the inserted
     character has close parenthesis syntax (*note Blinking::).

     Do not try substituting your own definition of
     `self-insert-command' for the standard one.  The editor command
     loop handles this function specially.

 -- Command: newline &optional number-of-newlines
     This command inserts newlines into the current buffer before point.
     If NUMBER-OF-NEWLINES is supplied, that many newline characters
     are inserted.

     This function calls `auto-fill-function' if the current column
     number is greater than the value of `fill-column' and
     NUMBER-OF-NEWLINES is `nil'.  Typically what `auto-fill-function'
     does is insert a newline; thus, the overall result in this case is
     to insert two newlines at different places: one at point, and
     another earlier in the line.  `newline' does not auto-fill if
     NUMBER-OF-NEWLINES is non-`nil'.

     This command indents to the left margin if that is not zero.
     *Note Margins::.

     The value returned is `nil'.  In an interactive call, COUNT is the
     numeric prefix argument.

 -- Variable: overwrite-mode
     This variable controls whether overwrite mode is in effect.  The
     value should be `overwrite-mode-textual', `overwrite-mode-binary',
     or `nil'.  `overwrite-mode-textual' specifies textual overwrite
     mode (treats newlines and tabs specially), and
     `overwrite-mode-binary' specifies binary overwrite mode (treats
     newlines and tabs like any other characters).


File: elisp,  Node: Deletion,  Next: User-Level Deletion,  Prev: Commands for Insertion,  Up: Text

32.6 Deleting Text
==================

Deletion means removing part of the text in a buffer, without saving it
in the kill ring (*note The Kill Ring::).  Deleted text can't be
yanked, but can be reinserted using the undo mechanism (*note Undo::).
Some deletion functions do save text in the kill ring in some special
cases.

   All of the deletion functions operate on the current buffer.

 -- Command: erase-buffer
     This function deletes the entire text of the current buffer (_not_
     just the accessible portion), leaving it empty.  If the buffer is
     read-only, it signals a `buffer-read-only' error; if some of the
     text in it is read-only, it signals a `text-read-only' error.
     Otherwise, it deletes the text without asking for any
     confirmation.  It returns `nil'.

     Normally, deleting a large amount of text from a buffer inhibits
     further auto-saving of that buffer "because it has shrunk."
     However, `erase-buffer' does not do this, the idea being that the
     future text is not really related to the former text, and its size
     should not be compared with that of the former text.

 -- Command: delete-region start end
     This command deletes the text between positions START and END in
     the current buffer, and returns `nil'.  If point was inside the
     deleted region, its value afterward is START.  Otherwise, point
     relocates with the surrounding text, as markers do.

 -- Function: delete-and-extract-region start end
     This function deletes the text between positions START and END in
     the current buffer, and returns a string containing the text just
     deleted.

     If point was inside the deleted region, its value afterward is
     START.  Otherwise, point relocates with the surrounding text, as
     markers do.

 -- Command: delete-char count &optional killp
     This command deletes COUNT characters directly after point, or
     before point if COUNT is negative.  If KILLP is non-`nil', then it
     saves the deleted characters in the kill ring.

     In an interactive call, COUNT is the numeric prefix argument, and
     KILLP is the unprocessed prefix argument.  Therefore, if a prefix
     argument is supplied, the text is saved in the kill ring.  If no
     prefix argument is supplied, then one character is deleted, but
     not saved in the kill ring.

     The value returned is always `nil'.

 -- Command: delete-backward-char count &optional killp
     This command deletes COUNT characters directly before point, or
     after point if COUNT is negative.  If KILLP is non-`nil', then it
     saves the deleted characters in the kill ring.

     In an interactive call, COUNT is the numeric prefix argument, and
     KILLP is the unprocessed prefix argument.  Therefore, if a prefix
     argument is supplied, the text is saved in the kill ring.  If no
     prefix argument is supplied, then one character is deleted, but
     not saved in the kill ring.

     The value returned is always `nil'.

 -- Command: backward-delete-char-untabify count &optional killp
     This command deletes COUNT characters backward, changing tabs into
     spaces.  When the next character to be deleted is a tab, it is
     first replaced with the proper number of spaces to preserve
     alignment and then one of those spaces is deleted instead of the
     tab.  If KILLP is non-`nil', then the command saves the deleted
     characters in the kill ring.

     Conversion of tabs to spaces happens only if COUNT is positive.
     If it is negative, exactly -COUNT characters after point are
     deleted.

     In an interactive call, COUNT is the numeric prefix argument, and
     KILLP is the unprocessed prefix argument.  Therefore, if a prefix
     argument is supplied, the text is saved in the kill ring.  If no
     prefix argument is supplied, then one character is deleted, but
     not saved in the kill ring.

     The value returned is always `nil'.

 -- User Option: backward-delete-char-untabify-method
     This option specifies how `backward-delete-char-untabify' should
     deal with whitespace.  Possible values include `untabify', the
     default, meaning convert a tab to many spaces and delete one;
     `hungry', meaning delete all tabs and spaces before point with one
     command; `all' meaning delete all tabs, spaces and newlines before
     point, and `nil', meaning do nothing special for whitespace
     characters.


File: elisp,  Node: User-Level Deletion,  Next: The Kill Ring,  Prev: Deletion,  Up: Text

32.7 User-Level Deletion Commands
=================================

This section describes higher-level commands for deleting text,
commands intended primarily for the user but useful also in Lisp
programs.

 -- Command: delete-horizontal-space &optional backward-only
     This function deletes all spaces and tabs around point.  It returns
     `nil'.

     If BACKWARD-ONLY is non-`nil', the function deletes spaces and
     tabs before point, but not after point.

     In the following examples, we call `delete-horizontal-space' four
     times, once on each line, with point between the second and third
     characters on the line each time.

          ---------- Buffer: foo ----------
          I -!-thought
          I -!-     thought
          We-!- thought
          Yo-!-u thought
          ---------- Buffer: foo ----------

          (delete-horizontal-space)   ; Four times.
               => nil

          ---------- Buffer: foo ----------
          Ithought
          Ithought
          Wethought
          You thought
          ---------- Buffer: foo ----------

 -- Command: delete-indentation &optional join-following-p
     This function joins the line point is on to the previous line,
     deleting any whitespace at the join and in some cases replacing it
     with one space.  If JOIN-FOLLOWING-P is non-`nil',
     `delete-indentation' joins this line to the following line
     instead.  The function returns `nil'.

     If there is a fill prefix, and the second of the lines being joined
     starts with the prefix, then `delete-indentation' deletes the fill
     prefix before joining the lines.  *Note Margins::.

     In the example below, point is located on the line starting
     `events', and it makes no difference if there are trailing spaces
     in the preceding line.

          ---------- Buffer: foo ----------
          When in the course of human
          -!-    events, it becomes necessary
          ---------- Buffer: foo ----------

          (delete-indentation)
               => nil

          ---------- Buffer: foo ----------
          When in the course of human-!- events, it becomes necessary
          ---------- Buffer: foo ----------

     After the lines are joined, the function `fixup-whitespace' is
     responsible for deciding whether to leave a space at the junction.

 -- Command: fixup-whitespace
     This function replaces all the horizontal whitespace surrounding
     point with either one space or no space, according to the context.
     It returns `nil'.

     At the beginning or end of a line, the appropriate amount of space
     is none.  Before a character with close parenthesis syntax, or
     after a character with open parenthesis or expression-prefix
     syntax, no space is also appropriate.  Otherwise, one space is
     appropriate.  *Note Syntax Class Table::.

     In the example below, `fixup-whitespace' is called the first time
     with point before the word `spaces' in the first line.  For the
     second invocation, point is directly after the `('.

          ---------- Buffer: foo ----------
          This has too many     -!-spaces
          This has too many spaces at the start of (-!-   this list)
          ---------- Buffer: foo ----------

          (fixup-whitespace)
               => nil
          (fixup-whitespace)
               => nil

          ---------- Buffer: foo ----------
          This has too many spaces
          This has too many spaces at the start of (this list)
          ---------- Buffer: foo ----------

 -- Command: just-one-space &optional n
     This command replaces any spaces and tabs around point with a
     single space, or N spaces if N is specified.  It returns `nil'.

 -- Command: delete-blank-lines
     This function deletes blank lines surrounding point.  If point is
     on a blank line with one or more blank lines before or after it,
     then all but one of them are deleted.  If point is on an isolated
     blank line, then it is deleted.  If point is on a nonblank line,
     the command deletes all blank lines immediately following it.

     A blank line is defined as a line containing only tabs and spaces.

     `delete-blank-lines' returns `nil'.


File: elisp,  Node: The Kill Ring,  Next: Undo,  Prev: User-Level Deletion,  Up: Text

32.8 The Kill Ring
==================

"Kill functions" delete text like the deletion functions, but save it
so that the user can reinsert it by "yanking".  Most of these functions
have `kill-' in their name.  By contrast, the functions whose names
start with `delete-' normally do not save text for yanking (though they
can still be undone); these are "deletion" functions.

   Most of the kill commands are primarily for interactive use, and are
not described here.  What we do describe are the functions provided for
use in writing such commands.  You can use these functions to write
commands for killing text.  When you need to delete text for internal
purposes within a Lisp function, you should normally use deletion
functions, so as not to disturb the kill ring contents.  *Note
Deletion::.

   Killed text is saved for later yanking in the "kill ring".  This is
a list that holds a number of recent kills, not just the last text
kill.  We call this a "ring" because yanking treats it as having
elements in a cyclic order.  The list is kept in the variable
`kill-ring', and can be operated on with the usual functions for lists;
there are also specialized functions, described in this section, that
treat it as a ring.

   Some people think this use of the word "kill" is unfortunate, since
it refers to operations that specifically _do not_ destroy the entities
"killed."  This is in sharp contrast to ordinary life, in which death
is permanent and "killed" entities do not come back to life.
Therefore, other metaphors have been proposed.  For example, the term
"cut ring" makes sense to people who, in pre-computer days, used
scissors and paste to cut up and rearrange manuscripts.  However, it
would be difficult to change the terminology now.

* Menu:

* Kill Ring Concepts::     What text looks like in the kill ring.
* Kill Functions::         Functions that kill text.
* Yanking::                How yanking is done.
* Yank Commands::          Commands that access the kill ring.
* Low-Level Kill Ring::	   Functions and variables for kill ring access.
* Internals of Kill Ring:: Variables that hold kill ring data.


File: elisp,  Node: Kill Ring Concepts,  Next: Kill Functions,  Up: The Kill Ring

32.8.1 Kill Ring Concepts
-------------------------

The kill ring records killed text as strings in a list, most recent
first.  A short kill ring, for example, might look like this:

     ("some text" "a different piece of text" "even older text")

When the list reaches `kill-ring-max' entries in length, adding a new
entry automatically deletes the last entry.

   When kill commands are interwoven with other commands, each kill
command makes a new entry in the kill ring.  Multiple kill commands in
succession build up a single kill ring entry, which would be yanked as a
unit; the second and subsequent consecutive kill commands add text to
the entry made by the first one.

   For yanking, one entry in the kill ring is designated the "front" of
the ring.  Some yank commands "rotate" the ring by designating a
different element as the "front."  But this virtual rotation doesn't
change the list itself--the most recent entry always comes first in the
list.


File: elisp,  Node: Kill Functions,  Next: Yanking,  Prev: Kill Ring Concepts,  Up: The Kill Ring

32.8.2 Functions for Killing
----------------------------

`kill-region' is the usual subroutine for killing text.  Any command
that calls this function is a "kill command" (and should probably have
`kill' in its name).  `kill-region' puts the newly killed text in a new
element at the beginning of the kill ring or adds it to the most recent
element.  It determines automatically (using `last-command') whether
the previous command was a kill command, and if so appends the killed
text to the most recent entry.

 -- Command: kill-region start end &optional yank-handler
     This function kills the text in the region defined by START and
     END.  The text is deleted but saved in the kill ring, along with
     its text properties.  The value is always `nil'.

     In an interactive call, START and END are point and the mark.

     If the buffer or text is read-only, `kill-region' modifies the kill
     ring just the same, then signals an error without modifying the
     buffer.  This is convenient because it lets the user use a series
     of kill commands to copy text from a read-only buffer into the
     kill ring.

     If YANK-HANDLER is non-`nil', this puts that value onto the string
     of killed text, as a `yank-handler' text property.  *Note
     Yanking::.  Note that if YANK-HANDLER is `nil', any `yank-handler'
     properties present on the killed text are copied onto the kill
     ring, like other text properties.

 -- User Option: kill-read-only-ok
     If this option is non-`nil', `kill-region' does not signal an
     error if the buffer or text is read-only.  Instead, it simply
     returns, updating the kill ring but not changing the buffer.

 -- Command: copy-region-as-kill start end
     This command saves the region defined by START and END on the kill
     ring (including text properties), but does not delete the text
     from the buffer.  It returns `nil'.

     The command does not set `this-command' to `kill-region', so a
     subsequent kill command does not append to the same kill ring
     entry.

     Don't call `copy-region-as-kill' in Lisp programs unless you aim to
     support Emacs 18.  For newer Emacs versions, it is better to use
     `kill-new' or `kill-append' instead.  *Note Low-Level Kill Ring::.


File: elisp,  Node: Yanking,  Next: Yank Commands,  Prev: Kill Functions,  Up: The Kill Ring

32.8.3 Yanking
--------------

Yanking means inserting text from the kill ring, but it does not insert
the text blindly.  Yank commands and some other commands use
`insert-for-yank' to perform special processing on the text that they
copy into the buffer.

 -- Function: insert-for-yank string
     This function normally works like `insert' except that it doesn't
     insert the text properties in the `yank-excluded-properties' list.
     However, if any part of STRING has a non-`nil' `yank-handler'
     text property, that property can do various special processing on
     that part of the text being inserted.

 -- Function: insert-buffer-substring-as-yank buf &optional start end
     This function resembles `insert-buffer-substring' except that it
     doesn't insert the text properties in the
     `yank-excluded-properties' list.

   You can put a `yank-handler' text property on all or part of the
text to control how it will be inserted if it is yanked.  The
`insert-for-yank' function looks for that property.  The property value
must be a list of one to four elements, with the following format
(where elements after the first may be omitted):

     (FUNCTION PARAM NOEXCLUDE UNDO)

   Here is what the elements do:

FUNCTION
     When FUNCTION is present and non-`nil', it is called instead of
     `insert' to insert the string.  FUNCTION takes one argument--the
     string to insert.

PARAM
     If PARAM is present and non-`nil', it replaces STRING (or the part
     of STRING being processed) as the object passed to FUNCTION (or
     `insert'); for example, if FUNCTION is `yank-rectangle', PARAM
     should be a list of strings to insert as a rectangle.

NOEXCLUDE
     If NOEXCLUDE is present and non-`nil', the normal removal of the
     yank-excluded-properties is not performed; instead FUNCTION is
     responsible for removing those properties.  This may be necessary
     if FUNCTION adjusts point before or after inserting the object.

UNDO
     If UNDO is present and non-`nil', it is a function that will be
     called by `yank-pop' to undo the insertion of the current object.
     It is called with two arguments, the start and end of the current
     region.  FUNCTION can set `yank-undo-function' to override the
     UNDO value.


File: elisp,  Node: Yank Commands,  Next: Low-Level Kill Ring,  Prev: Yanking,  Up: The Kill Ring

32.8.4 Functions for Yanking
----------------------------

This section describes higher-level commands for yanking, which are
intended primarily for the user but useful also in Lisp programs.  Both
`yank' and `yank-pop' honor the `yank-excluded-properties' variable and
`yank-handler' text property (*note Yanking::).

 -- Command: yank &optional arg
     This command inserts before point the text at the front of the
     kill ring.  It positions the mark at the beginning of that text,
     and point at the end.

     If ARG is a non-`nil' list (which occurs interactively when the
     user types `C-u' with no digits), then `yank' inserts the text as
     described above, but puts point before the yanked text and puts
     the mark after it.

     If ARG is a number, then `yank' inserts the ARGth most recently
     killed text--the ARGth element of the kill ring list, counted
     cyclically from the front, which is considered the first element
     for this purpose.

     `yank' does not alter the contents of the kill ring, unless it
     used text provided by another program, in which case it pushes
     that text onto the kill ring.  However if ARG is an integer
     different from one, it rotates the kill ring to place the yanked
     string at the front.

     `yank' returns `nil'.

 -- Command: yank-pop &optional arg
     This command replaces the just-yanked entry from the kill ring
     with a different entry from the kill ring.

     This is allowed only immediately after a `yank' or another
     `yank-pop'.  At such a time, the region contains text that was just
     inserted by yanking.  `yank-pop' deletes that text and inserts in
     its place a different piece of killed text.  It does not add the
     deleted text to the kill ring, since it is already in the kill
     ring somewhere.  It does however rotate the kill ring to place the
     newly yanked string at the front.

     If ARG is `nil', then the replacement text is the previous element
     of the kill ring.  If ARG is numeric, the replacement is the ARGth
     previous kill.  If ARG is negative, a more recent kill is the
     replacement.

     The sequence of kills in the kill ring wraps around, so that after
     the oldest one comes the newest one, and before the newest one
     goes the oldest.

     The return value is always `nil'.

 -- Variable: yank-undo-function
     If this variable is non-`nil', the function `yank-pop' uses its
     value instead of `delete-region' to delete the text inserted by
     the previous `yank' or `yank-pop' command.  The value must be a
     function of two arguments, the start and end of the current region.

     The function `insert-for-yank' automatically sets this variable
     according to the UNDO element of the `yank-handler' text property,
     if there is one.


File: elisp,  Node: Low-Level Kill Ring,  Next: Internals of Kill Ring,  Prev: Yank Commands,  Up: The Kill Ring

32.8.5 Low-Level Kill Ring
--------------------------

These functions and variables provide access to the kill ring at a
lower level, but still convenient for use in Lisp programs, because they
take care of interaction with window system selections (*note Window
System Selections::).

 -- Function: current-kill n &optional do-not-move
     The function `current-kill' rotates the yanking pointer, which
     designates the "front" of the kill ring, by N places (from newer
     kills to older ones), and returns the text at that place in the
     ring.

     If the optional second argument DO-NOT-MOVE is non-`nil', then
     `current-kill' doesn't alter the yanking pointer; it just returns
     the Nth kill, counting from the current yanking pointer.

     If N is zero, indicating a request for the latest kill,
     `current-kill' calls the value of `interprogram-paste-function'
     (documented below) before consulting the kill ring.  If that value
     is a function and calling it returns a string, `current-kill'
     pushes that string onto the kill ring and returns it.  It also
     sets the yanking pointer to point to that new entry, regardless of
     the value of DO-NOT-MOVE.  Otherwise, `current-kill' does not
     treat a zero value for N specially: it returns the entry pointed
     at by the yanking pointer and does not move the yanking pointer.

 -- Function: kill-new string &optional replace yank-handler
     This function pushes the text STRING onto the kill ring and makes
     the yanking pointer point to it.  It discards the oldest entry if
     appropriate.  It also invokes the value of
     `interprogram-cut-function' (see below).

     If REPLACE is non-`nil', then `kill-new' replaces the first
     element of the kill ring with STRING, rather than pushing STRING
     onto the kill ring.

     If YANK-HANDLER is non-`nil', this puts that value onto the string
     of killed text, as a `yank-handler' property.  *Note Yanking::.
     Note that if YANK-HANDLER is `nil', then `kill-new' copies any
     `yank-handler' properties present on STRING onto the kill ring, as
     it does with other text properties.

 -- Function: kill-append string before-p &optional yank-handler
     This function appends the text STRING to the first entry in the
     kill ring and makes the yanking pointer point to the combined
     entry.  Normally STRING goes at the end of the entry, but if
     BEFORE-P is non-`nil', it goes at the beginning.  This function
     also invokes the value of `interprogram-cut-function' (see below).
     This handles YANK-HANDLER just like `kill-new', except that if
     YANK-HANDLER is different from the `yank-handler' property of the
     first entry of the kill ring, `kill-append' pushes the
     concatenated string onto the kill ring, instead of replacing the
     original first entry with it.

 -- Variable: interprogram-paste-function
     This variable provides a way of transferring killed text from other
     programs, when you are using a window system.  Its value should be
     `nil' or a function of no arguments.

     If the value is a function, `current-kill' calls it to get the
     "most recent kill."  If the function returns a non-`nil' value,
     then that value is used as the "most recent kill."  If it returns
     `nil', then the front of the kill ring is used.

     The normal use of this hook is to get the window system's primary
     selection as the most recent kill, even if the selection belongs to
     another application.  *Note Window System Selections::.

 -- Variable: interprogram-cut-function
     This variable provides a way of communicating killed text to other
     programs, when you are using a window system.  Its value should be
     `nil' or a function of one required and one optional argument.

     If the value is a function, `kill-new' and `kill-append' call it
     with the new first element of the kill ring as the first argument.
     The second, optional, argument has the same meaning as the PUSH
     argument to `x-set-cut-buffer' (*note Definition of
     x-set-cut-buffer::) and only affects the second and later cut
     buffers.

     The normal use of this hook is to set the window system's primary
     selection (and first cut buffer) from the newly killed text.
     *Note Window System Selections::.


File: elisp,  Node: Internals of Kill Ring,  Prev: Low-Level Kill Ring,  Up: The Kill Ring

32.8.6 Internals of the Kill Ring
---------------------------------

The variable `kill-ring' holds the kill ring contents, in the form of a
list of strings.  The most recent kill is always at the front of the
list.

   The `kill-ring-yank-pointer' variable points to a link in the kill
ring list, whose CAR is the text to yank next.  We say it identifies
the "front" of the ring.  Moving `kill-ring-yank-pointer' to a
different link is called "rotating the kill ring".  We call the kill
ring a "ring" because the functions that move the yank pointer wrap
around from the end of the list to the beginning, or vice-versa.
Rotation of the kill ring is virtual; it does not change the value of
`kill-ring'.

   Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables
whose values are normally lists.  The word "pointer" in the name of the
`kill-ring-yank-pointer' indicates that the variable's purpose is to
identify one element of the list for use by the next yank command.

   The value of `kill-ring-yank-pointer' is always `eq' to one of the
links in the kill ring list.  The element it identifies is the CAR of
that link.  Kill commands, which change the kill ring, also set this
variable to the value of `kill-ring'.  The effect is to rotate the ring
so that the newly killed text is at the front.

   Here is a diagram that shows the variable `kill-ring-yank-pointer'
pointing to the second entry in the kill ring `("some text" "a
different piece of text" "yet older text")'.

     kill-ring                  ---- kill-ring-yank-pointer
       |                       |
       |                       v
       |     --- ---          --- ---      --- ---
        --> |   |   |------> |   |   |--> |   |   |--> nil
             --- ---          --- ---      --- ---
              |                |            |
              |                |            |
              |                |             -->"yet older text"
              |                |
              |                 --> "a different piece of text"
              |
               --> "some text"

This state of affairs might occur after `C-y' (`yank') immediately
followed by `M-y' (`yank-pop').

 -- Variable: kill-ring
     This variable holds the list of killed text sequences, most
     recently killed first.

 -- Variable: kill-ring-yank-pointer
     This variable's value indicates which element of the kill ring is
     at the "front" of the ring for yanking.  More precisely, the value
     is a tail of the value of `kill-ring', and its CAR is the kill
     string that `C-y' should yank.

 -- User Option: kill-ring-max
     The value of this variable is the maximum length to which the kill
     ring can grow, before elements are thrown away at the end.  The
     default value for `kill-ring-max' is 60.


File: elisp,  Node: Undo,  Next: Maintaining Undo,  Prev: The Kill Ring,  Up: Text

32.9 Undo
=========

Most buffers have an "undo list", which records all changes made to the
buffer's text so that they can be undone.  (The buffers that don't have
one are usually special-purpose buffers for which Emacs assumes that
undoing is not useful.  In particular, any buffer whose name begins
with a space has its undo recording off by default; see *Note Buffer
Names::.)  All the primitives that modify the text in the buffer
automatically add elements to the front of the undo list, which is in
the variable `buffer-undo-list'.

 -- Variable: buffer-undo-list
     This buffer-local variable's value is the undo list of the current
     buffer. A value of `t' disables the recording of undo information.

   Here are the kinds of elements an undo list can have:

`POSITION'
     This kind of element records a previous value of point; undoing
     this element moves point to POSITION.  Ordinary cursor motion does
     not make any sort of undo record, but deletion operations use
     these entries to record where point was before the command.

`(BEG . END)'
     This kind of element indicates how to delete text that was
     inserted.  Upon insertion, the text occupied the range BEG-END in
     the buffer.

`(TEXT . POSITION)'
     This kind of element indicates how to reinsert text that was
     deleted.  The deleted text itself is the string TEXT.  The place to
     reinsert it is `(abs POSITION)'.  If POSITION is positive, point
     was at the beginning of the deleted text, otherwise it was at the
     end.

`(t HIGH . LOW)'
     This kind of element indicates that an unmodified buffer became
     modified.  The elements HIGH and LOW are two integers, each
     recording 16 bits of the visited file's modification time as of
     when it was previously visited or saved.  `primitive-undo' uses
     those values to determine whether to mark the buffer as unmodified
     once again; it does so only if the file's modification time
     matches those numbers.

`(nil PROPERTY VALUE BEG . END)'
     This kind of element records a change in a text property.  Here's
     how you might undo the change:

          (put-text-property BEG END PROPERTY VALUE)

`(MARKER . ADJUSTMENT)'
     This kind of element records the fact that the marker MARKER was
     relocated due to deletion of surrounding text, and that it moved
     ADJUSTMENT character positions.  Undoing this element moves MARKER
     - ADJUSTMENT characters.

`(apply FUNNAME . ARGS)'
     This is an extensible undo item, which is undone by calling
     FUNNAME with arguments ARGS.

`(apply DELTA BEG END FUNNAME . ARGS)'
     This is an extensible undo item, which records a change limited to
     the range BEG to END, which increased the size of the buffer by
     DELTA.  It is undone by calling FUNNAME with arguments ARGS.

     This kind of element enables undo limited to a region to determine
     whether the element pertains to that region.

`nil'
     This element is a boundary.  The elements between two boundaries
     are called a "change group"; normally, each change group
     corresponds to one keyboard command, and undo commands normally
     undo an entire group as a unit.

 -- Function: undo-boundary
     This function places a boundary element in the undo list.  The undo
     command stops at such a boundary, and successive undo commands undo
     to earlier and earlier boundaries.  This function returns `nil'.

     The editor command loop automatically creates an undo boundary
     before each key sequence is executed.  Thus, each undo normally
     undoes the effects of one command.  Self-inserting input
     characters are an exception.  The command loop makes a boundary
     for the first such character; the next 19 consecutive
     self-inserting input characters do not make boundaries, and then
     the 20th does, and so on as long as self-inserting characters
     continue.

     All buffer modifications add a boundary whenever the previous
     undoable change was made in some other buffer.  This is to ensure
     that each command makes a boundary in each buffer where it makes
     changes.

     Calling this function explicitly is useful for splitting the
     effects of a command into more than one unit.  For example,
     `query-replace' calls `undo-boundary' after each replacement, so
     that the user can undo individual replacements one by one.

 -- Variable: undo-in-progress
     This variable is normally `nil', but the undo commands bind it to
     `t'.  This is so that various kinds of change hooks can tell when
     they're being called for the sake of undoing.

 -- Function: primitive-undo count list
     This is the basic function for undoing elements of an undo list.
     It undoes the first COUNT elements of LIST, returning the rest of
     LIST.

     `primitive-undo' adds elements to the buffer's undo list when it
     changes the buffer.  Undo commands avoid confusion by saving the
     undo list value at the beginning of a sequence of undo operations.
     Then the undo operations use and update the saved value.  The new
     elements added by undoing are not part of this saved value, so
     they don't interfere with continuing to undo.

     This function does not bind `undo-in-progress'.


File: elisp,  Node: Maintaining Undo,  Next: Filling,  Prev: Undo,  Up: Text

32.10 Maintaining Undo Lists
============================

This section describes how to enable and disable undo information for a
given buffer.  It also explains how the undo list is truncated
automatically so it doesn't get too big.

   Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled.  You can explicitly enable or
disable undo recording with the following two functions, or by setting
`buffer-undo-list' yourself.

 -- Command: buffer-enable-undo &optional buffer-or-name
     This command enables recording undo information for buffer
     BUFFER-OR-NAME, so that subsequent changes can be undone.  If no
     argument is supplied, then the current buffer is used.  This
     function does nothing if undo recording is already enabled in the
     buffer.  It returns `nil'.

     In an interactive call, BUFFER-OR-NAME is the current buffer.  You
     cannot specify any other buffer.

 -- Command: buffer-disable-undo &optional buffer-or-name
     This function discards the undo list of BUFFER-OR-NAME, and
     disables further recording of undo information.  As a result, it
     is no longer possible to undo either previous changes or any
     subsequent changes.  If the undo list of BUFFER-OR-NAME is already
     disabled, this function has no effect.

     This function returns `nil'.

   As editing continues, undo lists get longer and longer.  To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set.  (For this purpose, the "size" of
an undo list measures the cons cells that make up the list, plus the
strings of deleted text.)  Three variables control the range of
acceptable sizes: `undo-limit', `undo-strong-limit' and
`undo-outer-limit'.  In these variables, size is counted as the number
of bytes occupied, which includes both saved text and other data.

 -- User Option: undo-limit
     This is the soft limit for the acceptable size of an undo list.
     The change group at which this size is exceeded is the last one
     kept.

 -- User Option: undo-strong-limit
     This is the upper limit for the acceptable size of an undo list.
     The change group at which this size is exceeded is discarded
     itself (along with all older change groups).  There is one
     exception: the very latest change group is only discarded if it
     exceeds `undo-outer-limit'.

 -- User Option: undo-outer-limit
     If at garbage collection time the undo info for the current command
     exceeds this limit, Emacs discards the info and displays a warning.
     This is a last ditch limit to prevent memory overflow.

 -- User Option: undo-ask-before-discard
     If this variable is non-`nil', when the undo info exceeds
     `undo-outer-limit', Emacs asks in the echo area whether to discard
     the info.  The default value is `nil', which means to discard it
     automatically.

     This option is mainly intended for debugging.  Garbage collection
     is inhibited while the question is asked, which means that Emacs
     might leak memory if the user waits too long before answering the
     question.


File: elisp,  Node: Filling,  Next: Margins,  Prev: Maintaining Undo,  Up: Text

32.11 Filling
=============

"Filling" means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width.  Additionally, lines can be "justified", which means
inserting spaces to make the left and/or right margins line up
precisely.  The width is controlled by the variable `fill-column'.  For
ease of reading, lines should be no longer than 70 or so columns.

   You can use Auto Fill mode (*note Auto Filling::) to fill text
automatically as you insert it, but changes to existing text may leave
it improperly filled.  Then you must fill the text explicitly.

   Most of the commands in this section return values that are not
meaningful.  All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(*note Margins::).  If the current justification style is `none', the
filling functions don't actually do anything.

   Several of the filling functions have an argument JUSTIFY.  If it is
non-`nil', that requests some kind of justification.  It can be `left',
`right', `full', or `center', to request a specific style of
justification.  If it is `t', that means to use the current
justification style for this part of the text (see
`current-justification', below).  Any other value is treated as `full'.

   When you call the filling functions interactively, using a prefix
argument implies the value `full' for JUSTIFY.

 -- Command: fill-paragraph justify
     This command fills the paragraph at or after point.  If JUSTIFY is
     non-`nil', each line is justified as well.  It uses the ordinary
     paragraph motion commands to find paragraph boundaries.  *Note
     Paragraphs: (emacs)Paragraphs.

 -- Command: fill-region start end &optional justify nosqueeze to-eop
     This command fills each of the paragraphs in the region from START
     to END.  It justifies as well if JUSTIFY is non-`nil'.

     If NOSQUEEZE is non-`nil', that means to leave whitespace other
     than line breaks untouched.  If TO-EOP is non-`nil', that means to
     keep filling to the end of the paragraph--or the next hard
     newline, if `use-hard-newlines' is enabled (see below).

     The variable `paragraph-separate' controls how to distinguish
     paragraphs.  *Note Standard Regexps::.

 -- Command: fill-individual-paragraphs start end &optional justify
          citation-regexp
     This command fills each paragraph in the region according to its
     individual fill prefix.  Thus, if the lines of a paragraph were
     indented with spaces, the filled paragraph will remain indented in
     the same fashion.

     The first two arguments, START and END, are the beginning and end
     of the region to be filled.  The third and fourth arguments,
     JUSTIFY and CITATION-REGEXP, are optional.  If JUSTIFY is
     non-`nil', the paragraphs are justified as well as filled.  If
     CITATION-REGEXP is non-`nil', it means the function is operating
     on a mail message and therefore should not fill the header lines.
     If CITATION-REGEXP is a string, it is used as a regular
     expression; if it matches the beginning of a line, that line is
     treated as a citation marker.

     Ordinarily, `fill-individual-paragraphs' regards each change in
     indentation as starting a new paragraph.  If
     `fill-individual-varying-indent' is non-`nil', then only separator
     lines separate paragraphs.  That mode can handle indented
     paragraphs with additional indentation on the first line.

 -- User Option: fill-individual-varying-indent
     This variable alters the action of `fill-individual-paragraphs' as
     described above.

 -- Command: fill-region-as-paragraph start end &optional justify
          nosqueeze squeeze-after
     This command considers a region of text as a single paragraph and
     fills it.  If the region was made up of many paragraphs, the blank
     lines between paragraphs are removed.  This function justifies as
     well as filling when JUSTIFY is non-`nil'.

     If NOSQUEEZE is non-`nil', that means to leave whitespace other
     than line breaks untouched.  If SQUEEZE-AFTER is non-`nil', it
     specifies a position in the region, and means don't canonicalize
     spaces before that position.

     In Adaptive Fill mode, this command calls `fill-context-prefix' to
     choose a fill prefix by default.  *Note Adaptive Fill::.

 -- Command: justify-current-line &optional how eop nosqueeze
     This command inserts spaces between the words of the current line
     so that the line ends exactly at `fill-column'.  It returns `nil'.

     The argument HOW, if non-`nil' specifies explicitly the style of
     justification.  It can be `left', `right', `full', `center', or
     `none'.  If it is `t', that means to do follow specified
     justification style (see `current-justification', below).  `nil'
     means to do full justification.

     If EOP is non-`nil', that means do only left-justification if
     `current-justification' specifies full justification.  This is
     used for the last line of a paragraph; even if the paragraph as a
     whole is fully justified, the last line should not be.

     If NOSQUEEZE is non-`nil', that means do not change interior
     whitespace.

 -- User Option: default-justification
     This variable's value specifies the style of justification to use
     for text that doesn't specify a style with a text property.  The
     possible values are `left', `right', `full', `center', or `none'.
     The default value is `left'.

 -- Function: current-justification
     This function returns the proper justification style to use for
     filling the text around point.

     This returns the value of the `justification' text property at
     point, or the variable DEFAULT-JUSTIFICATION if there is no such
     text property.  However, it returns `nil' rather than `none' to
     mean "don't justify".

 -- User Option: sentence-end-double-space
     If this variable is non-`nil', a period followed by just one space
     does not count as the end of a sentence, and the filling functions
     avoid breaking the line at such a place.

 -- User Option: sentence-end-without-period
     If this variable is non-`nil', a sentence can end without a
     period.  This is used for languages like Thai, where sentences end
     with a double space but without a period.

 -- User Option: sentence-end-without-space
     If this variable is non-`nil', it should be a string of characters
     that can end a sentence without following spaces.

 -- Variable: fill-paragraph-function
     This variable provides a way for major modes to override the
     filling of paragraphs.  If the value is non-`nil',
     `fill-paragraph' calls this function to do the work.  If the
     function returns a non-`nil' value, `fill-paragraph' assumes the
     job is done, and immediately returns that value.

     The usual use of this feature is to fill comments in programming
     language modes.  If the function needs to fill a paragraph in the
     usual way, it can do so as follows:

          (let ((fill-paragraph-function nil))
            (fill-paragraph arg))

 -- Variable: use-hard-newlines
     If this variable is non-`nil', the filling functions do not delete
     newlines that have the `hard' text property.  These "hard
     newlines" act as paragraph separators.


File: elisp,  Node: Margins,  Next: Adaptive Fill,  Prev: Filling,  Up: Text

32.12 Margins for Filling
=========================

 -- User Option: fill-prefix
     This buffer-local variable, if non-`nil', specifies a string of
     text that appears at the beginning of normal text lines and should
     be disregarded when filling them.  Any line that fails to start
     with the fill prefix is considered the start of a paragraph; so is
     any line that starts with the fill prefix followed by additional
     whitespace.  Lines that start with the fill prefix but no
     additional whitespace are ordinary text lines that can be filled
     together.  The resulting filled lines also start with the fill
     prefix.

     The fill prefix follows the left margin whitespace, if any.

 -- User Option: fill-column
     This buffer-local variable specifies the maximum width of filled
     lines.  Its value should be an integer, which is a number of
     columns.  All the filling, justification, and centering commands
     are affected by this variable, including Auto Fill mode (*note
     Auto Filling::).

     As a practical matter, if you are writing text for other people to
     read, you should set `fill-column' to no more than 70.  Otherwise
     the line will be too long for people to read comfortably, and this
     can make the text seem clumsy.

 -- Variable: default-fill-column
     The value of this variable is the default value for `fill-column'
     in buffers that do not override it.  This is the same as
     `(default-value 'fill-column)'.

     The default value for `default-fill-column' is 70.

 -- Command: set-left-margin from to margin
     This sets the `left-margin' property on the text from FROM to TO
     to the value MARGIN.  If Auto Fill mode is enabled, this command
     also refills the region to fit the new margin.

 -- Command: set-right-margin from to margin
     This sets the `right-margin' property on the text from FROM to TO
     to the value MARGIN.  If Auto Fill mode is enabled, this command
     also refills the region to fit the new margin.

 -- Function: current-left-margin
     This function returns the proper left margin value to use for
     filling the text around point.  The value is the sum of the
     `left-margin' property of the character at the start of the
     current line (or zero if none), and the value of the variable
     `left-margin'.

 -- Function: current-fill-column
     This function returns the proper fill column value to use for
     filling the text around point.  The value is the value of the
     `fill-column' variable, minus the value of the `right-margin'
     property of the character after point.

 -- Command: move-to-left-margin &optional n force
     This function moves point to the left margin of the current line.
     The column moved to is determined by calling the function
     `current-left-margin'.  If the argument N is non-`nil',
     `move-to-left-margin' moves forward N-1 lines first.

     If FORCE is non-`nil', that says to fix the line's indentation if
     that doesn't match the left margin value.

 -- Function: delete-to-left-margin &optional from to
     This function removes left margin indentation from the text between
     FROM and TO.  The amount of indentation to delete is determined by
     calling `current-left-margin'.  In no case does this function
     delete non-whitespace.  If FROM and TO are omitted, they default
     to the whole buffer.

 -- Function: indent-to-left-margin
     This function adjusts the indentation at the beginning of the
     current line to the value specified by the variable `left-margin'.
     (That may involve either inserting or deleting whitespace.)  This
     function is value of `indent-line-function' in Paragraph-Indent
     Text mode.

 -- Variable: left-margin
     This variable specifies the base left margin column.  In
     Fundamental mode, `C-j' indents to this column.  This variable
     automatically becomes buffer-local when set in any fashion.

 -- Variable: fill-nobreak-predicate
     This variable gives major modes a way to specify not to break a
     line at certain places.  Its value should be a list of functions.
     Whenever filling considers breaking the line at a certain place in
     the buffer, it calls each of these functions with no arguments and
     with point located at that place.  If any of the functions returns
     non-`nil', then the line won't be broken there.


File: elisp,  Node: Adaptive Fill,  Next: Auto Filling,  Prev: Margins,  Up: Text

32.13 Adaptive Fill Mode
========================

When "Adaptive Fill Mode" is enabled, Emacs determines the fill prefix
automatically from the text in each paragraph being filled rather than
using a predetermined value.  During filling, this fill prefix gets
inserted at the start of the second and subsequent lines of the
paragraph as described in *Note Filling::, and in *Note Auto Filling::.

 -- User Option: adaptive-fill-mode
     Adaptive Fill mode is enabled when this variable is non-`nil'.  It
     is `t' by default.

 -- Function: fill-context-prefix from to
     This function implements the heart of Adaptive Fill mode; it
     chooses a fill prefix based on the text between FROM and TO,
     typically the start and end of a paragraph.  It does this by
     looking at the first two lines of the paragraph, based on the
     variables described below.

     Usually, this function returns the fill prefix, a string.  However,
     before doing this, the function makes a final check (not specially
     mentioned in the following) that a line starting with this prefix
     wouldn't look like the start of a paragraph.  Should this happen,
     the function signals the anomaly by returning `nil' instead.

     In detail, `fill-context-prefix' does this:

       1. It takes a candidate for the fill prefix from the first
          line--it tries first the function in `adaptive-fill-function'
          (if any), then the regular expression `adaptive-fill-regexp'
          (see below).  The first non-`nil' result of these, or the
          empty string if they're both `nil', becomes the first line's
          candidate.

       2. If the paragraph has as yet only one line, the function tests
          the validity of the prefix candidate just found.  The
          function then returns the candidate if it's valid, or a
          string of spaces otherwise.  (see the description of
          `adaptive-fill-first-line-regexp' below).

       3. When the paragraph already has two lines, the function next
          looks for a prefix candidate on the second line, in just the
          same way it did for the first line.  If it doesn't find one,
          it returns `nil'.

       4. The function now compares the two candidate prefixes
          heuristically: if the non-whitespace characters in the line 2
          candidate occur in the same order in the line 1 candidate,
          the function returns the line 2 candidate.  Otherwise, it
          returns the largest initial substring which is common to both
          candidates (which might be the empty string).

 -- User Option: adaptive-fill-regexp
     Adaptive Fill mode matches this regular expression against the text
     starting after the left margin whitespace (if any) on a line; the
     characters it matches are that line's candidate for the fill
     prefix.

     The default value matches whitespace with certain punctuation
     characters intermingled.

 -- User Option: adaptive-fill-first-line-regexp
     Used only in one-line paragraphs, this regular expression acts as
     an additional check of the validity of the one available candidate
     fill prefix: the candidate must match this regular expression, or
     match `comment-start-skip'.  If it doesn't, `fill-context-prefix'
     replaces the candidate with a string of spaces "of the same width"
     as it.

     The default value of this variable is `"\\`[ \t]*\\'"', which
     matches only a string of whitespace.  The effect of this default
     is to force the fill prefixes found in one-line paragraphs always
     to be pure whitespace.

 -- User Option: adaptive-fill-function
     You can specify more complex ways of choosing a fill prefix
     automatically by setting this variable to a function.  The
     function is called with point after the left margin (if any) of a
     line, and it must preserve point.  It should return either "that
     line's" fill prefix or `nil', meaning it has failed to determine a
     prefix.


File: elisp,  Node: Auto Filling,  Next: Sorting,  Prev: Adaptive Fill,  Up: Text

32.14 Auto Filling
==================

Auto Fill mode is a minor mode that fills lines automatically as text
is inserted.  This section describes the hook used by Auto Fill mode.
For a description of functions that you can call explicitly to fill and
justify existing text, see *Note Filling::.

   Auto Fill mode also enables the functions that change the margins and
justification style to refill portions of the text.  *Note Margins::.

 -- Variable: auto-fill-function
     The value of this buffer-local variable should be a function (of no
     arguments) to be called after self-inserting a character from the
     table `auto-fill-chars'.  It may be `nil', in which case nothing
     special is done in that case.

     The value of `auto-fill-function' is `do-auto-fill' when Auto-Fill
     mode is enabled.  That is a function whose sole purpose is to
     implement the usual strategy for breaking a line.

          In older Emacs versions, this variable was named
          `auto-fill-hook', but since it is not called with the
          standard convention for hooks, it was renamed to
          `auto-fill-function' in version 19.

 -- Variable: normal-auto-fill-function
     This variable specifies the function to use for
     `auto-fill-function', if and when Auto Fill is turned on.  Major
     modes can set buffer-local values for this variable to alter how
     Auto Fill works.

 -- Variable: auto-fill-chars
     A char table of characters which invoke `auto-fill-function' when
     self-inserted--space and newline in most language environments.
     They have an entry `t' in the table.


File: elisp,  Node: Sorting,  Next: Columns,  Prev: Auto Filling,  Up: Text

32.15 Sorting Text
==================

The sorting functions described in this section all rearrange text in a
buffer.  This is in contrast to the function `sort', which rearranges
the order of the elements of a list (*note Rearrangement::).  The
values returned by these functions are not meaningful.

 -- Function: sort-subr reverse nextrecfun endrecfun &optional
          startkeyfun endkeyfun predicate
     This function is the general text-sorting routine that subdivides a
     buffer into records and then sorts them.  Most of the commands in
     this section use this function.

     To understand how `sort-subr' works, consider the whole accessible
     portion of the buffer as being divided into disjoint pieces called
     "sort records".  The records may or may not be contiguous, but they
     must not overlap.  A portion of each sort record (perhaps all of
     it) is designated as the sort key.  Sorting rearranges the records
     in order by their sort keys.

     Usually, the records are rearranged in order of ascending sort key.
     If the first argument to the `sort-subr' function, REVERSE, is
     non-`nil', the sort records are rearranged in order of descending
     sort key.

     The next four arguments to `sort-subr' are functions that are
     called to move point across a sort record.  They are called many
     times from within `sort-subr'.

       1. NEXTRECFUN is called with point at the end of a record.  This
          function moves point to the start of the next record.  The
          first record is assumed to start at the position of point
          when `sort-subr' is called.  Therefore, you should usually
          move point to the beginning of the buffer before calling
          `sort-subr'.

          This function can indicate there are no more sort records by
          leaving point at the end of the buffer.

       2. ENDRECFUN is called with point within a record.  It moves
          point to the end of the record.

       3. STARTKEYFUN is called to move point from the start of a
          record to the start of the sort key.  This argument is
          optional; if it is omitted, the whole record is the sort key.
          If supplied, the function should either return a non-`nil'
          value to be used as the sort key, or return `nil' to indicate
          that the sort key is in the buffer starting at point.  In the
          latter case, ENDKEYFUN is called to find the end of the sort
          key.

       4. ENDKEYFUN is called to move point from the start of the sort
          key to the end of the sort key.  This argument is optional.
          If STARTKEYFUN returns `nil' and this argument is omitted (or
          `nil'), then the sort key extends to the end of the record.
          There is no need for ENDKEYFUN if STARTKEYFUN returns a
          non-`nil' value.

     The argument PREDICATE is the function to use to compare keys.  If
     keys are numbers, it defaults to `<'; otherwise it defaults to
     `string<'.

     As an example of `sort-subr', here is the complete function
     definition for `sort-lines':

          ;; Note that the first two lines of doc string
          ;; are effectively one line when viewed by a user.
          (defun sort-lines (reverse beg end)
            "Sort lines in region alphabetically;\
           argument means descending order.
          Called from a program, there are three arguments:
          REVERSE (non-nil means reverse order),\
           BEG and END (region to sort).
          The variable `sort-fold-case' determines\
           whether alphabetic case affects
          the sort order."
            (interactive "P\nr")
            (save-excursion
              (save-restriction
                (narrow-to-region beg end)
                (goto-char (point-min))
                (let ((inhibit-field-text-motion t))
                  (sort-subr reverse 'forward-line 'end-of-line)))))

     Here `forward-line' moves point to the start of the next record,
     and `end-of-line' moves point to the end of record.  We do not pass
     the arguments STARTKEYFUN and ENDKEYFUN, because the entire record
     is used as the sort key.

     The `sort-paragraphs' function is very much the same, except that
     its `sort-subr' call looks like this:

          (sort-subr reverse
                     (function
                       (lambda ()
                         (while (and (not (eobp))
                                (looking-at paragraph-separate))
                           (forward-line 1))))
                     'forward-paragraph)

     Markers pointing into any sort records are left with no useful
     position after `sort-subr' returns.

 -- User Option: sort-fold-case
     If this variable is non-`nil', `sort-subr' and the other buffer
     sorting functions ignore case when comparing strings.

 -- Command: sort-regexp-fields reverse record-regexp key-regexp start
          end
     This command sorts the region between START and END alphabetically
     as specified by RECORD-REGEXP and KEY-REGEXP.  If REVERSE is a
     negative integer, then sorting is in reverse order.

     Alphabetical sorting means that two sort keys are compared by
     comparing the first characters of each, the second characters of
     each, and so on.  If a mismatch is found, it means that the sort
     keys are unequal; the sort key whose character is less at the
     point of first mismatch is the lesser sort key.  The individual
     characters are compared according to their numerical character
     codes in the Emacs character set.

     The value of the RECORD-REGEXP argument specifies how to divide
     the buffer into sort records.  At the end of each record, a search
     is done for this regular expression, and the text that matches it
     is taken as the next record.  For example, the regular expression
     `^.+$', which matches lines with at least one character besides a
     newline, would make each such line into a sort record.  *Note
     Regular Expressions::, for a description of the syntax and meaning
     of regular expressions.

     The value of the KEY-REGEXP argument specifies what part of each
     record is the sort key.  The KEY-REGEXP could match the whole
     record, or only a part.  In the latter case, the rest of the
     record has no effect on the sorted order of records, but it is
     carried along when the record moves to its new position.

     The KEY-REGEXP argument can refer to the text matched by a
     subexpression of RECORD-REGEXP, or it can be a regular expression
     on its own.

     If KEY-REGEXP is:

    `\DIGIT'
          then the text matched by the DIGITth `\(...\)' parenthesis
          grouping in RECORD-REGEXP is the sort key.

    `\&'
          then the whole record is the sort key.

    a regular expression
          then `sort-regexp-fields' searches for a match for the regular
          expression within the record.  If such a match is found, it
          is the sort key.  If there is no match for KEY-REGEXP within
          a record then that record is ignored, which means its
          position in the buffer is not changed.  (The other records
          may move around it.)

     For example, if you plan to sort all the lines in the region by the
     first word on each line starting with the letter `f', you should
     set RECORD-REGEXP to `^.*$' and set KEY-REGEXP to `\<f\w*\>'.  The
     resulting expression looks like this:

          (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
                              (region-beginning)
                              (region-end))

     If you call `sort-regexp-fields' interactively, it prompts for
     RECORD-REGEXP and KEY-REGEXP in the minibuffer.

 -- Command: sort-lines reverse start end
     This command alphabetically sorts lines in the region between
     START and END.  If REVERSE is non-`nil', the sort is in reverse
     order.

 -- Command: sort-paragraphs reverse start end
     This command alphabetically sorts paragraphs in the region between
     START and END.  If REVERSE is non-`nil', the sort is in reverse
     order.

 -- Command: sort-pages reverse start end
     This command alphabetically sorts pages in the region between
     START and END.  If REVERSE is non-`nil', the sort is in reverse
     order.

 -- Command: sort-fields field start end
     This command sorts lines in the region between START and END,
     comparing them alphabetically by the FIELDth field of each line.
     Fields are separated by whitespace and numbered starting from 1.
     If FIELD is negative, sorting is by the -FIELDth field from the
     end of the line.  This command is useful for sorting tables.

 -- Command: sort-numeric-fields field start end
     This command sorts lines in the region between START and END,
     comparing them numerically by the FIELDth field of each line.
     Fields are separated by whitespace and numbered starting from 1.
     The specified field must contain a number in each line of the
     region.  Numbers starting with 0 are treated as octal, and numbers
     starting with `0x' are treated as hexadecimal.

     If FIELD is negative, sorting is by the -FIELDth field from the
     end of the line.  This command is useful for sorting tables.

 -- User Option: sort-numeric-base
     This variable specifies the default radix for
     `sort-numeric-fields' to parse numbers.

 -- Command: sort-columns reverse &optional beg end
     This command sorts the lines in the region between BEG and END,
     comparing them alphabetically by a certain range of columns.  The
     column positions of BEG and END bound the range of columns to sort
     on.

     If REVERSE is non-`nil', the sort is in reverse order.

     One unusual thing about this command is that the entire line
     containing position BEG, and the entire line containing position
     END, are included in the region sorted.

     Note that `sort-columns' rejects text that contains tabs, because
     tabs could be split across the specified columns.  Use `M-x
     untabify' to convert tabs to spaces before sorting.

     When possible, this command actually works by calling the `sort'
     utility program.


File: elisp,  Node: Columns,  Next: Indentation,  Prev: Sorting,  Up: Text

32.16 Counting Columns
======================

The column functions convert between a character position (counting
characters from the beginning of the buffer) and a column position
(counting screen characters from the beginning of a line).

   These functions count each character according to the number of
columns it occupies on the screen.  This means control characters count
as occupying 2 or 4 columns, depending upon the value of `ctl-arrow',
and tabs count as occupying a number of columns that depends on the
value of `tab-width' and on the column where the tab begins.  *Note
Usual Display::.

   Column number computations ignore the width of the window and the
amount of horizontal scrolling.  Consequently, a column value can be
arbitrarily high.  The first (or leftmost) column is numbered 0.  They
also ignore overlays and text properties, aside from invisibility.

 -- Function: current-column
     This function returns the horizontal position of point, measured in
     columns, counting from 0 at the left margin.  The column position
     is the sum of the widths of all the displayed representations of
     the characters between the start of the current line and point.

     For an example of using `current-column', see the description of
     `count-lines' in *Note Text Lines::.

 -- Function: move-to-column column &optional force
     This function moves point to COLUMN in the current line.  The
     calculation of COLUMN takes into account the widths of the
     displayed representations of the characters between the start of
     the line and point.

     If column COLUMN is beyond the end of the line, point moves to the
     end of the line.  If COLUMN is negative, point moves to the
     beginning of the line.

     If it is impossible to move to column COLUMN because that is in
     the middle of a multicolumn character such as a tab, point moves
     to the end of that character.  However, if FORCE is non-`nil', and
     COLUMN is in the middle of a tab, then `move-to-column' converts
     the tab into spaces so that it can move precisely to column
     COLUMN.  Other multicolumn characters can cause anomalies despite
     FORCE, since there is no way to split them.

     The argument FORCE also has an effect if the line isn't long
     enough to reach column COLUMN; if it is `t', that means to add
     whitespace at the end of the line to reach that column.

     If COLUMN is not an integer, an error is signaled.

     The return value is the column number actually moved to.


File: elisp,  Node: Indentation,  Next: Case Changes,  Prev: Columns,  Up: Text

32.17 Indentation
=================

The indentation functions are used to examine, move to, and change
whitespace that is at the beginning of a line.  Some of the functions
can also change whitespace elsewhere on a line.  Columns and indentation
count from zero at the left margin.

* Menu:

* Primitive Indent::      Functions used to count and insert indentation.
* Mode-Specific Indent::  Customize indentation for different modes.
* Region Indent::         Indent all the lines in a region.
* Relative Indent::       Indent the current line based on previous lines.
* Indent Tabs::           Adjustable, typewriter-like tab stops.
* Motion by Indent::      Move to first non-blank character.


File: elisp,  Node: Primitive Indent,  Next: Mode-Specific Indent,  Up: Indentation

32.17.1 Indentation Primitives
------------------------------

This section describes the primitive functions used to count and insert
indentation.  The functions in the following sections use these
primitives.  *Note Width::, for related functions.

 -- Function: current-indentation
     This function returns the indentation of the current line, which is
     the horizontal position of the first nonblank character.  If the
     contents are entirely blank, then this is the horizontal position
     of the end of the line.

 -- Command: indent-to column &optional minimum
     This function indents from point with tabs and spaces until COLUMN
     is reached.  If MINIMUM is specified and non-`nil', then at least
     that many spaces are inserted even if this requires going beyond
     COLUMN.  Otherwise the function does nothing if point is already
     beyond COLUMN.  The value is the column at which the inserted
     indentation ends.

     The inserted whitespace characters inherit text properties from the
     surrounding text (usually, from the preceding text only).  *Note
     Sticky Properties::.

 -- User Option: indent-tabs-mode
     If this variable is non-`nil', indentation functions can insert
     tabs as well as spaces.  Otherwise, they insert only spaces.
     Setting this variable automatically makes it buffer-local in the
     current buffer.


File: elisp,  Node: Mode-Specific Indent,  Next: Region Indent,  Prev: Primitive Indent,  Up: Indentation

32.17.2 Indentation Controlled by Major Mode
--------------------------------------------

An important function of each major mode is to customize the <TAB> key
to indent properly for the language being edited.  This section
describes the mechanism of the <TAB> key and how to control it.  The
functions in this section return unpredictable values.

 -- Variable: indent-line-function
     This variable's value is the function to be used by <TAB> (and
     various commands) to indent the current line.  The command
     `indent-according-to-mode' does no more than call this function.

     In Lisp mode, the value is the symbol `lisp-indent-line'; in C
     mode, `c-indent-line'; in Fortran mode, `fortran-indent-line'.
     The default value is `indent-relative'.

 -- Command: indent-according-to-mode
     This command calls the function in `indent-line-function' to
     indent the current line in a way appropriate for the current major
     mode.

 -- Command: indent-for-tab-command
     This command calls the function in `indent-line-function' to indent
     the current line; however, if that function is
     `indent-to-left-margin', `insert-tab' is called instead.  (That is
     a trivial command that inserts a tab character.)

 -- Command: newline-and-indent
     This function inserts a newline, then indents the new line (the one
     following the newline just inserted) according to the major mode.

     It does indentation by calling the current `indent-line-function'.
     In programming language modes, this is the same thing <TAB> does,
     but in some text modes, where <TAB> inserts a tab,
     `newline-and-indent' indents to the column specified by
     `left-margin'.

 -- Command: reindent-then-newline-and-indent
     This command reindents the current line, inserts a newline at
     point, and then indents the new line (the one following the
     newline just inserted).

     This command does indentation on both lines according to the
     current major mode, by calling the current value of
     `indent-line-function'.  In programming language modes, this is
     the same thing <TAB> does, but in some text modes, where <TAB>
     inserts a tab, `reindent-then-newline-and-indent' indents to the
     column specified by `left-margin'.


File: elisp,  Node: Region Indent,  Next: Relative Indent,  Prev: Mode-Specific Indent,  Up: Indentation

32.17.3 Indenting an Entire Region
----------------------------------

This section describes commands that indent all the lines in the
region.  They return unpredictable values.

 -- Command: indent-region start end to-column
     This command indents each nonblank line starting between START
     (inclusive) and END (exclusive).  If TO-COLUMN is `nil',
     `indent-region' indents each nonblank line by calling the current
     mode's indentation function, the value of `indent-line-function'.

     If TO-COLUMN is non-`nil', it should be an integer specifying the
     number of columns of indentation; then this function gives each
     line exactly that much indentation, by either adding or deleting
     whitespace.

     If there is a fill prefix, `indent-region' indents each line by
     making it start with the fill prefix.

 -- Variable: indent-region-function
     The value of this variable is a function that can be used by
     `indent-region' as a short cut.  It should take two arguments, the
     start and end of the region.  You should design the function so
     that it will produce the same results as indenting the lines of the
     region one by one, but presumably faster.

     If the value is `nil', there is no short cut, and `indent-region'
     actually works line by line.

     A short-cut function is useful in modes such as C mode and Lisp
     mode, where the `indent-line-function' must scan from the
     beginning of the function definition: applying it to each line
     would be quadratic in time.  The short cut can update the scan
     information as it moves through the lines indenting them; this
     takes linear time.  In a mode where indenting a line individually
     is fast, there is no need for a short cut.

     `indent-region' with a non-`nil' argument TO-COLUMN has a
     different meaning and does not use this variable.

 -- Command: indent-rigidly start end count
     This command indents all lines starting between START (inclusive)
     and END (exclusive) sideways by COUNT columns.  This "preserves
     the shape" of the affected region, moving it as a rigid unit.
     Consequently, this command is useful not only for indenting
     regions of unindented text, but also for indenting regions of
     formatted code.

     For example, if COUNT is 3, this command adds 3 columns of
     indentation to each of the lines beginning in the region specified.

     In Mail mode, `C-c C-y' (`mail-yank-original') uses
     `indent-rigidly' to indent the text copied from the message being
     replied to.

 -- Function: indent-code-rigidly start end columns &optional
          nochange-regexp
     This is like `indent-rigidly', except that it doesn't alter lines
     that start within strings or comments.

     In addition, it doesn't alter a line if NOCHANGE-REGEXP matches at
     the beginning of the line (if NOCHANGE-REGEXP is non-`nil').


File: elisp,  Node: Relative Indent,  Next: Indent Tabs,  Prev: Region Indent,  Up: Indentation

32.17.4 Indentation Relative to Previous Lines
----------------------------------------------

This section describes two commands that indent the current line based
on the contents of previous lines.

 -- Command: indent-relative &optional unindented-ok
     This command inserts whitespace at point, extending to the same
     column as the next "indent point" of the previous nonblank line.
     An indent point is a non-whitespace character following
     whitespace.  The next indent point is the first one at a column
     greater than the current column of point.  For example, if point
     is underneath and to the left of the first non-blank character of
     a line of text, it moves to that column by inserting whitespace.

     If the previous nonblank line has no next indent point (i.e., none
     at a great enough column position), `indent-relative' either does
     nothing (if UNINDENTED-OK is non-`nil') or calls
     `tab-to-tab-stop'.  Thus, if point is underneath and to the right
     of the last column of a short line of text, this command ordinarily
     moves point to the next tab stop by inserting whitespace.

     The return value of `indent-relative' is unpredictable.

     In the following example, point is at the beginning of the second
     line:

                      This line is indented twelve spaces.
          -!-The quick brown fox jumped.

     Evaluation of the expression `(indent-relative nil)' produces the
     following:

                      This line is indented twelve spaces.
                      -!-The quick brown fox jumped.

     In this next example, point is between the `m' and `p' of `jumped':

                      This line is indented twelve spaces.
          The quick brown fox jum-!-ped.

     Evaluation of the expression `(indent-relative nil)' produces the
     following:

                      This line is indented twelve spaces.
          The quick brown fox jum  -!-ped.

 -- Command: indent-relative-maybe
     This command indents the current line like the previous nonblank
     line, by calling `indent-relative' with `t' as the UNINDENTED-OK
     argument.  The return value is unpredictable.

     If the previous nonblank line has no indent points beyond the
     current column, this command does nothing.


File: elisp,  Node: Indent Tabs,  Next: Motion by Indent,  Prev: Relative Indent,  Up: Indentation

32.17.5 Adjustable "Tab Stops"
------------------------------

This section explains the mechanism for user-specified "tab stops" and
the mechanisms that use and set them.  The name "tab stops" is used
because the feature is similar to that of the tab stops on a
typewriter.  The feature works by inserting an appropriate number of
spaces and tab characters to reach the next tab stop column; it does not
affect the display of tab characters in the buffer (*note Usual
Display::).  Note that the <TAB> character as input uses this tab stop
feature only in a few major modes, such as Text mode.  *Note Tab Stops:
(emacs)Tab Stops.

 -- Command: tab-to-tab-stop
     This command inserts spaces or tabs before point, up to the next
     tab stop column defined by `tab-stop-list'.  It searches the list
     for an element greater than the current column number, and uses
     that element as the column to indent to.  It does nothing if no
     such element is found.

 -- User Option: tab-stop-list
     This variable is the list of tab stop columns used by
     `tab-to-tab-stops'.  The elements should be integers in increasing
     order.  The tab stop columns need not be evenly spaced.

     Use `M-x edit-tab-stops' to edit the location of tab stops
     interactively.


File: elisp,  Node: Motion by Indent,  Prev: Indent Tabs,  Up: Indentation

32.17.6 Indentation-Based Motion Commands
-----------------------------------------

These commands, primarily for interactive use, act based on the
indentation in the text.

 -- Command: back-to-indentation
     This command moves point to the first non-whitespace character in
     the current line (which is the line in which point is located).
     It returns `nil'.

 -- Command: backward-to-indentation &optional arg
     This command moves point backward ARG lines and then to the first
     nonblank character on that line.  It returns `nil'.  If ARG is
     omitted or `nil', it defaults to 1.

 -- Command: forward-to-indentation &optional arg
     This command moves point forward ARG lines and then to the first
     nonblank character on that line.  It returns `nil'.  If ARG is
     omitted or `nil', it defaults to 1.


File: elisp,  Node: Case Changes,  Next: Text Properties,  Prev: Indentation,  Up: Text

32.18 Case Changes
==================

The case change commands described here work on text in the current
buffer.  *Note Case Conversion::, for case conversion functions that
work on strings and characters.  *Note Case Tables::, for how to
customize which characters are upper or lower case and how to convert
them.

 -- Command: capitalize-region start end
     This function capitalizes all words in the region defined by START
     and END.  To capitalize means to convert each word's first
     character to upper case and convert the rest of each word to lower
     case.  The function returns `nil'.

     If one end of the region is in the middle of a word, the part of
     the word within the region is treated as an entire word.

     When `capitalize-region' is called interactively, START and END
     are point and the mark, with the smallest first.

          ---------- Buffer: foo ----------
          This is the contents of the 5th foo.
          ---------- Buffer: foo ----------

          (capitalize-region 1 44)
          => nil

          ---------- Buffer: foo ----------
          This Is The Contents Of The 5th Foo.
          ---------- Buffer: foo ----------

 -- Command: downcase-region start end
     This function converts all of the letters in the region defined by
     START and END to lower case.  The function returns `nil'.

     When `downcase-region' is called interactively, START and END are
     point and the mark, with the smallest first.

 -- Command: upcase-region start end
     This function converts all of the letters in the region defined by
     START and END to upper case.  The function returns `nil'.

     When `upcase-region' is called interactively, START and END are
     point and the mark, with the smallest first.

 -- Command: capitalize-word count
     This function capitalizes COUNT words after point, moving point
     over as it does.  To capitalize means to convert each word's first
     character to upper case and convert the rest of each word to lower
     case.  If COUNT is negative, the function capitalizes the -COUNT
     previous words but does not move point.  The value is `nil'.

     If point is in the middle of a word, the part of the word before
     point is ignored when moving forward.  The rest is treated as an
     entire word.

     When `capitalize-word' is called interactively, COUNT is set to
     the numeric prefix argument.

 -- Command: downcase-word count
     This function converts the COUNT words after point to all lower
     case, moving point over as it does.  If COUNT is negative, it
     converts the -COUNT previous words but does not move point.  The
     value is `nil'.

     When `downcase-word' is called interactively, COUNT is set to the
     numeric prefix argument.

 -- Command: upcase-word count
     This function converts the COUNT words after point to all upper
     case, moving point over as it does.  If COUNT is negative, it
     converts the -COUNT previous words but does not move point.  The
     value is `nil'.

     When `upcase-word' is called interactively, COUNT is set to the
     numeric prefix argument.


File: elisp,  Node: Text Properties,  Next: Substitution,  Prev: Case Changes,  Up: Text

32.19 Text Properties
=====================

Each character position in a buffer or a string can have a "text
property list", much like the property list of a symbol (*note Property
Lists::).  The properties belong to a particular character at a
particular place, such as, the letter `T' at the beginning of this
sentence or the first `o' in `foo'--if the same character occurs in two
different places, the two occurrences in general have different
properties.

   Each property has a name and a value.  Both of these can be any Lisp
object, but the name is normally a symbol.  Typically each property
name symbol is used for a particular purpose; for instance, the text
property `face' specifies the faces for displaying the character (*note
Special Properties::).  The usual way to access the property list is to
specify a name and ask what value corresponds to it.

   If a character has a `category' property, we call it the "property
category" of the character.  It should be a symbol.  The properties of
the symbol serve as defaults for the properties of the character.

   Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
`substring', `insert', and `buffer-substring'.

* Menu:

* Examining Properties::   Looking at the properties of one character.
* Changing Properties::	   Setting the properties of a range of text.
* Property Search::	   Searching for where a property changes value.
* Special Properties::	   Particular properties with special meanings.
* Format Properties::      Properties for representing formatting of text.
* Sticky Properties::      How inserted text gets properties from
                             neighboring text.
* Saving Properties::      Saving text properties in files, and reading
                             them back.
* Lazy Properties::        Computing text properties in a lazy fashion
                             only when text is examined.
* Clickable Text::         Using text properties to make regions of text
                             do something when you click on them.
* Links and Mouse-1::      How to make <Mouse-1> follow a link.
* Fields::                 The `field' property defines
                             fields within the buffer.
* Not Intervals::	   Why text properties do not use
			     Lisp-visible text intervals.


File: elisp,  Node: Examining Properties,  Next: Changing Properties,  Up: Text Properties

32.19.1 Examining Text Properties
---------------------------------

The simplest way to examine text properties is to ask for the value of
a particular property of a particular character.  For that, use
`get-text-property'.  Use `text-properties-at' to get the entire
property list of a character.  *Note Property Search::, for functions
to examine the properties of a number of characters at once.

   These functions handle both strings and buffers.  Keep in mind that
positions in a string start from 0, whereas positions in a buffer start
from 1.

 -- Function: get-text-property pos prop &optional object
     This function returns the value of the PROP property of the
     character after position POS in OBJECT (a buffer or string).  The
     argument OBJECT is optional and defaults to the current buffer.

     If there is no PROP property strictly speaking, but the character
     has a property category that is a symbol, then `get-text-property'
     returns the PROP property of that symbol.

 -- Function: get-char-property position prop &optional object
     This function is like `get-text-property', except that it checks
     overlays first and then text properties.  *Note Overlays::.

     The argument OBJECT may be a string, a buffer, or a window.  If it
     is a window, then the buffer displayed in that window is used for
     text properties and overlays, but only the overlays active for that
     window are considered.  If OBJECT is a buffer, then overlays in
     that buffer are considered first, in order of decreasing priority,
     followed by the text properties.  If OBJECT is a string, only text
     properties are considered, since strings never have overlays.

 -- Function: get-char-property-and-overlay position prop &optional
          object
     This is like `get-char-property', but gives extra information
     about the overlay that the property value comes from.

     Its value is a cons cell whose CAR is the property value, the same
     value `get-char-property' would return with the same arguments.
     Its CDR is the overlay in which the property was found, or `nil',
     if it was found as a text property or not found at all.

     If POSITION is at the end of OBJECT, both the CAR and the CDR of
     the value are `nil'.

 -- Variable: char-property-alias-alist
     This variable holds an alist which maps property names to a list of
     alternative property names.  If a character does not specify a
     direct value for a property, the alternative property names are
     consulted in order; the first non-`nil' value is used.  This
     variable takes precedence over `default-text-properties', and
     `category' properties take precedence over this variable.

 -- Function: text-properties-at position &optional object
     This function returns the entire property list of the character at
     POSITION in the string or buffer OBJECT.  If OBJECT is `nil', it
     defaults to the current buffer.

 -- Variable: default-text-properties
     This variable holds a property list giving default values for text
     properties.  Whenever a character does not specify a value for a
     property, neither directly, through a category symbol, or through
     `char-property-alias-alist', the value stored in this list is used
     instead.  Here is an example:

          (setq default-text-properties '(foo 69)
                char-property-alias-alist nil)
          ;; Make sure character 1 has no properties of its own.
          (set-text-properties 1 2 nil)
          ;; What we get, when we ask, is the default value.
          (get-text-property 1 'foo)
               => 69


File: elisp,  Node: Changing Properties,  Next: Property Search,  Prev: Examining Properties,  Up: Text Properties

32.19.2 Changing Text Properties
--------------------------------

The primitives for changing properties apply to a specified range of
text in a buffer or string.  The function `set-text-properties' (see
end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.

   Since text properties are considered part of the contents of the
buffer (or string), and can affect how a buffer looks on the screen,
any change in buffer text properties marks the buffer as modified.
Buffer text property changes are undoable also (*note Undo::).
Positions in a string start from 0, whereas positions in a buffer start
from 1.

 -- Function: put-text-property start end prop value &optional object
     This function sets the PROP property to VALUE for the text between
     START and END in the string or buffer OBJECT.  If OBJECT is `nil',
     it defaults to the current buffer.

 -- Function: add-text-properties start end props &optional object
     This function adds or overrides text properties for the text
     between START and END in the string or buffer OBJECT.  If OBJECT
     is `nil', it defaults to the current buffer.

     The argument PROPS specifies which properties to add.  It should
     have the form of a property list (*note Property Lists::): a list
     whose elements include the property names followed alternately by
     the corresponding values.

     The return value is `t' if the function actually changed some
     property's value; `nil' otherwise (if PROPS is `nil' or its values
     agree with those in the text).

     For example, here is how to set the `comment' and `face'
     properties of a range of text:

          (add-text-properties START END
                               '(comment t face highlight))

 -- Function: remove-text-properties start end props &optional object
     This function deletes specified text properties from the text
     between START and END in the string or buffer OBJECT.  If OBJECT
     is `nil', it defaults to the current buffer.

     The argument PROPS specifies which properties to delete.  It
     should have the form of a property list (*note Property Lists::):
     a list whose elements are property names alternating with
     corresponding values.  But only the names matter--the values that
     accompany them are ignored.  For example, here's how to remove the
     `face' property.

          (remove-text-properties START END '(face nil))

     The return value is `t' if the function actually changed some
     property's value; `nil' otherwise (if PROPS is `nil' or if no
     character in the specified text had any of those properties).

     To remove all text properties from certain text, use
     `set-text-properties' and specify `nil' for the new property list.

 -- Function: remove-list-of-text-properties start end
          list-of-properties &optional object
     Like `remove-text-properties' except that LIST-OF-PROPERTIES is a
     list of property names only, not an alternating list of property
     names and values.

 -- Function: set-text-properties start end props &optional object
     This function completely replaces the text property list for the
     text between START and END in the string or buffer OBJECT.  If
     OBJECT is `nil', it defaults to the current buffer.

     The argument PROPS is the new property list.  It should be a list
     whose elements are property names alternating with corresponding
     values.

     After `set-text-properties' returns, all the characters in the
     specified range have identical properties.

     If PROPS is `nil', the effect is to get rid of all properties from
     the specified range of text.  Here's an example:

          (set-text-properties START END nil)

     Do not rely on the return value of this function.

   The easiest way to make a string with text properties is with
`propertize':

 -- Function: propertize string &rest properties
     This function returns a copy of STRING which has the text
     properties PROPERTIES.  These properties apply to all the
     characters in the string that is returned.  Here is an example that
     constructs a string with a `face' property and a `mouse-face'
     property:

          (propertize "foo" 'face 'italic
                      'mouse-face 'bold-italic)
               => #("foo" 0 3 (mouse-face bold-italic face italic))

     To put different properties on various parts of a string, you can
     construct each part with `propertize' and then combine them with
     `concat':

          (concat
           (propertize "foo" 'face 'italic
                       'mouse-face 'bold-italic)
           " and "
           (propertize "bar" 'face 'italic
                       'mouse-face 'bold-italic))
               => #("foo and bar"
                           0 3 (face italic mouse-face bold-italic)
                           3 8 nil
                           8 11 (face italic mouse-face bold-italic))

   See also the function `buffer-substring-no-properties' (*note Buffer
Contents::) which copies text from the buffer but does not copy its
properties.


File: elisp,  Node: Property Search,  Next: Special Properties,  Prev: Changing Properties,  Up: Text Properties

32.19.3 Text Property Search Functions
--------------------------------------

In typical use of text properties, most of the time several or many
consecutive characters have the same value for a property.  Rather than
writing your programs to examine characters one by one, it is much
faster to process chunks of text that have the same property value.

   Here are functions you can use to do this.  They use `eq' for
comparing property values.  In all cases, OBJECT defaults to the
current buffer.

   For high performance, it's very important to use the LIMIT argument
to these functions, especially the ones that search for a single
property--otherwise, they may spend a long time scanning to the end of
the buffer, if the property you are interested in does not change.

   These functions do not move point; instead, they return a position
(or `nil').  Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.

 -- Function: next-property-change pos &optional object limit
     The function scans the text forward from position POS in the
     string or buffer OBJECT till it finds a change in some text
     property, then returns the position of the change.  In other
     words, it returns the position of the first character beyond POS
     whose properties are not identical to those of the character just
     after POS.

     If LIMIT is non-`nil', then the scan ends at position LIMIT.  If
     there is no property change before that point,
     `next-property-change' returns LIMIT.

     The value is `nil' if the properties remain unchanged all the way
     to the end of OBJECT and LIMIT is `nil'.  If the value is
     non-`nil', it is a position greater than or equal to POS.  The
     value equals POS only when LIMIT equals POS.

     Here is an example of how to scan the buffer by chunks of text
     within which all properties are constant:

          (while (not (eobp))
            (let ((plist (text-properties-at (point)))
                  (next-change
                   (or (next-property-change (point) (current-buffer))
                       (point-max))))
              Process text from point to NEXT-CHANGE...
              (goto-char next-change)))

 -- Function: previous-property-change pos &optional object limit
     This is like `next-property-change', but scans back from POS
     instead of forward.  If the value is non-`nil', it is a position
     less than or equal to POS; it equals POS only if LIMIT equals POS.

 -- Function: next-single-property-change pos prop &optional object
          limit
     The function scans text for a change in the PROP property, then
     returns the position of the change.  The scan goes forward from
     position POS in the string or buffer OBJECT.  In other words, this
     function returns the position of the first character beyond POS
     whose PROP property differs from that of the character just after
     POS.

     If LIMIT is non-`nil', then the scan ends at position LIMIT.  If
     there is no property change before that point,
     `next-single-property-change' returns LIMIT.

     The value is `nil' if the property remains unchanged all the way to
     the end of OBJECT and LIMIT is `nil'.  If the value is non-`nil',
     it is a position greater than or equal to POS; it equals POS only
     if LIMIT equals POS.

 -- Function: previous-single-property-change pos prop &optional object
          limit
     This is like `next-single-property-change', but scans back from
     POS instead of forward.  If the value is non-`nil', it is a
     position less than or equal to POS; it equals POS only if LIMIT
     equals POS.

 -- Function: next-char-property-change pos &optional limit
     This is like `next-property-change' except that it considers
     overlay properties as well as text properties, and if no change is
     found before the end of the buffer, it returns the maximum buffer
     position rather than `nil' (in this sense, it resembles the
     corresponding overlay function `next-overlay-change', rather than
     `next-property-change').  There is no OBJECT operand because this
     function operates only on the current buffer.  It returns the next
     address at which either kind of property changes.

 -- Function: previous-char-property-change pos &optional limit
     This is like `next-char-property-change', but scans back from POS
     instead of forward, and returns the minimum buffer position if no
     change is found.

 -- Function: next-single-char-property-change pos prop &optional
          object limit
     This is like `next-single-property-change' except that it
     considers overlay properties as well as text properties, and if no
     change is found before the end of the OBJECT, it returns the
     maximum valid position in OBJECT rather than `nil'.  Unlike
     `next-char-property-change', this function _does_ have an OBJECT
     operand; if OBJECT is not a buffer, only text-properties are
     considered.

 -- Function: previous-single-char-property-change pos prop &optional
          object limit
     This is like `next-single-char-property-change', but scans back
     from POS instead of forward, and returns the minimum valid
     position in OBJECT if no change is found.

 -- Function: text-property-any start end prop value &optional object
     This function returns non-`nil' if at least one character between
     START and END has a property PROP whose value is VALUE.  More
     precisely, it returns the position of the first such character.
     Otherwise, it returns `nil'.

     The optional fifth argument, OBJECT, specifies the string or
     buffer to scan.  Positions are relative to OBJECT.  The default
     for OBJECT is the current buffer.

 -- Function: text-property-not-all start end prop value &optional
          object
     This function returns non-`nil' if at least one character between
     START and END does not have a property PROP with value VALUE.
     More precisely, it returns the position of the first such
     character.  Otherwise, it returns `nil'.

     The optional fifth argument, OBJECT, specifies the string or
     buffer to scan.  Positions are relative to OBJECT.  The default
     for OBJECT is the current buffer.


File: elisp,  Node: Special Properties,  Next: Format Properties,  Prev: Property Search,  Up: Text Properties

32.19.4 Properties with Special Meanings
----------------------------------------

Here is a table of text property names that have special built-in
meanings.  The following sections list a few additional special property
names that control filling and property inheritance.  All other names
have no standard meaning, and you can use them as you like.

   Note: the properties `composition', `display', `invisible' and
`intangible' can also cause point to move to an acceptable place, after
each Emacs command.  *Note Adjusting Point::.

`category'
     If a character has a `category' property, we call it the "property
     category" of the character.  It should be a symbol.  The
     properties of this symbol serve as defaults for the properties of
     the character.

`face'
     You can use the property `face' to control the font and color of
     text.  *Note Faces::, for more information.

     In the simplest case, the value is a face name.  It can also be a
     list; then each element can be any of these possibilities;

        * A face name (a symbol or string).

        * A property list of face attributes.  This has the form
          (KEYWORD VALUE ...), where each KEYWORD is a face attribute
          name and VALUE is a meaningful value for that attribute.
          With this feature, you do not need to create a face each time
          you want to specify a particular attribute for certain text.
          *Note Face Attributes::.

        * A cons cell with the form `(foreground-color . COLOR-NAME)'
          or `(background-color . COLOR-NAME)'.  These are older,
          deprecated equivalents for `(:foreground COLOR-NAME)' and
          `(:background COLOR-NAME)'.  Please convert code that uses
          them.

     It works to use the latter two forms directly as the value of the
     `face' property.

     Font Lock mode (*note Font Lock Mode::) works in most buffers by
     dynamically updating the `face' property of characters based on
     the context.

`font-lock-face'
     The `font-lock-face' property is equivalent to the `face' property
     when Font Lock mode is enabled.  When Font Lock mode is disabled,
     `font-lock-face' has no effect.

     The `font-lock-mode' property is useful for special modes that
     implement their own highlighting.  *Note Precalculated
     Fontification::.

     This property is new in Emacs 22.1.

`mouse-face'
     The property `mouse-face' is used instead of `face' when the mouse
     is on or near the character.  For this purpose, "near" means that
     all text between the character and where the mouse is have the same
     `mouse-face' property value.

`fontified'
     This property says whether the text is ready for display.  If
     `nil', Emacs's redisplay routine calls the functions in
     `fontification-functions' (*note Auto Faces::) to prepare this
     part of the buffer before it is displayed.  It is used internally
     by the "just in time" font locking code.

`display'
     This property activates various features that change the way text
     is displayed.  For example, it can make text appear taller or
     shorter, higher or lower, wider or narrow, or replaced with an
     image.  *Note Display Property::.

`help-echo'
     If text has a string as its `help-echo' property, then when you
     move the mouse onto that text, Emacs displays that string in the
     echo area, or in the tooltip window (*note Tooltips:
     (emacs)Tooltips.).

     If the value of the `help-echo' property is a function, that
     function is called with three arguments, WINDOW, OBJECT and POS
     and should return a help string or `nil' for none.  The first
     argument, WINDOW is the window in which the help was found.  The
     second, OBJECT, is the buffer, overlay or string which had the
     `help-echo' property.  The POS argument is as follows:

        * If OBJECT is a buffer, POS is the position in the buffer.

        * If OBJECT is an overlay, that overlay has a `help-echo'
          property, and POS is the position in the overlay's buffer.

        * If OBJECT is a string (an overlay string or a string displayed
          with the `display' property), POS is the position in that
          string.

     If the value of the `help-echo' property is neither a function nor
     a string, it is evaluated to obtain a help string.

     You can alter the way help text is displayed by setting the
     variable `show-help-function' (*note Help display::).

     This feature is used in the mode line and for other active text.

`keymap'
     The `keymap' property specifies an additional keymap for commands.
     When this keymap applies, it is used for key lookup before the
     minor mode keymaps and before the buffer's local map.  *Note
     Active Keymaps::.  If the property value is a symbol, the symbol's
     function definition is used as the keymap.

     The property's value for the character before point applies if it
     is non-`nil' and rear-sticky, and the property's value for the
     character after point applies if it is non-`nil' and front-sticky.
     (For mouse clicks, the position of the click is used instead of
     the position of point.)

`local-map'
     This property works like `keymap' except that it specifies a
     keymap to use _instead of_ the buffer's local map.  For most
     purposes (perhaps all purposes), it is better to use the `keymap'
     property.

`syntax-table'
     The `syntax-table' property overrides what the syntax table says
     about this particular character.  *Note Syntax Properties::.

`read-only'
     If a character has the property `read-only', then modifying that
     character is not allowed.  Any command that would do so gets an
     error, `text-read-only'.  If the property value is a string, that
     string is used as the error message.

     Insertion next to a read-only character is an error if inserting
     ordinary text there would inherit the `read-only' property due to
     stickiness.  Thus, you can control permission to insert next to
     read-only text by controlling the stickiness.  *Note Sticky
     Properties::.

     Since changing properties counts as modifying the buffer, it is not
     possible to remove a `read-only' property unless you know the
     special trick: bind `inhibit-read-only' to a non-`nil' value and
     then remove the property.  *Note Read Only Buffers::.

`invisible'
     A non-`nil' `invisible' property can make a character invisible on
     the screen.  *Note Invisible Text::, for details.

`intangible'
     If a group of consecutive characters have equal and non-`nil'
     `intangible' properties, then you cannot place point between them.
     If you try to move point forward into the group, point actually
     moves to the end of the group.  If you try to move point backward
     into the group, point actually moves to the start of the group.

     If consecutive characters have unequal non-`nil' `intangible'
     properties, they belong to separate groups; each group is
     separately treated as described above.

     When the variable `inhibit-point-motion-hooks' is non-`nil', the
     `intangible' property is ignored.

`field'
     Consecutive characters with the same `field' property constitute a
     "field".  Some motion functions including `forward-word' and
     `beginning-of-line' stop moving at a field boundary.  *Note
     Fields::.

`cursor'
     Normally, the cursor is displayed at the end of any overlay and
     text property strings present at the current window position.  You
     can place the cursor on any desired character of these strings by
     giving that character a non-`nil' CURSOR text property.

`pointer'
     This specifies a specific pointer shape when the mouse pointer is
     over this text or image.  *Note Pointer Shape::, for possible
     pointer shapes.

`line-spacing'
     A newline can have a `line-spacing' text or overlay property that
     controls the height of the display line ending with that newline.
     The property value overrides the default frame line spacing and
     the buffer local `line-spacing' variable.  *Note Line Height::.

`line-height'
     A newline can have a `line-height' text or overlay property that
     controls the total height of the display line ending in that
     newline.  *Note Line Height::.

`modification-hooks'
     If a character has the property `modification-hooks', then its
     value should be a list of functions; modifying that character
     calls all of those functions.  Each function receives two
     arguments: the beginning and end of the part of the buffer being
     modified.  Note that if a particular modification hook function
     appears on several characters being modified by a single
     primitive, you can't predict how many times the function will be
     called.

     If these functions modify the buffer, they should bind
     `inhibit-modification-hooks' to `t' around doing so, to avoid
     confusing the internal mechanism that calls these hooks.

     Overlays also support the `modification-hooks' property, but the
     details are somewhat different (*note Overlay Properties::).

`insert-in-front-hooks'
`insert-behind-hooks'
     The operation of inserting text in a buffer also calls the
     functions listed in the `insert-in-front-hooks' property of the
     following character and in the `insert-behind-hooks' property of
     the preceding character.  These functions receive two arguments,
     the beginning and end of the inserted text.  The functions are
     called _after_ the actual insertion takes place.

     See also *Note Change Hooks::, for other hooks that are called
     when you change text in a buffer.

`point-entered'
`point-left'
     The special properties `point-entered' and `point-left' record
     hook functions that report motion of point.  Each time point
     moves, Emacs compares these two property values:

        * the `point-left' property of the character after the old
          location, and

        * the `point-entered' property of the character after the new
          location.

     If these two values differ, each of them is called (if not `nil')
     with two arguments: the old value of point, and the new one.

     The same comparison is made for the characters before the old and
     new locations.  The result may be to execute two `point-left'
     functions (which may be the same function) and/or two
     `point-entered' functions (which may be the same function).  In
     any case, all the `point-left' functions are called first,
     followed by all the `point-entered' functions.

     It is possible with `char-after' to examine characters at various
     buffer positions without moving point to those positions.  Only an
     actual change in the value of point runs these hook functions.

      -- Variable: inhibit-point-motion-hooks
          When this variable is non-`nil', `point-left' and
          `point-entered' hooks are not run, and the `intangible'
          property has no effect.  Do not set this variable globally;
          bind it with `let'.

      -- Variable: show-help-function
          If this variable is non-`nil', it specifies a function called
          to display help strings.  These may be `help-echo'
          properties, menu help strings (*note Simple Menu Items::,
          *note Extended Menu Items::), or tool bar help strings (*note
          Tool Bar::).  The specified function is called with one
          argument, the help string to display.  Tooltip mode (*note
          Tooltips: (emacs)Tooltips.) provides an example.

`composition'
     This text property is used to display a sequence of characters as a
     single glyph composed from components.  For instance, in Thai a
     base consonant is composed with the following combining vowel as a
     single glyph.  The value should be a character or a sequence
     (vector, list, or string) of integers.

        * If it is a character, it means to display that character
          instead of the text in the region.

        * If it is a string, it means to display that string's contents
          instead of the text in the region.

        * If it is a vector or list, the elements are characters
          interleaved with internal codes specifying how to compose the
          following character with the previous one.


File: elisp,  Node: Format Properties,  Next: Sticky Properties,  Prev: Special Properties,  Up: Text Properties

32.19.5 Formatted Text Properties
---------------------------------

These text properties affect the behavior of the fill commands.  They
are used for representing formatted text.  *Note Filling::, and *Note
Margins::.

`hard'
     If a newline character has this property, it is a "hard" newline.
     The fill commands do not alter hard newlines and do not move words
     across them.  However, this property takes effect only if the
     `use-hard-newlines' minor mode is enabled.  *Note Hard and Soft
     Newlines: (emacs)Hard and Soft Newlines.

`right-margin'
     This property specifies an extra right margin for filling this
     part of the text.

`left-margin'
     This property specifies an extra left margin for filling this part
     of the text.

`justification'
     This property specifies the style of justification for filling
     this part of the text.


File: elisp,  Node: Sticky Properties,  Next: Saving Properties,  Prev: Format Properties,  Up: Text Properties

32.19.6 Stickiness of Text Properties
-------------------------------------

Self-inserting characters normally take on the same properties as the
preceding character.  This is called "inheritance" of properties.

   In a Lisp program, you can do insertion with inheritance or without,
depending on your choice of insertion primitive.  The ordinary text
insertion functions such as `insert' do not inherit any properties.
They insert text with precisely the properties of the string being
inserted, and no others.  This is correct for programs that copy text
from one context to another--for example, into or out of the kill ring.
To insert with inheritance, use the special primitives described in this
section.  Self-inserting characters inherit properties because they work
using these primitives.

   When you do insertion with inheritance, _which_ properties are
inherited, and from where, depends on which properties are "sticky".
Insertion after a character inherits those of its properties that are
"rear-sticky".  Insertion before a character inherits those of its
properties that are "front-sticky".  When both sides offer different
sticky values for the same property, the previous character's value
takes precedence.

   By default, a text property is rear-sticky but not front-sticky;
thus, the default is to inherit all the properties of the preceding
character, and nothing from the following character.

   You can control the stickiness of various text properties with two
specific text properties, `front-sticky' and `rear-nonsticky', and with
the variable `text-property-default-nonsticky'.  You can use the
variable to specify a different default for a given property.  You can
use those two text properties to make any specific properties sticky or
nonsticky in any particular part of the text.

   If a character's `front-sticky' property is `t', then all its
properties are front-sticky.  If the `front-sticky' property is a list,
then the sticky properties of the character are those whose names are
in the list.  For example, if a character has a `front-sticky' property
whose value is `(face read-only)', then insertion before the character
can inherit its `face' property and its `read-only' property, but no
others.

   The `rear-nonsticky' property works the opposite way.  Most
properties are rear-sticky by default, so the `rear-nonsticky' property
says which properties are _not_ rear-sticky.  If a character's
`rear-nonsticky' property is `t', then none of its properties are
rear-sticky.  If the `rear-nonsticky' property is a list, properties
are rear-sticky _unless_ their names are in the list.

 -- Variable: text-property-default-nonsticky
     This variable holds an alist which defines the default
     rear-stickiness of various text properties.  Each element has the
     form `(PROPERTY . NONSTICKINESS)', and it defines the stickiness
     of a particular text property, PROPERTY.

     If NONSTICKINESS is non-`nil', this means that the property
     PROPERTY is rear-nonsticky by default.  Since all properties are
     front-nonsticky by default, this makes PROPERTY nonsticky in both
     directions by default.

     The text properties `front-sticky' and `rear-nonsticky', when
     used, take precedence over the default NONSTICKINESS specified in
     `text-property-default-nonsticky'.

   Here are the functions that insert text with inheritance of
properties:

 -- Function: insert-and-inherit &rest strings
     Insert the strings STRINGS, just like the function `insert', but
     inherit any sticky properties from the adjoining text.

 -- Function: insert-before-markers-and-inherit &rest strings
     Insert the strings STRINGS, just like the function
     `insert-before-markers', but inherit any sticky properties from the
     adjoining text.

   *Note Insertion::, for the ordinary insertion functions which do not
inherit.


File: elisp,  Node: Saving Properties,  Next: Lazy Properties,  Prev: Sticky Properties,  Up: Text Properties

32.19.7 Saving Text Properties in Files
---------------------------------------

You can save text properties in files (along with the text itself), and
restore the same text properties when visiting or inserting the files,
using these two hooks:

 -- Variable: write-region-annotate-functions
     This variable's value is a list of functions for `write-region' to
     run to encode text properties in some fashion as annotations to
     the text being written in the file.  *Note Writing to Files::.

     Each function in the list is called with two arguments: the start
     and end of the region to be written.  These functions should not
     alter the contents of the buffer.  Instead, they should return
     lists indicating annotations to write in the file in addition to
     the text in the buffer.

     Each function should return a list of elements of the form
     `(POSITION . STRING)', where POSITION is an integer specifying the
     relative position within the text to be written, and STRING is the
     annotation to add there.

     Each list returned by one of these functions must be already
     sorted in increasing order by POSITION.  If there is more than one
     function, `write-region' merges the lists destructively into one
     sorted list.

     When `write-region' actually writes the text from the buffer to the
     file, it intermixes the specified annotations at the corresponding
     positions.  All this takes place without modifying the buffer.

 -- Variable: after-insert-file-functions
     This variable holds a list of functions for `insert-file-contents'
     to call after inserting a file's contents.  These functions should
     scan the inserted text for annotations, and convert them to the
     text properties they stand for.

     Each function receives one argument, the length of the inserted
     text; point indicates the start of that text.  The function should
     scan that text for annotations, delete them, and create the text
     properties that the annotations specify.  The function should
     return the updated length of the inserted text, as it stands after
     those changes.  The value returned by one function becomes the
     argument to the next function.

     These functions should always return with point at the beginning of
     the inserted text.

     The intended use of `after-insert-file-functions' is for converting
     some sort of textual annotations into actual text properties.  But
     other uses may be possible.

   We invite users to write Lisp programs to store and retrieve text
properties in files, using these hooks, and thus to experiment with
various data formats and find good ones.  Eventually we hope users will
produce good, general extensions we can install in Emacs.

   We suggest not trying to handle arbitrary Lisp objects as text
property names or values--because a program that general is probably
difficult to write, and slow.  Instead, choose a set of possible data
types that are reasonably flexible, and not too hard to encode.

   *Note Format Conversion::, for a related feature.


File: elisp,  Node: Lazy Properties,  Next: Clickable Text,  Prev: Saving Properties,  Up: Text Properties

32.19.8 Lazy Computation of Text Properties
-------------------------------------------

Instead of computing text properties for all the text in the buffer,
you can arrange to compute the text properties for parts of the text
when and if something depends on them.

   The primitive that extracts text from the buffer along with its
properties is `buffer-substring'.  Before examining the properties,
this function runs the abnormal hook `buffer-access-fontify-functions'.

 -- Variable: buffer-access-fontify-functions
     This variable holds a list of functions for computing text
     properties.  Before `buffer-substring' copies the text and text
     properties for a portion of the buffer, it calls all the functions
     in this list.  Each of the functions receives two arguments that
     specify the range of the buffer being accessed.  (The buffer
     itself is always the current buffer.)

   The function `buffer-substring-no-properties' does not call these
functions, since it ignores text properties anyway.

   In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
`buffer-access-fontified-property'.

 -- Variable: buffer-access-fontified-property
     If this variable's value is non-`nil', it is a symbol which is used
     as a text property name.  A non-`nil' value for that text property
     means, "the other text properties for this character have already
     been computed."

     If all the characters in the range specified for `buffer-substring'
     have a non-`nil' value for this property, `buffer-substring' does
     not call the `buffer-access-fontify-functions' functions.  It
     assumes these characters already have the right text properties,
     and just copies the properties they already have.

     The normal way to use this feature is that the
     `buffer-access-fontify-functions' functions add this property, as
     well as others, to the characters they operate on.  That way, they
     avoid being called over and over for the same text.


File: elisp,  Node: Clickable Text,  Next: Links and Mouse-1,  Prev: Lazy Properties,  Up: Text Properties

32.19.9 Defining Clickable Text
-------------------------------

"Clickable text" is text that can be clicked, with either the the mouse
or via keyboard commands, to produce some result.  Many major modes use
clickable text to implement features such as hyper-links.  The `button'
package provides an easy way to insert and manipulate clickable text.
*Note Buttons::.

   In this section, we will explain how to manually set up clickable
text in a buffer using text properties.  This involves two things: (1)
indicating clickability when the mouse moves over the text, and (2)
making `RET' or a mouse click on that text do something.

   Indicating clickability usually involves highlighting the text, and
often involves displaying helpful information about the action, such as
which mouse button to press, or a short summary of the action.  This
can be done with the `mouse-face' and `help-echo' text properties.
*Note Special Properties::.  Here is an example of how Dired does it:

     (condition-case nil
         (if (dired-move-to-filename)
             (add-text-properties
              (point)
              (save-excursion
                (dired-move-to-end-of-filename)
                (point))
              '(mouse-face highlight
                help-echo "mouse-2: visit this file in other window")))
       (error nil))

The first two arguments to `add-text-properties' specify the beginning
and end of the text.

   The usual way to make the mouse do something when you click it on
this text is to define `mouse-2' in the major mode's keymap.  The job
of checking whether the click was on clickable text is done by the
command definition.  Here is how Dired does it:

     (defun dired-mouse-find-file-other-window (event)
       "In Dired, visit the file or directory name you click on."
       (interactive "e")
       (let (window pos file)
         (save-excursion
           (setq window (posn-window (event-end event))
                 pos (posn-point (event-end event)))
           (if (not (windowp window))
               (error "No file chosen"))
           (set-buffer (window-buffer window))
           (goto-char pos)
           (setq file (dired-get-file-for-visit)))
         (if (file-directory-p file)
             (or (and (cdr dired-subdir-alist)
                      (dired-goto-subdir file))
                 (progn
                   (select-window window)
                   (dired-other-window file)))
           (select-window window)
           (find-file-other-window (file-name-sans-versions file t)))))

The reason for the `save-excursion' construct is to avoid changing the
current buffer.  In this case, Dired uses the functions `posn-window'
and `posn-point' to determine which buffer the click happened in and
where, and in that buffer, `dired-get-file-for-visit' to determine which
file to visit.

   Instead of defining a mouse command for the major mode, you can
define a key binding for the clickable text itself, using the `keymap'
text property:

     (let ((map (make-sparse-keymap)))
       (define-key map [mouse-2] 'operate-this-button)
       (put-text-property (point)
                          (save-excursion
                            (dired-move-to-end-of-filename)
                            (point))
                          'keymap map))

This method makes it possible to define different commands for various
clickable pieces of text.  Also, the major mode definition (or the
global definition) remains available for the rest of the text in the
buffer.


File: elisp,  Node: Links and Mouse-1,  Next: Fields,  Prev: Clickable Text,  Up: Text Properties

32.19.10 Links and Mouse-1
--------------------------

The normal Emacs command for activating text in read-only buffers is
<Mouse-2>, which includes following textual links.  However, most
graphical applications use <Mouse-1> for following links.  For
compatibility, <Mouse-1> follows links in Emacs too, when you click on
a link quickly without moving the mouse.  The user can customize this
behavior through the variable `mouse-1-click-follows-link'.

   To define text as a link at the Lisp level, you should bind the
`mouse-2' event to a command to follow the link.  Then, to indicate that
<Mouse-1> should also follow the link, you should specify a
`follow-link' condition either as a text property or as a key binding:

`follow-link' property
     If the clickable text has a non-`nil' `follow-link' text or overlay
     property, that specifies the condition.

`follow-link' event
     If there is a binding for the `follow-link' event, either on the
     clickable text or in the local keymap, the binding is the
     condition.

   Regardless of how you set the `follow-link' condition, its value is
used as follows to determine whether the given position is inside a
link, and (if so) to compute an "action code" saying how <Mouse-1>
should handle the link.

`mouse-face'
     If the condition is `mouse-face', a position is inside a link if
     there is a non-`nil' `mouse-face' property at that position.  The
     action code is always `t'.

     For example, here is how Info mode handles <Mouse-1>:

          (define-key Info-mode-map [follow-link] 'mouse-face)

a function
     If the condition is a valid function, FUNC, then a position POS is
     inside a link if `(FUNC POS)' evaluates to non-`nil'.  The value
     returned by FUNC serves as the action code.

     For example, here is how pcvs enables <Mouse-1> to follow links on
     file names only:

          (define-key map [follow-link]
            (lambda (pos)
              (eq (get-char-property pos 'face) 'cvs-filename-face)))

anything else
     If the condition value is anything else, then the position is
     inside a link and the condition itself is the action code.
     Clearly you should only specify this kind of condition on the text
     that constitutes a link.

The action code tells <Mouse-1> how to follow the link:

a string or vector
     If the action code is a string or vector, the <Mouse-1> event is
     translated into the first element of the string or vector; i.e.,
     the action of the <Mouse-1> click is the local or global binding of
     that character or symbol.  Thus, if the action code is `"foo"',
     <Mouse-1> translates into `f'.  If it is `[foo]', <Mouse-1>
     translates into <foo>.

anything else
     For any other non-`nil' action code, the `mouse-1' event is
     translated into a `mouse-2' event at the same position.

   To define <Mouse-1> to activate a button defined with
`define-button-type', give the button a `follow-link' property with a
value as specified above to determine how to follow the link.  For
example, here is how Help mode handles <Mouse-1>:

     (define-button-type 'help-xref
       'follow-link t
       'action #'help-button-action)

   To define <Mouse-1> on a widget defined with `define-widget', give
the widget a `:follow-link' property with a value as specified above to
determine how to follow the link.

   For example, here is how the `link' widget specifies that a
<Mouse-1> click shall be translated to <RET>:

     (define-widget 'link 'item
       "An embedded link."
       :button-prefix 'widget-link-prefix
       :button-suffix 'widget-link-suffix
       :follow-link "\C-m"
       :help-echo "Follow the link."
       :format "%[%t%]")

 -- Function: mouse-on-link-p pos
     This function returns non-`nil' if position POS in the current
     buffer is on a link.  POS can also be a mouse event location, as
     returned by `event-start' (*note Accessing Mouse::).


File: elisp,  Node: Fields,  Next: Not Intervals,  Prev: Links and Mouse-1,  Up: Text Properties

32.19.11 Defining and Using Fields
----------------------------------

A field is a range of consecutive characters in the buffer that are
identified by having the same value (comparing with `eq') of the
`field' property (either a text-property or an overlay property).  This
section describes special functions that are available for operating on
fields.

   You specify a field with a buffer position, POS.  We think of each
field as containing a range of buffer positions, so the position you
specify stands for the field containing that position.

   When the characters before and after POS are part of the same field,
there is no doubt which field contains POS: the one those characters
both belong to.  When POS is at a boundary between fields, which field
it belongs to depends on the stickiness of the `field' properties of
the two surrounding characters (*note Sticky Properties::).  The field
whose property would be inherited by text inserted at POS is the field
that contains POS.

   There is an anomalous case where newly inserted text at POS would
not inherit the `field' property from either side.  This happens if the
previous character's `field' property is not rear-sticky, and the
following character's `field' property is not front-sticky.  In this
case, POS belongs to neither the preceding field nor the following
field; the field functions treat it as belonging to an empty field
whose beginning and end are both at POS.

   In all of these functions, if POS is omitted or `nil', the value of
point is used by default.  If narrowing is in effect, then POS should
fall within the accessible portion.  *Note Narrowing::.

 -- Function: field-beginning &optional pos escape-from-edge limit
     This function returns the beginning of the field specified by POS.

     If POS is at the beginning of its field, and ESCAPE-FROM-EDGE is
     non-`nil', then the return value is always the beginning of the
     preceding field that _ends_ at POS, regardless of the stickiness
     of the `field' properties around POS.

     If LIMIT is non-`nil', it is a buffer position; if the beginning
     of the field is before LIMIT, then LIMIT will be returned instead.

 -- Function: field-end &optional pos escape-from-edge limit
     This function returns the end of the field specified by POS.

     If POS is at the end of its field, and ESCAPE-FROM-EDGE is
     non-`nil', then the return value is always the end of the following
     field that _begins_ at POS, regardless of the stickiness of the
     `field' properties around POS.

     If LIMIT is non-`nil', it is a buffer position; if the end of the
     field is after LIMIT, then LIMIT will be returned instead.

 -- Function: field-string &optional pos
     This function returns the contents of the field specified by POS,
     as a string.

 -- Function: field-string-no-properties &optional pos
     This function returns the contents of the field specified by POS,
     as a string, discarding text properties.

 -- Function: delete-field &optional pos
     This function deletes the text of the field specified by POS.

 -- Function: constrain-to-field new-pos old-pos &optional
          escape-from-edge only-in-line inhibit-capture-property
     This function "constrains" NEW-POS to the field that OLD-POS
     belongs to--in other words, it returns the position closest to
     NEW-POS that is in the same field as OLD-POS.

     If NEW-POS is `nil', then `constrain-to-field' uses the value of
     point instead, and moves point to the resulting position as well
     as returning it.

     If OLD-POS is at the boundary of two fields, then the acceptable
     final positions depend on the argument ESCAPE-FROM-EDGE.  If
     ESCAPE-FROM-EDGE is `nil', then NEW-POS must be in the field whose
     `field' property equals what new characters inserted at OLD-POS
     would inherit.  (This depends on the stickiness of the `field'
     property for the characters before and after OLD-POS.)  If
     ESCAPE-FROM-EDGE is non-`nil', NEW-POS can be anywhere in the two
     adjacent fields.  Additionally, if two fields are separated by
     another field with the special value `boundary', then any point
     within this special field is also considered to be "on the
     boundary."

     Commands like `C-a' with no argumemt, that normally move backward
     to a specific kind of location and stay there once there, probably
     should specify `nil' for ESCAPE-FROM-EDGE.  Other motion commands
     that check fields should probably pass `t'.

     If the optional argument ONLY-IN-LINE is non-`nil', and
     constraining NEW-POS in the usual way would move it to a different
     line, NEW-POS is returned unconstrained.  This used in commands
     that move by line, such as `next-line' and `beginning-of-line', so
     that they respect field boundaries only in the case where they can
     still move to the right line.

     If the optional argument INHIBIT-CAPTURE-PROPERTY is non-`nil',
     and OLD-POS has a non-`nil' property of that name, then any field
     boundaries are ignored.

     You can cause `constrain-to-field' to ignore all field boundaries
     (and so never constrain anything) by binding the variable
     `inhibit-field-text-motion' to a non-`nil' value.


File: elisp,  Node: Not Intervals,  Prev: Fields,  Up: Text Properties

32.19.12 Why Text Properties are not Intervals
----------------------------------------------

Some editors that support adding attributes to text in the buffer do so
by letting the user specify "intervals" within the text, and adding the
properties to the intervals.  Those editors permit the user or the
programmer to determine where individual intervals start and end.  We
deliberately provided a different sort of interface in Emacs Lisp to
avoid certain paradoxical behavior associated with text modification.

   If the actual subdivision into intervals is meaningful, that means
you can distinguish between a buffer that is just one interval with a
certain property, and a buffer containing the same text subdivided into
two intervals, both of which have that property.

   Suppose you take the buffer with just one interval and kill part of
the text.  The text remaining in the buffer is one interval, and the
copy in the kill ring (and the undo list) becomes a separate interval.
Then if you yank back the killed text, you get two intervals with the
same properties.  Thus, editing does not preserve the distinction
between one interval and two.

   Suppose we "fix" this problem by coalescing the two intervals when
the text is inserted.  That works fine if the buffer originally was a
single interval.  But suppose instead that we have two adjacent
intervals with the same properties, and we kill the text of one interval
and yank it back.  The same interval-coalescence feature that rescues
the other case causes trouble in this one: after yanking, we have just
one interval.  One again, editing does not preserve the distinction
between one interval and two.

   Insertion of text at the border between intervals also raises
questions that have no satisfactory answer.

   However, it is easy to arrange for editing to behave consistently for
questions of the form, "What are the properties of this character?"  So
we have decided these are the only questions that make sense; we have
not implemented asking questions about where intervals start or end.

   In practice, you can usually use the text property search functions
in place of explicit interval boundaries.  You can think of them as
finding the boundaries of intervals, assuming that intervals are always
coalesced whenever possible.  *Note Property Search::.

   Emacs also provides explicit intervals as a presentation feature; see
*Note Overlays::.


File: elisp,  Node: Substitution,  Next: Transposition,  Prev: Text Properties,  Up: Text

32.20 Substituting for a Character Code
=======================================

The following functions replace characters within a specified region
based on their character codes.

 -- Function: subst-char-in-region start end old-char new-char
          &optional noundo
     This function replaces all occurrences of the character OLD-CHAR
     with the character NEW-CHAR in the region of the current buffer
     defined by START and END.

     If NOUNDO is non-`nil', then `subst-char-in-region' does not
     record the change for undo and does not mark the buffer as
     modified.  This was useful for controlling the old selective
     display feature (*note Selective Display::).

     `subst-char-in-region' does not move point and returns `nil'.

          ---------- Buffer: foo ----------
          This is the contents of the buffer before.
          ---------- Buffer: foo ----------

          (subst-char-in-region 1 20 ?i ?X)
               => nil

          ---------- Buffer: foo ----------
          ThXs Xs the contents of the buffer before.
          ---------- Buffer: foo ----------

 -- Function: translate-region start end table
     This function applies a translation table to the characters in the
     buffer between positions START and END.

     The translation table TABLE is a string or a char-table; `(aref
     TABLE OCHAR)' gives the translated character corresponding to
     OCHAR.  If TABLE is a string, any characters with codes larger
     than the length of TABLE are not altered by the translation.

     The return value of `translate-region' is the number of characters
     that were actually changed by the translation.  This does not
     count characters that were mapped into themselves in the
     translation table.


File: elisp,  Node: Registers,  Next: Base 64,  Prev: Transposition,  Up: Text

32.21 Registers
===============

A register is a sort of variable used in Emacs editing that can hold a
variety of different kinds of values.  Each register is named by a
single character.  All ASCII characters and their meta variants (but
with the exception of `C-g') can be used to name registers.  Thus,
there are 255 possible registers.  A register is designated in Emacs
Lisp by the character that is its name.

 -- Variable: register-alist
     This variable is an alist of elements of the form `(NAME .
     CONTENTS)'.  Normally, there is one element for each Emacs
     register that has been used.

     The object NAME is a character (an integer) identifying the
     register.

   The CONTENTS of a register can have several possible types:

a number
     A number stands for itself.  If `insert-register' finds a number
     in the register, it converts the number to decimal.

a marker
     A marker represents a buffer position to jump to.

a string
     A string is text saved in the register.

a rectangle
     A rectangle is represented by a list of strings.

`(WINDOW-CONFIGURATION POSITION)'
     This represents a window configuration to restore in one frame,
     and a position to jump to in the current buffer.

`(FRAME-CONFIGURATION POSITION)'
     This represents a frame configuration to restore, and a position
     to jump to in the current buffer.

(file FILENAME)
     This represents a file to visit; jumping to this value visits file
     FILENAME.

(file-query FILENAME POSITION)
     This represents a file to visit and a position in it; jumping to
     this value visits file FILENAME and goes to buffer position
     POSITION.  Restoring this type of position asks the user for
     confirmation first.

   The functions in this section return unpredictable values unless
otherwise stated.

 -- Function: get-register reg
     This function returns the contents of the register REG, or `nil'
     if it has no contents.

 -- Function: set-register reg value
     This function sets the contents of register REG to VALUE.  A
     register can be set to any value, but the other register functions
     expect only certain data types.  The return value is VALUE.

 -- Command: view-register reg
     This command displays what is contained in register REG.

 -- Command: insert-register reg &optional beforep
     This command inserts contents of register REG into the current
     buffer.

     Normally, this command puts point before the inserted text, and the
     mark after it.  However, if the optional second argument BEFOREP
     is non-`nil', it puts the mark before and point after.  You can
     pass a non-`nil' second argument BEFOREP to this function
     interactively by supplying any prefix argument.

     If the register contains a rectangle, then the rectangle is
     inserted with its upper left corner at point.  This means that
     text is inserted in the current line and underneath it on
     successive lines.

     If the register contains something other than saved text (a
     string) or a rectangle (a list), currently useless things happen.
     This may be changed in the future.


File: elisp,  Node: Transposition,  Next: Registers,  Prev: Substitution,  Up: Text

32.22 Transposition of Text
===========================

This subroutine is used by the transposition commands.

 -- Function: transpose-regions start1 end1 start2 end2 &optional
          leave-markers
     This function exchanges two nonoverlapping portions of the buffer.
     Arguments START1 and END1 specify the bounds of one portion and
     arguments START2 and END2 specify the bounds of the other portion.

     Normally, `transpose-regions' relocates markers with the transposed
     text; a marker previously positioned within one of the two
     transposed portions moves along with that portion, thus remaining
     between the same two characters in their new position.  However,
     if LEAVE-MARKERS is non-`nil', `transpose-regions' does not do
     this--it leaves all markers unrelocated.


File: elisp,  Node: Base 64,  Next: MD5 Checksum,  Prev: Registers,  Up: Text

32.23 Base 64 Encoding
======================

Base 64 code is used in email to encode a sequence of 8-bit bytes as a
longer sequence of ASCII graphic characters.  It is defined in Internet
RFC(1)2045.  This section describes the functions for converting to and
from this code.

 -- Function: base64-encode-region beg end &optional no-line-break
     This function converts the region from BEG to END into base 64
     code.  It returns the length of the encoded text.  An error is
     signaled if a character in the region is multibyte, i.e. in a
     multibyte buffer the region must contain only characters from the
     charsets `ascii', `eight-bit-control' and `eight-bit-graphic'.

     Normally, this function inserts newline characters into the encoded
     text, to avoid overlong lines.  However, if the optional argument
     NO-LINE-BREAK is non-`nil', these newlines are not added, so the
     output is just one long line.

 -- Function: base64-encode-string string &optional no-line-break
     This function converts the string STRING into base 64 code.  It
     returns a string containing the encoded text.  As for
     `base64-encode-region', an error is signaled if a character in the
     string is multibyte.

     Normally, this function inserts newline characters into the encoded
     text, to avoid overlong lines.  However, if the optional argument
     NO-LINE-BREAK is non-`nil', these newlines are not added, so the
     result string is just one long line.

 -- Function: base64-decode-region beg end
     This function converts the region from BEG to END from base 64
     code into the corresponding decoded text.  It returns the length of
     the decoded text.

     The decoding functions ignore newline characters in the encoded
     text.

 -- Function: base64-decode-string string
     This function converts the string STRING from base 64 code into
     the corresponding decoded text.  It returns a unibyte string
     containing the decoded text.

     The decoding functions ignore newline characters in the encoded
     text.

   ---------- Footnotes ----------

   (1) An RFC, an acronym for "Request for Comments", is a numbered
Internet informational document describing a standard.  RFCs are
usually written by technical experts acting on their own initiative,
and are traditionally written in a pragmatic, experience-driven manner.


File: elisp,  Node: MD5 Checksum,  Next: Atomic Changes,  Prev: Base 64,  Up: Text

32.24 MD5 Checksum
==================

MD5 cryptographic checksums, or "message digests", are 128-bit
"fingerprints" of a document or program.  They are used to verify that
you have an exact and unaltered copy of the data.  The algorithm to
calculate the MD5 message digest is defined in Internet RFC(1)1321.
This section describes the Emacs facilities for computing message
digests.

 -- Function: md5 object &optional start end coding-system noerror
     This function returns the MD5 message digest of OBJECT, which
     should be a buffer or a string.

     The two optional arguments START and END are character positions
     specifying the portion of OBJECT to compute the message digest
     for.  If they are `nil' or omitted, the digest is computed for the
     whole of OBJECT.

     The function `md5' does not compute the message digest directly
     from the internal Emacs representation of the text (*note Text
     Representations::).  Instead, it encodes the text using a coding
     system, and computes the message digest from the encoded text.  The
     optional fourth argument CODING-SYSTEM specifies which coding
     system to use for encoding the text.  It should be the same coding
     system that you used to read the text, or that you used or will use
     when saving or sending the text.  *Note Coding Systems::, for more
     information about coding systems.

     If CODING-SYSTEM is `nil' or omitted, the default depends on
     OBJECT.  If OBJECT is a buffer, the default for CODING-SYSTEM is
     whatever coding system would be chosen by default for writing this
     text into a file.  If OBJECT is a string, the user's most
     preferred coding system (*note prefer-coding-system:
     (emacs)Recognize Coding.) is used.

     Normally, `md5' signals an error if the text can't be encoded
     using the specified or chosen coding system.  However, if NOERROR
     is non-`nil', it silently uses `raw-text' coding instead.

   ---------- Footnotes ----------

   (1) For an explanation of what is an RFC, see the footnote in *Note
Base 64::.


File: elisp,  Node: Atomic Changes,  Next: Change Hooks,  Prev: MD5 Checksum,  Up: Text

32.25 Atomic Change Groups
==========================

In data base terminology, an "atomic" change is an indivisible
change--it can succeed entirely or it can fail entirely, but it cannot
partly succeed.  A Lisp program can make a series of changes to one or
several buffers as an "atomic change group", meaning that either the
entire series of changes will be installed in their buffers or, in case
of an error, none of them will be.

   To do this for one buffer, the one already current, simply write a
call to `atomic-change-group' around the code that makes the changes,
like this:

     (atomic-change-group
       (insert foo)
       (delete-region x y))

If an error (or other nonlocal exit) occurs inside the body of
`atomic-change-group', it unmakes all the changes in that buffer that
were during the execution of the body.  This kind of change group has
no effect on any other buffers--any such changes remain.

   If you need something more sophisticated, such as to make changes in
various buffers constitute one atomic group, you must directly call
lower-level functions that `atomic-change-group' uses.

 -- Function: prepare-change-group &optional buffer
     This function sets up a change group for buffer BUFFER, which
     defaults to the current buffer.  It returns a "handle" that
     represents the change group.  You must use this handle to activate
     the change group and subsequently to finish it.

   To use the change group, you must "activate" it.  You must do this
before making any changes in the text of BUFFER.

 -- Function: activate-change-group handle
     This function activates the change group that HANDLE designates.

   After you activate the change group, any changes you make in that
buffer become part of it.  Once you have made all the desired changes
in the buffer, you must "finish" the change group.  There are two ways
to do this: you can either accept (and finalize) all the changes, or
cancel them all.

 -- Function: accept-change-group handle
     This function accepts all the changes in the change group
     specified by HANDLE, making them final.

 -- Function: cancel-change-group handle
     This function cancels and undoes all the changes in the change
     group specified by HANDLE.

   Your code should use `unwind-protect' to make sure the group is
always finished.  The call to `activate-change-group' should be inside
the `unwind-protect', in case the user types `C-g' just after it runs.
(This is one reason why `prepare-change-group' and
`activate-change-group' are separate functions, because normally you
would call `prepare-change-group' before the start of that
`unwind-protect'.)  Once you finish the group, don't use the handle
again--in particular, don't try to finish the same group twice.

   To make a multibuffer change group, call `prepare-change-group' once
for each buffer you want to cover, then use `nconc' to combine the
returned values, like this:

     (nconc (prepare-change-group buffer-1)
            (prepare-change-group buffer-2))

   You can then activate the multibuffer change group with a single call
to `activate-change-group', and finish it with a single call to
`accept-change-group' or `cancel-change-group'.

   Nested use of several change groups for the same buffer works as you
would expect.  Non-nested use of change groups for the same buffer will
get Emacs confused, so don't let it happen; the first change group you
start for any given buffer should be the last one finished.


File: elisp,  Node: Change Hooks,  Prev: Atomic Changes,  Up: Text

32.26 Change Hooks
==================

These hook variables let you arrange to take notice of all changes in
all buffers (or in a particular buffer, if you make them buffer-local).
See also *Note Special Properties::, for how to detect changes to
specific parts of the text.

   The functions you use in these hooks should save and restore the
match data if they do anything that uses regular expressions;
otherwise, they will interfere in bizarre ways with the editing
operations that call them.

 -- Variable: before-change-functions
     This variable holds a list of functions to call before any buffer
     modification.  Each function gets two arguments, the beginning and
     end of the region that is about to change, represented as
     integers.  The buffer that is about to change is always the
     current buffer.

 -- Variable: after-change-functions
     This variable holds a list of functions to call after any buffer
     modification.  Each function receives three arguments: the
     beginning and end of the region just changed, and the length of
     the text that existed before the change.  All three arguments are
     integers.  The buffer that's about to change is always the current
     buffer.

     The length of the old text is the difference between the buffer
     positions before and after that text as it was before the change.
     As for the changed text, its length is simply the difference
     between the first two arguments.

   Output of messages into the `*Messages*' buffer does not call these
functions.

 -- Macro: combine-after-change-calls body...
     The macro executes BODY normally, but arranges to call the
     after-change functions just once for a series of several
     changes--if that seems safe.

     If a program makes several text changes in the same area of the
     buffer, using the macro `combine-after-change-calls' around that
     part of the program can make it run considerably faster when
     after-change hooks are in use.  When the after-change hooks are
     ultimately called, the arguments specify a portion of the buffer
     including all of the changes made within the
     `combine-after-change-calls' body.

     *Warning:* You must not alter the values of
     `after-change-functions' within the body of a
     `combine-after-change-calls' form.

     *Warning:* if the changes you combine occur in widely scattered
     parts of the buffer, this will still work, but it is not advisable,
     because it may lead to inefficient behavior for some change hook
     functions.

 -- Variable: first-change-hook
     This variable is a normal hook that is run whenever a buffer is
     changed that was previously in the unmodified state.

 -- Variable: inhibit-modification-hooks
     If this variable is non-`nil', all of the change hooks are
     disabled; none of them run.  This affects all the hook variables
     described above in this section, as well as the hooks attached to
     certain special text properties (*note Special Properties::) and
     overlay properties (*note Overlay Properties::).

     Also, this variable is bound to non-`nil' while running those same
     hook variables, so that by default modifying the buffer from a
     modification hook does not cause other modification hooks to be
     run.  If you do want modification hooks to be run in a particular
     piece of code that is itself run from a modification hook, then
     rebind locally `inhibit-modification-hooks' to `nil'.


File: elisp,  Node: Non-ASCII Characters,  Next: Searching and Matching,  Prev: Text,  Up: Top

33 Non-ASCII Characters
***********************

This chapter covers the special issues relating to non-ASCII characters
and how they are stored in strings and buffers.

* Menu:

* Text Representations::    Unibyte and multibyte representations
* Converting Representations::  Converting unibyte to multibyte and vice versa.
* Selecting a Representation::  Treating a byte sequence as unibyte or multi.
* Character Codes::         How unibyte and multibyte relate to
                                codes of individual characters.
* Character Sets::          The space of possible character codes
                                is divided into various character sets.
* Chars and Bytes::         More information about multibyte encodings.
* Splitting Characters::    Converting a character to its byte sequence.
* Scanning Charsets::       Which character sets are used in a buffer?
* Translation of Characters::   Translation tables are used for conversion.
* Coding Systems::          Coding systems are conversions for saving files.
* Input Methods::           Input methods allow users to enter various
                                non-ASCII characters without special keyboards.
* Locales::                 Interacting with the POSIX locale.


File: elisp,  Node: Text Representations,  Next: Converting Representations,  Up: Non-ASCII Characters

33.1 Text Representations
=========================

Emacs has two "text representations"--two ways to represent text in a
string or buffer.  These are called "unibyte" and "multibyte".  Each
string, and each buffer, uses one of these two representations.  For
most purposes, you can ignore the issue of representations, because
Emacs converts text between them as appropriate.  Occasionally in Lisp
programming you will need to pay attention to the difference.

   In unibyte representation, each character occupies one byte and
therefore the possible character codes range from 0 to 255.  Codes 0
through 127 are ASCII characters; the codes from 128 through 255 are
used for one non-ASCII character set (you can choose which character
set by setting the variable `nonascii-insert-offset').

   In multibyte representation, a character may occupy more than one
byte, and as a result, the full range of Emacs character codes can be
stored.  The first byte of a multibyte character is always in the range
128 through 159 (octal 0200 through 0237).  These values are called
"leading codes".  The second and subsequent bytes of a multibyte
character are always in the range 160 through 255 (octal 0240 through
0377); these values are "trailing codes".

   Some sequences of bytes are not valid in multibyte text: for example,
a single isolated byte in the range 128 through 159 is not allowed.  But
character codes 128 through 159 can appear in multibyte text,
represented as two-byte sequences.  All the character codes 128 through
255 are possible (though slightly abnormal) in multibyte text; they
appear in multibyte buffers and strings when you do explicit encoding
and decoding (*note Explicit Encoding::).

   In a buffer, the buffer-local value of the variable
`enable-multibyte-characters' specifies the representation used.  The
representation for a string is determined and recorded in the string
when the string is constructed.

 -- Variable: enable-multibyte-characters
     This variable specifies the current buffer's text representation.
     If it is non-`nil', the buffer contains multibyte text; otherwise,
     it contains unibyte text.

     You cannot set this variable directly; instead, use the function
     `set-buffer-multibyte' to change a buffer's representation.

 -- Variable: default-enable-multibyte-characters
     This variable's value is entirely equivalent to `(default-value
     'enable-multibyte-characters)', and setting this variable changes
     that default value.  Setting the local binding of
     `enable-multibyte-characters' in a specific buffer is not allowed,
     but changing the default value is supported, and it is a reasonable
     thing to do, because it has no effect on existing buffers.

     The `--unibyte' command line option does its job by setting the
     default value to `nil' early in startup.

 -- Function: position-bytes position
     Return the byte-position corresponding to buffer position POSITION
     in the current buffer.  This is 1 at the start of the buffer, and
     counts upward in bytes.  If POSITION is out of range, the value is
     `nil'.

 -- Function: byte-to-position byte-position
     Return the buffer position corresponding to byte-position
     BYTE-POSITION in the current buffer.  If BYTE-POSITION is out of
     range, the value is `nil'.

 -- Function: multibyte-string-p string
     Return `t' if STRING is a multibyte string.

 -- Function: string-bytes string
     This function returns the number of bytes in STRING.  If STRING is
     a multibyte string, this can be greater than `(length STRING)'.


File: elisp,  Node: Converting Representations,  Next: Selecting a Representation,  Prev: Text Representations,  Up: Non-ASCII Characters

33.2 Converting Text Representations
====================================

Emacs can convert unibyte text to multibyte; it can also convert
multibyte text to unibyte, though this conversion loses information.  In
general these conversions happen when inserting text into a buffer, or
when putting text from several strings together in one string.  You can
also explicitly convert a string's contents to either representation.

   Emacs chooses the representation for a string based on the text that
it is constructed from.  The general rule is to convert unibyte text to
multibyte text when combining it with other multibyte text, because the
multibyte representation is more general and can hold whatever
characters the unibyte text has.

   When inserting text into a buffer, Emacs converts the text to the
buffer's representation, as specified by `enable-multibyte-characters'
in that buffer.  In particular, when you insert multibyte text into a
unibyte buffer, Emacs converts the text to unibyte, even though this
conversion cannot in general preserve all the characters that might be
in the multibyte text.  The other natural alternative, to convert the
buffer contents to multibyte, is not acceptable because the buffer's
representation is a choice made by the user that cannot be overridden
automatically.

   Converting unibyte text to multibyte text leaves ASCII characters
unchanged, and likewise character codes 128 through 159.  It converts
the non-ASCII codes 160 through 255 by adding the value
`nonascii-insert-offset' to each character code.  By setting this
variable, you specify which character set the unibyte characters
correspond to (*note Character Sets::).  For example, if
`nonascii-insert-offset' is 2048, which is `(- (make-char
'latin-iso8859-1) 128)', then the unibyte non-ASCII characters
correspond to Latin 1.  If it is 2688, which is `(- (make-char
'greek-iso8859-7) 128)', then they correspond to Greek letters.

   Converting multibyte text to unibyte is simpler: it discards all but
the low 8 bits of each character code.  If `nonascii-insert-offset' has
a reasonable value, corresponding to the beginning of some character
set, this conversion is the inverse of the other: converting unibyte
text to multibyte and back to unibyte reproduces the original unibyte
text.

 -- Variable: nonascii-insert-offset
     This variable specifies the amount to add to a non-ASCII character
     when converting unibyte text to multibyte.  It also applies when
     `self-insert-command' inserts a character in the unibyte non-ASCII
     range, 128 through 255.  However, the functions `insert' and
     `insert-char' do not perform this conversion.

     The right value to use to select character set CS is `(-
     (make-char CS) 128)'.  If the value of `nonascii-insert-offset' is
     zero, then conversion actually uses the value for the Latin 1
     character set, rather than zero.

 -- Variable: nonascii-translation-table
     This variable provides a more general alternative to
     `nonascii-insert-offset'.  You can use it to specify independently
     how to translate each code in the range of 128 through 255 into a
     multibyte character.  The value should be a char-table, or `nil'.
     If this is non-`nil', it overrides `nonascii-insert-offset'.

   The next three functions either return the argument STRING, or a
newly created string with no text properties.

 -- Function: string-make-unibyte string
     This function converts the text of STRING to unibyte
     representation, if it isn't already, and returns the result.  If
     STRING is a unibyte string, it is returned unchanged.  Multibyte
     character codes are converted to unibyte according to
     `nonascii-translation-table' or, if that is `nil', using
     `nonascii-insert-offset'.  If the lookup in the translation table
     fails, this function takes just the low 8 bits of each character.

 -- Function: string-make-multibyte string
     This function converts the text of STRING to multibyte
     representation, if it isn't already, and returns the result.  If
     STRING is a multibyte string or consists entirely of ASCII
     characters, it is returned unchanged.  In particular, if STRING is
     unibyte and entirely ASCII, the returned string is unibyte.  (When
     the characters are all ASCII, Emacs primitives will treat the
     string the same way whether it is unibyte or multibyte.)  If
     STRING is unibyte and contains non-ASCII characters, the function
     `unibyte-char-to-multibyte' is used to convert each unibyte
     character to a multibyte character.

 -- Function: string-to-multibyte string
     This function returns a multibyte string containing the same
     sequence of character codes as STRING.  Unlike
     `string-make-multibyte', this function unconditionally returns a
     multibyte string.  If STRING is a multibyte string, it is returned
     unchanged.

 -- Function: multibyte-char-to-unibyte char
     This convert the multibyte character CHAR to a unibyte character,
     based on `nonascii-translation-table' and `nonascii-insert-offset'.

 -- Function: unibyte-char-to-multibyte char
     This convert the unibyte character CHAR to a multibyte character,
     based on `nonascii-translation-table' and `nonascii-insert-offset'.


File: elisp,  Node: Selecting a Representation,  Next: Character Codes,  Prev: Converting Representations,  Up: Non-ASCII Characters

33.3 Selecting a Representation
===============================

Sometimes it is useful to examine an existing buffer or string as
multibyte when it was unibyte, or vice versa.

 -- Function: set-buffer-multibyte multibyte
     Set the representation type of the current buffer.  If MULTIBYTE
     is non-`nil', the buffer becomes multibyte.  If MULTIBYTE is
     `nil', the buffer becomes unibyte.

     This function leaves the buffer contents unchanged when viewed as a
     sequence of bytes.  As a consequence, it can change the contents
     viewed as characters; a sequence of two bytes which is treated as
     one character in multibyte representation will count as two
     characters in unibyte representation.  Character codes 128 through
     159 are an exception.  They are represented by one byte in a
     unibyte buffer, but when the buffer is set to multibyte, they are
     converted to two-byte sequences, and vice versa.

     This function sets `enable-multibyte-characters' to record which
     representation is in use.  It also adjusts various data in the
     buffer (including overlays, text properties and markers) so that
     they cover the same text as they did before.

     You cannot use `set-buffer-multibyte' on an indirect buffer,
     because indirect buffers always inherit the representation of the
     base buffer.

 -- Function: string-as-unibyte string
     This function returns a string with the same bytes as STRING but
     treating each byte as a character.  This means that the value may
     have more characters than STRING has.

     If STRING is already a unibyte string, then the value is STRING
     itself.  Otherwise it is a newly created string, with no text
     properties.  If STRING is multibyte, any characters it contains of
     charset `eight-bit-control' or `eight-bit-graphic' are converted
     to the corresponding single byte.

 -- Function: string-as-multibyte string
     This function returns a string with the same bytes as STRING but
     treating each multibyte sequence as one character.  This means
     that the value may have fewer characters than STRING has.

     If STRING is already a multibyte string, then the value is STRING
     itself.  Otherwise it is a newly created string, with no text
     properties.  If STRING is unibyte and contains any individual
     8-bit bytes (i.e. not part of a multibyte form), they are
     converted to the corresponding multibyte character of charset
     `eight-bit-control' or `eight-bit-graphic'.


File: elisp,  Node: Character Codes,  Next: Character Sets,  Prev: Selecting a Representation,  Up: Non-ASCII Characters

33.4 Character Codes
====================

The unibyte and multibyte text representations use different character
codes.  The valid character codes for unibyte representation range from
0 to 255--the values that can fit in one byte.  The valid character
codes for multibyte representation range from 0 to 524287, but not all
values in that range are valid.  The values 128 through 255 are not
entirely proper in multibyte text, but they can occur if you do explicit
encoding and decoding (*note Explicit Encoding::).  Some other character
codes cannot occur at all in multibyte text.  Only the ASCII codes 0
through 127 are completely legitimate in both representations.

 -- Function: char-valid-p charcode &optional genericp
     This returns `t' if CHARCODE is valid (either for unibyte text or
     for multibyte text).

          (char-valid-p 65)
               => t
          (char-valid-p 256)
               => nil
          (char-valid-p 2248)
               => t

     If the optional argument GENERICP is non-`nil', this function also
     returns `t' if CHARCODE is a generic character (*note Splitting
     Characters::).


File: elisp,  Node: Character Sets,  Next: Chars and Bytes,  Prev: Character Codes,  Up: Non-ASCII Characters

33.5 Character Sets
===================

Emacs classifies characters into various "character sets", each of
which has a name which is a symbol.  Each character belongs to one and
only one character set.

   In general, there is one character set for each distinct script.  For
example, `latin-iso8859-1' is one character set, `greek-iso8859-7' is
another, and `ascii' is another.  An Emacs character set can hold at
most 9025 characters; therefore, in some cases, characters that would
logically be grouped together are split into several character sets.
For example, one set of Chinese characters, generally known as Big 5,
is divided into two Emacs character sets, `chinese-big5-1' and
`chinese-big5-2'.

   ASCII characters are in character set `ascii'.  The non-ASCII
characters 128 through 159 are in character set `eight-bit-control',
and codes 160 through 255 are in character set `eight-bit-graphic'.

 -- Function: charsetp object
     Returns `t' if OBJECT is a symbol that names a character set,
     `nil' otherwise.

 -- Variable: charset-list
     The value is a list of all defined character set names.

 -- Function: charset-list
     This function returns the value of `charset-list'.  It is only
     provided for backward compatibility.

 -- Function: char-charset character
     This function returns the name of the character set that CHARACTER
     belongs to, or the symbol `unknown' if CHARACTER is not a valid
     character.

 -- Function: charset-plist charset
     This function returns the charset property list of the character
     set CHARSET.  Although CHARSET is a symbol, this is not the same
     as the property list of that symbol.  Charset properties are used
     for special purposes within Emacs.

 -- Command: list-charset-chars charset
     This command displays a list of characters in the character set
     CHARSET.


File: elisp,  Node: Chars and Bytes,  Next: Splitting Characters,  Prev: Character Sets,  Up: Non-ASCII Characters

33.6 Characters and Bytes
=========================

In multibyte representation, each character occupies one or more bytes.
Each character set has an "introduction sequence", which is normally
one or two bytes long.  (Exception: the `ascii' character set and the
`eight-bit-graphic' character set have a zero-length introduction
sequence.)  The introduction sequence is the beginning of the byte
sequence for any character in the character set.  The rest of the
character's bytes distinguish it from the other characters in the same
character set.  Depending on the character set, there are either one or
two distinguishing bytes; the number of such bytes is called the
"dimension" of the character set.

 -- Function: charset-dimension charset
     This function returns the dimension of CHARSET; at present, the
     dimension is always 1 or 2.

 -- Function: charset-bytes charset
     This function returns the number of bytes used to represent a
     character in character set CHARSET.

   This is the simplest way to determine the byte length of a character
set's introduction sequence:

     (- (charset-bytes CHARSET)
        (charset-dimension CHARSET))


File: elisp,  Node: Splitting Characters,  Next: Scanning Charsets,  Prev: Chars and Bytes,  Up: Non-ASCII Characters

33.7 Splitting Characters
=========================

The functions in this section convert between characters and the byte
values used to represent them.  For most purposes, there is no need to
be concerned with the sequence of bytes used to represent a character,
because Emacs translates automatically when necessary.

 -- Function: split-char character
     Return a list containing the name of the character set of
     CHARACTER, followed by one or two byte values (integers) which
     identify CHARACTER within that character set.  The number of byte
     values is the character set's dimension.

     If CHARACTER is invalid as a character code, `split-char' returns
     a list consisting of the symbol `unknown' and CHARACTER.

          (split-char 2248)
               => (latin-iso8859-1 72)
          (split-char 65)
               => (ascii 65)
          (split-char 128)
               => (eight-bit-control 128)

 -- Function: make-char charset &optional code1 code2
     This function returns the character in character set CHARSET whose
     position codes are CODE1 and CODE2.  This is roughly the inverse
     of `split-char'.  Normally, you should specify either one or both
     of CODE1 and CODE2 according to the dimension of CHARSET.  For
     example,

          (make-char 'latin-iso8859-1 72)
               => 2248

     Actually, the eighth bit of both CODE1 and CODE2 is zeroed before
     they are used to index CHARSET.  Thus you may use, for instance,
     an ISO 8859 character code rather than subtracting 128, as is
     necessary to index the corresponding Emacs charset.

   If you call `make-char' with no BYTE-VALUES, the result is a
"generic character" which stands for CHARSET.  A generic character is
an integer, but it is _not_ valid for insertion in the buffer as a
character.  It can be used in `char-table-range' to refer to the whole
character set (*note Char-Tables::).  `char-valid-p' returns `nil' for
generic characters.  For example:

     (make-char 'latin-iso8859-1)
          => 2176
     (char-valid-p 2176)
          => nil
     (char-valid-p 2176 t)
          => t
     (split-char 2176)
          => (latin-iso8859-1 0)

   The character sets `ascii', `eight-bit-control', and
`eight-bit-graphic' don't have corresponding generic characters.  If
CHARSET is one of them and you don't supply CODE1, `make-char' returns
the character code corresponding to the smallest code in CHARSET.


File: elisp,  Node: Scanning Charsets,  Next: Translation of Characters,  Prev: Splitting Characters,  Up: Non-ASCII Characters

33.8 Scanning for Character Sets
================================

Sometimes it is useful to find out which character sets appear in a
part of a buffer or a string.  One use for this is in determining which
coding systems (*note Coding Systems::) are capable of representing all
of the text in question.

 -- Function: charset-after &optional pos
     This function return the charset of a character in the current
     buffer at position POS.  If POS is omitted or `nil', it defaults
     to the current value of point.  If POS is out of range, the value
     is `nil'.

 -- Function: find-charset-region beg end &optional translation
     This function returns a list of the character sets that appear in
     the current buffer between positions BEG and END.

     The optional argument TRANSLATION specifies a translation table to
     be used in scanning the text (*note Translation of Characters::).
     If it is non-`nil', then each character in the region is translated
     through this table, and the value returned describes the translated
     characters instead of the characters actually in the buffer.

 -- Function: find-charset-string string &optional translation
     This function returns a list of the character sets that appear in
     the string STRING.  It is just like `find-charset-region', except
     that it applies to the contents of STRING instead of part of the
     current buffer.


File: elisp,  Node: Translation of Characters,  Next: Coding Systems,  Prev: Scanning Charsets,  Up: Non-ASCII Characters

33.9 Translation of Characters
==============================

A "translation table" is a char-table that specifies a mapping of
characters into characters.  These tables are used in encoding and
decoding, and for other purposes.  Some coding systems specify their
own particular translation tables; there are also default translation
tables which apply to all other coding systems.

   For instance, the coding-system `utf-8' has a translation table that
maps characters of various charsets (e.g., `latin-iso8859-X') into
Unicode character sets.  This way, it can encode Latin-2 characters
into UTF-8.  Meanwhile, `unify-8859-on-decoding-mode' operates by
specifying `standard-translation-table-for-decode' to translate Latin-X
characters into corresponding Unicode characters.

 -- Function: make-translation-table &rest translations
     This function returns a translation table based on the argument
     TRANSLATIONS.  Each element of TRANSLATIONS should be a list of
     elements of the form `(FROM . TO)'; this says to translate the
     character FROM into TO.

     The arguments and the forms in each argument are processed in
     order, and if a previous form already translates TO to some other
     character, say TO-ALT, FROM is also translated to TO-ALT.

     You can also map one whole character set into another character
     set with the same dimension.  To do this, you specify a generic
     character (which designates a character set) for FROM (*note
     Splitting Characters::).  In this case, if TO is also a generic
     character, its character set should have the same dimension as
     FROM's.  Then the translation table translates each character of
     FROM's character set into the corresponding character of TO's
     character set.  If FROM is a generic character and TO is an
     ordinary character, then the translation table translates every
     character of FROM's character set into TO.

   In decoding, the translation table's translations are applied to the
characters that result from ordinary decoding.  If a coding system has
property `translation-table-for-decode', that specifies the translation
table to use.  (This is a property of the coding system, as returned by
`coding-system-get', not a property of the symbol that is the coding
system's name. *Note Basic Concepts of Coding Systems: Coding System
Basics.)  Otherwise, if `standard-translation-table-for-decode' is
non-`nil', decoding uses that table.

   In encoding, the translation table's translations are applied to the
characters in the buffer, and the result of translation is actually
encoded.  If a coding system has property
`translation-table-for-encode', that specifies the translation table to
use.  Otherwise the variable `standard-translation-table-for-encode'
specifies the translation table.

 -- Variable: standard-translation-table-for-decode
     This is the default translation table for decoding, for coding
     systems that don't specify any other translation table.

 -- Variable: standard-translation-table-for-encode
     This is the default translation table for encoding, for coding
     systems that don't specify any other translation table.

 -- Variable: translation-table-for-input
     Self-inserting characters are translated through this translation
     table before they are inserted.  Search commands also translate
     their input through this table, so they can compare more reliably
     with what's in the buffer.

     `set-buffer-file-coding-system' sets this variable so that your
     keyboard input gets translated into the character sets that the
     buffer is likely to contain.  This variable automatically becomes
     buffer-local when set.


File: elisp,  Node: Coding Systems,  Next: Input Methods,  Prev: Translation of Characters,  Up: Non-ASCII Characters

33.10 Coding Systems
====================

When Emacs reads or writes a file, and when Emacs sends text to a
subprocess or receives text from a subprocess, it normally performs
character code conversion and end-of-line conversion as specified by a
particular "coding system".

   How to define a coding system is an arcane matter, and is not
documented here.

* Menu:

* Coding System Basics::        Basic concepts.
* Encoding and I/O::            How file I/O functions handle coding systems.
* Lisp and Coding Systems::     Functions to operate on coding system names.
* User-Chosen Coding Systems::  Asking the user to choose a coding system.
* Default Coding Systems::      Controlling the default choices.
* Specifying Coding Systems::   Requesting a particular coding system
                                    for a single file operation.
* Explicit Encoding::           Encoding or decoding text without doing I/O.
* Terminal I/O Encoding::       Use of encoding for terminal I/O.
* MS-DOS File Types::           How DOS "text" and "binary" files
                                    relate to coding systems.


File: elisp,  Node: Coding System Basics,  Next: Encoding and I/O,  Up: Coding Systems

33.10.1 Basic Concepts of Coding Systems
----------------------------------------

"Character code conversion" involves conversion between the encoding
used inside Emacs and some other encoding.  Emacs supports many
different encodings, in that it can convert to and from them.  For
example, it can convert text to or from encodings such as Latin 1, Latin
2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022.  In some
cases, Emacs supports several alternative encodings for the same
characters; for example, there are three coding systems for the Cyrillic
(Russian) alphabet: ISO, Alternativnyj, and KOI8.

   Most coding systems specify a particular character code for
conversion, but some of them leave the choice unspecified--to be chosen
heuristically for each file, based on the data.

   In general, a coding system doesn't guarantee roundtrip identity:
decoding a byte sequence using coding system, then encoding the
resulting text in the same coding system, can produce a different byte
sequence.  However, the following coding systems do guarantee that the
byte sequence will be the same as what you originally decoded:

     chinese-big5 chinese-iso-8bit cyrillic-iso-8bit emacs-mule
     greek-iso-8bit hebrew-iso-8bit iso-latin-1 iso-latin-2 iso-latin-3
     iso-latin-4 iso-latin-5 iso-latin-8 iso-latin-9 iso-safe
     japanese-iso-8bit japanese-shift-jis korean-iso-8bit raw-text

   Encoding buffer text and then decoding the result can also fail to
reproduce the original text.  For instance, if you encode Latin-2
characters with `utf-8' and decode the result using the same coding
system, you'll get Unicode characters (of charset
`mule-unicode-0100-24ff').  If you encode Unicode characters with
`iso-latin-2' and decode the result with the same coding system, you'll
get Latin-2 characters.

   "End of line conversion" handles three different conventions used on
various systems for representing end of line in files.  The Unix
convention is to use the linefeed character (also called newline).  The
DOS convention is to use a carriage-return and a linefeed at the end of
a line.  The Mac convention is to use just carriage-return.

   "Base coding systems" such as `latin-1' leave the end-of-line
conversion unspecified, to be chosen based on the data.  "Variant
coding systems" such as `latin-1-unix', `latin-1-dos' and `latin-1-mac'
specify the end-of-line conversion explicitly as well.  Most base
coding systems have three corresponding variants whose names are formed
by adding `-unix', `-dos' and `-mac'.

   The coding system `raw-text' is special in that it prevents
character code conversion, and causes the buffer visited with that
coding system to be a unibyte buffer.  It does not specify the
end-of-line conversion, allowing that to be determined as usual by the
data, and has the usual three variants which specify the end-of-line
conversion.  `no-conversion' is equivalent to `raw-text-unix': it
specifies no conversion of either character codes or end-of-line.

   The coding system `emacs-mule' specifies that the data is
represented in the internal Emacs encoding.  This is like `raw-text' in
that no code conversion happens, but different in that the result is
multibyte data.

 -- Function: coding-system-get coding-system property
     This function returns the specified property of the coding system
     CODING-SYSTEM.  Most coding system properties exist for internal
     purposes, but one that you might find useful is `mime-charset'.
     That property's value is the name used in MIME for the character
     coding which this coding system can read and write.  Examples:

          (coding-system-get 'iso-latin-1 'mime-charset)
               => iso-8859-1
          (coding-system-get 'iso-2022-cn 'mime-charset)
               => iso-2022-cn
          (coding-system-get 'cyrillic-koi8 'mime-charset)
               => koi8-r

     The value of the `mime-charset' property is also defined as an
     alias for the coding system.


File: elisp,  Node: Encoding and I/O,  Next: Lisp and Coding Systems,  Prev: Coding System Basics,  Up: Coding Systems

33.10.2 Encoding and I/O
------------------------

The principal purpose of coding systems is for use in reading and
writing files.  The function `insert-file-contents' uses a coding
system for decoding the file data, and `write-region' uses one to
encode the buffer contents.

   You can specify the coding system to use either explicitly (*note
Specifying Coding Systems::), or implicitly using a default mechanism
(*note Default Coding Systems::).  But these methods may not completely
specify what to do.  For example, they may choose a coding system such
as `undefined' which leaves the character code conversion to be
determined from the data.  In these cases, the I/O operation finishes
the job of choosing a coding system.  Very often you will want to find
out afterwards which coding system was chosen.

 -- Variable: buffer-file-coding-system
     This buffer-local variable records the coding system that was used
     to visit the current buffer.  It is used for saving the buffer,
     and for writing part of the buffer with `write-region'.  If the
     text to be written cannot be safely encoded using the coding
     system specified by this variable, these operations select an
     alternative encoding by calling the function
     `select-safe-coding-system' (*note User-Chosen Coding Systems::).
     If selecting a different encoding requires to ask the user to
     specify a coding system, `buffer-file-coding-system' is updated to
     the newly selected coding system.

     `buffer-file-coding-system' does _not_ affect sending text to a
     subprocess.

 -- Variable: save-buffer-coding-system
     This variable specifies the coding system for saving the buffer (by
     overriding `buffer-file-coding-system').  Note that it is not used
     for `write-region'.

     When a command to save the buffer starts out to use
     `buffer-file-coding-system' (or `save-buffer-coding-system'), and
     that coding system cannot handle the actual text in the buffer,
     the command asks the user to choose another coding system (by
     calling `select-safe-coding-system').  After that happens, the
     command also updates `buffer-file-coding-system' to represent the
     coding system that the user specified.

 -- Variable: last-coding-system-used
     I/O operations for files and subprocesses set this variable to the
     coding system name that was used.  The explicit encoding and
     decoding functions (*note Explicit Encoding::) set it too.

     *Warning:* Since receiving subprocess output sets this variable,
     it can change whenever Emacs waits; therefore, you should copy the
     value shortly after the function call that stores the value you are
     interested in.

   The variable `selection-coding-system' specifies how to encode
selections for the window system.  *Note Window System Selections::.

 -- Variable: file-name-coding-system
     The variable `file-name-coding-system' specifies the coding system
     to use for encoding file names.  Emacs encodes file names using
     that coding system for all file operations.  If
     `file-name-coding-system' is `nil', Emacs uses a default coding
     system determined by the selected language environment.  In the
     default language environment, any non-ASCII characters in file
     names are not encoded specially; they appear in the file system
     using the internal Emacs representation.

   *Warning:* if you change `file-name-coding-system' (or the language
environment) in the middle of an Emacs session, problems can result if
you have already visited files whose names were encoded using the
earlier coding system and are handled differently under the new coding
system.  If you try to save one of these buffers under the visited file
name, saving may use the wrong file name, or it may get an error.  If
such a problem happens, use `C-x C-w' to specify a new file name for
that buffer.


File: elisp,  Node: Lisp and Coding Systems,  Next: User-Chosen Coding Systems,  Prev: Encoding and I/O,  Up: Coding Systems

33.10.3 Coding Systems in Lisp
------------------------------

Here are the Lisp facilities for working with coding systems:

 -- Function: coding-system-list &optional base-only
     This function returns a list of all coding system names (symbols).
     If BASE-ONLY is non-`nil', the value includes only the base
     coding systems.  Otherwise, it includes alias and variant coding
     systems as well.

 -- Function: coding-system-p object
     This function returns `t' if OBJECT is a coding system name or
     `nil'.

 -- Function: check-coding-system coding-system
     This function checks the validity of CODING-SYSTEM.  If that is
     valid, it returns CODING-SYSTEM.  Otherwise it signals an error
     with condition `coding-system-error'.

 -- Function: coding-system-eol-type coding-system
     This function returns the type of end-of-line (a.k.a. "eol")
     conversion used by CODING-SYSTEM.  If CODING-SYSTEM specifies a
     certain eol conversion, the return value is an integer 0, 1, or 2,
     standing for `unix', `dos', and `mac', respectively.  If
     CODING-SYSTEM doesn't specify eol conversion explicitly, the
     return value is a vector of coding systems, each one with one of
     the possible eol conversion types, like this:

          (coding-system-eol-type 'latin-1)
               => [latin-1-unix latin-1-dos latin-1-mac]

     If this function returns a vector, Emacs will decide, as part of
     the text encoding or decoding process, what eol conversion to use.
     For decoding, the end-of-line format of the text is
     auto-detected, and the eol conversion is set to match it (e.g.,
     DOS-style CRLF format will imply `dos' eol conversion).  For
     encoding, the eol conversion is taken from the appropriate default
     coding system (e.g., `default-buffer-file-coding-system' for
     `buffer-file-coding-system'), or from the default eol conversion
     appropriate for the underlying platform.

 -- Function: coding-system-change-eol-conversion coding-system eol-type
     This function returns a coding system which is like CODING-SYSTEM
     except for its eol conversion, which is specified by `eol-type'.
     EOL-TYPE should be `unix', `dos', `mac', or `nil'.  If it is
     `nil', the returned coding system determines the end-of-line
     conversion from the data.

     EOL-TYPE may also be 0, 1 or 2, standing for `unix', `dos' and
     `mac', respectively.

 -- Function: coding-system-change-text-conversion eol-coding
          text-coding
     This function returns a coding system which uses the end-of-line
     conversion of EOL-CODING, and the text conversion of TEXT-CODING.
     If TEXT-CODING is `nil', it returns `undecided', or one of its
     variants according to EOL-CODING.

 -- Function: find-coding-systems-region from to
     This function returns a list of coding systems that could be used
     to encode a text between FROM and TO.  All coding systems in the
     list can safely encode any multibyte characters in that portion of
     the text.

     If the text contains no multibyte characters, the function returns
     the list `(undecided)'.

 -- Function: find-coding-systems-string string
     This function returns a list of coding systems that could be used
     to encode the text of STRING.  All coding systems in the list can
     safely encode any multibyte characters in STRING.  If the text
     contains no multibyte characters, this returns the list
     `(undecided)'.

 -- Function: find-coding-systems-for-charsets charsets
     This function returns a list of coding systems that could be used
     to encode all the character sets in the list CHARSETS.

 -- Function: detect-coding-region start end &optional highest
     This function chooses a plausible coding system for decoding the
     text from START to END.  This text should be a byte sequence
     (*note Explicit Encoding::).

     Normally this function returns a list of coding systems that could
     handle decoding the text that was scanned.  They are listed in
     order of decreasing priority.  But if HIGHEST is non-`nil', then
     the return value is just one coding system, the one that is
     highest in priority.

     If the region contains only ASCII characters except for such
     ISO-2022 control characters ISO-2022 as `ESC', the value is
     `undecided' or `(undecided)', or a variant specifying end-of-line
     conversion, if that can be deduced from the text.

 -- Function: detect-coding-string string &optional highest
     This function is like `detect-coding-region' except that it
     operates on the contents of STRING instead of bytes in the buffer.

   *Note Process Information: Coding systems for a subprocess, in
particular the description of the functions `process-coding-system' and
`set-process-coding-system', for how to examine or set the coding
systems used for I/O to a subprocess.


File: elisp,  Node: User-Chosen Coding Systems,  Next: Default Coding Systems,  Prev: Lisp and Coding Systems,  Up: Coding Systems

33.10.4 User-Chosen Coding Systems
----------------------------------

 -- Function: select-safe-coding-system from to &optional
          default-coding-system accept-default-p file
     This function selects a coding system for encoding specified text,
     asking the user to choose if necessary.  Normally the specified
     text is the text in the current buffer between FROM and TO.  If
     FROM is a string, the string specifies the text to encode, and TO
     is ignored.

     If DEFAULT-CODING-SYSTEM is non-`nil', that is the first coding
     system to try; if that can handle the text,
     `select-safe-coding-system' returns that coding system.  It can
     also be a list of coding systems; then the function tries each of
     them one by one.  After trying all of them, it next tries the
     current buffer's value of `buffer-file-coding-system' (if it is not
     `undecided'), then the value of
     `default-buffer-file-coding-system' and finally the user's most
     preferred coding system, which the user can set using the command
     `prefer-coding-system' (*note Recognizing Coding Systems:
     (emacs)Recognize Coding.).

     If one of those coding systems can safely encode all the specified
     text, `select-safe-coding-system' chooses it and returns it.
     Otherwise, it asks the user to choose from a list of coding systems
     which can encode all the text, and returns the user's choice.

     DEFAULT-CODING-SYSTEM can also be a list whose first element is t
     and whose other elements are coding systems.  Then, if no coding
     system in the list can handle the text, `select-safe-coding-system'
     queries the user immediately, without trying any of the three
     alternatives described above.

     The optional argument ACCEPT-DEFAULT-P, if non-`nil', should be a
     function to determine whether a coding system selected without
     user interaction is acceptable. `select-safe-coding-system' calls
     this function with one argument, the base coding system of the
     selected coding system.  If ACCEPT-DEFAULT-P returns `nil',
     `select-safe-coding-system' rejects the silently selected coding
     system, and asks the user to select a coding system from a list of
     possible candidates.

     If the variable `select-safe-coding-system-accept-default-p' is
     non-`nil', its value overrides the value of ACCEPT-DEFAULT-P.

     As a final step, before returning the chosen coding system,
     `select-safe-coding-system' checks whether that coding system is
     consistent with what would be selected if the contents of the
     region were read from a file.  (If not, this could lead to data
     corruption in a file subsequently re-visited and edited.)
     Normally, `select-safe-coding-system' uses `buffer-file-name' as
     the file for this purpose, but if FILE is non-`nil', it uses that
     file instead (this can be relevant for `write-region' and similar
     functions).  If it detects an apparent inconsistency,
     `select-safe-coding-system' queries the user before selecting the
     coding system.

   Here are two functions you can use to let the user specify a coding
system, with completion.  *Note Completion::.

 -- Function: read-coding-system prompt &optional default
     This function reads a coding system using the minibuffer,
     prompting with string PROMPT, and returns the coding system name
     as a symbol.  If the user enters null input, DEFAULT specifies
     which coding system to return.  It should be a symbol or a string.

 -- Function: read-non-nil-coding-system prompt
     This function reads a coding system using the minibuffer,
     prompting with string PROMPT, and returns the coding system name
     as a symbol.  If the user tries to enter null input, it asks the
     user to try again.  *Note Coding Systems::.


File: elisp,  Node: Default Coding Systems,  Next: Specifying Coding Systems,  Prev: User-Chosen Coding Systems,  Up: Coding Systems

33.10.5 Default Coding Systems
------------------------------

This section describes variables that specify the default coding system
for certain files or when running certain subprograms, and the function
that I/O operations use to access them.

   The idea of these variables is that you set them once and for all to
the defaults you want, and then do not change them again.  To specify a
particular coding system for a particular operation in a Lisp program,
don't change these variables; instead, override them using
`coding-system-for-read' and `coding-system-for-write' (*note
Specifying Coding Systems::).

 -- Variable: auto-coding-regexp-alist
     This variable is an alist of text patterns and corresponding coding
     systems. Each element has the form `(REGEXP . CODING-SYSTEM)'; a
     file whose first few kilobytes match REGEXP is decoded with
     CODING-SYSTEM when its contents are read into a buffer.  The
     settings in this alist take priority over `coding:' tags in the
     files and the contents of `file-coding-system-alist' (see below).
     The default value is set so that Emacs automatically recognizes
     mail files in Babyl format and reads them with no code conversions.

 -- Variable: file-coding-system-alist
     This variable is an alist that specifies the coding systems to use
     for reading and writing particular files.  Each element has the
     form `(PATTERN . CODING)', where PATTERN is a regular expression
     that matches certain file names.  The element applies to file
     names that match PATTERN.

     The CDR of the element, CODING, should be either a coding system,
     a cons cell containing two coding systems, or a function name (a
     symbol with a function definition).  If CODING is a coding system,
     that coding system is used for both reading the file and writing
     it.  If CODING is a cons cell containing two coding systems, its
     CAR specifies the coding system for decoding, and its CDR
     specifies the coding system for encoding.

     If CODING is a function name, the function should take one
     argument, a list of all arguments passed to
     `find-operation-coding-system'.  It must return a coding system or
     a cons cell containing two coding systems.  This value has the same
     meaning as described above.

 -- Variable: process-coding-system-alist
     This variable is an alist specifying which coding systems to use
     for a subprocess, depending on which program is running in the
     subprocess.  It works like `file-coding-system-alist', except that
     PATTERN is matched against the program name used to start the
     subprocess.  The coding system or systems specified in this alist
     are used to initialize the coding systems used for I/O to the
     subprocess, but you can specify other coding systems later using
     `set-process-coding-system'.

   *Warning:* Coding systems such as `undecided', which determine the
coding system from the data, do not work entirely reliably with
asynchronous subprocess output.  This is because Emacs handles
asynchronous subprocess output in batches, as it arrives.  If the coding
system leaves the character code conversion unspecified, or leaves the
end-of-line conversion unspecified, Emacs must try to detect the proper
conversion from one batch at a time, and this does not always work.

   Therefore, with an asynchronous subprocess, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion--that is, one like `latin-1-unix', rather
than `undecided' or `latin-1'.

 -- Variable: network-coding-system-alist
     This variable is an alist that specifies the coding system to use
     for network streams.  It works much like
     `file-coding-system-alist', with the difference that the PATTERN
     in an element may be either a port number or a regular expression.
     If it is a regular expression, it is matched against the network
     service name used to open the network stream.

 -- Variable: default-process-coding-system
     This variable specifies the coding systems to use for subprocess
     (and network stream) input and output, when nothing else specifies
     what to do.

     The value should be a cons cell of the form `(INPUT-CODING .
     OUTPUT-CODING)'.  Here INPUT-CODING applies to input from the
     subprocess, and OUTPUT-CODING applies to output to it.

 -- Variable: auto-coding-functions
     This variable holds a list of functions that try to determine a
     coding system for a file based on its undecoded contents.

     Each function in this list should be written to look at text in the
     current buffer, but should not modify it in any way.  The buffer
     will contain undecoded text of parts of the file.  Each function
     should take one argument, SIZE, which tells it how many characters
     to look at, starting from point.  If the function succeeds in
     determining a coding system for the file, it should return that
     coding system.  Otherwise, it should return `nil'.

     If a file has a `coding:' tag, that takes precedence, so these
     functions won't be called.

 -- Function: find-operation-coding-system operation &rest arguments
     This function returns the coding system to use (by default) for
     performing OPERATION with ARGUMENTS.  The value has this form:

          (DECODING-SYSTEM . ENCODING-SYSTEM)

     The first element, DECODING-SYSTEM, is the coding system to use
     for decoding (in case OPERATION does decoding), and
     ENCODING-SYSTEM is the coding system for encoding (in case
     OPERATION does encoding).

     The argument OPERATION is a symbol, one of `write-region',
     `start-process', `call-process', `call-process-region',
     `insert-file-contents', or `open-network-stream'.  These are the
     names of the Emacs I/O primitives that can do character code and
     eol conversion.

     The remaining arguments should be the same arguments that might be
     given to the corresponding I/O primitive.  Depending on the
     primitive, one of those arguments is selected as the "target".
     For example, if OPERATION does file I/O, whichever argument
     specifies the file name is the target.  For subprocess primitives,
     the process name is the target.  For `open-network-stream', the
     target is the service name or port number.

     Depending on OPERATION, this function looks up the target in
     `file-coding-system-alist', `process-coding-system-alist', or
     `network-coding-system-alist'.  If the target is found in the
     alist, `find-operation-coding-system' returns its association in
     the alist; otherwise it returns `nil'.

     If OPERATION is `insert-file-contents', the argument corresponding
     to the target may be a cons cell of the form `(FILENAME .
     BUFFER)').  In that case, FILENAME is a file name to look up in
     `file-coding-system-alist', and BUFFER is a buffer that contains
     the file's contents (not yet decoded).  If
     `file-coding-system-alist' specifies a function to call for this
     file, and that function needs to examine the file's contents (as
     it usually does), it should examine the contents of BUFFER instead
     of reading the file.


File: elisp,  Node: Specifying Coding Systems,  Next: Explicit Encoding,  Prev: Default Coding Systems,  Up: Coding Systems

33.10.6 Specifying a Coding System for One Operation
----------------------------------------------------

You can specify the coding system for a specific operation by binding
the variables `coding-system-for-read' and/or `coding-system-for-write'.

 -- Variable: coding-system-for-read
     If this variable is non-`nil', it specifies the coding system to
     use for reading a file, or for input from a synchronous subprocess.

     It also applies to any asynchronous subprocess or network stream,
     but in a different way: the value of `coding-system-for-read' when
     you start the subprocess or open the network stream specifies the
     input decoding method for that subprocess or network stream.  It
     remains in use for that subprocess or network stream unless and
     until overridden.

     The right way to use this variable is to bind it with `let' for a
     specific I/O operation.  Its global value is normally `nil', and
     you should not globally set it to any other value.  Here is an
     example of the right way to use the variable:

          ;; Read the file with no character code conversion.
          ;; Assume crlf represents end-of-line.
          (let ((coding-system-for-read 'emacs-mule-dos))
            (insert-file-contents filename))

     When its value is non-`nil', this variable takes precedence over
     all other methods of specifying a coding system to use for input,
     including `file-coding-system-alist',
     `process-coding-system-alist' and `network-coding-system-alist'.

 -- Variable: coding-system-for-write
     This works much like `coding-system-for-read', except that it
     applies to output rather than input.  It affects writing to files,
     as well as sending output to subprocesses and net connections.

     When a single operation does both input and output, as do
     `call-process-region' and `start-process', both
     `coding-system-for-read' and `coding-system-for-write' affect it.

 -- Variable: inhibit-eol-conversion
     When this variable is non-`nil', no end-of-line conversion is done,
     no matter which coding system is specified.  This applies to all
     the Emacs I/O and subprocess primitives, and to the explicit
     encoding and decoding functions (*note Explicit Encoding::).


File: elisp,  Node: Explicit Encoding,  Next: Terminal I/O Encoding,  Prev: Specifying Coding Systems,  Up: Coding Systems

33.10.7 Explicit Encoding and Decoding
--------------------------------------

All the operations that transfer text in and out of Emacs have the
ability to use a coding system to encode or decode the text.  You can
also explicitly encode and decode text using the functions in this
section.

   The result of encoding, and the input to decoding, are not ordinary
text.  They logically consist of a series of byte values; that is, a
series of characters whose codes are in the range 0 through 255.  In a
multibyte buffer or string, character codes 128 through 159 are
represented by multibyte sequences, but this is invisible to Lisp
programs.

   The usual way to read a file into a buffer as a sequence of bytes, so
you can decode the contents explicitly, is with
`insert-file-contents-literally' (*note Reading from Files::);
alternatively, specify a non-`nil' RAWFILE argument when visiting a
file with `find-file-noselect'.  These methods result in a unibyte
buffer.

   The usual way to use the byte sequence that results from explicitly
encoding text is to copy it to a file or process--for example, to write
it with `write-region' (*note Writing to Files::), and suppress
encoding by binding `coding-system-for-write' to `no-conversion'.

   Here are the functions to perform explicit encoding or decoding.  The
encoding functions produce sequences of bytes; the decoding functions
are meant to operate on sequences of bytes.  All of these functions
discard text properties.

 -- Command: encode-coding-region start end coding-system
     This command encodes the text from START to END according to
     coding system CODING-SYSTEM.  The encoded text replaces the
     original text in the buffer.  The result of encoding is logically a
     sequence of bytes, but the buffer remains multibyte if it was
     multibyte before.

     This command returns the length of the encoded text.

 -- Function: encode-coding-string string coding-system &optional nocopy
     This function encodes the text in STRING according to coding
     system CODING-SYSTEM.  It returns a new string containing the
     encoded text, except when NOCOPY is non-`nil', in which case the
     function may return STRING itself if the encoding operation is
     trivial.  The result of encoding is a unibyte string.

 -- Command: decode-coding-region start end coding-system
     This command decodes the text from START to END according to
     coding system CODING-SYSTEM.  The decoded text replaces the
     original text in the buffer.  To make explicit decoding useful,
     the text before decoding ought to be a sequence of byte values,
     but both multibyte and unibyte buffers are acceptable.

     This command returns the length of the decoded text.

 -- Function: decode-coding-string string coding-system &optional nocopy
     This function decodes the text in STRING according to coding
     system CODING-SYSTEM.  It returns a new string containing the
     decoded text, except when NOCOPY is non-`nil', in which case the
     function may return STRING itself if the decoding operation is
     trivial.  To make explicit decoding useful, the contents of STRING
     ought to be a sequence of byte values, but a multibyte string is
     acceptable.

 -- Function: decode-coding-inserted-region from to filename &optional
          visit beg end replace
     This function decodes the text from FROM to TO as if it were being
     read from file FILENAME using `insert-file-contents' using the
     rest of the arguments provided.

     The normal way to use this function is after reading text from a
     file without decoding, if you decide you would rather have decoded
     it.  Instead of deleting the text and reading it again, this time
     with decoding, you can call this function.


File: elisp,  Node: Terminal I/O Encoding,  Next: MS-DOS File Types,  Prev: Explicit Encoding,  Up: Coding Systems

33.10.8 Terminal I/O Encoding
-----------------------------

Emacs can decode keyboard input using a coding system, and encode
terminal output.  This is useful for terminals that transmit or display
text using a particular encoding such as Latin-1.  Emacs does not set
`last-coding-system-used' for encoding or decoding for the terminal.

 -- Function: keyboard-coding-system
     This function returns the coding system that is in use for decoding
     keyboard input--or `nil' if no coding system is to be used.

 -- Command: set-keyboard-coding-system coding-system
     This command specifies CODING-SYSTEM as the coding system to use
     for decoding keyboard input.  If CODING-SYSTEM is `nil', that
     means do not decode keyboard input.

 -- Function: terminal-coding-system
     This function returns the coding system that is in use for encoding
     terminal output--or `nil' for no encoding.

 -- Command: set-terminal-coding-system coding-system
     This command specifies CODING-SYSTEM as the coding system to use
     for encoding terminal output.  If CODING-SYSTEM is `nil', that
     means do not encode terminal output.


File: elisp,  Node: MS-DOS File Types,  Prev: Terminal I/O Encoding,  Up: Coding Systems

33.10.9 MS-DOS File Types
-------------------------

On MS-DOS and Microsoft Windows, Emacs guesses the appropriate
end-of-line conversion for a file by looking at the file's name.  This
feature classifies files as "text files" and "binary files".  By
"binary file" we mean a file of literal byte values that are not
necessarily meant to be characters; Emacs does no end-of-line conversion
and no character code conversion for them.  On the other hand, the bytes
in a text file are intended to represent characters; when you create a
new file whose name implies that it is a text file, Emacs uses DOS
end-of-line conversion.

 -- Variable: buffer-file-type
     This variable, automatically buffer-local in each buffer, records
     the file type of the buffer's visited file.  When a buffer does
     not specify a coding system with `buffer-file-coding-system', this
     variable is used to determine which coding system to use when
     writing the contents of the buffer.  It should be `nil' for text,
     `t' for binary.  If it is `t', the coding system is
     `no-conversion'.  Otherwise, `undecided-dos' is used.

     Normally this variable is set by visiting a file; it is set to
     `nil' if the file was visited without any actual conversion.

 -- User Option: file-name-buffer-file-type-alist
     This variable holds an alist for recognizing text and binary files.
     Each element has the form (REGEXP . TYPE), where REGEXP is matched
     against the file name, and TYPE may be `nil' for text, `t' for
     binary, or a function to call to compute which.  If it is a
     function, then it is called with a single argument (the file name)
     and should return `t' or `nil'.

     When running on MS-DOS or MS-Windows, Emacs checks this alist to
     decide which coding system to use when reading a file.  For a text
     file, `undecided-dos' is used.  For a binary file, `no-conversion'
     is used.

     If no element in this alist matches a given file name, then
     `default-buffer-file-type' says how to treat the file.

 -- User Option: default-buffer-file-type
     This variable says how to handle files for which
     `file-name-buffer-file-type-alist' says nothing about the type.

     If this variable is non-`nil', then these files are treated as
     binary: the coding system `no-conversion' is used.  Otherwise,
     nothing special is done for them--the coding system is deduced
     solely from the file contents, in the usual Emacs fashion.


File: elisp,  Node: Input Methods,  Next: Locales,  Prev: Coding Systems,  Up: Non-ASCII Characters

33.11 Input Methods
===================

"Input methods" provide convenient ways of entering non-ASCII
characters from the keyboard.  Unlike coding systems, which translate
non-ASCII characters to and from encodings meant to be read by
programs, input methods provide human-friendly commands.  (*Note Input
Methods: (emacs)Input Methods, for information on how users use input
methods to enter text.)  How to define input methods is not yet
documented in this manual, but here we describe how to use them.

   Each input method has a name, which is currently a string; in the
future, symbols may also be usable as input method names.

 -- Variable: current-input-method
     This variable holds the name of the input method now active in the
     current buffer.  (It automatically becomes local in each buffer
     when set in any fashion.)  It is `nil' if no input method is
     active in the buffer now.

 -- User Option: default-input-method
     This variable holds the default input method for commands that
     choose an input method.  Unlike `current-input-method', this
     variable is normally global.

 -- Command: set-input-method input-method
     This command activates input method INPUT-METHOD for the current
     buffer.  It also sets `default-input-method' to INPUT-METHOD.  If
     INPUT-METHOD is `nil', this command deactivates any input method
     for the current buffer.

 -- Function: read-input-method-name prompt &optional default
          inhibit-null
     This function reads an input method name with the minibuffer,
     prompting with PROMPT.  If DEFAULT is non-`nil', that is returned
     by default, if the user enters empty input.  However, if
     INHIBIT-NULL is non-`nil', empty input signals an error.

     The returned value is a string.

 -- Variable: input-method-alist
     This variable defines all the supported input methods.  Each
     element defines one input method, and should have the form:

          (INPUT-METHOD LANGUAGE-ENV ACTIVATE-FUNC
           TITLE DESCRIPTION ARGS...)

     Here INPUT-METHOD is the input method name, a string; LANGUAGE-ENV
     is another string, the name of the language environment this input
     method is recommended for.  (That serves only for documentation
     purposes.)

     ACTIVATE-FUNC is a function to call to activate this method.  The
     ARGS, if any, are passed as arguments to ACTIVATE-FUNC.  All told,
     the arguments to ACTIVATE-FUNC are INPUT-METHOD and the ARGS.

     TITLE is a string to display in the mode line while this method is
     active.  DESCRIPTION is a string describing this method and what
     it is good for.

   The fundamental interface to input methods is through the variable
`input-method-function'.  *Note Reading One Event::, and *Note Invoking
the Input Method::.


File: elisp,  Node: Locales,  Prev: Input Methods,  Up: Non-ASCII Characters

33.12 Locales
=============

POSIX defines a concept of "locales" which control which language to
use in language-related features.  These Emacs variables control how
Emacs interacts with these features.

 -- Variable: locale-coding-system
     This variable specifies the coding system to use for decoding
     system error messages and--on X Window system only--keyboard
     input, for encoding the format argument to `format-time-string',
     and for decoding the return value of `format-time-string'.

 -- Variable: system-messages-locale
     This variable specifies the locale to use for generating system
     error messages.  Changing the locale can cause messages to come
     out in a different language or in a different orthography.  If the
     variable is `nil', the locale is specified by environment
     variables in the usual POSIX fashion.

 -- Variable: system-time-locale
     This variable specifies the locale to use for formatting time
     values.  Changing the locale can cause messages to appear
     according to the conventions of a different language.  If the
     variable is `nil', the locale is specified by environment
     variables in the usual POSIX fashion.

 -- Function: locale-info item
     This function returns locale data ITEM for the current POSIX
     locale, if available.  ITEM should be one of these symbols:

    `codeset'
          Return the character set as a string (locale item `CODESET').

    `days'
          Return a 7-element vector of day names (locale items `DAY_1'
          through `DAY_7');

    `months'
          Return a 12-element vector of month names (locale items
          `MON_1' through `MON_12').

    `paper'
          Return a list `(WIDTH HEIGHT)' for the default paper size
          measured in millimeters (locale items `PAPER_WIDTH' and
          `PAPER_HEIGHT').

     If the system can't provide the requested information, or if ITEM
     is not one of those symbols, the value is `nil'.  All strings in
     the return value are decoded using `locale-coding-system'.  *Note
     Locales: (libc)Locales, for more information about locales and
     locale items.


File: elisp,  Node: Searching and Matching,  Next: Syntax Tables,  Prev: Non-ASCII Characters,  Up: Top

34 Searching and Matching
*************************

GNU Emacs provides two ways to search through a buffer for specified
text: exact string searches and regular expression searches.  After a
regular expression search, you can examine the "match data" to
determine which text matched the whole regular expression or various
portions of it.

* Menu:

* String Search::         Search for an exact match.
* Searching and Case::    Case-independent or case-significant searching.
* Regular Expressions::   Describing classes of strings.
* Regexp Search::         Searching for a match for a regexp.
* POSIX Regexps::         Searching POSIX-style for the longest match.
* Match Data::            Finding out which part of the text matched,
                            after a string or regexp search.
* Search and Replace::	  Commands that loop, searching and replacing.
* Standard Regexps::      Useful regexps for finding sentences, pages,...

   The `skip-chars...' functions also perform a kind of searching.
*Note Skipping Characters::.  To search for changes in character
properties, see *Note Property Search::.


File: elisp,  Node: String Search,  Next: Searching and Case,  Up: Searching and Matching

34.1 Searching for Strings
==========================

These are the primitive functions for searching through the text in a
buffer.  They are meant for use in programs, but you may call them
interactively.  If you do so, they prompt for the search string; the
arguments LIMIT and NOERROR are `nil', and REPEAT is 1.

   These search functions convert the search string to multibyte if the
buffer is multibyte; they convert the search string to unibyte if the
buffer is unibyte.  *Note Text Representations::.

 -- Command: search-forward string &optional limit noerror repeat
     This function searches forward from point for an exact match for
     STRING.  If successful, it sets point to the end of the occurrence
     found, and returns the new value of point.  If no match is found,
     the value and side effects depend on NOERROR (see below).

     In the following example, point is initially at the beginning of
     the line.  Then `(search-forward "fox")' moves point after the last
     letter of `fox':

          ---------- Buffer: foo ----------
          -!-The quick brown fox jumped over the lazy dog.
          ---------- Buffer: foo ----------

          (search-forward "fox")
               => 20

          ---------- Buffer: foo ----------
          The quick brown fox-!- jumped over the lazy dog.
          ---------- Buffer: foo ----------

     The argument LIMIT specifies the upper bound to the search.  (It
     must be a position in the current buffer.)  No match extending
     after that position is accepted.  If LIMIT is omitted or `nil', it
     defaults to the end of the accessible portion of the buffer.

     What happens when the search fails depends on the value of
     NOERROR.  If NOERROR is `nil', a `search-failed' error is
     signaled.  If NOERROR is `t', `search-forward' returns `nil' and
     does nothing.  If NOERROR is neither `nil' nor `t', then
     `search-forward' moves point to the upper bound and returns `nil'.
     (It would be more consistent now to return the new position of
     point in that case, but some existing programs may depend on a
     value of `nil'.)

     The argument NOERROR only affects valid searches which fail to
     find a match.  Invalid arguments cause errors regardless of
     NOERROR.

     If REPEAT is supplied (it must be a positive number), then the
     search is repeated that many times (each time starting at the end
     of the previous time's match).  If these successive searches
     succeed, the function succeeds, moving point and returning its new
     value.  Otherwise the search fails, with results depending on the
     value of NOERROR, as described above.

 -- Command: search-backward string &optional limit noerror repeat
     This function searches backward from point for STRING.  It is just
     like `search-forward' except that it searches backwards and leaves
     point at the beginning of the match.

 -- Command: word-search-forward string &optional limit noerror repeat
     This function searches forward from point for a "word" match for
     STRING.  If it finds a match, it sets point to the end of the
     match found, and returns the new value of point.

     Word matching regards STRING as a sequence of words, disregarding
     punctuation that separates them.  It searches the buffer for the
     same sequence of words.  Each word must be distinct in the buffer
     (searching for the word `ball' does not match the word `balls'),
     but the details of punctuation and spacing are ignored (searching
     for `ball boy' does match `ball.  Boy!').

     In this example, point is initially at the beginning of the
     buffer; the search leaves it between the `y' and the `!'.

          ---------- Buffer: foo ----------
          -!-He said "Please!  Find
          the ball boy!"
          ---------- Buffer: foo ----------

          (word-search-forward "Please find the ball, boy.")
               => 35

          ---------- Buffer: foo ----------
          He said "Please!  Find
          the ball boy-!-!"
          ---------- Buffer: foo ----------

     If LIMIT is non-`nil', it must be a position in the current
     buffer; it specifies the upper bound to the search.  The match
     found must not extend after that position.

     If NOERROR is `nil', then `word-search-forward' signals an error
     if the search fails.  If NOERROR is `t', then it returns `nil'
     instead of signaling an error.  If NOERROR is neither `nil' nor
     `t', it moves point to LIMIT (or the end of the accessible portion
     of the buffer) and returns `nil'.

     If REPEAT is non-`nil', then the search is repeated that many
     times.  Point is positioned at the end of the last match.

 -- Command: word-search-backward string &optional limit noerror repeat
     This function searches backward from point for a word match to
     STRING.  This function is just like `word-search-forward' except
     that it searches backward and normally leaves point at the
     beginning of the match.


File: elisp,  Node: Searching and Case,  Next: Regular Expressions,  Prev: String Search,  Up: Searching and Matching

34.2 Searching and Case
=======================

By default, searches in Emacs ignore the case of the text they are
searching through; if you specify searching for `FOO', then `Foo' or
`foo' is also considered a match.  This applies to regular expressions,
too; thus, `[aB]' would match `a' or `A' or `b' or `B'.

   If you do not want this feature, set the variable `case-fold-search'
to `nil'.  Then all letters must match exactly, including case.  This
is a buffer-local variable; altering the variable affects only the
current buffer.  (*Note Intro to Buffer-Local::.)  Alternatively, you
may change the value of `default-case-fold-search', which is the
default value of `case-fold-search' for buffers that do not override it.

   Note that the user-level incremental search feature handles case
distinctions differently.  When given a lower case letter, it looks for
a match of either case, but when given an upper case letter, it looks
for an upper case letter only.  But this has nothing to do with the
searching functions used in Lisp code.

 -- User Option: case-replace
     This variable determines whether the higher level replacement
     functions should preserve case.  If the variable is `nil', that
     means to use the replacement text verbatim.  A non-`nil' value
     means to convert the case of the replacement text according to the
     text being replaced.

     This variable is used by passing it as an argument to the function
     `replace-match'.  *Note Replacing Match::.

 -- User Option: case-fold-search
     This buffer-local variable determines whether searches should
     ignore case.  If the variable is `nil' they do not ignore case;
     otherwise they do ignore case.

 -- Variable: default-case-fold-search
     The value of this variable is the default value for
     `case-fold-search' in buffers that do not override it.  This is the
     same as `(default-value 'case-fold-search)'.


File: elisp,  Node: Regular Expressions,  Next: Regexp Search,  Prev: Searching and Case,  Up: Searching and Matching

34.3 Regular Expressions
========================

A "regular expression" ("regexp", for short) is a pattern that denotes
a (possibly infinite) set of strings.  Searching for matches for a
regexp is a very powerful operation.  This section explains how to write
regexps; the following section says how to search for them.

   For convenient interactive development of regular expressions, you
can use the `M-x re-builder' command.  It provides a convenient
interface for creating regular expressions, by giving immediate visual
feedback in a separate buffer.  As you edit the regexp, all its matches
in the target buffer are highlighted.  Each parenthesized
sub-expression of the regexp is shown in a distinct face, which makes
it easier to verify even very complex regexps.

* Menu:

* Syntax of Regexps::       Rules for writing regular expressions.
* Regexp Example::          Illustrates regular expression syntax.
* Regexp Functions::        Functions for operating on regular expressions.


File: elisp,  Node: Syntax of Regexps,  Next: Regexp Example,  Up: Regular Expressions

34.3.1 Syntax of Regular Expressions
------------------------------------

Regular expressions have a syntax in which a few characters are special
constructs and the rest are "ordinary".  An ordinary character is a
simple regular expression that matches that character and nothing else.
The special characters are `.', `*', `+', `?', `[', `^', `$', and `\';
no new special characters will be defined in the future.  The character
`]' is special if it ends a character alternative (see later).  The
character `-' is special inside a character alternative.  A `[:' and
balancing `:]' enclose a character class inside a character
alternative.  Any other character appearing in a regular expression is
ordinary, unless a `\' precedes it.

   For example, `f' is not a special character, so it is ordinary, and
therefore `f' is a regular expression that matches the string `f' and
no other string.  (It does _not_ match the string `fg', but it does
match a _part_ of that string.)  Likewise, `o' is a regular expression
that matches only `o'.

   Any two regular expressions A and B can be concatenated.  The result
is a regular expression that matches a string if A matches some amount
of the beginning of that string and B matches the rest of the string.

   As a simple example, we can concatenate the regular expressions `f'
and `o' to get the regular expression `fo', which matches only the
string `fo'.  Still trivial.  To do something more powerful, you need
to use one of the special regular expression constructs.

* Menu:

* Regexp Special::      Special characters in regular expressions.
* Char Classes::        Character classes used in regular expressions.
* Regexp Backslash::    Backslash-sequences in regular expressions.


File: elisp,  Node: Regexp Special,  Next: Char Classes,  Up: Syntax of Regexps

34.3.1.1 Special Characters in Regular Expressions
..................................................

Here is a list of the characters that are special in a regular
expression.

`.' (Period)
     is a special character that matches any single character except a
     newline.  Using concatenation, we can make regular expressions
     like `a.b', which matches any three-character string that begins
     with `a' and ends with `b'.

`*'
     is not a construct by itself; it is a postfix operator that means
     to match the preceding regular expression repetitively as many
     times as possible.  Thus, `o*' matches any number of `o's
     (including no `o's).

     `*' always applies to the _smallest_ possible preceding
     expression.  Thus, `fo*' has a repeating `o', not a repeating
     `fo'.  It matches `f', `fo', `foo', and so on.

     The matcher processes a `*' construct by matching, immediately, as
     many repetitions as can be found.  Then it continues with the rest
     of the pattern.  If that fails, backtracking occurs, discarding
     some of the matches of the `*'-modified construct in the hope that
     that will make it possible to match the rest of the pattern.  For
     example, in matching `ca*ar' against the string `caaar', the `a*'
     first tries to match all three `a's; but the rest of the pattern is
     `ar' and there is only `r' left to match, so this try fails.  The
     next alternative is for `a*' to match only two `a's.  With this
     choice, the rest of the regexp matches successfully.

     *Warning:* Nested repetition operators can run for an indefinitely
     long time, if they lead to ambiguous matching.  For example,
     trying to match the regular expression `\(x+y*\)*a' against the
     string `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz' could take hours
     before it ultimately fails.  Emacs must try each way of grouping
     the `x's before concluding that none of them can work.  Even
     worse, `\(x*\)*' can match the null string in infinitely many
     ways, so it causes an infinite loop.  To avoid these problems,
     check nested repetitions carefully, to make sure that they do not
     cause combinatorial explosions in backtracking.

`+'
     is a postfix operator, similar to `*' except that it must match
     the preceding expression at least once.  So, for example, `ca+r'
     matches the strings `car' and `caaaar' but not the string `cr',
     whereas `ca*r' matches all three strings.

`?'
     is a postfix operator, similar to `*' except that it must match the
     preceding expression either once or not at all.  For example,
     `ca?r' matches `car' or `cr'; nothing else.

`*?', `+?', `??'
     These are "non-greedy" variants of the operators `*', `+' and `?'.
     Where those operators match the largest possible substring
     (consistent with matching the entire containing expression), the
     non-greedy variants match the smallest possible substring
     (consistent with matching the entire containing expression).

     For example, the regular expression `c[ad]*a' when applied to the
     string `cdaaada' matches the whole string; but the regular
     expression `c[ad]*?a', applied to that same string, matches just
     `cda'.  (The smallest possible match here for `[ad]*?' that
     permits the whole expression to match is `d'.)

`[ ... ]'
     is a "character alternative", which begins with `[' and is
     terminated by `]'.  In the simplest case, the characters between
     the two brackets are what this character alternative can match.

     Thus, `[ad]' matches either one `a' or one `d', and `[ad]*'
     matches any string composed of just `a's and `d's (including the
     empty string), from which it follows that `c[ad]*r' matches `cr',
     `car', `cdr', `caddaar', etc.

     You can also include character ranges in a character alternative,
     by writing the starting and ending characters with a `-' between
     them.  Thus, `[a-z]' matches any lower-case ASCII letter.  Ranges
     may be intermixed freely with individual characters, as in
     `[a-z$%.]', which matches any lower case ASCII letter or `$', `%'
     or period.

     Note that the usual regexp special characters are not special
     inside a character alternative.  A completely different set of
     characters is special inside character alternatives: `]', `-' and
     `^'.

     To include a `]' in a character alternative, you must make it the
     first character.  For example, `[]a]' matches `]' or `a'.  To
     include a `-', write `-' as the first or last character of the
     character alternative, or put it after a range.  Thus, `[]-]'
     matches both `]' and `-'.

     To include `^' in a character alternative, put it anywhere but at
     the beginning.

     The beginning and end of a range of multibyte characters must be in
     the same character set (*note Character Sets::).  Thus,
     `"[\x8e0-\x97c]"' is invalid because character 0x8e0 (`a' with
     grave accent) is in the Emacs character set for Latin-1 but the
     character 0x97c (`u' with diaeresis) is in the Emacs character set
     for Latin-2.  (We use Lisp string syntax to write that example,
     and a few others in the next few paragraphs, in order to include
     hex escape sequences in them.)

     If a range starts with a unibyte character C and ends with a
     multibyte character C2, the range is divided into two parts: one
     is `C..?\377', the other is `C1..C2', where C1 is the first
     character of the charset to which C2 belongs.

     You cannot always match all non-ASCII characters with the regular
     expression `"[\200-\377]"'.  This works when searching a unibyte
     buffer or string (*note Text Representations::), but not in a
     multibyte buffer or string, because many non-ASCII characters have
     codes above octal 0377.  However, the regular expression
     `"[^\000-\177]"' does match all non-ASCII characters (see below
     regarding `^'), in both multibyte and unibyte representations,
     because only the ASCII characters are excluded.

     A character alternative can also specify named character classes
     (*note Char Classes::).  This is a POSIX feature whose syntax is
     `[:CLASS:]'.  Using a character class is equivalent to mentioning
     each of the characters in that class; but the latter is not
     feasible in practice, since some classes include thousands of
     different characters.

`[^ ... ]'
     `[^' begins a "complemented character alternative".  This matches
     any character except the ones specified.  Thus, `[^a-z0-9A-Z]'
     matches all characters _except_ letters and digits.

     `^' is not special in a character alternative unless it is the
     first character.  The character following the `^' is treated as if
     it were first (in other words, `-' and `]' are not special there).

     A complemented character alternative can match a newline, unless
     newline is mentioned as one of the characters not to match.  This
     is in contrast to the handling of regexps in programs such as
     `grep'.

`^'
     When matching a buffer, `^' matches the empty string, but only at
     the beginning of a line in the text being matched (or the
     beginning of the accessible portion of the buffer).  Otherwise it
     fails to match anything.  Thus, `^foo' matches a `foo' that occurs
     at the beginning of a line.

     When matching a string instead of a buffer, `^' matches at the
     beginning of the string or after a newline character.

     For historical compatibility reasons, `^' can be used only at the
     beginning of the regular expression, or after `\(', `\(?:' or `\|'.

`$'
     is similar to `^' but matches only at the end of a line (or the
     end of the accessible portion of the buffer).  Thus, `x+$' matches
     a string of one `x' or more at the end of a line.

     When matching a string instead of a buffer, `$' matches at the end
     of the string or before a newline character.

     For historical compatibility reasons, `$' can be used only at the
     end of the regular expression, or before `\)' or `\|'.

`\'
     has two functions: it quotes the special characters (including
     `\'), and it introduces additional special constructs.

     Because `\' quotes special characters, `\$' is a regular
     expression that matches only `$', and `\[' is a regular expression
     that matches only `[', and so on.

     Note that `\' also has special meaning in the read syntax of Lisp
     strings (*note String Type::), and must be quoted with `\'.  For
     example, the regular expression that matches the `\' character is
     `\\'.  To write a Lisp string that contains the characters `\\',
     Lisp syntax requires you to quote each `\' with another `\'.
     Therefore, the read syntax for a regular expression matching `\'
     is `"\\\\"'.

   *Please note:* For historical compatibility, special characters are
treated as ordinary ones if they are in contexts where their special
meanings make no sense.  For example, `*foo' treats `*' as ordinary
since there is no preceding expression on which the `*' can act.  It is
poor practice to depend on this behavior; quote the special character
anyway, regardless of where it appears.

   As a `\' is not special inside a character alternative, it can never
remove the special meaning of `-' or `]'.  So you should not quote
these characters when they have no special meaning either.  This would
not clarify anything, since backslashes can legitimately precede these
characters where they _have_ special meaning, as in `[^\]' (`"[^\\]"'
for Lisp string syntax), which matches any single character except a
backslash.

   In practice, most `]' that occur in regular expressions close a
character alternative and hence are special.  However, occasionally a
regular expression may try to match a complex pattern of literal `['
and `]'.  In such situations, it sometimes may be necessary to
carefully parse the regexp from the start to determine which square
brackets enclose a character alternative.  For example, `[^][]]'
consists of the complemented character alternative `[^][]' (which
matches any single character that is not a square bracket), followed by
a literal `]'.

   The exact rules are that at the beginning of a regexp, `[' is
special and `]' not.  This lasts until the first unquoted `[', after
which we are in a character alternative; `[' is no longer special
(except when it starts a character class) but `]' is special, unless it
immediately follows the special `[' or that `[' followed by a `^'.
This lasts until the next special `]' that does not end a character
class.  This ends the character alternative and restores the ordinary
syntax of regular expressions; an unquoted `[' is special again and a
`]' not.


File: elisp,  Node: Char Classes,  Next: Regexp Backslash,  Prev: Regexp Special,  Up: Syntax of Regexps

34.3.1.2 Character Classes
..........................

Here is a table of the classes you can use in a character alternative,
and what they mean:

`[:ascii:]'
     This matches any ASCII character (codes 0-127).

`[:alnum:]'
     This matches any letter or digit.  (At present, for multibyte
     characters, it matches anything that has word syntax.)

`[:alpha:]'
     This matches any letter.  (At present, for multibyte characters, it
     matches anything that has word syntax.)

`[:blank:]'
     This matches space and tab only.

`[:cntrl:]'
     This matches any ASCII control character.

`[:digit:]'
     This matches `0' through `9'.  Thus, `[-+[:digit:]]' matches any
     digit, as well as `+' and `-'.

`[:graph:]'
     This matches graphic characters--everything except ASCII control
     characters, space, and the delete character.

`[:lower:]'
     This matches any lower-case letter, as determined by the current
     case table (*note Case Tables::).

`[:multibyte:]'
     This matches any multibyte character (*note Text
     Representations::).

`[:nonascii:]'
     This matches any non-ASCII character.

`[:print:]'
     This matches printing characters--everything except ASCII control
     characters and the delete character.

`[:punct:]'
     This matches any punctuation character.  (At present, for multibyte
     characters, it matches anything that has non-word syntax.)

`[:space:]'
     This matches any character that has whitespace syntax (*note
     Syntax Class Table::).

`[:unibyte:]'
     This matches any unibyte character (*note Text Representations::).

`[:upper:]'
     This matches any upper-case letter, as determined by the current
     case table (*note Case Tables::).

`[:word:]'
     This matches any character that has word syntax (*note Syntax
     Class Table::).

`[:xdigit:]'
     This matches the hexadecimal digits: `0' through `9', `a' through
     `f' and `A' through `F'.


File: elisp,  Node: Regexp Backslash,  Prev: Char Classes,  Up: Syntax of Regexps

34.3.1.3 Backslash Constructs in Regular Expressions
....................................................

For the most part, `\' followed by any character matches only that
character.  However, there are several exceptions: certain
two-character sequences starting with `\' that have special meanings.
(The character after the `\' in such a sequence is always ordinary when
used on its own.)  Here is a table of the special `\' constructs.

`\|'
     specifies an alternative.  Two regular expressions A and B with
     `\|' in between form an expression that matches anything that
     either A or B matches.

     Thus, `foo\|bar' matches either `foo' or `bar' but no other string.

     `\|' applies to the largest possible surrounding expressions.
     Only a surrounding `\( ... \)' grouping can limit the grouping
     power of `\|'.

     If you need full backtracking capability to handle multiple uses of
     `\|', use the POSIX regular expression functions (*note POSIX
     Regexps::).

`\{M\}'
     is a postfix operator that repeats the previous pattern exactly M
     times.  Thus, `x\{5\}' matches the string `xxxxx' and nothing
     else.  `c[ad]\{3\}r' matches string such as `caaar', `cdddr',
     `cadar', and so on.

`\{M,N\}'
     is a more general postfix operator that specifies repetition with a
     minimum of M repeats and a maximum of N repeats.  If M is omitted,
     the minimum is 0; if N is omitted, there is no maximum.

     For example, `c[ad]\{1,2\}r' matches the strings `car', `cdr',
     `caar', `cadr', `cdar', and `cddr', and nothing else.
     `\{0,1\}' or `\{,1\}' is equivalent to `?'.
     `\{0,\}' or `\{,\}' is equivalent to `*'.
     `\{1,\}' is equivalent to `+'.

`\( ... \)'
     is a grouping construct that serves three purposes:

       1. To enclose a set of `\|' alternatives for other operations.
          Thus, the regular expression `\(foo\|bar\)x' matches either
          `foox' or `barx'.

       2. To enclose a complicated expression for the postfix operators
          `*', `+' and `?' to operate on.  Thus, `ba\(na\)*' matches
          `ba', `bana', `banana', `bananana', etc., with any number
          (zero or more) of `na' strings.

       3. To record a matched substring for future reference with
          `\DIGIT' (see below).

     This last application is not a consequence of the idea of a
     parenthetical grouping; it is a separate feature that was assigned
     as a second meaning to the same `\( ... \)' construct because, in
     practice, there was usually no conflict between the two meanings.
     But occasionally there is a conflict, and that led to the
     introduction of shy groups.

`\(?: ... \)'
     is the "shy group" construct.  A shy group serves the first two
     purposes of an ordinary group (controlling the nesting of other
     operators), but it does not get a number, so you cannot refer back
     to its value with `\DIGIT'.

     Shy groups are particularly useful for mechanically-constructed
     regular expressions because they can be added automatically
     without altering the numbering of any ordinary, non-shy groups.

`\DIGIT'
     matches the same text that matched the DIGITth occurrence of a
     grouping (`\( ... \)') construct.

     In other words, after the end of a group, the matcher remembers the
     beginning and end of the text matched by that group.  Later on in
     the regular expression you can use `\' followed by DIGIT to match
     that same text, whatever it may have been.

     The strings matching the first nine grouping constructs appearing
     in the entire regular expression passed to a search or matching
     function are assigned numbers 1 through 9 in the order that the
     open parentheses appear in the regular expression.  So you can use
     `\1' through `\9' to refer to the text matched by the
     corresponding grouping constructs.

     For example, `\(.*\)\1' matches any newline-free string that is
     composed of two identical halves.  The `\(.*\)' matches the first
     half, which may be anything, but the `\1' that follows must match
     the same exact text.

     If a `\( ... \)' construct matches more than once (which can
     happen, for instance, if it is followed by `*'), only the last
     match is recorded.

     If a particular grouping construct in the regular expression was
     never matched--for instance, if it appears inside of an
     alternative that wasn't used, or inside of a repetition that
     repeated zero times--then the corresponding `\DIGIT' construct
     never matches anything.  To use an artificial example,,
     `\(foo\(b*\)\|lose\)\2' cannot match `lose': the second
     alternative inside the larger group matches it, but then `\2' is
     undefined and can't match anything.  But it can match `foobb',
     because the first alternative matches `foob' and `\2' matches `b'.

`\w'
     matches any word-constituent character.  The editor syntax table
     determines which characters these are.  *Note Syntax Tables::.

`\W'
     matches any character that is not a word constituent.

`\sCODE'
     matches any character whose syntax is CODE.  Here CODE is a
     character that represents a syntax code: thus, `w' for word
     constituent, `-' for whitespace, `(' for open parenthesis, etc.
     To represent whitespace syntax, use either `-' or a space
     character.  *Note Syntax Class Table::, for a list of syntax codes
     and the characters that stand for them.

`\SCODE'
     matches any character whose syntax is not CODE.

`\cC'
     matches any character whose category is C.  Here C is a character
     that represents a category: thus, `c' for Chinese characters or
     `g' for Greek characters in the standard category table.

`\CC'
     matches any character whose category is not C.

   The following regular expression constructs match the empty
string--that is, they don't use up any characters--but whether they
match depends on the context.  For all, the beginning and end of the
accessible portion of the buffer are treated as if they were the actual
beginning and end of the buffer.

`\`'
     matches the empty string, but only at the beginning of the buffer
     or string being matched against.

`\''
     matches the empty string, but only at the end of the buffer or
     string being matched against.

`\='
     matches the empty string, but only at point.  (This construct is
     not defined when matching against a string.)

`\b'
     matches the empty string, but only at the beginning or end of a
     word.  Thus, `\bfoo\b' matches any occurrence of `foo' as a
     separate word.  `\bballs?\b' matches `ball' or `balls' as a
     separate word.

     `\b' matches at the beginning or end of the buffer (or string)
     regardless of what text appears next to it.

`\B'
     matches the empty string, but _not_ at the beginning or end of a
     word, nor at the beginning or end of the buffer (or string).

`\<'
     matches the empty string, but only at the beginning of a word.
     `\<' matches at the beginning of the buffer (or string) only if a
     word-constituent character follows.

`\>'
     matches the empty string, but only at the end of a word.  `\>'
     matches at the end of the buffer (or string) only if the contents
     end with a word-constituent character.

`\_<'
     matches the empty string, but only at the beginning of a symbol.  A
     symbol is a sequence of one or more word or symbol constituent
     characters.  `\_<' matches at the beginning of the buffer (or
     string) only if a symbol-constituent character follows.

`\_>'
     matches the empty string, but only at the end of a symbol.  `\_>'
     matches at the end of the buffer (or string) only if the contents
     end with a symbol-constituent character.

   Not every string is a valid regular expression.  For example, a
string that ends inside a character alternative without terminating `]'
is invalid, and so is a string that ends with a single `\'.  If an
invalid regular expression is passed to any of the search functions, an
`invalid-regexp' error is signaled.


File: elisp,  Node: Regexp Example,  Next: Regexp Functions,  Prev: Syntax of Regexps,  Up: Regular Expressions

34.3.2 Complex Regexp Example
-----------------------------

Here is a complicated regexp which was formerly used by Emacs to
recognize the end of a sentence together with any whitespace that
follows.  (Nowadays Emacs uses a similar but more complex default
regexp constructed by the function `sentence-end'.  *Note Standard
Regexps::.)

   First, we show the regexp as a string in Lisp syntax to distinguish
spaces from tab characters.  The string constant begins and ends with a
double-quote.  `\"' stands for a double-quote as part of the string,
`\\' for a backslash as part of the string, `\t' for a tab and `\n' for
a newline.

     "[.?!][]\"')}]*\\($\\| $\\|\t\\|  \\)[ \t\n]*"

In contrast, if you evaluate this string, you will see the following:

     "[.?!][]\"')}]*\\($\\| $\\|\t\\|  \\)[ \t\n]*"
          => "[.?!][]\"')}]*\\($\\| $\\|  \\|  \\)[
     ]*"

In this output, tab and newline appear as themselves.

   This regular expression contains four parts in succession and can be
deciphered as follows:

`[.?!]'
     The first part of the pattern is a character alternative that
     matches any one of three characters: period, question mark, and
     exclamation mark.  The match must begin with one of these three
     characters.  (This is one point where the new default regexp used
     by Emacs differs from the old.  The new value also allows some
     non-ASCII characters that end a sentence without any following
     whitespace.)

`[]\"')}]*'
     The second part of the pattern matches any closing braces and
     quotation marks, zero or more of them, that may follow the period,
     question mark or exclamation mark.  The `\"' is Lisp syntax for a
     double-quote in a string.  The `*' at the end indicates that the
     immediately preceding regular expression (a character alternative,
     in this case) may be repeated zero or more times.

`\\($\\| $\\|\t\\|  \\)'
     The third part of the pattern matches the whitespace that follows
     the end of a sentence: the end of a line (optionally with a
     space), or a tab, or two spaces.  The double backslashes mark the
     parentheses and vertical bars as regular expression syntax; the
     parentheses delimit a group and the vertical bars separate
     alternatives.  The dollar sign is used to match the end of a line.

`[ \t\n]*'
     Finally, the last part of the pattern matches any additional
     whitespace beyond the minimum needed to end a sentence.


File: elisp,  Node: Regexp Functions,  Prev: Regexp Example,  Up: Regular Expressions

34.3.3 Regular Expression Functions
-----------------------------------

These functions operate on regular expressions.

 -- Function: regexp-quote string
     This function returns a regular expression whose only exact match
     is STRING.  Using this regular expression in `looking-at' will
     succeed only if the next characters in the buffer are STRING;
     using it in a search function will succeed if the text being
     searched contains STRING.

     This allows you to request an exact string match or search when
     calling a function that wants a regular expression.

          (regexp-quote "^The cat$")
               => "\\^The cat\\$"

     One use of `regexp-quote' is to combine an exact string match with
     context described as a regular expression.  For example, this
     searches for the string that is the value of STRING, surrounded by
     whitespace:

          (re-search-forward
           (concat "\\s-" (regexp-quote string) "\\s-"))

 -- Function: regexp-opt strings &optional paren
     This function returns an efficient regular expression that will
     match any of the strings in the list STRINGS.  This is useful when
     you need to make matching or searching as fast as possible--for
     example, for Font Lock mode.

     If the optional argument PAREN is non-`nil', then the returned
     regular expression is always enclosed by at least one
     parentheses-grouping construct.  If PAREN is `words', then that
     construct is additionally surrounded by `\<' and `\>'.

     This simplified definition of `regexp-opt' produces a regular
     expression which is equivalent to the actual value (but not as
     efficient):

          (defun regexp-opt (strings paren)
            (let ((open-paren (if paren "\\(" ""))
                  (close-paren (if paren "\\)" "")))
              (concat open-paren
                      (mapconcat 'regexp-quote strings "\\|")
                      close-paren)))

 -- Function: regexp-opt-depth regexp
     This function returns the total number of grouping constructs
     (parenthesized expressions) in REGEXP.  (This does not include shy
     groups.)


File: elisp,  Node: Regexp Search,  Next: POSIX Regexps,  Prev: Regular Expressions,  Up: Searching and Matching

34.4 Regular Expression Searching
=================================

In GNU Emacs, you can search for the next match for a regular
expression either incrementally or not.  For incremental search
commands, see *Note Regular Expression Search: (emacs)Regexp Search.
Here we describe only the search functions useful in programs.  The
principal one is `re-search-forward'.

   These search functions convert the regular expression to multibyte if
the buffer is multibyte; they convert the regular expression to unibyte
if the buffer is unibyte.  *Note Text Representations::.

 -- Command: re-search-forward regexp &optional limit noerror repeat
     This function searches forward in the current buffer for a string
     of text that is matched by the regular expression REGEXP.  The
     function skips over any amount of text that is not matched by
     REGEXP, and leaves point at the end of the first match found.  It
     returns the new value of point.

     If LIMIT is non-`nil', it must be a position in the current
     buffer.  It specifies the upper bound to the search.  No match
     extending after that position is accepted.

     If REPEAT is supplied, it must be a positive number; the search is
     repeated that many times; each repetition starts at the end of the
     previous match.  If all these successive searches succeed, the
     search succeeds, moving point and returning its new value.
     Otherwise the search fails.  What `re-search-forward' does when
     the search fails depends on the value of NOERROR:

    `nil'
          Signal a `search-failed' error.

    `t'
          Do nothing and return `nil'.

    anything else
          Move point to LIMIT (or the end of the accessible portion of
          the buffer) and return `nil'.

     In the following example, point is initially before the `T'.
     Evaluating the search call moves point to the end of that line
     (between the `t' of `hat' and the newline).

          ---------- Buffer: foo ----------
          I read "-!-The cat in the hat
          comes back" twice.
          ---------- Buffer: foo ----------

          (re-search-forward "[a-z]+" nil t 5)
               => 27

          ---------- Buffer: foo ----------
          I read "The cat in the hat-!-
          comes back" twice.
          ---------- Buffer: foo ----------

 -- Command: re-search-backward regexp &optional limit noerror repeat
     This function searches backward in the current buffer for a string
     of text that is matched by the regular expression REGEXP, leaving
     point at the beginning of the first text found.

     This function is analogous to `re-search-forward', but they are not
     simple mirror images.  `re-search-forward' finds the match whose
     beginning is as close as possible to the starting point.  If
     `re-search-backward' were a perfect mirror image, it would find the
     match whose end is as close as possible.  However, in fact it
     finds the match whose beginning is as close as possible (and yet
     ends before the starting point).  The reason for this is that
     matching a regular expression at a given spot always works from
     beginning to end, and starts at a specified beginning position.

     A true mirror-image of `re-search-forward' would require a special
     feature for matching regular expressions from end to beginning.
     It's not worth the trouble of implementing that.

 -- Function: string-match regexp string &optional start
     This function returns the index of the start of the first match for
     the regular expression REGEXP in STRING, or `nil' if there is no
     match.  If START is non-`nil', the search starts at that index in
     STRING.

     For example,

          (string-match
           "quick" "The quick brown fox jumped quickly.")
               => 4
          (string-match
           "quick" "The quick brown fox jumped quickly." 8)
               => 27

     The index of the first character of the string is 0, the index of
     the second character is 1, and so on.

     After this function returns, the index of the first character
     beyond the match is available as `(match-end 0)'.  *Note Match
     Data::.

          (string-match
           "quick" "The quick brown fox jumped quickly." 8)
               => 27

          (match-end 0)
               => 32

 -- Function: looking-at regexp
     This function determines whether the text in the current buffer
     directly following point matches the regular expression REGEXP.
     "Directly following" means precisely that: the search is
     "anchored" and it can succeed only starting with the first
     character following point.  The result is `t' if so, `nil'
     otherwise.

     This function does not move point, but it updates the match data,
     which you can access using `match-beginning' and `match-end'.
     *Note Match Data::.

     In this example, point is located directly before the `T'.  If it
     were anywhere else, the result would be `nil'.

          ---------- Buffer: foo ----------
          I read "-!-The cat in the hat
          comes back" twice.
          ---------- Buffer: foo ----------

          (looking-at "The cat in the hat$")
               => t

 -- Function: looking-back regexp &optional limit
     This function returns `t' if REGEXP matches text before point,
     ending at point, and `nil' otherwise.

     Because regular expression matching works only going forward, this
     is implemented by searching backwards from point for a match that
     ends at point.  That can be quite slow if it has to search a long
     distance.  You can bound the time required by specifying LIMIT,
     which says not to search before LIMIT.  In this case, the match
     that is found must begin at or after LIMIT.

          ---------- Buffer: foo ----------
          I read "-!-The cat in the hat
          comes back" twice.
          ---------- Buffer: foo ----------

          (looking-back "read \"" 3)
               => t
          (looking-back "read \"" 4)
               => nil

 -- Variable: search-spaces-regexp
     If this variable is non-`nil', it should be a regular expression
     that says how to search for whitespace.  In that case, any group of
     spaces in a regular expression being searched for stands for use of
     this regular expression.  However, spaces inside of constructs
     such as `[...]' and `*', `+', `?' are not affected by
     `search-spaces-regexp'.

     Since this variable affects all regular expression search and match
     constructs, you should bind it temporarily for as small as possible
     a part of the code.


File: elisp,  Node: POSIX Regexps,  Next: Match Data,  Prev: Regexp Search,  Up: Searching and Matching

34.5 POSIX Regular Expression Searching
=======================================

The usual regular expression functions do backtracking when necessary
to handle the `\|' and repetition constructs, but they continue this
only until they find _some_ match.  Then they succeed and report the
first match found.

   This section describes alternative search functions which perform the
full backtracking specified by the POSIX standard for regular expression
matching.  They continue backtracking until they have tried all
possibilities and found all matches, so they can report the longest
match, as required by POSIX.  This is much slower, so use these
functions only when you really need the longest match.

   The POSIX search and match functions do not properly support the
non-greedy repetition operators.  This is because POSIX backtracking
conflicts with the semantics of non-greedy repetition.

 -- Function: posix-search-forward regexp &optional limit noerror repeat
     This is like `re-search-forward' except that it performs the full
     backtracking specified by the POSIX standard for regular expression
     matching.

 -- Function: posix-search-backward regexp &optional limit noerror
          repeat
     This is like `re-search-backward' except that it performs the full
     backtracking specified by the POSIX standard for regular expression
     matching.

 -- Function: posix-looking-at regexp
     This is like `looking-at' except that it performs the full
     backtracking specified by the POSIX standard for regular expression
     matching.

 -- Function: posix-string-match regexp string &optional start
     This is like `string-match' except that it performs the full
     backtracking specified by the POSIX standard for regular expression
     matching.


File: elisp,  Node: Match Data,  Next: Search and Replace,  Prev: POSIX Regexps,  Up: Searching and Matching

34.6 The Match Data
===================

Emacs keeps track of the start and end positions of the segments of
text found during a search; this is called the "match data".  Thanks to
the match data, you can search for a complex pattern, such as a date in
a mail message, and then extract parts of the match under control of
the pattern.

   Because the match data normally describe the most recent search only,
you must be careful not to do another search inadvertently between the
search you wish to refer back to and the use of the match data.  If you
can't avoid another intervening search, you must save and restore the
match data around it, to prevent it from being overwritten.

* Menu:

* Replacing Match::	  Replacing a substring that was matched.
* Simple Match Data::     Accessing single items of match data,
			    such as where a particular subexpression started.
* Entire Match Data::     Accessing the entire match data at once, as a list.
* Saving Match Data::     Saving and restoring the match data.


File: elisp,  Node: Replacing Match,  Next: Simple Match Data,  Up: Match Data

34.6.1 Replacing the Text that Matched
--------------------------------------

This function replaces all or part of the text matched by the last
search.  It works by means of the match data.

 -- Function: replace-match replacement &optional fixedcase literal
          string subexp
     This function replaces the text in the buffer (or in STRING) that
     was matched by the last search.  It replaces that text with
     REPLACEMENT.

     If you did the last search in a buffer, you should specify `nil'
     for STRING and make sure that the current buffer when you call
     `replace-match' is the one in which you did the searching or
     matching.  Then `replace-match' does the replacement by editing
     the buffer; it leaves point at the end of the replacement text, and
     returns `t'.

     If you did the search in a string, pass the same string as STRING.
     Then `replace-match' does the replacement by constructing and
     returning a new string.

     If FIXEDCASE is non-`nil', then `replace-match' uses the
     replacement text without case conversion; otherwise, it converts
     the replacement text depending upon the capitalization of the text
     to be replaced.  If the original text is all upper case, this
     converts the replacement text to upper case.  If all words of the
     original text are capitalized, this capitalizes all the words of
     the replacement text.  If all the words are one-letter and they
     are all upper case, they are treated as capitalized words rather
     than all-upper-case words.

     If LITERAL is non-`nil', then REPLACEMENT is inserted exactly as
     it is, the only alterations being case changes as needed.  If it
     is `nil' (the default), then the character `\' is treated
     specially.  If a `\' appears in REPLACEMENT, then it must be part
     of one of the following sequences:

    `\&'
          `\&' stands for the entire text being replaced.

    `\N'
          `\N', where N is a digit, stands for the text that matched
          the Nth subexpression in the original regexp.  Subexpressions
          are those expressions grouped inside `\(...\)'.  If the Nth
          subexpression never matched, an empty string is substituted.

    `\\'
          `\\' stands for a single `\' in the replacement text.

     These substitutions occur after case conversion, if any, so the
     strings they substitute are never case-converted.

     If SUBEXP is non-`nil', that says to replace just subexpression
     number SUBEXP of the regexp that was matched, not the entire
     match.  For example, after matching `foo \(ba*r\)', calling
     `replace-match' with 1 as SUBEXP means to replace just the text
     that matched `\(ba*r\)'.


File: elisp,  Node: Simple Match Data,  Next: Entire Match Data,  Prev: Replacing Match,  Up: Match Data

34.6.2 Simple Match Data Access
-------------------------------

This section explains how to use the match data to find out what was
matched by the last search or match operation, if it succeeded.

   You can ask about the entire matching text, or about a particular
parenthetical subexpression of a regular expression.  The COUNT
argument in the functions below specifies which.  If COUNT is zero, you
are asking about the entire match.  If COUNT is positive, it specifies
which subexpression you want.

   Recall that the subexpressions of a regular expression are those
expressions grouped with escaped parentheses, `\(...\)'.  The COUNTth
subexpression is found by counting occurrences of `\(' from the
beginning of the whole regular expression.  The first subexpression is
numbered 1, the second 2, and so on.  Only regular expressions can have
subexpressions--after a simple string search, the only information
available is about the entire match.

   Every successful search sets the match data.  Therefore, you should
query the match data immediately after searching, before calling any
other function that might perform another search.  Alternatively, you
may save and restore the match data (*note Saving Match Data::) around
the call to functions that could perform another search.

   A search which fails may or may not alter the match data.  In the
past, a failing search did not do this, but we may change it in the
future.  So don't try to rely on the value of the match data after a
failing search.

 -- Function: match-string count &optional in-string
     This function returns, as a string, the text matched in the last
     search or match operation.  It returns the entire text if COUNT is
     zero, or just the portion corresponding to the COUNTth
     parenthetical subexpression, if COUNT is positive.

     If the last such operation was done against a string with
     `string-match', then you should pass the same string as the
     argument IN-STRING.  After a buffer search or match, you should
     omit IN-STRING or pass `nil' for it; but you should make sure that
     the current buffer when you call `match-string' is the one in
     which you did the searching or matching.

     The value is `nil' if COUNT is out of range, or for a
     subexpression inside a `\|' alternative that wasn't used or a
     repetition that repeated zero times.

 -- Function: match-string-no-properties count &optional in-string
     This function is like `match-string' except that the result has no
     text properties.

 -- Function: match-beginning count
     This function returns the position of the start of text matched by
     the last regular expression searched for, or a subexpression of it.

     If COUNT is zero, then the value is the position of the start of
     the entire match.  Otherwise, COUNT specifies a subexpression in
     the regular expression, and the value of the function is the
     starting position of the match for that subexpression.

     The value is `nil' for a subexpression inside a `\|' alternative
     that wasn't used or a repetition that repeated zero times.

 -- Function: match-end count
     This function is like `match-beginning' except that it returns the
     position of the end of the match, rather than the position of the
     beginning.

   Here is an example of using the match data, with a comment showing
the positions within the text:

     (string-match "\\(qu\\)\\(ick\\)"
                   "The quick fox jumped quickly.")
                   ;0123456789
          => 4

     (match-string 0 "The quick fox jumped quickly.")
          => "quick"
     (match-string 1 "The quick fox jumped quickly.")
          => "qu"
     (match-string 2 "The quick fox jumped quickly.")
          => "ick"

     (match-beginning 1)       ; The beginning of the match
          => 4                 ;   with `qu' is at index 4.

     (match-beginning 2)       ; The beginning of the match
          => 6                 ;   with `ick' is at index 6.

     (match-end 1)             ; The end of the match
          => 6                 ;   with `qu' is at index 6.

     (match-end 2)             ; The end of the match
          => 9                 ;   with `ick' is at index 9.

   Here is another example.  Point is initially located at the beginning
of the line.  Searching moves point to between the space and the word
`in'.  The beginning of the entire match is at the 9th character of the
buffer (`T'), and the beginning of the match for the first
subexpression is at the 13th character (`c').

     (list
       (re-search-forward "The \\(cat \\)")
       (match-beginning 0)
       (match-beginning 1))
         => (9 9 13)

     ---------- Buffer: foo ----------
     I read "The cat -!-in the hat comes back" twice.
             ^   ^
             9  13
     ---------- Buffer: foo ----------

(In this case, the index returned is a buffer position; the first
character of the buffer counts as 1.)


File: elisp,  Node: Entire Match Data,  Next: Saving Match Data,  Prev: Simple Match Data,  Up: Match Data

34.6.3 Accessing the Entire Match Data
--------------------------------------

The functions `match-data' and `set-match-data' read or write the
entire match data, all at once.

 -- Function: match-data &optional integers reuse reseat
     This function returns a list of positions (markers or integers)
     that record all the information on what text the last search
     matched.  Element zero is the position of the beginning of the
     match for the whole expression; element one is the position of the
     end of the match for the expression.  The next two elements are
     the positions of the beginning and end of the match for the first
     subexpression, and so on.  In general, element number 2N
     corresponds to `(match-beginning N)'; and element number 2N + 1
     corresponds to `(match-end N)'.

     Normally all the elements are markers or `nil', but if INTEGERS is
     non-`nil', that means to use integers instead of markers.  (In
     that case, the buffer itself is appended as an additional element
     at the end of the list, to facilitate complete restoration of the
     match data.)  If the last match was done on a string with
     `string-match', then integers are always used, since markers can't
     point into a string.

     If REUSE is non-`nil', it should be a list.  In that case,
     `match-data' stores the match data in REUSE.  That is, REUSE is
     destructively modified.  REUSE does not need to have the right
     length.  If it is not long enough to contain the match data, it is
     extended.  If it is too long, the length of REUSE stays the same,
     but the elements that were not used are set to `nil'.  The purpose
     of this feature is to reduce the need for garbage collection.

     If RESEAT is non-`nil', all markers on the REUSE list are reseated
     to point to nowhere.

     As always, there must be no possibility of intervening searches
     between the call to a search function and the call to `match-data'
     that is intended to access the match data for that search.

          (match-data)
               =>  (#<marker at 9 in foo>
                    #<marker at 17 in foo>
                    #<marker at 13 in foo>
                    #<marker at 17 in foo>)

 -- Function: set-match-data match-list &optional reseat
     This function sets the match data from the elements of MATCH-LIST,
     which should be a list that was the value of a previous call to
     `match-data'.  (More precisely, anything that has the same format
     will work.)

     If MATCH-LIST refers to a buffer that doesn't exist, you don't get
     an error; that sets the match data in a meaningless but harmless
     way.

     If RESEAT is non-`nil', all markers on the MATCH-LIST list are
     reseated to point to nowhere.

     `store-match-data' is a semi-obsolete alias for `set-match-data'.


File: elisp,  Node: Saving Match Data,  Prev: Entire Match Data,  Up: Match Data

34.6.4 Saving and Restoring the Match Data
------------------------------------------

When you call a function that may do a search, you may need to save and
restore the match data around that call, if you want to preserve the
match data from an earlier search for later use.  Here is an example
that shows the problem that arises if you fail to save the match data:

     (re-search-forward "The \\(cat \\)")
          => 48
     (foo)                   ; Perhaps `foo' does
                             ;   more searching.
     (match-end 0)
          => 61              ; Unexpected result--not 48!

   You can save and restore the match data with `save-match-data':

 -- Macro: save-match-data body...
     This macro executes BODY, saving and restoring the match data
     around it.  The return value is the value of the last form in BODY.

   You could use `set-match-data' together with `match-data' to imitate
the effect of the special form `save-match-data'.  Here is how:

     (let ((data (match-data)))
       (unwind-protect
           ...   ; Ok to change the original match data.
         (set-match-data data)))

   Emacs automatically saves and restores the match data when it runs
process filter functions (*note Filter Functions::) and process
sentinels (*note Sentinels::).


File: elisp,  Node: Search and Replace,  Next: Standard Regexps,  Prev: Match Data,  Up: Searching and Matching

34.7 Search and Replace
=======================

If you want to find all matches for a regexp in part of the buffer, and
replace them, the best way is to write an explicit loop using
`re-search-forward' and `replace-match', like this:

     (while (re-search-forward "foo[ \t]+bar" nil t)
       (replace-match "foobar"))

*Note Replacing the Text that Matched: Replacing Match, for a
description of `replace-match'.

   However, replacing matches in a string is more complex, especially
if you want to do it efficiently.  So Emacs provides a function to do
this.

 -- Function: replace-regexp-in-string regexp rep string &optional
          fixedcase literal subexp start
     This function copies STRING and searches it for matches for
     REGEXP, and replaces them with REP.  It returns the modified copy.
     If START is non-`nil', the search for matches starts at that
     index in STRING, so matches starting before that index are not
     changed.

     This function uses `replace-match' to do the replacement, and it
     passes the optional arguments FIXEDCASE, LITERAL and SUBEXP along
     to `replace-match'.

     Instead of a string, REP can be a function.  In that case,
     `replace-regexp-in-string' calls REP for each match, passing the
     text of the match as its sole argument.  It collects the value REP
     returns and passes that to `replace-match' as the replacement
     string.  The match-data at this point are the result of matching
     REGEXP against a substring of STRING.

   If you want to write a command along the lines of `query-replace',
you can use `perform-replace' to do the work.

 -- Function: perform-replace from-string replacements query-flag
          regexp-flag delimited-flag &optional repeat-count map start
          end
     This function is the guts of `query-replace' and related commands.
     It searches for occurrences of FROM-STRING in the text between
     positions START and END and replaces some or all of them.  If
     START is `nil' (or omitted), point is used instead, and the end of
     the buffer's accessible portion is used for END.

     If QUERY-FLAG is `nil', it replaces all occurrences; otherwise, it
     asks the user what to do about each one.

     If REGEXP-FLAG is non-`nil', then FROM-STRING is considered a
     regular expression; otherwise, it must match literally.  If
     DELIMITED-FLAG is non-`nil', then only replacements surrounded by
     word boundaries are considered.

     The argument REPLACEMENTS specifies what to replace occurrences
     with.  If it is a string, that string is used.  It can also be a
     list of strings, to be used in cyclic order.

     If REPLACEMENTS is a cons cell, `(FUNCTION . DATA)', this means to
     call FUNCTION after each match to get the replacement text.  This
     function is called with two arguments: DATA, and the number of
     replacements already made.

     If REPEAT-COUNT is non-`nil', it should be an integer.  Then it
     specifies how many times to use each of the strings in the
     REPLACEMENTS list before advancing cyclically to the next one.

     If FROM-STRING contains upper-case letters, then `perform-replace'
     binds `case-fold-search' to `nil', and it uses the `replacements'
     without altering the case of them.

     Normally, the keymap `query-replace-map' defines the possible user
     responses for queries.  The argument MAP, if non-`nil', specifies
     a keymap to use instead of `query-replace-map'.

 -- Variable: query-replace-map
     This variable holds a special keymap that defines the valid user
     responses for `perform-replace' and the commands that use it, as
     well as `y-or-n-p' and `map-y-or-n-p'.  This map is unusual in two
     ways:

        * The "key bindings" are not commands, just symbols that are
          meaningful to the functions that use this map.

        * Prefix keys are not supported; each key binding must be for a
          single-event key sequence.  This is because the functions
          don't use `read-key-sequence' to get the input; instead, they
          read a single event and look it up "by hand."

   Here are the meaningful "bindings" for `query-replace-map'.  Several
of them are meaningful only for `query-replace' and friends.

`act'
     Do take the action being considered--in other words, "yes."

`skip'
     Do not take action for this question--in other words, "no."

`exit'
     Answer this question "no," and give up on the entire series of
     questions, assuming that the answers will be "no."

`act-and-exit'
     Answer this question "yes," and give up on the entire series of
     questions, assuming that subsequent answers will be "no."

`act-and-show'
     Answer this question "yes," but show the results--don't advance yet
     to the next question.

`automatic'
     Answer this question and all subsequent questions in the series
     with "yes," without further user interaction.

`backup'
     Move back to the previous place that a question was asked about.

`edit'
     Enter a recursive edit to deal with this question--instead of any
     other action that would normally be taken.

`delete-and-edit'
     Delete the text being considered, then enter a recursive edit to
     replace it.

`recenter'
     Redisplay and center the window, then ask the same question again.

`quit'
     Perform a quit right away.  Only `y-or-n-p' and related functions
     use this answer.

`help'
     Display some help, then ask again.


File: elisp,  Node: Standard Regexps,  Prev: Search and Replace,  Up: Searching and Matching

34.8 Standard Regular Expressions Used in Editing
=================================================

This section describes some variables that hold regular expressions
used for certain purposes in editing:

 -- Variable: page-delimiter
     This is the regular expression describing line-beginnings that
     separate pages.  The default value is `"^\014"' (i.e., `"^^L"' or
     `"^\C-l"'); this matches a line that starts with a formfeed
     character.

   The following two regular expressions should _not_ assume the match
always starts at the beginning of a line; they should not use `^' to
anchor the match.  Most often, the paragraph commands do check for a
match only at the beginning of a line, which means that `^' would be
superfluous.  When there is a nonzero left margin, they accept matches
that start after the left margin.  In that case, a `^' would be
incorrect.  However, a `^' is harmless in modes where a left margin is
never used.

 -- Variable: paragraph-separate
     This is the regular expression for recognizing the beginning of a
     line that separates paragraphs.  (If you change this, you may have
     to change `paragraph-start' also.)  The default value is
     `"[ \t\f]*$"', which matches a line that consists entirely of
     spaces, tabs, and form feeds (after its left margin).

 -- Variable: paragraph-start
     This is the regular expression for recognizing the beginning of a
     line that starts _or_ separates paragraphs.  The default value is
     `"\f\\|[ \t]*$"', which matches a line containing only whitespace
     or starting with a form feed (after its left margin).

 -- Variable: sentence-end
     If non-`nil', the value should be a regular expression describing
     the end of a sentence, including the whitespace following the
     sentence.  (All paragraph boundaries also end sentences,
     regardless.)

     If the value is `nil', the default, then the function
     `sentence-end' has to construct the regexp.  That is why you
     should always call the function `sentence-end' to obtain the
     regexp to be used to recognize the end of a sentence.

 -- Function: sentence-end
     This function returns the value of the variable `sentence-end', if
     non-`nil'.  Otherwise it returns a default value based on the
     values of the variables `sentence-end-double-space' (*note
     Definition of sentence-end-double-space::),
     `sentence-end-without-period' and `sentence-end-without-space'.


File: elisp,  Node: Syntax Tables,  Next: Abbrevs,  Prev: Searching and Matching,  Up: Top

35 Syntax Tables
****************

A "syntax table" specifies the syntactic textual function of each
character.  This information is used by the "parsing functions", the
complex movement commands, and others to determine where words, symbols,
and other syntactic constructs begin and end.  The current syntax table
controls the meaning of the word motion functions (*note Word Motion::)
and the list motion functions (*note List Motion::), as well as the
functions in this chapter.

* Menu:

* Basics: Syntax Basics.     Basic concepts of syntax tables.
* Desc: Syntax Descriptors.  How characters are classified.
* Syntax Table Functions::   How to create, examine and alter syntax tables.
* Syntax Properties::        Overriding syntax with text properties.
* Motion and Syntax::	     Moving over characters with certain syntaxes.
* Parsing Expressions::      Parsing balanced expressions
                                using the syntax table.
* Standard Syntax Tables::   Syntax tables used by various major modes.
* Syntax Table Internals::   How syntax table information is stored.
* Categories::               Another way of classifying character syntax.


File: elisp,  Node: Syntax Basics,  Next: Syntax Descriptors,  Up: Syntax Tables

35.1 Syntax Table Concepts
==========================

A "syntax table" provides Emacs with the information that determines
the syntactic use of each character in a buffer.  This information is
used by the parsing commands, the complex movement commands, and others
to determine where words, symbols, and other syntactic constructs begin
and end.  The current syntax table controls the meaning of the word
motion functions (*note Word Motion::) and the list motion functions
(*note List Motion::) as well as the functions in this chapter.

A syntax table is a char-table (*note Char-Tables::).  The element at
index C describes the character with code C.  The element's value
should be a list that encodes the syntax of the character in question.

   Syntax tables are used only for moving across text, not for the Emacs
Lisp reader.  Emacs Lisp uses built-in syntactic rules when reading Lisp
expressions, and these rules cannot be changed.  (Some Lisp systems
provide ways to redefine the read syntax, but we decided to leave this
feature out of Emacs Lisp for simplicity.)

   Each buffer has its own major mode, and each major mode has its own
idea of the syntactic class of various characters.  For example, in Lisp
mode, the character `;' begins a comment, but in C mode, it terminates
a statement.  To support these variations, Emacs makes the choice of
syntax table local to each buffer.  Typically, each major mode has its
own syntax table and installs that table in each buffer that uses that
mode.  Changing this table alters the syntax in all those buffers as
well as in any buffers subsequently put in that mode.  Occasionally
several similar modes share one syntax table.  *Note Example Major
Modes::, for an example of how to set up a syntax table.

   A syntax table can inherit the data for some characters from the
standard syntax table, while specifying other characters itself.  The
"inherit" syntax class means "inherit this character's syntax from the
standard syntax table."  Just changing the standard syntax for a
character affects all syntax tables that inherit from it.

 -- Function: syntax-table-p object
     This function returns `t' if OBJECT is a syntax table.


File: elisp,  Node: Syntax Descriptors,  Next: Syntax Table Functions,  Prev: Syntax Basics,  Up: Syntax Tables

35.2 Syntax Descriptors
=======================

This section describes the syntax classes and flags that denote the
syntax of a character, and how they are represented as a "syntax
descriptor", which is a Lisp string that you pass to
`modify-syntax-entry' to specify the syntax you want.

   The syntax table specifies a syntax class for each character.  There
is no necessary relationship between the class of a character in one
syntax table and its class in any other table.

   Each class is designated by a mnemonic character, which serves as the
name of the class when you need to specify a class.  Usually the
designator character is one that is often assigned that class; however,
its meaning as a designator is unvarying and independent of what syntax
that character currently has.  Thus, `\' as a designator character
always gives "escape character" syntax, regardless of what syntax `\'
currently has.

   A syntax descriptor is a Lisp string that specifies a syntax class, a
matching character (used only for the parenthesis classes) and flags.
The first character is the designator for a syntax class.  The second
character is the character to match; if it is unused, put a space there.
Then come the characters for any desired flags.  If no matching
character or flags are needed, one character is sufficient.

   For example, the syntax descriptor for the character `*' in C mode
is `. 23' (i.e., punctuation, matching character slot unused, second
character of a comment-starter, first character of a comment-ender),
and the entry for `/' is `. 14' (i.e., punctuation, matching character
slot unused, first character of a comment-starter, second character of
a comment-ender).

* Menu:

* Syntax Class Table::      Table of syntax classes.
* Syntax Flags::            Additional flags each character can have.


File: elisp,  Node: Syntax Class Table,  Next: Syntax Flags,  Up: Syntax Descriptors

35.2.1 Table of Syntax Classes
------------------------------

Here is a table of syntax classes, the characters that stand for them,
their meanings, and examples of their use.

 -- Syntax class: whitespace character
     "Whitespace characters" (designated by ` ' or `-') separate
     symbols and words from each other.  Typically, whitespace
     characters have no other syntactic significance, and multiple
     whitespace characters are syntactically equivalent to a single
     one.  Space, tab, newline and formfeed are classified as
     whitespace in almost all major modes.

 -- Syntax class: word constituent
     "Word constituents" (designated by `w') are parts of words in
     human languages, and are typically used in variable and command
     names in programs.  All upper- and lower-case letters, and the
     digits, are typically word constituents.

 -- Syntax class: symbol constituent
     "Symbol constituents" (designated by `_') are the extra characters
     that are used in variable and command names along with word
     constituents.  For example, the symbol constituents class is used
     in Lisp mode to indicate that certain characters may be part of
     symbol names even though they are not part of English words.
     These characters are `$&*+-_<>'.  In standard C, the only
     non-word-constituent character that is valid in symbols is
     underscore (`_').

 -- Syntax class: punctuation character
     "Punctuation characters" (designated by `.') are those characters
     that are used as punctuation in English, or are used in some way
     in a programming language to separate symbols from one another.
     Some programming language modes, such as Emacs Lisp mode, have no
     characters in this class since the few characters that are not
     symbol or word constituents all have other uses.  Other
     programming language modes, such as C mode, use punctuation syntax
     for operators.

 -- Syntax class: open parenthesis character
 -- Syntax class: close parenthesis character
     Open and close "parenthesis characters" are characters used in
     dissimilar pairs to surround sentences or expressions.  Such a
     grouping is begun with an open parenthesis character and
     terminated with a close.  Each open parenthesis character matches
     a particular close parenthesis character, and vice versa.
     Normally, Emacs indicates momentarily the matching open
     parenthesis when you insert a close parenthesis.  *Note Blinking::.

     The class of open parentheses is designated by `(', and that of
     close parentheses by `)'.

     In English text, and in C code, the parenthesis pairs are `()',
     `[]', and `{}'.  In Emacs Lisp, the delimiters for lists and
     vectors (`()' and `[]') are classified as parenthesis characters.

 -- Syntax class: string quote
     "String quote characters" (designated by `"') are used in many
     languages, including Lisp and C, to delimit string constants.  The
     same string quote character appears at the beginning and the end
     of a string.  Such quoted strings do not nest.

     The parsing facilities of Emacs consider a string as a single
     token.  The usual syntactic meanings of the characters in the
     string are suppressed.

     The Lisp modes have two string quote characters: double-quote (`"')
     and vertical bar (`|').  `|' is not used in Emacs Lisp, but it is
     used in Common Lisp.  C also has two string quote characters:
     double-quote for strings, and single-quote (`'') for character
     constants.

     English text has no string quote characters because English is not
     a programming language.  Although quotation marks are used in
     English, we do not want them to turn off the usual syntactic
     properties of other characters in the quotation.

 -- Syntax class: escape-syntax character
     An "escape character" (designated by `\') starts an escape
     sequence such as is used in C string and character constants.  The
     character `\' belongs to this class in both C and Lisp.  (In C, it
     is used thus only inside strings, but it turns out to cause no
     trouble to treat it this way throughout C code.)

     Characters in this class count as part of words if
     `words-include-escapes' is non-`nil'.  *Note Word Motion::.

 -- Syntax class: character quote
     A "character quote character" (designated by `/') quotes the
     following character so that it loses its normal syntactic meaning.
     This differs from an escape character in that only the character
     immediately following is ever affected.

     Characters in this class count as part of words if
     `words-include-escapes' is non-`nil'.  *Note Word Motion::.

     This class is used for backslash in TeX mode.

 -- Syntax class: paired delimiter
     "Paired delimiter characters" (designated by `$') are like string
     quote characters except that the syntactic properties of the
     characters between the delimiters are not suppressed.  Only TeX
     mode uses a paired delimiter presently--the `$' that both enters
     and leaves math mode.

 -- Syntax class: expression prefix
     An "expression prefix operator" (designated by `'') is used for
     syntactic operators that are considered as part of an expression
     if they appear next to one.  In Lisp modes, these characters
     include the apostrophe, `'' (used for quoting), the comma, `,'
     (used in macros), and `#' (used in the read syntax for certain
     data types).

 -- Syntax class: comment starter
 -- Syntax class: comment ender
     The "comment starter" and "comment ender" characters are used in
     various languages to delimit comments.  These classes are
     designated by `<' and `>', respectively.

     English text has no comment characters.  In Lisp, the semicolon
     (`;') starts a comment and a newline or formfeed ends one.

 -- Syntax class: inherit standard syntax
     This syntax class does not specify a particular syntax.  It says
     to look in the standard syntax table to find the syntax of this
     character.  The designator for this syntax class is `@'.

 -- Syntax class: generic comment delimiter
     A "generic comment delimiter" (designated by `!') starts or ends a
     special kind of comment.  _Any_ generic comment delimiter matches
     _any_ generic comment delimiter, but they cannot match a comment
     starter or comment ender; generic comment delimiters can only
     match each other.

     This syntax class is primarily meant for use with the
     `syntax-table' text property (*note Syntax Properties::).  You can
     mark any range of characters as forming a comment, by giving the
     first and last characters of the range `syntax-table' properties
     identifying them as generic comment delimiters.

 -- Syntax class: generic string delimiter
     A "generic string delimiter" (designated by `|') starts or ends a
     string.  This class differs from the string quote class in that
     _any_ generic string delimiter can match any other generic string
     delimiter; but they do not match ordinary string quote characters.

     This syntax class is primarily meant for use with the
     `syntax-table' text property (*note Syntax Properties::).  You can
     mark any range of characters as forming a string constant, by
     giving the first and last characters of the range `syntax-table'
     properties identifying them as generic string delimiters.


File: elisp,  Node: Syntax Flags,  Prev: Syntax Class Table,  Up: Syntax Descriptors

35.2.2 Syntax Flags
-------------------

In addition to the classes, entries for characters in a syntax table
can specify flags.  There are seven possible flags, represented by the
characters `1', `2', `3', `4', `b', `n', and `p'.

   All the flags except `n' and `p' are used to describe
multi-character comment delimiters.  The digit flags indicate that a
character can _also_ be part of a comment sequence, in addition to the
syntactic properties associated with its character class.  The flags
are independent of the class and each other for the sake of characters
such as `*' in C mode, which is a punctuation character, _and_ the
second character of a start-of-comment sequence (`/*'), _and_ the first
character of an end-of-comment sequence (`*/').

   Here is a table of the possible flags for a character C, and what
they mean:

   * `1' means C is the start of a two-character comment-start sequence.

   * `2' means C is the second character of such a sequence.

   * `3' means C is the start of a two-character comment-end sequence.

   * `4' means C is the second character of such a sequence.

   * `b' means that C as a comment delimiter belongs to the alternative
     "b" comment style.

     Emacs supports two comment styles simultaneously in any one syntax
     table.  This is for the sake of C++.  Each style of comment syntax
     has its own comment-start sequence and its own comment-end
     sequence.  Each comment must stick to one style or the other;
     thus, if it starts with the comment-start sequence of style "b,"
     it must also end with the comment-end sequence of style "b."

     The two comment-start sequences must begin with the same
     character; only the second character may differ.  Mark the second
     character of the "b"-style comment-start sequence with the `b'
     flag.

     A comment-end sequence (one or two characters) applies to the "b"
     style if its first character has the `b' flag set; otherwise, it
     applies to the "a" style.

     The appropriate comment syntax settings for C++ are as follows:

    `/'
          `124b'

    `*'
          `23'

    newline
          `>b'

     This defines four comment-delimiting sequences:

    `/*'
          This is a comment-start sequence for "a" style because the
          second character, `*', does not have the `b' flag.

    `//'
          This is a comment-start sequence for "b" style because the
          second character, `/', does have the `b' flag.

    `*/'
          This is a comment-end sequence for "a" style because the first
          character, `*', does not have the `b' flag.

    newline
          This is a comment-end sequence for "b" style, because the
          newline character has the `b' flag.

   * `n' on a comment delimiter character specifies that this kind of
     comment can be nested.  For a two-character comment delimiter, `n'
     on either character makes it nestable.

   * `p' identifies an additional "prefix character" for Lisp syntax.
     These characters are treated as whitespace when they appear between
     expressions.  When they appear within an expression, they are
     handled according to their usual syntax classes.

     The function `backward-prefix-chars' moves back over these
     characters, as well as over characters whose primary syntax class
     is prefix (`'').  *Note Motion and Syntax::.


File: elisp,  Node: Syntax Table Functions,  Next: Syntax Properties,  Prev: Syntax Descriptors,  Up: Syntax Tables

35.3 Syntax Table Functions
===========================

In this section we describe functions for creating, accessing and
altering syntax tables.

 -- Function: make-syntax-table &optional table
     This function creates a new syntax table, with all values
     initialized to `nil'.  If TABLE is non-`nil', it becomes the
     parent of the new syntax table, otherwise the standard syntax
     table is the parent.  Like all char-tables, a syntax table
     inherits from its parent.  Thus the original syntax of all
     characters in the returned syntax table is determined by the
     parent.  *Note Char-Tables::.

     Most major mode syntax tables are created in this way.

 -- Function: copy-syntax-table &optional table
     This function constructs a copy of TABLE and returns it.  If TABLE
     is not supplied (or is `nil'), it returns a copy of the standard
     syntax table.  Otherwise, an error is signaled if TABLE is not a
     syntax table.

 -- Command: modify-syntax-entry char syntax-descriptor &optional table
     This function sets the syntax entry for CHAR according to
     SYNTAX-DESCRIPTOR.  The syntax is changed only for TABLE, which
     defaults to the current buffer's syntax table, and not in any
     other syntax table.  The argument SYNTAX-DESCRIPTOR specifies the
     desired syntax; this is a string beginning with a class designator
     character, and optionally containing a matching character and
     flags as well.  *Note Syntax Descriptors::.

     This function always returns `nil'.  The old syntax information in
     the table for this character is discarded.

     An error is signaled if the first character of the syntax
     descriptor is not one of the seventeen syntax class designator
     characters.  An error is also signaled if CHAR is not a character.

     Examples:

          ;; Put the space character in class whitespace.
          (modify-syntax-entry ?\s " ")
               => nil

          ;; Make `$' an open parenthesis character,
          ;;   with `^' as its matching close.
          (modify-syntax-entry ?$ "(^")
               => nil

          ;; Make `^' a close parenthesis character,
          ;;   with `$' as its matching open.
          (modify-syntax-entry ?^ ")$")
               => nil

          ;; Make `/' a punctuation character,
          ;;   the first character of a start-comment sequence,
          ;;   and the second character of an end-comment sequence.
          ;;   This is used in C mode.
          (modify-syntax-entry ?/ ". 14")
               => nil

 -- Function: char-syntax character
     This function returns the syntax class of CHARACTER, represented
     by its mnemonic designator character.  This returns _only_ the
     class, not any matching parenthesis or flags.

     An error is signaled if CHAR is not a character.

     The following examples apply to C mode.  The first example shows
     that the syntax class of space is whitespace (represented by a
     space).  The second example shows that the syntax of `/' is
     punctuation.  This does not show the fact that it is also part of
     comment-start and -end sequences.  The third example shows that
     open parenthesis is in the class of open parentheses.  This does
     not show the fact that it has a matching character, `)'.

          (string (char-syntax ?\s))
               => " "

          (string (char-syntax ?/))
               => "."

          (string (char-syntax ?\())
               => "("

     We use `string' to make it easier to see the character returned by
     `char-syntax'.

 -- Function: set-syntax-table table
     This function makes TABLE the syntax table for the current buffer.
     It returns TABLE.

 -- Function: syntax-table
     This function returns the current syntax table, which is the table
     for the current buffer.

 -- Macro: with-syntax-table TABLE BODY...
     This macro executes BODY using TABLE as the current syntax table.
     It returns the value of the last form in BODY, after restoring the
     old current syntax table.

     Since each buffer has its own current syntax table, we should make
     that more precise: `with-syntax-table' temporarily alters the
     current syntax table of whichever buffer is current at the time
     the macro execution starts.  Other buffers are not affected.


File: elisp,  Node: Syntax Properties,  Next: Motion and Syntax,  Prev: Syntax Table Functions,  Up: Syntax Tables

35.4 Syntax Properties
======================

When the syntax table is not flexible enough to specify the syntax of a
language, you can use `syntax-table' text properties to override the
syntax table for specific character occurrences in the buffer.  *Note
Text Properties::.  You can use Font Lock mode to set `syntax-table'
text properties.  *Note Setting Syntax Properties::.

   The valid values of `syntax-table' text property are:

SYNTAX-TABLE
     If the property value is a syntax table, that table is used
     instead of the current buffer's syntax table to determine the
     syntax for this occurrence of the character.

`(SYNTAX-CODE . MATCHING-CHAR)'
     A cons cell of this format specifies the syntax for this
     occurrence of the character.  (*note Syntax Table Internals::)

`nil'
     If the property is `nil', the character's syntax is determined from
     the current syntax table in the usual way.

 -- Variable: parse-sexp-lookup-properties
     If this is non-`nil', the syntax scanning functions pay attention
     to syntax text properties.  Otherwise they use only the current
     syntax table.


File: elisp,  Node: Motion and Syntax,  Next: Parsing Expressions,  Prev: Syntax Properties,  Up: Syntax Tables

35.5 Motion and Syntax
======================

This section describes functions for moving across characters that have
certain syntax classes.

 -- Function: skip-syntax-forward syntaxes &optional limit
     This function moves point forward across characters having syntax
     classes mentioned in SYNTAXES (a string of syntax class
     characters).  It stops when it encounters the end of the buffer, or
     position LIMIT (if specified), or a character it is not supposed
     to skip.

     If SYNTAXES starts with `^', then the function skips characters
     whose syntax is _not_ in SYNTAXES.

     The return value is the distance traveled, which is a nonnegative
     integer.

 -- Function: skip-syntax-backward syntaxes &optional limit
     This function moves point backward across characters whose syntax
     classes are mentioned in SYNTAXES.  It stops when it encounters
     the beginning of the buffer, or position LIMIT (if specified), or
     a character it is not supposed to skip.

     If SYNTAXES starts with `^', then the function skips characters
     whose syntax is _not_ in SYNTAXES.

     The return value indicates the distance traveled.  It is an
     integer that is zero or less.

 -- Function: backward-prefix-chars
     This function moves point backward over any number of characters
     with expression prefix syntax.  This includes both characters in
     the expression prefix syntax class, and characters with the `p'
     flag.


File: elisp,  Node: Parsing Expressions,  Next: Standard Syntax Tables,  Prev: Motion and Syntax,  Up: Syntax Tables

35.6 Parsing Expressions
========================

This section describes functions for parsing and scanning balanced
expressions, also known as "sexps".  Basically, a sexp is either a
balanced parenthetical grouping, a string, or a symbol name (a sequence
of characters whose syntax is either word constituent or symbol
constituent).  However, characters whose syntax is expression prefix
are treated as part of the sexp if they appear next to it.

   The syntax table controls the interpretation of characters, so these
functions can be used for Lisp expressions when in Lisp mode and for C
expressions when in C mode.  *Note List Motion::, for convenient
higher-level functions for moving over balanced expressions.

   A character's syntax controls how it changes the state of the
parser, rather than describing the state itself.  For example, a string
delimiter character toggles the parser state between "in-string" and
"in-code," but the syntax of characters does not directly say whether
they are inside a string.  For example (note that 15 is the syntax code
for generic string delimiters),

     (put-text-property 1 9 'syntax-table '(15 . nil))

does not tell Emacs that the first eight chars of the current buffer
are a string, but rather that they are all string delimiters.  As a
result, Emacs treats them as four consecutive empty string constants.

* Menu:

* Motion via Parsing::       Motion functions that work by parsing.
* Position Parse::           Determining the syntactic state of a position.
* Parser State::             How Emacs represents a syntactic state.
* Low-Level Parsing::        Parsing across a specified region.
* Control Parsing::          Parameters that affect parsing.


File: elisp,  Node: Motion via Parsing,  Next: Position Parse,  Up: Parsing Expressions

35.6.1 Motion Commands Based on Parsing
---------------------------------------

This section describes simple point-motion functions that operate based
on parsing expressions.

 -- Function: scan-lists from count depth
     This function scans forward COUNT balanced parenthetical groupings
     from position FROM.  It returns the position where the scan stops.
     If COUNT is negative, the scan moves backwards.

     If DEPTH is nonzero, parenthesis depth counting begins from that
     value.  The only candidates for stopping are places where the
     depth in parentheses becomes zero; `scan-lists' counts COUNT such
     places and then stops.  Thus, a positive value for DEPTH means go
     out DEPTH levels of parenthesis.

     Scanning ignores comments if `parse-sexp-ignore-comments' is
     non-`nil'.

     If the scan reaches the beginning or end of the buffer (or its
     accessible portion), and the depth is not zero, an error is
     signaled.  If the depth is zero but the count is not used up,
     `nil' is returned.

 -- Function: scan-sexps from count
     This function scans forward COUNT sexps from position FROM.  It
     returns the position where the scan stops.  If COUNT is negative,
     the scan moves backwards.

     Scanning ignores comments if `parse-sexp-ignore-comments' is
     non-`nil'.

     If the scan reaches the beginning or end of (the accessible part
     of) the buffer while in the middle of a parenthetical grouping, an
     error is signaled.  If it reaches the beginning or end between
     groupings but before count is used up, `nil' is returned.

 -- Function: forward-comment count
     This function moves point forward across COUNT complete comments
       (that is, including the starting delimiter and the terminating
     delimiter if any), plus any whitespace encountered on the way.  It
     moves backward if COUNT is negative.  If it encounters anything
     other than a comment or whitespace, it stops, leaving point at the
     place where it stopped.  This includes (for instance) finding the
     end of a comment when moving forward and expecting the beginning
     of one.  The function also stops immediately after moving over the
     specified number of complete comments.  If COUNT comments are
     found as expected, with nothing except whitespace between them, it
     returns `t'; otherwise it returns `nil'.

     This function cannot tell whether the "comments" it traverses are
     embedded within a string.  If they look like comments, it treats
     them as comments.

   To move forward over all comments and whitespace following point, use
`(forward-comment (buffer-size))'.  `(buffer-size)' is a good argument
to use, because the number of comments in the buffer cannot exceed that
many.


File: elisp,  Node: Position Parse,  Next: Parser State,  Prev: Motion via Parsing,  Up: Parsing Expressions

35.6.2 Finding the Parse State for a Position
---------------------------------------------

For syntactic analysis, such as in indentation, often the useful thing
is to compute the syntactic state corresponding to a given buffer
position.  This function does that conveniently.

 -- Function: syntax-ppss &optional pos
     This function returns the parser state (see next section) that the
     parser would reach at position POS starting from the beginning of
     the buffer.  This is equivalent to `(parse-partial-sexp
     (point-min) POS)', except that `syntax-ppss' uses a cache to speed
     up the computation.  Due to this optimization, the 2nd value
     (previous complete subexpression) and 6th value (minimum
     parenthesis depth) of the returned parser state are not meaningful.

   `syntax-ppss' automatically hooks itself to
`before-change-functions' to keep its cache consistent.  But updating
can fail if `syntax-ppss' is called while `before-change-functions' is
temporarily let-bound, or if the buffer is modified without obeying the
hook, such as when using `inhibit-modification-hooks'.  For this
reason, it is sometimes necessary to flush the cache manually.

 -- Function: syntax-ppss-flush-cache beg
     This function flushes the cache used by `syntax-ppss', starting at
     position BEG.

   Major modes can make `syntax-ppss' run faster by specifying where it
needs to start parsing.

 -- Variable: syntax-begin-function
     If this is non-`nil', it should be a function that moves to an
     earlier buffer position where the parser state is equivalent to
     `nil'--in other words, a position outside of any comment, string,
     or parenthesis.  `syntax-ppss' uses it to further optimize its
     computations, when the cache gives no help.


File: elisp,  Node: Parser State,  Next: Low-Level Parsing,  Prev: Position Parse,  Up: Parsing Expressions

35.6.3 Parser State
-------------------

A "parser state" is a list of ten elements describing the final state
of parsing text syntactically as part of an expression.  The parsing
functions in the following sections return a parser state as the value,
and in some cases accept one as an argument also, so that you can
resume parsing after it stops.  Here are the meanings of the elements
of the parser state:

  0. The depth in parentheses, counting from 0.  *Warning:* this can be
     negative if there are more close parens than open parens between
     the start of the defun and point.

  1. The character position of the start of the innermost parenthetical
     grouping containing the stopping point; `nil' if none.

  2. The character position of the start of the last complete
     subexpression terminated; `nil' if none.

  3. Non-`nil' if inside a string.  More precisely, this is the
     character that will terminate the string, or `t' if a generic
     string delimiter character should terminate it.

  4. `t' if inside a comment (of either style), or the comment nesting
     level if inside a kind of comment that can be nested.

  5. `t' if point is just after a quote character.

  6. The minimum parenthesis depth encountered during this scan.

  7. What kind of comment is active: `nil' for a comment of style "a"
     or when not inside a comment, `t' for a comment of style "b," and
     `syntax-table' for a comment that should be ended by a generic
     comment delimiter character.

  8. The string or comment start position.  While inside a comment,
     this is the position where the comment began; while inside a
     string, this is the position where the string began.  When outside
     of strings and comments, this element is `nil'.

  9. Internal data for continuing the parsing.  The meaning of this
     data is subject to change; it is used if you pass this list as the
     STATE argument to another call.

   Elements 1, 2, and 6 are ignored in a state which you pass as an
argument to continue parsing, and elements 8 and 9 are used only in
trivial cases.  Those elements serve primarily to convey information to
the Lisp program which does the parsing.

   One additional piece of useful information is available from a
parser state using this function:

 -- Function: syntax-ppss-toplevel-pos state
     This function extracts, from parser state STATE, the last position
     scanned in the parse which was at top level in grammatical
     structure.  "At top level" means outside of any parentheses,
     comments, or strings.

     The value is `nil' if STATE represents a parse which has arrived
     at a top level position.

   We have provided this access function rather than document how the
data is represented in the state, because we plan to change the
representation in the future.


File: elisp,  Node: Low-Level Parsing,  Next: Control Parsing,  Prev: Parser State,  Up: Parsing Expressions

35.6.4 Low-Level Parsing
------------------------

The most basic way to use the expression parser is to tell it to start
at a given position with a certain state, and parse up to a specified
end position.

 -- Function: parse-partial-sexp start limit &optional target-depth
          stop-before state stop-comment
     This function parses a sexp in the current buffer starting at
     START, not scanning past LIMIT.  It stops at position LIMIT or
     when certain criteria described below are met, and sets point to
     the location where parsing stops.  It returns a parser state
     describing the status of the parse at the point where it stops.

     If the third argument TARGET-DEPTH is non-`nil', parsing stops if
     the depth in parentheses becomes equal to TARGET-DEPTH.  The depth
     starts at 0, or at whatever is given in STATE.

     If the fourth argument STOP-BEFORE is non-`nil', parsing stops
     when it comes to any character that starts a sexp.  If
     STOP-COMMENT is non-`nil', parsing stops when it comes to the
     start of a comment.  If STOP-COMMENT is the symbol `syntax-table',
     parsing stops after the start of a comment or a string, or the end
     of a comment or a string, whichever comes first.

     If STATE is `nil', START is assumed to be at the top level of
     parenthesis structure, such as the beginning of a function
     definition.  Alternatively, you might wish to resume parsing in the
     middle of the structure.  To do this, you must provide a STATE
     argument that describes the initial status of parsing.  The value
     returned by a previous call to `parse-partial-sexp' will do nicely.


File: elisp,  Node: Control Parsing,  Prev: Low-Level Parsing,  Up: Parsing Expressions

35.6.5 Parameters to Control Parsing
------------------------------------

 -- Variable: multibyte-syntax-as-symbol
     If this variable is non-`nil', `scan-sexps' treats all non-ASCII
     characters as symbol constituents regardless of what the syntax
     table says about them.  (However, text properties can still
     override the syntax.)

 -- User Option: parse-sexp-ignore-comments
     If the value is non-`nil', then comments are treated as whitespace
     by the functions in this section and by `forward-sexp',
     `scan-lists' and `scan-sexps'.

   The behavior of `parse-partial-sexp' is also affected by
`parse-sexp-lookup-properties' (*note Syntax Properties::).

   You can use `forward-comment' to move forward or backward over one
comment or several comments.


File: elisp,  Node: Standard Syntax Tables,  Next: Syntax Table Internals,  Prev: Parsing Expressions,  Up: Syntax Tables

35.7 Some Standard Syntax Tables
================================

Most of the major modes in Emacs have their own syntax tables.  Here
are several of them:

 -- Function: standard-syntax-table
     This function returns the standard syntax table, which is the
     syntax table used in Fundamental mode.

 -- Variable: text-mode-syntax-table
     The value of this variable is the syntax table used in Text mode.

 -- Variable: c-mode-syntax-table
     The value of this variable is the syntax table for C-mode buffers.

 -- Variable: emacs-lisp-mode-syntax-table
     The value of this variable is the syntax table used in Emacs Lisp
     mode by editing commands.  (It has no effect on the Lisp `read'
     function.)


File: elisp,  Node: Syntax Table Internals,  Next: Categories,  Prev: Standard Syntax Tables,  Up: Syntax Tables

35.8 Syntax Table Internals
===========================

Lisp programs don't usually work with the elements directly; the
Lisp-level syntax table functions usually work with syntax descriptors
(*note Syntax Descriptors::).  Nonetheless, here we document the
internal format.  This format is used mostly when manipulating syntax
properties.

   Each element of a syntax table is a cons cell of the form
`(SYNTAX-CODE . MATCHING-CHAR)'.  The CAR, SYNTAX-CODE, is an integer
that encodes the syntax class, and any flags.  The CDR, MATCHING-CHAR,
is non-`nil' if a character to match was specified.

   This table gives the value of SYNTAX-CODE which corresponds to each
syntactic type.

     Integer Class          Integer Class          Integer Class
     0    whitespace        5    close parenthesis 10    character quote
     1    punctuation       6    expression prefix 11    comment-start
     2    word              7    string quote      12    comment-end
     3    symbol            8    paired delimiter  13    inherit
     4    open parenthesis  9    escape            14    generic comment
     15   generic string                           

   For example, the usual syntax value for `(' is `(4 . 41)'.  (41 is
the character code for `)'.)

   The flags are encoded in higher order bits, starting 16 bits from the
least significant bit.  This table gives the power of two which
corresponds to each syntax flag.

     Prefix Flag            Prefix Flag            Prefix Flag
     `1'    `(lsh 1 16)'    `4'    `(lsh 1 19)'    `b'    `(lsh 1 21)'
     `2'    `(lsh 1 17)'    `p'    `(lsh 1 20)'    `n'    `(lsh 1 22)'
     `3'    `(lsh 1 18)'                           

 -- Function: string-to-syntax DESC
     This function returns the internal form corresponding to the syntax
     descriptor DESC, a cons cell `(SYNTAX-CODE . MATCHING-CHAR)'.

 -- Function: syntax-after pos
     This function returns the syntax code of the character in the
     buffer after position POS, taking account of syntax properties as
     well as the syntax table.  If POS is outside the buffer's
     accessible portion (*note accessible portion: Narrowing.), this
     function returns `nil'.

 -- Function: syntax-class syntax
     This function returns the syntax class of the syntax code SYNTAX.
     (It masks off the high 16 bits that hold the flags encoded in the
     syntax descriptor.)  If SYNTAX is `nil', it returns `nil'; this is
     so evaluating the expression

          (syntax-class (syntax-after pos))

     where `pos' is outside the buffer's accessible portion, will yield
     `nil' without throwing errors or producing wrong syntax class
     codes.


File: elisp,  Node: Categories,  Prev: Syntax Table Internals,  Up: Syntax Tables

35.9 Categories
===============

"Categories" provide an alternate way of classifying characters
syntactically.  You can define several categories as needed, then
independently assign each character to one or more categories.  Unlike
syntax classes, categories are not mutually exclusive; it is normal for
one character to belong to several categories.

   Each buffer has a "category table" which records which categories
are defined and also which characters belong to each category.  Each
category table defines its own categories, but normally these are
initialized by copying from the standard categories table, so that the
standard categories are available in all modes.

   Each category has a name, which is an ASCII printing character in
the range ` ' to `~'.  You specify the name of a category when you
define it with `define-category'.

   The category table is actually a char-table (*note Char-Tables::).
The element of the category table at index C is a "category set"--a
bool-vector--that indicates which categories character C belongs to.
In this category set, if the element at index CAT is `t', that means
category CAT is a member of the set, and that character C belongs to
category CAT.

   For the next three functions, the optional argument TABLE defaults
to the current buffer's category table.

 -- Function: define-category char docstring &optional table
     This function defines a new category, with name CHAR and
     documentation DOCSTRING, for the category table TABLE.

 -- Function: category-docstring category &optional table
     This function returns the documentation string of category CATEGORY
     in category table TABLE.

          (category-docstring ?a)
               => "ASCII"
          (category-docstring ?l)
               => "Latin"

 -- Function: get-unused-category &optional table
     This function returns a category name (a character) which is not
     currently defined in TABLE.  If all possible categories are in use
     in TABLE, it returns `nil'.

 -- Function: category-table
     This function returns the current buffer's category table.

 -- Function: category-table-p object
     This function returns `t' if OBJECT is a category table, otherwise
     `nil'.

 -- Function: standard-category-table
     This function returns the standard category table.

 -- Function: copy-category-table &optional table
     This function constructs a copy of TABLE and returns it.  If TABLE
     is not supplied (or is `nil'), it returns a copy of the standard
     category table.  Otherwise, an error is signaled if TABLE is not a
     category table.

 -- Function: set-category-table table
     This function makes TABLE the category table for the current
     buffer.  It returns TABLE.

 -- Function: make-category-table
     This creates and returns an empty category table.  In an empty
     category table, no categories have been allocated, and no
     characters belong to any categories.

 -- Function: make-category-set categories
     This function returns a new category set--a bool-vector--whose
     initial contents are the categories listed in the string
     CATEGORIES.  The elements of CATEGORIES should be category names;
     the new category set has `t' for each of those categories, and
     `nil' for all other categories.

          (make-category-set "al")
               => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"

 -- Function: char-category-set char
     This function returns the category set for character CHAR in the
     current buffer's category table.  This is the bool-vector which
     records which categories the character CHAR belongs to.  The
     function `char-category-set' does not allocate storage, because it
     returns the same bool-vector that exists in the category table.

          (char-category-set ?a)
               => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"

 -- Function: category-set-mnemonics category-set
     This function converts the category set CATEGORY-SET into a string
     containing the characters that designate the categories that are
     members of the set.

          (category-set-mnemonics (char-category-set ?a))
               => "al"

 -- Function: modify-category-entry character category &optional table
          reset
     This function modifies the category set of CHARACTER in category
     table TABLE (which defaults to the current buffer's category
     table).

     Normally, it modifies the category set by adding CATEGORY to it.
     But if RESET is non-`nil', then it deletes CATEGORY instead.

 -- Command: describe-categories &optional buffer-or-name
     This function describes the category specifications in the current
     category table.  It inserts the descriptions in a buffer, and then
     displays that buffer.  If BUFFER-OR-NAME is non-`nil', it
     describes the category table of that buffer instead.


File: elisp,  Node: Abbrevs,  Next: Processes,  Prev: Syntax Tables,  Up: Top

36 Abbrevs and Abbrev Expansion
*******************************

An abbreviation or "abbrev" is a string of characters that may be
expanded to a longer string.  The user can insert the abbrev string and
find it replaced automatically with the expansion of the abbrev.  This
saves typing.

   The set of abbrevs currently in effect is recorded in an "abbrev
table".  Each buffer has a local abbrev table, but normally all buffers
in the same major mode share one abbrev table.  There is also a global
abbrev table.  Normally both are used.

   An abbrev table is represented as an obarray containing a symbol for
each abbreviation.  The symbol's name is the abbreviation; its value is
the expansion; its function definition is the hook function to do the
expansion (*note Defining Abbrevs::); its property list cell typically
contains the use count, the number of times the abbreviation has been
expanded.  Alternatively, the use count is on the `count' property and
the system-abbrev flag is on the `system-type' property.  Abbrevs with
a non-`nil' `system-type' property are called "system" abbrevs.  They
are usually defined by modes or packages, instead of by the user, and
are treated specially in certain respects.

   Because the symbols used for abbrevs are not interned in the usual
obarray, they will never appear as the result of reading a Lisp
expression; in fact, normally they are never used except by the code
that handles abbrevs.  Therefore, it is safe to use them in an
extremely nonstandard way.  *Note Creating Symbols::.

   For the user-level commands for abbrevs, see *Note Abbrev Mode:
(emacs)Abbrevs.

* Menu:

* Abbrev Mode::                 Setting up Emacs for abbreviation.
* Tables: Abbrev Tables.        Creating and working with abbrev tables.
* Defining Abbrevs::            Specifying abbreviations and their expansions.
* Files: Abbrev Files.          Saving abbrevs in files.
* Expansion: Abbrev Expansion.  Controlling expansion; expansion subroutines.
* Standard Abbrev Tables::      Abbrev tables used by various major modes.


File: elisp,  Node: Abbrev Mode,  Next: Abbrev Tables,  Prev: Abbrevs,  Up: Abbrevs

36.1 Setting Up Abbrev Mode
===========================

Abbrev mode is a minor mode controlled by the value of the variable
`abbrev-mode'.

 -- Variable: abbrev-mode
     A non-`nil' value of this variable turns on the automatic expansion
     of abbrevs when their abbreviations are inserted into a buffer.
     If the value is `nil', abbrevs may be defined, but they are not
     expanded automatically.

     This variable automatically becomes buffer-local when set in any
     fashion.

 -- Variable: default-abbrev-mode
     This is the value of `abbrev-mode' for buffers that do not
     override it.  This is the same as `(default-value 'abbrev-mode)'.


File: elisp,  Node: Abbrev Tables,  Next: Defining Abbrevs,  Prev: Abbrev Mode,  Up: Abbrevs

36.2 Abbrev Tables
==================

This section describes how to create and manipulate abbrev tables.

 -- Function: make-abbrev-table
     This function creates and returns a new, empty abbrev table--an
     obarray containing no symbols.  It is a vector filled with zeros.

 -- Function: clear-abbrev-table table
     This function undefines all the abbrevs in abbrev table TABLE,
     leaving it empty.  It always returns `nil'.

 -- Function: copy-abbrev-table table
     This function returns a copy of abbrev table TABLE--a new abbrev
     table that contains the same abbrev definitions.  The only
     difference between TABLE and the returned copy is that this
     function sets the property lists of all copied abbrevs to 0.

 -- Function: define-abbrev-table tabname definitions
     This function defines TABNAME (a symbol) as an abbrev table name,
     i.e., as a variable whose value is an abbrev table.  It defines
     abbrevs in the table according to DEFINITIONS, a list of elements
     of the form `(ABBREVNAME EXPANSION HOOK USECOUNT SYSTEM-FLAG)'.
     If an element of DEFINITIONS has length less than five, omitted
     elements default to `nil'.  A value of `nil' for USECOUNT is
     equivalent to zero.  The return value is always `nil'.

     If this function is called more than once for the same TABNAME,
     subsequent calls add the definitions in DEFINITIONS to TABNAME,
     rather than overriding the entire original contents.  (A
     subsequent call only overrides abbrevs explicitly redefined or
     undefined in DEFINITIONS.)

 -- Variable: abbrev-table-name-list
     This is a list of symbols whose values are abbrev tables.
     `define-abbrev-table' adds the new abbrev table name to this list.

 -- Function: insert-abbrev-table-description name &optional human
     This function inserts before point a description of the abbrev
     table named NAME.  The argument NAME is a symbol whose value is an
     abbrev table.  The return value is always `nil'.

     If HUMAN is non-`nil', the description is human-oriented.  System
     abbrevs are listed and identified as such.  Otherwise the
     description is a Lisp expression--a call to `define-abbrev-table'
     that would define NAME as it is currently defined, but without the
     system abbrevs.  (The mode or package using NAME is supposed to
     add these to NAME separately.)


File: elisp,  Node: Defining Abbrevs,  Next: Abbrev Files,  Prev: Abbrev Tables,  Up: Abbrevs

36.3 Defining Abbrevs
=====================

`define-abbrev' is the low-level basic function for defining an abbrev
in a specified abbrev table.  When major modes predefine standard
abbrevs, they should call `define-abbrev' and specify `t' for
SYSTEM-FLAG.  Be aware that any saved non-"system" abbrevs are restored
at startup, i.e. before some major modes are loaded.  Major modes
should therefore not assume that when they are first loaded their abbrev
tables are empty.

 -- Function: define-abbrev table name expansion &optional hook count
          system-flag
     This function defines an abbrev named NAME, in TABLE, to expand to
     EXPANSION and call HOOK.  The return value is NAME.

     The value of COUNT, if specified, initializes the abbrev's
     usage-count.  If COUNT is not specified or `nil', the use count is
     initialized to zero.

     The argument NAME should be a string.  The argument EXPANSION is
     normally the desired expansion (a string), or `nil' to undefine
     the abbrev.  If it is anything but a string or `nil', then the
     abbreviation "expands" solely by running HOOK.

     The argument HOOK is a function or `nil'.  If HOOK is non-`nil',
     then it is called with no arguments after the abbrev is replaced
     with EXPANSION; point is located at the end of EXPANSION when HOOK
     is called.

     If HOOK is a non-`nil' symbol whose `no-self-insert' property is
     non-`nil', HOOK can explicitly control whether to insert the
     self-inserting input character that triggered the expansion.  If
     HOOK returns non-`nil' in this case, that inhibits insertion of
     the character.  By contrast, if HOOK returns `nil',
     `expand-abbrev' also returns `nil', as if expansion had not really
     occurred.

     If SYSTEM-FLAG is non-`nil', that marks the abbrev as a "system"
     abbrev with the `system-type' property.  Unless SYSTEM-FLAG has
     the value `force', a "system" abbrev will not overwrite an
     existing definition for a non-"system" abbrev of the same name.

     Normally the function `define-abbrev' sets the variable
     `abbrevs-changed' to `t', if it actually changes the abbrev.
     (This is so that some commands will offer to save the abbrevs.)  It
     does not do this for a "system" abbrev, since those won't be saved
     anyway.

 -- User Option: only-global-abbrevs
     If this variable is non-`nil', it means that the user plans to use
     global abbrevs only.  This tells the commands that define
     mode-specific abbrevs to define global ones instead.  This
     variable does not alter the behavior of the functions in this
     section; it is examined by their callers.


File: elisp,  Node: Abbrev Files,  Next: Abbrev Expansion,  Prev: Defining Abbrevs,  Up: Abbrevs

36.4 Saving Abbrevs in Files
============================

A file of saved abbrev definitions is actually a file of Lisp code.
The abbrevs are saved in the form of a Lisp program to define the same
abbrev tables with the same contents.  Therefore, you can load the file
with `load' (*note How Programs Do Loading::).  However, the function
`quietly-read-abbrev-file' is provided as a more convenient interface.

   User-level facilities such as `save-some-buffers' can save abbrevs
in a file automatically, under the control of variables described here.

 -- User Option: abbrev-file-name
     This is the default file name for reading and saving abbrevs.

 -- Function: quietly-read-abbrev-file &optional filename
     This function reads abbrev definitions from a file named FILENAME,
     previously written with `write-abbrev-file'.  If FILENAME is
     omitted or `nil', the file specified in `abbrev-file-name' is
     used.  `save-abbrevs' is set to `t' so that changes will be saved.

     This function does not display any messages.  It returns `nil'.

 -- User Option: save-abbrevs
     A non-`nil' value for `save-abbrevs' means that Emacs should offer
     the user to save abbrevs when files are saved.  If the value is
     `silently', Emacs saves the abbrevs without asking the user.
     `abbrev-file-name' specifies the file to save the abbrevs in.

 -- Variable: abbrevs-changed
     This variable is set non-`nil' by defining or altering any abbrevs
     (except "system" abbrevs).  This serves as a flag for various
     Emacs commands to offer to save your abbrevs.

 -- Command: write-abbrev-file &optional filename
     Save all abbrev definitions (except "system" abbrevs), for all
     abbrev tables listed in `abbrev-table-name-list', in the file
     FILENAME, in the form of a Lisp program that when loaded will
     define the same abbrevs.  If FILENAME is `nil' or omitted,
     `abbrev-file-name' is used.  This function returns `nil'.


File: elisp,  Node: Abbrev Expansion,  Next: Standard Abbrev Tables,  Prev: Abbrev Files,  Up: Abbrevs

36.5 Looking Up and Expanding Abbreviations
===========================================

Abbrevs are usually expanded by certain interactive commands, including
`self-insert-command'.  This section describes the subroutines used in
writing such commands, as well as the variables they use for
communication.

 -- Function: abbrev-symbol abbrev &optional table
     This function returns the symbol representing the abbrev named
     ABBREV.  The value returned is `nil' if that abbrev is not
     defined.  The optional second argument TABLE is the abbrev table
     to look it up in.  If TABLE is `nil', this function tries first
     the current buffer's local abbrev table, and second the global
     abbrev table.

 -- Function: abbrev-expansion abbrev &optional table
     This function returns the string that ABBREV would expand into (as
     defined by the abbrev tables used for the current buffer).  If
     ABBREV is not a valid abbrev, the function returns `nil'.  The
     optional argument TABLE specifies the abbrev table to use, as in
     `abbrev-symbol'.

 -- Command: expand-abbrev
     This command expands the abbrev before point, if any.  If point
     does not follow an abbrev, this command does nothing.  The command
     returns the abbrev symbol if it did expansion, `nil' otherwise.

     If the abbrev symbol has a hook function which is a symbol whose
     `no-self-insert' property is non-`nil', and if the hook function
     returns `nil' as its value, then `expand-abbrev' returns `nil'
     even though expansion did occur.

 -- Command: abbrev-prefix-mark &optional arg
     This command marks the current location of point as the beginning
     of an abbrev.  The next call to `expand-abbrev' will use the text
     from here to point (where it is then) as the abbrev to expand,
     rather than using the previous word as usual.

     First, this command expands any abbrev before point, unless ARG is
     non-`nil'.  (Interactively, ARG is the prefix argument.)  Then it
     inserts a hyphen before point, to indicate the start of the next
     abbrev to be expanded.  The actual expansion removes the hyphen.

 -- User Option: abbrev-all-caps
     When this is set non-`nil', an abbrev entered entirely in upper
     case is expanded using all upper case.  Otherwise, an abbrev
     entered entirely in upper case is expanded by capitalizing each
     word of the expansion.

 -- Variable: abbrev-start-location
     The value of this variable is a buffer position (an integer or a
     marker) for `expand-abbrev' to use as the start of the next abbrev
     to be expanded.  The value can also be `nil', which means to use
     the word before point instead.  `abbrev-start-location' is set to
     `nil' each time `expand-abbrev' is called.  This variable is also
     set by `abbrev-prefix-mark'.

 -- Variable: abbrev-start-location-buffer
     The value of this variable is the buffer for which
     `abbrev-start-location' has been set.  Trying to expand an abbrev
     in any other buffer clears `abbrev-start-location'.  This variable
     is set by `abbrev-prefix-mark'.

 -- Variable: last-abbrev
     This is the `abbrev-symbol' of the most recent abbrev expanded.
     This information is left by `expand-abbrev' for the sake of the
     `unexpand-abbrev' command (*note Expanding Abbrevs:
     (emacs)Expanding Abbrevs.).

 -- Variable: last-abbrev-location
     This is the location of the most recent abbrev expanded.  This
     contains information left by `expand-abbrev' for the sake of the
     `unexpand-abbrev' command.

 -- Variable: last-abbrev-text
     This is the exact expansion text of the most recent abbrev
     expanded, after case conversion (if any).  Its value is `nil' if
     the abbrev has already been unexpanded.  This contains information
     left by `expand-abbrev' for the sake of the `unexpand-abbrev'
     command.

 -- Variable: pre-abbrev-expand-hook
     This is a normal hook whose functions are executed, in sequence,
     just before any expansion of an abbrev.  *Note Hooks::.  Since it
     is a normal hook, the hook functions receive no arguments.
     However, they can find the abbrev to be expanded by looking in the
     buffer before point.  Running the hook is the first thing that
     `expand-abbrev' does, and so a hook function can be used to change
     the current abbrev table before abbrev lookup happens.  (Although
     you have to do this carefully.  See the example below.)

   The following sample code shows a simple use of
`pre-abbrev-expand-hook'.  It assumes that `foo-mode' is a mode for
editing certain files in which lines that start with `#' are comments.
You want to use Text mode abbrevs for those lines.  The regular local
abbrev table, `foo-mode-abbrev-table' is appropriate for all other
lines.  Then you can put the following code in your `.emacs' file.
*Note Standard Abbrev Tables::, for the definitions of
`local-abbrev-table' and `text-mode-abbrev-table'.

     (defun foo-mode-pre-abbrev-expand ()
       (when (save-excursion (forward-line 0) (eq (char-after) ?#))
         (let ((local-abbrev-table text-mode-abbrev-table)
     	  ;; Avoid infinite loop.
     	  (pre-abbrev-expand-hook nil))
           (expand-abbrev))
         ;; We have already called `expand-abbrev' in this hook.
         ;; Hence we want the "actual" call following this hook to be a no-op.
         (setq abbrev-start-location (point-max)
     	  abbrev-start-location-buffer (current-buffer))))

     (add-hook 'foo-mode-hook
     	  #'(lambda ()
     	      (add-hook 'pre-abbrev-expand-hook
     			'foo-mode-pre-abbrev-expand
     			nil t)))

   Note that `foo-mode-pre-abbrev-expand' just returns `nil' without
doing anything for lines not starting with `#'.  Hence abbrevs expand
normally using `foo-mode-abbrev-table' as local abbrev table for such
lines.


File: elisp,  Node: Standard Abbrev Tables,  Prev: Abbrev Expansion,  Up: Abbrevs

36.6 Standard Abbrev Tables
===========================

Here we list the variables that hold the abbrev tables for the
preloaded major modes of Emacs.

 -- Variable: global-abbrev-table
     This is the abbrev table for mode-independent abbrevs.  The abbrevs
     defined in it apply to all buffers.  Each buffer may also have a
     local abbrev table, whose abbrev definitions take precedence over
     those in the global table.

 -- Variable: local-abbrev-table
     The value of this buffer-local variable is the (mode-specific)
     abbreviation table of the current buffer.

 -- Variable: fundamental-mode-abbrev-table
     This is the local abbrev table used in Fundamental mode; in other
     words, it is the local abbrev table in all buffers in Fundamental
     mode.

 -- Variable: text-mode-abbrev-table
     This is the local abbrev table used in Text mode.

 -- Variable: lisp-mode-abbrev-table
     This is the local abbrev table used in Lisp mode and Emacs Lisp
     mode.


File: elisp,  Node: Processes,  Next: Display,  Prev: Abbrevs,  Up: Top

37 Processes
************

In the terminology of operating systems, a "process" is a space in
which a program can execute.  Emacs runs in a process.  Emacs Lisp
programs can invoke other programs in processes of their own.  These are
called "subprocesses" or "child processes" of the Emacs process, which
is their "parent process".

   A subprocess of Emacs may be "synchronous" or "asynchronous",
depending on how it is created.  When you create a synchronous
subprocess, the Lisp program waits for the subprocess to terminate
before continuing execution.  When you create an asynchronous
subprocess, it can run in parallel with the Lisp program.  This kind of
subprocess is represented within Emacs by a Lisp object which is also
called a "process."  Lisp programs can use this object to communicate
with the subprocess or to control it.  For example, you can send
signals, obtain status information, receive output from the process, or
send input to it.

 -- Function: processp object
     This function returns `t' if OBJECT is a process, `nil' otherwise.

* Menu:

* Subprocess Creation::      Functions that start subprocesses.
* Shell Arguments::          Quoting an argument to pass it to a shell.
* Synchronous Processes::    Details of using synchronous subprocesses.
* Asynchronous Processes::   Starting up an asynchronous subprocess.
* Deleting Processes::       Eliminating an asynchronous subprocess.
* Process Information::      Accessing run-status and other attributes.
* Input to Processes::       Sending input to an asynchronous subprocess.
* Signals to Processes::     Stopping, continuing or interrupting
                               an asynchronous subprocess.
* Output from Processes::    Collecting output from an asynchronous subprocess.
* Sentinels::                Sentinels run when process run-status changes.
* Query Before Exit::        Whether to query if exiting will kill a process.
* Transaction Queues::	     Transaction-based communication with subprocesses.
* Network::                  Opening network connections.
* Network Servers::          Network servers let Emacs accept net connections.
* Datagrams::                UDP network connections.
* Low-Level Network::        Lower-level but more general function
                               to create connections and servers.
* Misc Network::             Additional relevant functions for network connections.
* Byte Packing::             Using bindat to pack and unpack binary data.


File: elisp,  Node: Subprocess Creation,  Next: Shell Arguments,  Up: Processes

37.1 Functions that Create Subprocesses
=======================================

There are three functions that create a new subprocess in which to run
a program.  One of them, `start-process', creates an asynchronous
process and returns a process object (*note Asynchronous Processes::).
The other two, `call-process' and `call-process-region', create a
synchronous process and do not return a process object (*note
Synchronous Processes::).

   Synchronous and asynchronous processes are explained in the following
sections.  Since the three functions are all called in a similar
fashion, their common arguments are described here.

   In all cases, the function's PROGRAM argument specifies the program
to be run.  An error is signaled if the file is not found or cannot be
executed.  If the file name is relative, the variable `exec-path'
contains a list of directories to search.  Emacs initializes
`exec-path' when it starts up, based on the value of the environment
variable `PATH'.  The standard file name constructs, `~', `.', and
`..', are interpreted as usual in `exec-path', but environment variable
substitutions (`$HOME', etc.) are not recognized; use
`substitute-in-file-name' to perform them (*note File Name
Expansion::).  `nil' in this list refers to `default-directory'.

   Executing a program can also try adding suffixes to the specified
name:

 -- Variable: exec-suffixes
     This variable is a list of suffixes (strings) to try adding to the
     specified program file name.  The list should include `""' if you
     want the name to be tried exactly as specified.  The default value
     is system-dependent.

   *Please note:* The argument PROGRAM contains only the name of the
program; it may not contain any command-line arguments.  You must use
ARGS to provide those.

   Each of the subprocess-creating functions has a BUFFER-OR-NAME
argument which specifies where the standard output from the program will
go.  It should be a buffer or a buffer name; if it is a buffer name,
that will create the buffer if it does not already exist.  It can also
be `nil', which says to discard the output unless a filter function
handles it.  (*Note Filter Functions::, and *Note Read and Print::.)
Normally, you should avoid having multiple processes send output to the
same buffer because their output would be intermixed randomly.

   All three of the subprocess-creating functions have a `&rest'
argument, ARGS.  The ARGS must all be strings, and they are supplied to
PROGRAM as separate command line arguments.  Wildcard characters and
other shell constructs have no special meanings in these strings, since
the strings are passed directly to the specified program.

   The subprocess gets its current directory from the value of
`default-directory' (*note File Name Expansion::).

   The subprocess inherits its environment from Emacs, but you can
specify overrides for it with `process-environment'.  *Note System
Environment::.

 -- Variable: exec-directory
     The value of this variable is a string, the name of a directory
     that contains programs that come with GNU Emacs, programs intended
     for Emacs to invoke.  The program `movemail' is an example of such
     a program; Rmail uses it to fetch new mail from an inbox.

 -- User Option: exec-path
     The value of this variable is a list of directories to search for
     programs to run in subprocesses.  Each element is either the name
     of a directory (i.e., a string), or `nil', which stands for the
     default directory (which is the value of `default-directory').  

     The value of `exec-path' is used by `call-process' and
     `start-process' when the PROGRAM argument is not an absolute file
     name.


File: elisp,  Node: Shell Arguments,  Next: Synchronous Processes,  Prev: Subprocess Creation,  Up: Processes

37.2 Shell Arguments
====================

Lisp programs sometimes need to run a shell and give it a command that
contains file names that were specified by the user.  These programs
ought to be able to support any valid file name.  But the shell gives
special treatment to certain characters, and if these characters occur
in the file name, they will confuse the shell.  To handle these
characters, use the function `shell-quote-argument':

 -- Function: shell-quote-argument argument
     This function returns a string which represents, in shell syntax,
     an argument whose actual contents are ARGUMENT.  It should work
     reliably to concatenate the return value into a shell command and
     then pass it to a shell for execution.

     Precisely what this function does depends on your operating
     system.  The function is designed to work with the syntax of your
     system's standard shell; if you use an unusual shell, you will
     need to redefine this function.

          ;; This example shows the behavior on GNU and Unix systems.
          (shell-quote-argument "foo > bar")
               => "foo\\ \\>\\ bar"

          ;; This example shows the behavior on MS-DOS and MS-Windows.
          (shell-quote-argument "foo > bar")
               => "\"foo > bar\""

     Here's an example of using `shell-quote-argument' to construct a
     shell command:

          (concat "diff -c "
                  (shell-quote-argument oldfile)
                  " "
                  (shell-quote-argument newfile))


File: elisp,  Node: Synchronous Processes,  Next: Asynchronous Processes,  Prev: Shell Arguments,  Up: Processes

37.3 Creating a Synchronous Process
===================================

After a "synchronous process" is created, Emacs waits for the process
to terminate before continuing.  Starting Dired on GNU or Unix(1) is an
example of this: it runs `ls' in a synchronous process, then modifies
the output slightly.  Because the process is synchronous, the entire
directory listing arrives in the buffer before Emacs tries to do
anything with it.

   While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing `C-g'.  The first `C-g' tries to kill the
subprocess with a `SIGINT' signal; but it waits until the subprocess
actually terminates before quitting.  If during that time the user
types another `C-g', that kills the subprocess instantly with `SIGKILL'
and quits immediately (except on MS-DOS, where killing other processes
doesn't work).  *Note Quitting::.

   The synchronous subprocess functions return an indication of how the
process terminated.

   The output from a synchronous subprocess is generally decoded using a
coding system, much like text read from a file.  The input sent to a
subprocess by `call-process-region' is encoded using a coding system,
much like text written into a file.  *Note Coding Systems::.

 -- Function: call-process program &optional infile destination display
          &rest args
     This function calls PROGRAM in a separate process and waits for it
     to finish.

     The standard input for the process comes from file INFILE if
     INFILE is not `nil', and from the null device otherwise.  The
     argument DESTINATION says where to put the process output.  Here
     are the possibilities:

    a buffer
          Insert the output in that buffer, before point.  This
          includes both the standard output stream and the standard
          error stream of the process.

    a string
          Insert the output in a buffer with that name, before point.

    `t'
          Insert the output in the current buffer, before point.

    `nil'
          Discard the output.

    0
          Discard the output, and return `nil' immediately without
          waiting for the subprocess to finish.

          In this case, the process is not truly synchronous, since it
          can run in parallel with Emacs; but you can think of it as
          synchronous in that Emacs is essentially finished with the
          subprocess as soon as this function returns.

          MS-DOS doesn't support asynchronous subprocesses, so this
          option doesn't work there.

    `(REAL-DESTINATION ERROR-DESTINATION)'
          Keep the standard output stream separate from the standard
          error stream; deal with the ordinary output as specified by
          REAL-DESTINATION, and dispose of the error output according
          to ERROR-DESTINATION.  If ERROR-DESTINATION is `nil', that
          means to discard the error output, `t' means mix it with the
          ordinary output, and a string specifies a file name to
          redirect error output into.

          You can't directly specify a buffer to put the error output
          in; that is too difficult to implement.  But you can achieve
          this result by sending the error output to a temporary file
          and then inserting the file into a buffer.

     If DISPLAY is non-`nil', then `call-process' redisplays the buffer
     as output is inserted.  (However, if the coding system chosen for
     decoding output is `undecided', meaning deduce the encoding from
     the actual data, then redisplay sometimes cannot continue once
     non-ASCII characters are encountered.  There are fundamental
     reasons why it is hard to fix this; see *Note Output from
     Processes::.)

     Otherwise the function `call-process' does no redisplay, and the
     results become visible on the screen only when Emacs redisplays
     that buffer in the normal course of events.

     The remaining arguments, ARGS, are strings that specify command
     line arguments for the program.

     The value returned by `call-process' (unless you told it not to
     wait) indicates the reason for process termination.  A number
     gives the exit status of the subprocess; 0 means success, and any
     other value means failure.  If the process terminated with a
     signal, `call-process' returns a string describing the signal.

     In the examples below, the buffer `foo' is current.

          (call-process "pwd" nil t)
               => 0

          ---------- Buffer: foo ----------
          /usr/user/lewis/manual
          ---------- Buffer: foo ----------

          (call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
               => 0

          ---------- Buffer: bar ----------
          lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh

          ---------- Buffer: bar ----------

     Here is a good example of the use of `call-process', which used to
     be found in the definition of `insert-directory':

          (call-process insert-directory-program nil t nil SWITCHES
                        (if full-directory-p
                            (concat (file-name-as-directory file) ".")
                          file))

 -- Function: process-file program &optional infile buffer display
          &rest args
     This function processes files synchronously in a separate process.
     It is similar to `call-process' but may invoke a file handler
     based on the value of the variable `default-directory'.  The
     current working directory of the subprocess is `default-directory'.

     The arguments are handled in almost the same way as for
     `call-process', with the following differences:

     Some file handlers may not support all combinations and forms of
     the arguments INFILE, BUFFER, and DISPLAY.  For example, some file
     handlers might behave as if DISPLAY were `nil', regardless of the
     value actually passed.  As another example, some file handlers
     might not support separating standard output and error output by
     way of the BUFFER argument.

     If a file handler is invoked, it determines the program to run
     based on the first argument PROGRAM.  For instance, consider that a
     handler for remote files is invoked.  Then the path that is used
     for searching the program might be different than `exec-path'.

     The second argument INFILE may invoke a file handler.  The file
     handler could be different from the handler chosen for the
     `process-file' function itself.  (For example, `default-directory'
     could be on a remote host, whereas INFILE is on another remote
     host.  Or `default-directory' could be non-special, whereas INFILE
     is on a remote host.)

     If BUFFER is a list of the form `(REAL-DESTINATION
     ERROR-DESTINATION)', and ERROR-DESTINATION names a file, then the
     same remarks as for INFILE apply.

     The remaining arguments (ARGS) will be passed to the process
     verbatim.  Emacs is not involved in processing file names that are
     present in ARGS.  To avoid confusion, it may be best to avoid
     absolute file names in ARGS, but rather to specify all file names
     as relative to `default-directory'.  The function
     `file-relative-name' is useful for constructing such relative file
     names.

 -- Function: call-process-region start end program &optional delete
          destination display &rest args
     This function sends the text from START to END as standard input
     to a process running PROGRAM.  It deletes the text sent if DELETE
     is non-`nil'; this is useful when DESTINATION is `t', to insert
     the output in the current buffer in place of the input.

     The arguments DESTINATION and DISPLAY control what to do with the
     output from the subprocess, and whether to update the display as
     it comes in.  For details, see the description of `call-process',
     above.  If DESTINATION is the integer 0, `call-process-region'
     discards the output and returns `nil' immediately, without waiting
     for the subprocess to finish (this only works if asynchronous
     subprocesses are supported).

     The remaining arguments, ARGS, are strings that specify command
     line arguments for the program.

     The return value of `call-process-region' is just like that of
     `call-process': `nil' if you told it to return without waiting;
     otherwise, a number or string which indicates how the subprocess
     terminated.

     In the following example, we use `call-process-region' to run the
     `cat' utility, with standard input being the first five characters
     in buffer `foo' (the word `input').  `cat' copies its standard
     input into its standard output.  Since the argument DESTINATION is
     `t', this output is inserted in the current buffer.

          ---------- Buffer: foo ----------
          input-!-
          ---------- Buffer: foo ----------

          (call-process-region 1 6 "cat" nil t)
               => 0

          ---------- Buffer: foo ----------
          inputinput-!-
          ---------- Buffer: foo ----------

     The `shell-command-on-region' command uses `call-process-region'
     like this:

          (call-process-region
           start end
           shell-file-name      ; Name of program.
           nil                  ; Do not delete region.
           buffer               ; Send output to `buffer'.
           nil                  ; No redisplay during output.
           "-c" command)        ; Arguments for the shell.

 -- Function: call-process-shell-command command &optional infile
          destination display &rest args
     This function executes the shell command COMMAND synchronously in
     a separate process.  The final arguments ARGS are additional
     arguments to add at the end of COMMAND.  The other arguments are
     handled as in `call-process'.

 -- Function: shell-command-to-string command
     This function executes COMMAND (a string) as a shell command, then
     returns the command's output as a string.

   ---------- Footnotes ----------

   (1) On other systems, Emacs uses a Lisp emulation of `ls'; see *Note
Contents of Directories::.


File: elisp,  Node: Asynchronous Processes,  Next: Deleting Processes,  Prev: Synchronous Processes,  Up: Processes

37.4 Creating an Asynchronous Process
=====================================

After an "asynchronous process" is created, Emacs and the subprocess
both continue running immediately.  The process thereafter runs in
parallel with Emacs, and the two can communicate with each other using
the functions described in the following sections.  However,
communication is only partially asynchronous: Emacs sends data to the
process only when certain functions are called, and Emacs accepts data
from the process only when Emacs is waiting for input or for a time
delay.

   Here we describe how to create an asynchronous process.

 -- Function: start-process name buffer-or-name program &rest args
     This function creates a new asynchronous subprocess and starts the
     program PROGRAM running in it.  It returns a process object that
     stands for the new subprocess in Lisp.  The argument NAME
     specifies the name for the process object; if a process with this
     name already exists, then NAME is modified (by appending `<1>',
     etc.) to be unique.  The buffer BUFFER-OR-NAME is the buffer to
     associate with the process.

     The remaining arguments, ARGS, are strings that specify command
     line arguments for the program.

     In the example below, the first process is started and runs
     (rather, sleeps) for 100 seconds.  Meanwhile, the second process
     is started, and given the name `my-process<1>' for the sake of
     uniqueness.  It inserts the directory listing at the end of the
     buffer `foo', before the first process finishes.  Then it
     finishes, and a message to that effect is inserted in the buffer.
     Much later, the first process finishes, and another message is
     inserted in the buffer for it.

          (start-process "my-process" "foo" "sleep" "100")
               => #<process my-process>

          (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
               => #<process my-process<1>>

          ---------- Buffer: foo ----------
          total 2
          lrwxrwxrwx  1 lewis     14 Jul 22 10:12 gnuemacs --> /emacs
          -rwxrwxrwx  1 lewis     19 Jul 30 21:02 lemon

          Process my-process<1> finished

          Process my-process finished
          ---------- Buffer: foo ----------

 -- Function: start-process-shell-command name buffer-or-name command
          &rest command-args
     This function is like `start-process' except that it uses a shell
     to execute the specified command.  The argument COMMAND is a shell
     command name, and COMMAND-ARGS are the arguments for the shell
     command.  The variable `shell-file-name' specifies which shell to
     use.

     The point of running a program through the shell, rather than
     directly with `start-process', is so that you can employ shell
     features such as wildcards in the arguments.  It follows that if
     you include an arbitrary user-specified arguments in the command,
     you should quote it with `shell-quote-argument' first, so that any
     special shell characters do _not_ have their special shell
     meanings.  *Note Shell Arguments::.

 -- Variable: process-connection-type
     This variable controls the type of device used to communicate with
     asynchronous subprocesses.  If it is non-`nil', then PTYs are
     used, when available.  Otherwise, pipes are used.

     PTYs are usually preferable for processes visible to the user, as
     in Shell mode, because they allow job control (`C-c', `C-z', etc.)
     to work between the process and its children, whereas pipes do
     not.  For subprocesses used for internal purposes by programs, it
     is often better to use a pipe, because they are more efficient.  In
     addition, the total number of PTYs is limited on many systems and
     it is good not to waste them.

     The value of `process-connection-type' takes effect when
     `start-process' is called.  So you can specify how to communicate
     with one subprocess by binding the variable around the call to
     `start-process'.

          (let ((process-connection-type nil))  ; Use a pipe.
            (start-process ...))

     To determine whether a given subprocess actually got a pipe or a
     PTY, use the function `process-tty-name' (*note Process
     Information::).


File: elisp,  Node: Deleting Processes,  Next: Process Information,  Prev: Asynchronous Processes,  Up: Processes

37.5 Deleting Processes
=======================

"Deleting a process" disconnects Emacs immediately from the subprocess.
Processes are deleted automatically after they terminate, but not
necessarily right away.  You can delete a process explicitly at any
time.  If you delete a terminated process explicitly before it is
deleted automatically, no harm results.  Deleting a running process
sends a signal to terminate it (and its child processes if any), and
calls the process sentinel if it has one.  *Note Sentinels::.

   When a process is deleted, the process object itself continues to
exist as long as other Lisp objects point to it.  All the Lisp
primitives that work on process objects accept deleted processes, but
those that do I/O or send signals will report an error.  The process
mark continues to point to the same place as before, usually into a
buffer where output from the process was being inserted.

 -- User Option: delete-exited-processes
     This variable controls automatic deletion of processes that have
     terminated (due to calling `exit' or to a signal).  If it is
     `nil', then they continue to exist until the user runs
     `list-processes'.  Otherwise, they are deleted immediately after
     they exit.

 -- Function: delete-process process
     This function deletes a process, killing it with a `SIGKILL'
     signal.  The argument may be a process, the name of a process, a
     buffer, or the name of a buffer.  (A buffer or buffer-name stands
     for the process that `get-buffer-process' returns.)  Calling
     `delete-process' on a running process terminates it, updates the
     process status, and runs the sentinel (if any) immediately.  If the
     process has already terminated, calling `delete-process' has no
     effect on its status, or on the running of its sentinel (which will
     happen sooner or later).

          (delete-process "*shell*")
               => nil


File: elisp,  Node: Process Information,  Next: Input to Processes,  Prev: Deleting Processes,  Up: Processes

37.6 Process Information
========================

Several functions return information about processes.  `list-processes'
is provided for interactive use.

 -- Command: list-processes &optional query-only
     This command displays a listing of all living processes.  In
     addition, it finally deletes any process whose status was `Exited'
     or `Signaled'.  It returns `nil'.

     If QUERY-ONLY is non-`nil' then it lists only processes whose
     query flag is non-`nil'.  *Note Query Before Exit::.

 -- Function: process-list
     This function returns a list of all processes that have not been
     deleted.

          (process-list)
               => (#<process display-time> #<process shell>)

 -- Function: get-process name
     This function returns the process named NAME, or `nil' if there is
     none.  An error is signaled if NAME is not a string.

          (get-process "shell")
               => #<process shell>

 -- Function: process-command process
     This function returns the command that was executed to start
     PROCESS.  This is a list of strings, the first string being the
     program executed and the rest of the strings being the arguments
     that were given to the program.

          (process-command (get-process "shell"))
               => ("/bin/csh" "-i")

 -- Function: process-id process
     This function returns the PID of PROCESS.  This is an integer that
     distinguishes the process PROCESS from all other processes running
     on the same computer at the current time.  The PID of a process is
     chosen by the operating system kernel when the process is started
     and remains constant as long as the process exists.

 -- Function: process-name process
     This function returns the name of PROCESS.

 -- Function: process-status process-name
     This function returns the status of PROCESS-NAME as a symbol.  The
     argument PROCESS-NAME must be a process, a buffer, a process name
     (string) or a buffer name (string).

     The possible values for an actual subprocess are:

    `run'
          for a process that is running.

    `stop'
          for a process that is stopped but continuable.

    `exit'
          for a process that has exited.

    `signal'
          for a process that has received a fatal signal.

    `open'
          for a network connection that is open.

    `closed'
          for a network connection that is closed.  Once a connection
          is closed, you cannot reopen it, though you might be able to
          open a new connection to the same place.

    `connect'
          for a non-blocking connection that is waiting to complete.

    `failed'
          for a non-blocking connection that has failed to complete.

    `listen'
          for a network server that is listening.

    `nil'
          if PROCESS-NAME is not the name of an existing process.

          (process-status "shell")
               => run
          (process-status (get-buffer "*shell*"))
               => run
          x
               => #<process xx<1>>
          (process-status x)
               => exit

     For a network connection, `process-status' returns one of the
     symbols `open' or `closed'.  The latter means that the other side
     closed the connection, or Emacs did `delete-process'.

 -- Function: process-exit-status process
     This function returns the exit status of PROCESS or the signal
     number that killed it.  (Use the result of `process-status' to
     determine which of those it is.)  If PROCESS has not yet
     terminated, the value is 0.

 -- Function: process-tty-name process
     This function returns the terminal name that PROCESS is using for
     its communication with Emacs--or `nil' if it is using pipes
     instead of a terminal (see `process-connection-type' in *Note
     Asynchronous Processes::).

 -- Function: process-coding-system process
     This function returns a cons cell describing the coding systems in
     use for decoding output from PROCESS and for encoding input to
     PROCESS (*note Coding Systems::).  The value has this form:

          (CODING-SYSTEM-FOR-DECODING . CODING-SYSTEM-FOR-ENCODING)

 -- Function: set-process-coding-system process &optional
          decoding-system encoding-system
     This function specifies the coding systems to use for subsequent
     output from and input to PROCESS.  It will use DECODING-SYSTEM to
     decode subprocess output, and ENCODING-SYSTEM to encode subprocess
     input.

   Every process also has a property list that you can use to store
miscellaneous values associated with the process.

 -- Function: process-get process propname
     This function returns the value of the PROPNAME property of
     PROCESS.

 -- Function: process-put process propname value
     This function sets the value of the PROPNAME property of PROCESS
     to VALUE.

 -- Function: process-plist process
     This function returns the process plist of PROCESS.

 -- Function: set-process-plist process plist
     This function sets the process plist of PROCESS to PLIST.


File: elisp,  Node: Input to Processes,  Next: Signals to Processes,  Prev: Process Information,  Up: Processes

37.7 Sending Input to Processes
===============================

Asynchronous subprocesses receive input when it is sent to them by
Emacs, which is done with the functions in this section.  You must
specify the process to send input to, and the input data to send.  The
data appears on the "standard input" of the subprocess.

   Some operating systems have limited space for buffered input in a
PTY.  On these systems, Emacs sends an EOF periodically amidst the
other characters, to force them through.  For most programs, these EOFs
do no harm.

   Subprocess input is normally encoded using a coding system before the
subprocess receives it, much like text written into a file.  You can use
`set-process-coding-system' to specify which coding system to use
(*note Process Information::).  Otherwise, the coding system comes from
`coding-system-for-write', if that is non-`nil'; or else from the
defaulting mechanism (*note Default Coding Systems::).

   Sometimes the system is unable to accept input for that process,
because the input buffer is full.  When this happens, the send functions
wait a short while, accepting output from subprocesses, and then try
again.  This gives the subprocess a chance to read more of its pending
input and make space in the buffer.  It also allows filters, sentinels
and timers to run--so take account of that in writing your code.

   In these functions, the PROCESS argument can be a process or the
name of a process, or a buffer or buffer name (which stands for a
process via `get-buffer-process').  `nil' means the current buffer's
process.

 -- Function: process-send-string process string
     This function sends PROCESS the contents of STRING as standard
     input.  If it is `nil', the current buffer's process is used.

     The function returns `nil'.

          (process-send-string "shell<1>" "ls\n")
               => nil


          ---------- Buffer: *shell* ----------
          ...
          introduction.texi               syntax-tables.texi~
          introduction.texi~              text.texi
          introduction.txt                text.texi~
          ...
          ---------- Buffer: *shell* ----------

 -- Function: process-send-region process start end
     This function sends the text in the region defined by START and
     END as standard input to PROCESS.

     An error is signaled unless both START and END are integers or
     markers that indicate positions in the current buffer.  (It is
     unimportant which number is larger.)

 -- Function: process-send-eof &optional process
     This function makes PROCESS see an end-of-file in its input.  The
     EOF comes after any text already sent to it.

     The function returns PROCESS.

          (process-send-eof "shell")
               => "shell"

 -- Function: process-running-child-p process
     This function will tell you whether a subprocess has given control
     of its terminal to its own child process.  The value is `t' if
     this is true, or if Emacs cannot tell; it is `nil' if Emacs can be
     certain that this is not so.


File: elisp,  Node: Signals to Processes,  Next: Output from Processes,  Prev: Input to Processes,  Up: Processes

37.8 Sending Signals to Processes
=================================

"Sending a signal" to a subprocess is a way of interrupting its
activities.  There are several different signals, each with its own
meaning.  The set of signals and their names is defined by the operating
system.  For example, the signal `SIGINT' means that the user has typed
`C-c', or that some analogous thing has happened.

   Each signal has a standard effect on the subprocess.  Most signals
kill the subprocess, but some stop or resume execution instead.  Most
signals can optionally be handled by programs; if the program handles
the signal, then we can say nothing in general about its effects.

   You can send signals explicitly by calling the functions in this
section.  Emacs also sends signals automatically at certain times:
killing a buffer sends a `SIGHUP' signal to all its associated
processes; killing Emacs sends a `SIGHUP' signal to all remaining
processes.  (`SIGHUP' is a signal that usually indicates that the user
hung up the phone.)

   Each of the signal-sending functions takes two optional arguments:
PROCESS and CURRENT-GROUP.

   The argument PROCESS must be either a process, a process name, a
buffer, a buffer name, or `nil'.  A buffer or buffer name stands for a
process through `get-buffer-process'.  `nil' stands for the process
associated with the current buffer.  An error is signaled if PROCESS
does not identify a process.

   The argument CURRENT-GROUP is a flag that makes a difference when
you are running a job-control shell as an Emacs subprocess.  If it is
non-`nil', then the signal is sent to the current process-group of the
terminal that Emacs uses to communicate with the subprocess.  If the
process is a job-control shell, this means the shell's current subjob.
If it is `nil', the signal is sent to the process group of the
immediate subprocess of Emacs.  If the subprocess is a job-control
shell, this is the shell itself.

   The flag CURRENT-GROUP has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes.  For the same reason,
job-control shells won't work when a pipe is used.  See
`process-connection-type' in *Note Asynchronous Processes::.

 -- Function: interrupt-process &optional process current-group
     This function interrupts the process PROCESS by sending the signal
     `SIGINT'.  Outside of Emacs, typing the "interrupt character"
     (normally `C-c' on some systems, and `DEL' on others) sends this
     signal.  When the argument CURRENT-GROUP is non-`nil', you can
     think of this function as "typing `C-c'" on the terminal by which
     Emacs talks to the subprocess.

 -- Function: kill-process &optional process current-group
     This function kills the process PROCESS by sending the signal
     `SIGKILL'.  This signal kills the subprocess immediately, and
     cannot be handled by the subprocess.

 -- Function: quit-process &optional process current-group
     This function sends the signal `SIGQUIT' to the process PROCESS.
     This signal is the one sent by the "quit character" (usually `C-b'
     or `C-\') when you are not inside Emacs.

 -- Function: stop-process &optional process current-group
     This function stops the process PROCESS by sending the signal
     `SIGTSTP'.  Use `continue-process' to resume its execution.

     Outside of Emacs, on systems with job control, the "stop character"
     (usually `C-z') normally sends this signal.  When CURRENT-GROUP is
     non-`nil', you can think of this function as "typing `C-z'" on the
     terminal Emacs uses to communicate with the subprocess.

 -- Function: continue-process &optional process current-group
     This function resumes execution of the process PROCESS by sending
     it the signal `SIGCONT'.  This presumes that PROCESS was stopped
     previously.

 -- Function: signal-process process signal
     This function sends a signal to process PROCESS.  The argument
     SIGNAL specifies which signal to send; it should be an integer.

     The PROCESS argument can be a system process ID; that allows you
     to send signals to processes that are not children of Emacs.


File: elisp,  Node: Output from Processes,  Next: Sentinels,  Prev: Signals to Processes,  Up: Processes

37.9 Receiving Output from Processes
====================================

There are two ways to receive the output that a subprocess writes to
its standard output stream.  The output can be inserted in a buffer,
which is called the associated buffer of the process, or a function
called the "filter function" can be called to act on the output.  If
the process has no buffer and no filter function, its output is
discarded.

   When a subprocess terminates, Emacs reads any pending output, then
stops reading output from that subprocess.  Therefore, if the
subprocess has children that are still live and still producing output,
Emacs won't receive that output.

   Output from a subprocess can arrive only while Emacs is waiting: when
reading terminal input, in `sit-for' and `sleep-for' (*note Waiting::),
and in `accept-process-output' (*note Accepting Output::).  This
minimizes the problem of timing errors that usually plague parallel
programming.  For example, you can safely create a process and only
then specify its buffer or filter function; no output can arrive before
you finish, if the code in between does not call any primitive that
waits.

 -- Variable: process-adaptive-read-buffering
     On some systems, when Emacs reads the output from a subprocess, the
     output data is read in very small blocks, potentially resulting in
     very poor performance.  This behavior can be remedied to some
     extent by setting the variable PROCESS-ADAPTIVE-READ-BUFFERING to a
     non-`nil' value (the default), as it will automatically delay
     reading from such processes, thus allowing them to produce more
     output before Emacs tries to read it.

   It is impossible to separate the standard output and standard error
streams of the subprocess, because Emacs normally spawns the subprocess
inside a pseudo-TTY, and a pseudo-TTY has only one output channel.  If
you want to keep the output to those streams separate, you should
redirect one of them to a file--for example, by using an appropriate
shell command.

* Menu:

* Process Buffers::         If no filter, output is put in a buffer.
* Filter Functions::        Filter functions accept output from the process.
* Decoding Output::         Filters can get unibyte or multibyte strings.
* Accepting Output::        How to wait until process output arrives.


File: elisp,  Node: Process Buffers,  Next: Filter Functions,  Up: Output from Processes

37.9.1 Process Buffers
----------------------

A process can (and usually does) have an "associated buffer", which is
an ordinary Emacs buffer that is used for two purposes: storing the
output from the process, and deciding when to kill the process.  You
can also use the buffer to identify a process to operate on, since in
normal practice only one process is associated with any given buffer.
Many applications of processes also use the buffer for editing input to
be sent to the process, but this is not built into Emacs Lisp.

   Unless the process has a filter function (*note Filter Functions::),
its output is inserted in the associated buffer.  The position to insert
the output is determined by the `process-mark', which is then updated
to point to the end of the text just inserted.  Usually, but not
always, the `process-mark' is at the end of the buffer.

 -- Function: process-buffer process
     This function returns the associated buffer of the process PROCESS.

          (process-buffer (get-process "shell"))
               => #<buffer *shell*>

 -- Function: process-mark process
     This function returns the process marker for PROCESS, which is the
     marker that says where to insert output from the process.

     If PROCESS does not have a buffer, `process-mark' returns a marker
     that points nowhere.

     Insertion of process output in a buffer uses this marker to decide
     where to insert, and updates it to point after the inserted text.
     That is why successive batches of output are inserted
     consecutively.

     Filter functions normally should use this marker in the same
     fashion as is done by direct insertion of output in the buffer.  A
     good example of a filter function that uses `process-mark' is
     found at the end of the following section.

     When the user is expected to enter input in the process buffer for
     transmission to the process, the process marker separates the new
     input from previous output.

 -- Function: set-process-buffer process buffer
     This function sets the buffer associated with PROCESS to BUFFER.
     If BUFFER is `nil', the process becomes associated with no buffer.

 -- Function: get-buffer-process buffer-or-name
     This function returns a nondeleted process associated with the
     buffer specified by BUFFER-OR-NAME.  If there are several processes
     associated with it, this function chooses one (currently, the one
     most recently created, but don't count on that).  Deletion of a
     process (see `delete-process') makes it ineligible for this
     function to return.

     It is usually a bad idea to have more than one process associated
     with the same buffer.

          (get-buffer-process "*shell*")
               => #<process shell>

     Killing the process's buffer deletes the process, which kills the
     subprocess with a `SIGHUP' signal (*note Signals to Processes::).


File: elisp,  Node: Filter Functions,  Next: Decoding Output,  Prev: Process Buffers,  Up: Output from Processes

37.9.2 Process Filter Functions
-------------------------------

A process "filter function" is a function that receives the standard
output from the associated process.  If a process has a filter, then
_all_ output from that process is passed to the filter.  The process
buffer is used directly for output from the process only when there is
no filter.

   The filter function can only be called when Emacs is waiting for
something, because process output arrives only at such times.  Emacs
waits when reading terminal input, in `sit-for' and `sleep-for' (*note
Waiting::), and in `accept-process-output' (*note Accepting Output::).

   A filter function must accept two arguments: the associated process
and a string, which is output just received from it.  The function is
then free to do whatever it chooses with the output.

   Quitting is normally inhibited within a filter function--otherwise,
the effect of typing `C-g' at command level or to quit a user command
would be unpredictable.  If you want to permit quitting inside a filter
function, bind `inhibit-quit' to `nil'.  In most cases, the right way
to do this is with the macro `with-local-quit'.  *Note Quitting::.

   If an error happens during execution of a filter function, it is
caught automatically, so that it doesn't stop the execution of whatever
program was running when the filter function was started.  However, if
`debug-on-error' is non-`nil', the error-catching is turned off.  This
makes it possible to use the Lisp debugger to debug the filter
function.  *Note Debugger::.

   Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of Emacs when there is no
filter.  Such filter functions need to use `set-buffer' in order to be
sure to insert in that buffer.  To avoid setting the current buffer
semipermanently, these filter functions must save and restore the
current buffer.  They should also update the process marker, and in some
cases update the value of point.  Here is how to do these things:

     (defun ordinary-insertion-filter (proc string)
       (with-current-buffer (process-buffer proc)
         (let ((moving (= (point) (process-mark proc))))
           (save-excursion
             ;; Insert the text, advancing the process marker.
             (goto-char (process-mark proc))
             (insert string)
             (set-marker (process-mark proc) (point)))
           (if moving (goto-char (process-mark proc))))))

The reason to use `with-current-buffer', rather than using
`save-excursion' to save and restore the current buffer, is so as to
preserve the change in point made by the second call to `goto-char'.

   To make the filter force the process buffer to be visible whenever
new text arrives, insert the following line just before the
`with-current-buffer' construct:

     (display-buffer (process-buffer proc))

   To force point to the end of the new output, no matter where it was
previously, eliminate the variable `moving' and call `goto-char'
unconditionally.

   In earlier Emacs versions, every filter function that did regular
expression searching or matching had to explicitly save and restore the
match data.  Now Emacs does this automatically for filter functions;
they never need to do it explicitly.  *Note Match Data::.

   A filter function that writes the output into the buffer of the
process should check whether the buffer is still alive.  If it tries to
insert into a dead buffer, it will get an error.  The expression
`(buffer-name (process-buffer PROCESS))' returns `nil' if the buffer is
dead.

   The output to the function may come in chunks of any size.  A program
that produces the same output twice in a row may send it as one batch of
200 characters one time, and five batches of 40 characters the next.  If
the filter looks for certain text strings in the subprocess output, make
sure to handle the case where one of these strings is split across two
or more batches of output.

 -- Function: set-process-filter process filter
     This function gives PROCESS the filter function FILTER.  If FILTER
     is `nil', it gives the process no filter.

 -- Function: process-filter process
     This function returns the filter function of PROCESS, or `nil' if
     it has none.

   Here is an example of use of a filter function:

     (defun keep-output (process output)
        (setq kept (cons output kept)))
          => keep-output
     (setq kept nil)
          => nil
     (set-process-filter (get-process "shell") 'keep-output)
          => keep-output
     (process-send-string "shell" "ls ~/other\n")
          => nil
     kept
          => ("lewis@slug[8] % "
     "FINAL-W87-SHORT.MSS    backup.otl              kolstad.mss~
     address.txt             backup.psf              kolstad.psf
     backup.bib~             david.mss               resume-Dec-86.mss~
     backup.err              david.psf               resume-Dec.psf
     backup.mss              dland                   syllabus.mss
     "
     "#backups.mss#          backup.mss~             kolstad.mss
     ")


File: elisp,  Node: Decoding Output,  Next: Accepting Output,  Prev: Filter Functions,  Up: Output from Processes

37.9.3 Decoding Process Output
------------------------------

When Emacs writes process output directly into a multibyte buffer, it
decodes the output according to the process output coding system.  If
the coding system is `raw-text' or `no-conversion', Emacs converts the
unibyte output to multibyte using `string-to-multibyte', and inserts
the resulting multibyte text.

   You can use `set-process-coding-system' to specify which coding
system to use (*note Process Information::).  Otherwise, the coding
system comes from `coding-system-for-read', if that is non-`nil'; or
else from the defaulting mechanism (*note Default Coding Systems::).

   *Warning:* Coding systems such as `undecided' which determine the
coding system from the data do not work entirely reliably with
asynchronous subprocess output.  This is because Emacs has to process
asynchronous subprocess output in batches, as it arrives.  Emacs must
try to detect the proper coding system from one batch at a time, and
this does not always work.  Therefore, if at all possible, specify a
coding system that determines both the character code conversion and
the end of line conversion--that is, one like `latin-1-unix', rather
than `undecided' or `latin-1'.

   When Emacs calls a process filter function, it provides the process
output as a multibyte string or as a unibyte string according to the
process's filter multibyte flag.  If the flag is non-`nil', Emacs
decodes the output according to the process output coding system to
produce a multibyte string, and passes that to the process.  If the
flag is `nil', Emacs puts the output into a unibyte string, with no
decoding, and passes that.

   When you create a process, the filter multibyte flag takes its
initial value from `default-enable-multibyte-characters'.  If you want
to change the flag later on, use `set-process-filter-multibyte'.

 -- Function: set-process-filter-multibyte process multibyte
     This function sets the filter multibyte flag of PROCESS to
     MULTIBYTE.

 -- Function: process-filter-multibyte-p process
     This function returns the filter multibyte flag of PROCESS.


File: elisp,  Node: Accepting Output,  Prev: Decoding Output,  Up: Output from Processes

37.9.4 Accepting Output from Processes
--------------------------------------

Output from asynchronous subprocesses normally arrives only while Emacs
is waiting for some sort of external event, such as elapsed time or
terminal input.  Occasionally it is useful in a Lisp program to
explicitly permit output to arrive at a specific point, or even to wait
until output arrives from a process.

 -- Function: accept-process-output &optional process seconds millisec
          just-this-one
     This function allows Emacs to read pending output from processes.
     The output is inserted in the associated buffers or given to their
     filter functions.  If PROCESS is non-`nil' then this function does
     not return until some output has been received from PROCESS.

     The arguments SECONDS and MILLISEC let you specify timeout
     periods.  The former specifies a period measured in seconds and the
     latter specifies one measured in milliseconds.  The two time
     periods thus specified are added together, and
     `accept-process-output' returns after that much time, whether or
     not there has been any subprocess output.

     The argument MILLISEC is semi-obsolete nowadays because SECONDS
     can be a floating point number to specify waiting a fractional
     number of seconds.  If SECONDS is 0, the function accepts whatever
     output is pending but does not wait.

     If PROCESS is a process, and the argument JUST-THIS-ONE is
     non-`nil', only output from that process is handled, suspending
     output from other processes until some output has been received
     from that process or the timeout expires.  If JUST-THIS-ONE is an
     integer, also inhibit running timers.  This feature is generally
     not recommended, but may be necessary for specific applications,
     such as speech synthesis.

     The function `accept-process-output' returns non-`nil' if it did
     get some output, or `nil' if the timeout expired before output
     arrived.


File: elisp,  Node: Sentinels,  Next: Query Before Exit,  Prev: Output from Processes,  Up: Processes

37.10 Sentinels: Detecting Process Status Changes
=================================================

A "process sentinel" is a function that is called whenever the
associated process changes status for any reason, including signals
(whether sent by Emacs or caused by the process's own actions) that
terminate, stop, or continue the process.  The process sentinel is also
called if the process exits.  The sentinel receives two arguments: the
process for which the event occurred, and a string describing the type
of event.

   The string describing the event looks like one of the following:

   * `"finished\n"'.

   * `"exited abnormally with code EXITCODE\n"'.

   * `"NAME-OF-SIGNAL\n"'.

   * `"NAME-OF-SIGNAL (core dumped)\n"'.

   A sentinel runs only while Emacs is waiting (e.g., for terminal
input, or for time to elapse, or for process output).  This avoids the
timing errors that could result from running them at random places in
the middle of other Lisp programs.  A program can wait, so that
sentinels will run, by calling `sit-for' or `sleep-for' (*note
Waiting::), or `accept-process-output' (*note Accepting Output::).
Emacs also allows sentinels to run when the command loop is reading
input.  `delete-process' calls the sentinel when it terminates a
running process.

   Emacs does not keep a queue of multiple reasons to call the sentinel
of one process; it records just the current status and the fact that
there has been a change.  Therefore two changes in status, coming in
quick succession, can call the sentinel just once.  However, process
termination will always run the sentinel exactly once.  This is because
the process status can't change again after termination.

   Emacs explicitly checks for output from the process before running
the process sentinel.  Once the sentinel runs due to process
termination, no further output can arrive from the process.

   A sentinel that writes the output into the buffer of the process
should check whether the buffer is still alive.  If it tries to insert
into a dead buffer, it will get an error.  If the buffer is dead,
`(buffer-name (process-buffer PROCESS))' returns `nil'.

   Quitting is normally inhibited within a sentinel--otherwise, the
effect of typing `C-g' at command level or to quit a user command would
be unpredictable.  If you want to permit quitting inside a sentinel,
bind `inhibit-quit' to `nil'.  In most cases, the right way to do this
is with the macro `with-local-quit'.  *Note Quitting::.

   If an error happens during execution of a sentinel, it is caught
automatically, so that it doesn't stop the execution of whatever
programs was running when the sentinel was started.  However, if
`debug-on-error' is non-`nil', the error-catching is turned off.  This
makes it possible to use the Lisp debugger to debug the sentinel.
*Note Debugger::.

   While a sentinel is running, the process sentinel is temporarily set
to `nil' so that the sentinel won't run recursively.  For this reason
it is not possible for a sentinel to specify a new sentinel.

   In earlier Emacs versions, every sentinel that did regular expression
searching or matching had to explicitly save and restore the match data.
Now Emacs does this automatically for sentinels; they never need to do
it explicitly.  *Note Match Data::.

 -- Function: set-process-sentinel process sentinel
     This function associates SENTINEL with PROCESS.  If SENTINEL is
     `nil', then the process will have no sentinel.  The default
     behavior when there is no sentinel is to insert a message in the
     process's buffer when the process status changes.

     Changes in process sentinel take effect immediately--if the
     sentinel is slated to be run but has not been called yet, and you
     specify a new sentinel, the eventual call to the sentinel will use
     the new one.

          (defun msg-me (process event)
             (princ
               (format "Process: %s had the event `%s'" process event)))
          (set-process-sentinel (get-process "shell") 'msg-me)
               => msg-me
          (kill-process (get-process "shell"))
               -| Process: #<process shell> had the event `killed'
               => #<process shell>

 -- Function: process-sentinel process
     This function returns the sentinel of PROCESS, or `nil' if it has
     none.

 -- Function: waiting-for-user-input-p
     While a sentinel or filter function is running, this function
     returns non-`nil' if Emacs was waiting for keyboard input from the
     user at the time the sentinel or filter function was called, `nil'
     if it was not.


File: elisp,  Node: Query Before Exit,  Next: Transaction Queues,  Prev: Sentinels,  Up: Processes

37.11 Querying Before Exit
==========================

When Emacs exits, it terminates all its subprocesses by sending them
the `SIGHUP' signal.  Because subprocesses may be doing valuable work,
Emacs normally asks the user to confirm that it is ok to terminate
them.  Each process has a query flag which, if non-`nil', says that
Emacs should ask for confirmation before exiting and thus killing that
process.  The default for the query flag is `t', meaning _do_ query.

 -- Function: process-query-on-exit-flag process
     This returns the query flag of PROCESS.

 -- Function: set-process-query-on-exit-flag process flag
     This function sets the query flag of PROCESS to FLAG.  It returns
     FLAG.

          ;; Don't query about the shell process
          (set-process-query-on-exit-flag (get-process "shell") nil)
               => t

 -- Function: process-kill-without-query process &optional do-query
     This function clears the query flag of PROCESS, so that Emacs will
     not query the user on account of that process.

     Actually, the function does more than that: it returns the old
     value of the process's query flag, and sets the query flag to
     DO-QUERY.  Please don't use this function to do those things any
     more--please use the newer, cleaner functions
     `process-query-on-exit-flag' and `set-process-query-on-exit-flag'
     in all but the simplest cases.  The only way you should use
     `process-kill-without-query' nowadays is like this:

          ;; Don't query about the shell process
          (process-kill-without-query (get-process "shell"))


File: elisp,  Node: Transaction Queues,  Next: Network,  Prev: Query Before Exit,  Up: Processes

37.12 Transaction Queues
========================

You can use a "transaction queue" to communicate with a subprocess
using transactions.  First use `tq-create' to create a transaction
queue communicating with a specified process.  Then you can call
`tq-enqueue' to send a transaction.

 -- Function: tq-create process
     This function creates and returns a transaction queue
     communicating with PROCESS.  The argument PROCESS should be a
     subprocess capable of sending and receiving streams of bytes.  It
     may be a child process, or it may be a TCP connection to a server,
     possibly on another machine.

 -- Function: tq-enqueue queue question regexp closure fn &optional
          delay-question
     This function sends a transaction to queue QUEUE.  Specifying the
     queue has the effect of specifying the subprocess to talk to.

     The argument QUESTION is the outgoing message that starts the
     transaction.  The argument FN is the function to call when the
     corresponding answer comes back; it is called with two arguments:
     CLOSURE, and the answer received.

     The argument REGEXP is a regular expression that should match text
     at the end of the entire answer, but nothing before; that's how
     `tq-enqueue' determines where the answer ends.

     If the argument DELAY-QUESTION is non-nil, delay sending this
     question until the process has finished replying to any previous
     questions.  This produces more reliable results with some
     processes.

     The return value of `tq-enqueue' itself is not meaningful.

 -- Function: tq-close queue
     Shut down transaction queue QUEUE, waiting for all pending
     transactions to complete, and then terminate the connection or
     child process.

   Transaction queues are implemented by means of a filter function.
*Note Filter Functions::.


File: elisp,  Node: Network,  Next: Network Servers,  Prev: Transaction Queues,  Up: Processes

37.13 Network Connections
=========================

Emacs Lisp programs can open stream (TCP) and datagram (UDP) network
connections to other processes on the same machine or other machines.
A network connection is handled by Lisp much like a subprocess, and is
represented by a process object.  However, the process you are
communicating with is not a child of the Emacs process, so it has no
process ID, and you can't kill it or send it signals.  All you can do
is send and receive data.  `delete-process' closes the connection, but
does not kill the program at the other end; that program must decide
what to do about closure of the connection.

   Lisp programs can listen for connections by creating network
servers.  A network server is also represented by a kind of process
object, but unlike a network connection, the network server never
transfers data itself.  When it receives a connection request, it
creates a new network connection to represent the connection just made.
(The network connection inherits certain information, including the
process plist, from the server.)  The network server then goes back to
listening for more connection requests.

   Network connections and servers are created by calling
`make-network-process' with an argument list consisting of
keyword/argument pairs, for example `:server t' to create a server
process, or `:type 'datagram' to create a datagram connection.  *Note
Low-Level Network::, for details.  You can also use the
`open-network-stream' function described below.

   You can distinguish process objects representing network connections
and servers from those representing subprocesses with the
`process-status' function.  The possible status values for network
connections are `open', `closed', `connect', and `failed'.  For a
network server, the status is always `listen'.  None of those values is
possible for a real subprocess.  *Note Process Information::.

   You can stop and resume operation of a network process by calling
`stop-process' and `continue-process'.  For a server process, being
stopped means not accepting new connections.  (Up to 5 connection
requests will be queued for when you resume the server; you can
increase this limit, unless it is imposed by the operating system.)
For a network stream connection, being stopped means not processing
input (any arriving input waits until you resume the connection).  For
a datagram connection, some number of packets may be queued but input
may be lost.  You can use the function `process-command' to determine
whether a network connection or server is stopped; a non-`nil' value
means yes.

 -- Function: open-network-stream name buffer-or-name host service
     This function opens a TCP connection, and returns a process object
     that represents the connection.

     The NAME argument specifies the name for the process object.  It
     is modified as necessary to make it unique.

     The BUFFER-OR-NAME argument is the buffer to associate with the
     connection.  Output from the connection is inserted in the buffer,
     unless you specify a filter function to handle the output.  If
     BUFFER-OR-NAME is `nil', it means that the connection is not
     associated with any buffer.

     The arguments HOST and SERVICE specify where to connect to; HOST
     is the host name (a string), and SERVICE is the name of a defined
     network service (a string) or a port number (an integer).

 -- Function: process-contact process &optional key
     This function returns information about how a network process was
     set up.  For a connection, when KEY is `nil', it returns
     `(HOSTNAME SERVICE)' which specifies what you connected to.

     If KEY is `t', the value is the complete status information for
     the connection or server; that is, the list of keywords and values
     specified in `make-network-process', except that some of the
     values represent the current status instead of what you specified:

    `:buffer'
          The associated value is the process buffer.

    `:filter'
          The associated value is the process filter function.

    `:sentinel'
          The associated value is the process sentinel function.

    `:remote'
          In a connection, the address in internal format of the remote
          peer.

    `:local'
          The local address, in internal format.

    `:service'
          In a server, if you specified `t' for SERVICE, this value is
          the actual port number.

     `:local' and `:remote' are included even if they were not
     specified explicitly in `make-network-process'.

     If KEY is a keyword, the function returns the value corresponding
     to that keyword.

     For an ordinary child process, this function always returns `t'.


File: elisp,  Node: Network Servers,  Next: Datagrams,  Prev: Network,  Up: Processes

37.14 Network Servers
=====================

You create a server by calling `make-network-process' with `:server t'.
The server will listen for connection requests from clients.  When it
accepts a client connection request, that creates a new network
connection, itself a process object, with the following parameters:

   * The connection's process name is constructed by concatenating the
     server process' NAME with a client identification string.  The
     client identification string for an IPv4 connection looks like
     `<A.B.C.D:P>'.  Otherwise, it is a unique number in brackets, as
     in `<NNN>'.  The number is unique for each connection in the Emacs
     session.

   * If the server's filter is non-`nil', the connection process does
     not get a separate process buffer; otherwise, Emacs creates a new
     buffer for the purpose.  The buffer name is the server's buffer
     name or process name, concatenated with the client identification
     string.

     The server's process buffer value is never used directly by Emacs,
     but it is passed to the log function, which can log connections by
     inserting text there.

   * The communication type and the process filter and sentinel are
     inherited from those of the server.  The server never directly
     uses its filter and sentinel; their sole purpose is to initialize
     connections made to the server.

   * The connection's process contact info is set according to the
     client's addressing information (typically an IP address and a
     port number).  This information is associated with the
     `process-contact' keywords `:host', `:service', `:remote'.

   * The connection's local address is set up according to the port
     number used for the connection.

   * The client process' plist is initialized from the server's plist.


File: elisp,  Node: Datagrams,  Next: Low-Level Network,  Prev: Network Servers,  Up: Processes

37.15 Datagrams
===============

A datagram connection communicates with individual packets rather than
streams of data.  Each call to `process-send' sends one datagram packet
(*note Input to Processes::), and each datagram received results in one
call to the filter function.

   The datagram connection doesn't have to talk with the same remote
peer all the time.  It has a "remote peer address" which specifies
where to send datagrams to.  Each time an incoming datagram is passed
to the filter function, the peer address is set to the address that
datagram came from; that way, if the filter function sends a datagram,
it will go back to that place.  You can specify the remote peer address
when you create the datagram connection using the `:remote' keyword.
You can change it later on by calling `set-process-datagram-address'.

 -- Function: process-datagram-address process
     If PROCESS is a datagram connection or server, this function
     returns its remote peer address.

 -- Function: set-process-datagram-address process address
     If PROCESS is a datagram connection or server, this function sets
     its remote peer address to ADDRESS.


File: elisp,  Node: Low-Level Network,  Next: Misc Network,  Prev: Datagrams,  Up: Processes

37.16 Low-Level Network Access
==============================

You can also create network connections by operating at a lower level
than that of `open-network-stream', using `make-network-process'.

* Menu:

* Proc: Network Processes.   Using `make-network-process'.
* Options: Network Options.  Further control over network connections.
* Features: Network Feature Testing.
                             Determining which network features work on
                               the machine you are using.


File: elisp,  Node: Network Processes,  Next: Network Options,  Up: Low-Level Network

37.16.1 `make-network-process'
------------------------------

The basic function for creating network connections and network servers
is `make-network-process'.  It can do either of those jobs, depending
on the arguments you give it.

 -- Function: make-network-process &rest args
     This function creates a network connection or server and returns
     the process object that represents it.  The arguments ARGS are a
     list of keyword/argument pairs.  Omitting a keyword is always
     equivalent to specifying it with value `nil', except for
     `:coding', `:filter-multibyte', and `:reuseaddr'.  Here are the
     meaningful keywords:

    :name NAME
          Use the string NAME as the process name.  It is modified if
          necessary to make it unique.

    :type TYPE
          Specify the communication type.  A value of `nil' specifies a
          stream connection (the default); `datagram' specifies a
          datagram connection.  Both connections and servers can be of
          either type.

    :server SERVER-FLAG
          If SERVER-FLAG is non-`nil', create a server.  Otherwise,
          create a connection.  For a stream type server, SERVER-FLAG
          may be an integer which then specifies the length of the
          queue of pending connections to the server.  The default
          queue length is 5.

    :host HOST
          Specify the host to connect to.  HOST should be a host name or
          Internet address, as a string, or the symbol `local' to
          specify the local host.  If you specify HOST for a server, it
          must specify a valid address for the local host, and only
          clients connecting to that address will be accepted.

    :service SERVICE
          SERVICE specifies a port number to connect to, or, for a
          server, the port number to listen on.  It should be a service
          name that translates to a port number, or an integer
          specifying the port number directly.  For a server, it can
          also be `t', which means to let the system select an unused
          port number.

    :family FAMILY
          FAMILY specifies the address (and protocol) family for
          communication.  `nil' means determine the proper address
          family automatically for the given HOST and SERVICE.  `local'
          specifies a Unix socket, in which case HOST is ignored.
          `ipv4' and `ipv6' specify to use IPv4 and IPv6 respectively.

    :local LOCAL-ADDRESS
          For a server process, LOCAL-ADDRESS is the address to listen
          on.  It overrides FAMILY, HOST and SERVICE, and you may as
          well not specify them.

    :remote REMOTE-ADDRESS
          For a connection, REMOTE-ADDRESS is the address to connect to.
          It overrides FAMILY, HOST and SERVICE, and you may as well
          not specify them.

          For a datagram server, REMOTE-ADDRESS specifies the initial
          setting of the remote datagram address.

          The format of LOCAL-ADDRESS or REMOTE-ADDRESS depends on the
          address family:

             - An IPv4 address is represented as a five-element vector
               of four 8-bit integers and one 16-bit integer `[A B C D
               P]' corresponding to numeric IPv4 address A.B.C.D and
               port number P.

             - An IPv6 address is represented as a nine-element vector
               of 16-bit integers `[A B C D E F G H P]' corresponding
               to numeric IPv6 address A:B:C:D:E:F:G:H and port number
               P.

             - A local address is represented as a string which
               specifies the address in the local address space.

             - An "unsupported family" address is represented by a cons
               `(F . AV)', where F is the family number and AV is a
               vector specifying the socket address using one element
               per address data byte.  Do not rely on this format in
               portable code, as it may depend on implementation
               defined constants, data sizes, and data structure
               alignment.

    :nowait BOOL
          If BOOL is non-`nil' for a stream connection, return without
          waiting for the connection to complete.  When the connection
          succeeds or fails, Emacs will call the sentinel function,
          with a second argument matching `"open"' (if successful) or
          `"failed"'.  The default is to block, so that
          `make-network-process' does not return until the connection
          has succeeded or failed.

    :stop STOPPED
          Start the network connection or server in the `stopped' state
          if STOPPED is non-`nil'.

    :buffer BUFFER
          Use BUFFER as the process buffer.

    :coding CODING
          Use CODING as the coding system for this process.  To specify
          different coding systems for decoding data from the
          connection and for encoding data sent to it, specify
          `(DECODING .  ENCODING)' for CODING.

          If you don't specify this keyword at all, the default is to
          determine the coding systems from the data.

    :noquery QUERY-FLAG
          Initialize the process query flag to QUERY-FLAG.  *Note Query
          Before Exit::.

    :filter FILTER
          Initialize the process filter to FILTER.

    :filter-multibyte BOOL
          If BOOL is non-`nil', strings given to the process filter are
          multibyte, otherwise they are unibyte.  If you don't specify
          this keyword at all, the default is that the strings are
          multibyte if `default-enable-multibyte-characters' is
          non-`nil'.

    :sentinel SENTINEL
          Initialize the process sentinel to SENTINEL.

    :log LOG
          Initialize the log function of a server process to LOG.  The
          log function is called each time the server accepts a network
          connection from a client.  The arguments passed to the log
          function are SERVER, CONNECTION, and MESSAGE, where SERVER is
          the server process, CONNECTION is the new process for the
          connection, and MESSAGE is a string describing what has
          happened.

    :plist PLIST
          Initialize the process plist to PLIST.

     The original argument list, modified with the actual connection
     information, is available via the `process-contact' function.


File: elisp,  Node: Network Options,  Next: Network Feature Testing,  Prev: Network Processes,  Up: Low-Level Network

37.16.2 Network Options
-----------------------

The following network options can be specified when you create a
network process.  Except for `:reuseaddr', you can also set or modify
these options later, using `set-network-process-option'.

   For a server process, the options specified with
`make-network-process' are not inherited by the client connections, so
you will need to set the necessary options for each child connection as
it is created.

:bindtodevice DEVICE-NAME
     If DEVICE-NAME is a non-empty string identifying a network
     interface name (see `network-interface-list'), only handle packets
     received on that interface.  If DEVICE-NAME is `nil' (the
     default), handle packets received on any interface.

     Using this option may require special privileges on some systems.

:broadcast BROADCAST-FLAG
     If BROADCAST-FLAG is non-`nil' for a datagram process, the process
     will receive datagram packet sent to a broadcast address, and be
     able to send packets to a broadcast address.  Ignored for a stream
     connection.

:dontroute DONTROUTE-FLAG
     If DONTROUTE-FLAG is non-`nil', the process can only send to hosts
     on the same network as the local host.

:keepalive KEEPALIVE-FLAG
     If KEEPALIVE-FLAG is non-`nil' for a stream connection, enable
     exchange of low-level keep-alive messages.

:linger LINGER-ARG
     If LINGER-ARG is non-`nil', wait for successful transmission of
     all queued packets on the connection before it is deleted (see
     `delete-process').  If LINGER-ARG is an integer, it specifies the
     maximum time in seconds to wait for queued packets to be sent
     before closing the connection.  Default is `nil' which means to
     discard unsent queued packets when the process is deleted.

:oobinline OOBINLINE-FLAG
     If OOBINLINE-FLAG is non-`nil' for a stream connection, receive
     out-of-band data in the normal data stream.  Otherwise, ignore
     out-of-band data.

:priority PRIORITY
     Set the priority for packets sent on this connection to the integer
     PRIORITY.  The interpretation of this number is protocol specific,
     such as setting the TOS (type of service) field on IP packets sent
     on this connection.  It may also have system dependent effects,
     such as selecting a specific output queue on the network interface.

:reuseaddr REUSEADDR-FLAG
     If REUSEADDR-FLAG is non-`nil' (the default) for a stream server
     process, allow this server to reuse a specific port number (see
     `:service') unless another process on this host is already
     listening on that port.  If REUSEADDR-FLAG is `nil', there may be
     a period of time after the last use of that port (by any process
     on the host), where it is not possible to make a new server on
     that port.

 -- Function: set-network-process-option process option value
     This function sets or modifies a network option for network process
     PROCESS.  See `make-network-process' for details of options OPTION
     and their corresponding values VALUE.

     The current setting of an option is available via the
     `process-contact' function.


File: elisp,  Node: Network Feature Testing,  Prev: Network Options,  Up: Low-Level Network

37.16.3 Testing Availability of Network Features
------------------------------------------------

To test for the availability of a given network feature, use `featurep'
like this:

     (featurep 'make-network-process '(KEYWORD VALUE))

The result of the first form is `t' if it works to specify KEYWORD with
value VALUE in `make-network-process'.  The result of the second form
is `t' if KEYWORD is supported by `make-network-process'.  Here are
some of the KEYWORD--VALUE pairs you can test in this way.

`(:nowait t)'
     Non-`nil' if non-blocking connect is supported.

`(:type datagram)'
     Non-`nil' if datagrams are supported.

`(:family local)'
     Non-`nil' if local (a.k.a. "UNIX domain") sockets are supported.

`(:family ipv6)'
     Non-`nil' if IPv6 is supported.

`(:service t)'
     Non-`nil' if the system can select the port for a server.

   To test for the availability of a given network option, use
`featurep' like this:

     (featurep 'make-network-process 'KEYWORD)

Here are some of the options you can test in this way.

`:bindtodevice'
`:broadcast'
`:dontroute'
`:keepalive'
`:linger'
`:oobinline'
`:priority'
`:reuseaddr'
     That particular network option is supported by
     `make-network-process' and `set-network-process-option'.


File: elisp,  Node: Misc Network,  Next: Byte Packing,  Prev: Low-Level Network,  Up: Processes

37.17 Misc Network Facilities
=============================

These additional functions are useful for creating and operating on
network connections.  Note that they are supported only on some systems.

 -- Function: network-interface-list
     This function returns a list describing the network interfaces of
     the machine you are using.  The value is an alist whose elements
     have the form `(NAME . ADDRESS)'.  ADDRESS has the same form as
     the LOCAL-ADDRESS and REMOTE-ADDRESS arguments to
     `make-network-process'.

 -- Function: network-interface-info ifname
     This function returns information about the network interface named
     IFNAME.  The value is a list of the form `(ADDR BCAST NETMASK
     HWADDR FLAGS)'.

    ADDR
          The Internet protocol address.

    BCAST
          The broadcast address.

    NETMASK
          The network mask.

    HWADDR
          The layer 2 address (Ethernet MAC address, for instance).

    FLAGS
          The current flags of the interface.

 -- Function: format-network-address address &optional omit-port
     This function converts the Lisp representation of a network
     address to a string.

     A five-element vector `[A B C D P]' represents an IPv4 address
     A.B.C.D and port number P.  `format-network-address' converts that
     to the string `"A.B.C.D:P"'.

     A nine-element vector `[A B C D E F G H P]' represents an IPv6
     address along with a port number.  `format-network-address'
     converts that to the string `"[A:B:C:D:E:F:G:H]:P"'.

     If the vector does not include the port number, P, or if OMIT-PORT
     is non-`nil', the result does not include the `:P' suffix.


File: elisp,  Node: Byte Packing,  Prev: Misc Network,  Up: Processes

37.18 Packing and Unpacking Byte Arrays
=======================================

This section describes how to pack and unpack arrays of bytes, usually
for binary network protocols.  These functions convert byte arrays to
alists, and vice versa.  The byte array can be represented as a unibyte
string or as a vector of integers, while the alist associates symbols
either with fixed-size objects or with recursive sub-alists.

   Conversion from byte arrays to nested alists is also known as
"deserializing" or "unpacking", while going in the opposite direction
is also known as "serializing" or "packing".

* Menu:

* Bindat Spec::         Describing data layout.
* Bindat Functions::    Doing the unpacking and packing.
* Bindat Examples::     Samples of what bindat.el can do for you!


File: elisp,  Node: Bindat Spec,  Next: Bindat Functions,  Up: Byte Packing

37.18.1 Describing Data Layout
------------------------------

To control unpacking and packing, you write a "data layout
specification", a special nested list describing named and typed
"fields".  This specification controls length of each field to be
processed, and how to pack or unpack it.  We normally keep bindat specs
in variables whose names end in `-bindat-spec'; that kind of name is
automatically recognized as "risky."

   A field's "type" describes the size (in bytes) of the object that
the field represents and, in the case of multibyte fields, how the
bytes are ordered within the field.  The two possible orderings are
"big endian" (also known as "network byte ordering") and "little
endian."  For instance, the number `#x23cd' (decimal 9165) in big
endian would be the two bytes `#x23' `#xcd'; and in little endian,
`#xcd' `#x23'.  Here are the possible type values:

`u8'
`byte'
     Unsigned byte, with length 1.

`u16'
`word'
`short'
     Unsigned integer in network byte order, with length 2.

`u24'
     Unsigned integer in network byte order, with length 3.

`u32'
`dword'
`long'
     Unsigned integer in network byte order, with length 4.  Note:
     These values may be limited by Emacs' integer implementation
     limits.

`u16r'
`u24r'
`u32r'
     Unsigned integer in little endian order, with length 2, 3 and 4,
     respectively.

`str LEN'
     String of length LEN.

`strz LEN'
     Zero-terminated string, in a fixed-size field with length LEN.

`vec LEN [TYPE]'
     Vector of LEN elements of type TYPE, or bytes if not TYPE is
     specified.  The TYPE is any of the simple types above, or another
     vector specified as a list `(vec LEN [TYPE])'.

`ip'
     Four-byte vector representing an Internet address.  For example:
     `[127 0 0 1]' for localhost.

`bits LEN'
     List of set bits in LEN bytes.  The bytes are taken in big endian
     order and the bits are numbered starting with `8 * LEN - 1' and
     ending with zero.  For example: `bits 2' unpacks `#x28' `#x1c' to
     `(2 3 4 11 13)' and `#x1c' `#x28' to `(3 5 10 11 12)'.

`(eval FORM)'
     FORM is a Lisp expression evaluated at the moment the field is
     unpacked or packed.  The result of the evaluation should be one of
     the above-listed type specifications.

   For a fixed-size field, the length LEN is given as an integer
specifying the number of bytes in the field.

   When the length of a field is not fixed, it typically depends on the
value of a preceding field.  In this case, the length LEN can be given
either as a list `(NAME ...)' identifying a "field name" in the format
specified for `bindat-get-field' below, or by an expression `(eval
FORM)' where FORM should evaluate to an integer, specifying the field
length.

   A field specification generally has the form `([NAME] HANDLER)'.
The square braces indicate that NAME is optional.  (Don't use names
that are symbols meaningful as type specifications (above) or handler
specifications (below), since that would be ambiguous.)  NAME can be a
symbol or the expression `(eval FORM)', in which case FORM should
evaluate to a symbol.

   HANDLER describes how to unpack or pack the field and can be one of
the following:

`TYPE'
     Unpack/pack this field according to the type specification TYPE.

`eval FORM'
     Evaluate FORM, a Lisp expression, for side-effect only.  If the
     field name is specified, the value is bound to that field name.

`fill LEN'
     Skip LEN bytes.  In packing, this leaves them unchanged, which
     normally means they remain zero.  In unpacking, this means they
     are ignored.

`align LEN'
     Skip to the next multiple of LEN bytes.

`struct SPEC-NAME'
     Process SPEC-NAME as a sub-specification.  This describes a
     structure nested within another structure.

`union FORM (TAG SPEC)...'
     Evaluate FORM, a Lisp expression, find the first TAG that matches
     it, and process its associated data layout specification SPEC.
     Matching can occur in one of three ways:

        * If a TAG has the form `(eval EXPR)', evaluate EXPR with the
          variable `tag' dynamically bound to the value of FORM.  A
          non-`nil' result indicates a match.

        * TAG matches if it is `equal' to the value of FORM.

        * TAG matches unconditionally if it is `t'.

`repeat COUNT FIELD-SPECS...'
     Process the FIELD-SPECS recursively, in order, then repeat
     starting from the first one, processing all the specs COUNT times
     overall.  The COUNT is given using the same formats as a field
     length--if an `eval' form is used, it is evaluated just once.  For
     correct operation, each spec in FIELD-SPECS must include a name.

   For the `(eval FORM)' forms used in a bindat specification, the FORM
can access and update these dynamically bound variables during
evaluation:

`last'
     Value of the last field processed.

`bindat-raw'
     The data as a byte array.

`bindat-idx'
     Current index (within `bindat-raw') for unpacking or packing.

`struct'
     The alist containing the structured data that have been unpacked so
     far, or the entire structure being packed.  You can use
     `bindat-get-field' to access specific fields of this structure.

`count'
`index'
     Inside a `repeat' block, these contain the maximum number of
     repetitions (as specified by the COUNT parameter), and the current
     repetition number (counting from 0).  Setting `count' to zero will
     terminate the inner-most repeat block after the current repetition
     has completed.


File: elisp,  Node: Bindat Functions,  Next: Bindat Examples,  Prev: Bindat Spec,  Up: Byte Packing

37.18.2 Functions to Unpack and Pack Bytes
------------------------------------------

In the following documentation, SPEC refers to a data layout
specification, `bindat-raw' to a byte array, and STRUCT to an alist
representing unpacked field data.

 -- Function: bindat-unpack spec bindat-raw &optional bindat-idx
     This function unpacks data from the unibyte string or byte array
     `bindat-raw' according to SPEC.  Normally this starts unpacking at
     the beginning of the byte array, but if BINDAT-IDX is non-`nil', it
     specifies a zero-based starting position to use instead.

     The value is an alist or nested alist in which each element
     describes one unpacked field.

 -- Function: bindat-get-field struct &rest name
     This function selects a field's data from the nested alist STRUCT.
     Usually STRUCT was returned by `bindat-unpack'.  If NAME
     corresponds to just one argument, that means to extract a
     top-level field value.  Multiple NAME arguments specify repeated
     lookup of sub-structures.  An integer name acts as an array index.

     For example, if NAME is `(a b 2 c)', that means to find field `c'
     in the third element of subfield `b' of field `a'.  (This
     corresponds to `struct.a.b[2].c' in C.)

   Although packing and unpacking operations change the organization of
data (in memory), they preserve the data's "total length", which is the
sum of all the fields' lengths, in bytes.  This value is not generally
inherent in either the specification or alist alone; instead, both
pieces of information contribute to its calculation.  Likewise, the
length of a string or array being unpacked may be longer than the data's
total length as described by the specification.

 -- Function: bindat-length spec struct
     This function returns the total length of the data in STRUCT,
     according to SPEC.

 -- Function: bindat-pack spec struct &optional bindat-raw bindat-idx
     This function returns a byte array packed according to SPEC from
     the data in the alist STRUCT.  Normally it creates and fills a new
     byte array starting at the beginning.  However, if BINDAT-RAW is
     non-`nil', it specifies a pre-allocated unibyte string or vector to
     pack into.  If BINDAT-IDX is non-`nil', it specifies the starting
     offset for packing into `bindat-raw'.

     When pre-allocating, you should make sure `(length BINDAT-RAW)'
     meets or exceeds the total length to avoid an out-of-range error.

 -- Function: bindat-ip-to-string ip
     Convert the Internet address vector IP to a string in the usual
     dotted notation.

          (bindat-ip-to-string [127 0 0 1])
               => "127.0.0.1"


File: elisp,  Node: Bindat Examples,  Prev: Bindat Functions,  Up: Byte Packing

37.18.3 Examples of Byte Unpacking and Packing
----------------------------------------------

Here is a complete example of byte unpacking and packing:

     (defvar fcookie-index-spec
       '((:version  u32)
         (:count    u32)
         (:longest  u32)
         (:shortest u32)
         (:flags    u32)
         (:delim    u8)
         (:ignored  fill 3)
         (:offset   repeat (:count)
                    (:foo u32)))
       "Description of a fortune cookie index file's contents.")

     (defun fcookie (cookies &optional index)
       "Display a random fortune cookie from file COOKIES.
     Optional second arg INDEX specifies the associated index
     filename, which is by default constructed by appending
     \".dat\" to COOKIES.  Display cookie text in possibly
     new buffer \"*Fortune Cookie: BASENAME*\" where BASENAME
     is COOKIES without the directory part."
       (interactive "fCookies file: ")
       (let* ((info (with-temp-buffer
                      (insert-file-contents-literally
                       (or index (concat cookies ".dat")))
                      (bindat-unpack fcookie-index-spec
                                     (buffer-string))))
              (sel (random (bindat-get-field info :count)))
              (beg (cdar (bindat-get-field info :offset sel)))
              (end (or (cdar (bindat-get-field info
                                               :offset (1+ sel)))
                       (nth 7 (file-attributes cookies)))))
         (switch-to-buffer
          (get-buffer-create
           (format "*Fortune Cookie: %s*"
                   (file-name-nondirectory cookies))))
         (erase-buffer)
         (insert-file-contents-literally
          cookies nil beg (- end 3))))

     (defun fcookie-create-index (cookies &optional index delim)
       "Scan file COOKIES, and write out its index file.
     Optional second arg INDEX specifies the index filename,
     which is by default constructed by appending \".dat\" to
     COOKIES.  Optional third arg DELIM specifies the unibyte
     character which, when found on a line of its own in
     COOKIES, indicates the border between entries."
       (interactive "fCookies file: ")
       (setq delim (or delim ?%))
       (let ((delim-line (format "\n%c\n" delim))
             (count 0)
             (max 0)
             min p q len offsets)
         (unless (= 3 (string-bytes delim-line))
           (error "Delimiter cannot be represented in one byte"))
         (with-temp-buffer
           (insert-file-contents-literally cookies)
           (while (and (setq p (point))
                       (search-forward delim-line (point-max) t)
                       (setq len (- (point) 3 p)))
             (setq count (1+ count)
                   max (max max len)
                   min (min (or min max) len)
                   offsets (cons (1- p) offsets))))
         (with-temp-buffer
           (set-buffer-multibyte nil)
           (insert
            (bindat-pack
             fcookie-index-spec
             `((:version . 2)
               (:count . ,count)
               (:longest . ,max)
               (:shortest . ,min)
               (:flags . 0)
               (:delim . ,delim)
               (:offset . ,(mapcar (lambda (o)
                                     (list (cons :foo o)))
                                   (nreverse offsets))))))
           (let ((coding-system-for-write 'raw-text-unix))
             (write-file (or index (concat cookies ".dat")))))))

   Following is an example of defining and unpacking a complex
structure.  Consider the following C structures:

     struct header {
         unsigned long    dest_ip;
         unsigned long    src_ip;
         unsigned short   dest_port;
         unsigned short   src_port;
     };

     struct data {
         unsigned char    type;
         unsigned char    opcode;
         unsigned short   length;  /* In network byte order */
         unsigned char    id[8];   /* null-terminated string  */
         unsigned char    data[/* (length + 3) & ~3 */];
     };

     struct packet {
         struct header    header;
         unsigned long    counters[2];  /* In little endian order */
         unsigned char    items;
         unsigned char    filler[3];
         struct data      item[/* items */];

     };

   The corresponding data layout specification:

     (setq header-spec
           '((dest-ip   ip)
             (src-ip    ip)
             (dest-port u16)
             (src-port  u16)))

     (setq data-spec
           '((type      u8)
             (opcode    u8)
             (length    u16)  ;; network byte order
             (id        strz 8)
             (data      vec (length))
             (align     4)))

     (setq packet-spec
           '((header    struct header-spec)
             (counters  vec 2 u32r)   ;; little endian order
             (items     u8)
             (fill      3)
             (item      repeat (items)
                        (struct data-spec))))

   A binary data representation:

     (setq binary-data
           [ 192 168 1 100 192 168 1 101 01 28 21 32
             160 134 1 0 5 1 0 0 2 0 0 0
             2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0
             1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ])

   The corresponding decoded structure:

     (setq decoded (bindat-unpack packet-spec binary-data))
          =>
     ((header
       (dest-ip   . [192 168 1 100])
       (src-ip    . [192 168 1 101])
       (dest-port . 284)
       (src-port  . 5408))
      (counters . [100000 261])
      (items . 2)
      (item ((data . [1 2 3 4 5])
             (id . "ABCDEF")
             (length . 5)
             (opcode . 3)
             (type . 2))
            ((data . [6 7 8 9 10 11 12])
             (id . "BCDEFG")
             (length . 7)
             (opcode . 4)
             (type . 1))))

   Fetching data from this structure:

     (bindat-get-field decoded 'item 1 'id)
          => "BCDEFG"


File: elisp,  Node: Display,  Next: System Interface,  Prev: Processes,  Up: Top

38 Emacs Display
****************

This chapter describes a number of features related to the display that
Emacs presents to the user.

* Menu:

* Refresh Screen::      Clearing the screen and redrawing everything on it.
* Forcing Redisplay::   Forcing redisplay.
* Truncation::          Folding or wrapping long text lines.
* The Echo Area::       Displaying messages at the bottom of the screen.
* Warnings::            Displaying warning messages for the user.
* Invisible Text::      Hiding part of the buffer text.
* Selective Display::   Hiding part of the buffer text (the old way).
* Temporary Displays::  Displays that go away automatically.
* Overlays::            Use overlays to highlight parts of the buffer.
* Width::               How wide a character or string is on the screen.
* Line Height::         Controlling the height of lines.
* Faces::               A face defines a graphics style for text characters:
                          font, colors, etc.
* Fringes::             Controlling window fringes.
* Scroll Bars::         Controlling vertical scroll bars.
* Display Property::    Enabling special display features.
* Images::              Displaying images in Emacs buffers.
* Buttons::             Adding clickable buttons to Emacs buffers.
* Abstract Display::    Emacs' Widget for Object Collections.
* Blinking::            How Emacs shows the matching open parenthesis.
* Usual Display::       The usual conventions for displaying nonprinting chars.
* Display Tables::      How to specify other conventions.
* Beeping::             Audible signal to the user.
* Window Systems::      Which window system is being used.


File: elisp,  Node: Refresh Screen,  Next: Forcing Redisplay,  Up: Display

38.1 Refreshing the Screen
==========================

The function `redraw-frame' clears and redisplays the entire contents
of a given frame (*note Frames::).  This is useful if the screen is
corrupted.

 -- Function: redraw-frame frame
     This function clears and redisplays frame FRAME.

   Even more powerful is `redraw-display':

 -- Command: redraw-display
     This function clears and redisplays all visible frames.

   In Emacs, processing user input takes priority over redisplay.  If
you call these functions when input is available, they don't redisplay
immediately, but the requested redisplay does happen eventually--after
all the input has been processed.

   Normally, suspending and resuming Emacs also refreshes the screen.
Some terminal emulators record separate contents for display-oriented
programs such as Emacs and for ordinary sequential display.  If you are
using such a terminal, you might want to inhibit the redisplay on
resumption.

 -- Variable: no-redraw-on-reenter
     This variable controls whether Emacs redraws the entire screen
     after it has been suspended and resumed.  Non-`nil' means there is
     no need to redraw, `nil' means redrawing is needed.  The default
     is `nil'.


File: elisp,  Node: Forcing Redisplay,  Next: Truncation,  Prev: Refresh Screen,  Up: Display

38.2 Forcing Redisplay
======================

Emacs normally tries to redisplay the screen whenever it waits for
input.  With this function you can request an immediate attempt to
redisplay, in the middle of Lisp code, without actually waiting for
input.

 -- Function: redisplay &optional force
     This function tries immediately to redisplay, provided there are no
     pending input events.  It is equivalent to `(sit-for 0)'.

     If the optional argument FORCE is non-`nil', it does all pending
     redisplay work even if input is available, with no pre-emption.

     The function returns `t' if it actually tried to redisplay, and
     `nil' otherwise.  A value of `t' does not mean that redisplay
     proceeded to completion; it could have been pre-empted by newly
     arriving terminal input.

   `redisplay' with no argument tries immediately to redisplay, but has
no effect on the usual rules for what parts of the screen to redisplay.
By contrast, the following function adds certain windows to the
pending redisplay work (as if their contents had completely changed),
but doesn't immediately try to do any redisplay work.

 -- Function: force-window-update &optional object
     This function forces some or all windows to be updated on next
     redisplay.  If OBJECT is a window, it requires eventual redisplay
     of that window.  If OBJECT is a buffer or buffer name, it requires
     eventual redisplay of all windows displaying that buffer.  If
     OBJECT is `nil' (or omitted), it requires eventual redisplay of
     all windows.

   `force-window-update' does not do a redisplay immediately.  (Emacs
will do that when it waits for input.)  Rather, its effect is to put
more work on the queue to be done by redisplay whenever there is a
chance.

   Emacs redisplay normally stops if input arrives, and does not happen
at all if input is available before it starts.  Most of the time, this
is exactly what you want.  However, you can prevent preemption by
binding `redisplay-dont-pause' to a non-`nil' value.

 -- Variable: redisplay-dont-pause
     If this variable is non-`nil', pending input does not prevent or
     halt redisplay; redisplay occurs, and finishes, regardless of
     whether input is available.

 -- Variable: redisplay-preemption-period
     This variable specifies how many seconds Emacs waits between checks
     for new input during redisplay.  (The default is 0.1 seconds.)  If
     input has arrived when Emacs checks, it pre-empts redisplay and
     processes the available input before trying again to redisplay.

     If this variable is `nil', Emacs does not check for input during
     redisplay, and redisplay cannot be preempted by input.

     This variable is only obeyed on graphical terminals.  For text
     terminals, see *Note Terminal Output::.


File: elisp,  Node: Truncation,  Next: The Echo Area,  Prev: Forcing Redisplay,  Up: Display

38.3 Truncation
===============

When a line of text extends beyond the right edge of a window, Emacs
can "continue" the line (make it "wrap" to the next screen line), or
"truncate" the line (limit it to one screen line).  The additional
screen lines used to display a long text line are called "continuation"
lines.  Continuation is not the same as filling; continuation happens
on the screen only, not in the buffer contents, and it breaks a line
precisely at the right margin, not at a word boundary.  *Note Filling::.

   On a graphical display, tiny arrow images in the window fringes
indicate truncated and continued lines (*note Fringes::).  On a text
terminal, a `$' in the rightmost column of the window indicates
truncation; a `\' on the rightmost column indicates a line that
"wraps."  (The display table can specify alternate characters to use
for this; *note Display Tables::).

 -- User Option: truncate-lines
     This buffer-local variable controls how Emacs displays lines that
     extend beyond the right edge of the window.  The default is `nil',
     which specifies continuation.  If the value is non-`nil', then
     these lines are truncated.

     If the variable `truncate-partial-width-windows' is non-`nil',
     then truncation is always used for side-by-side windows (within one
     frame) regardless of the value of `truncate-lines'.

 -- User Option: default-truncate-lines
     This variable is the default value for `truncate-lines', for
     buffers that do not have buffer-local values for it.

 -- User Option: truncate-partial-width-windows
     This variable controls display of lines that extend beyond the
     right edge of the window, in side-by-side windows (*note Splitting
     Windows::).  If it is non-`nil', these lines are truncated;
     otherwise, `truncate-lines' says what to do with them.

   When horizontal scrolling (*note Horizontal Scrolling::) is in use in
a window, that forces truncation.

   If your buffer contains _very_ long lines, and you use continuation
to display them, just thinking about them can make Emacs redisplay
slow.  The column computation and indentation functions also become
slow.  Then you might find it advisable to set `cache-long-line-scans'
to `t'.

 -- Variable: cache-long-line-scans
     If this variable is non-`nil', various indentation and motion
     functions, and Emacs redisplay, cache the results of scanning the
     buffer, and consult the cache to avoid rescanning regions of the
     buffer unless they are modified.

     Turning on the cache slows down processing of short lines somewhat.

     This variable is automatically buffer-local in every buffer.


File: elisp,  Node: The Echo Area,  Next: Warnings,  Prev: Truncation,  Up: Display

38.4 The Echo Area
==================

The "echo area" is used for displaying error messages (*note Errors::),
for messages made with the `message' primitive, and for echoing
keystrokes.  It is not the same as the minibuffer, despite the fact
that the minibuffer appears (when active) in the same place on the
screen as the echo area.  The `GNU Emacs Manual' specifies the rules
for resolving conflicts between the echo area and the minibuffer for
use of that screen space (*note The Minibuffer: (emacs)Minibuffer.).

   You can write output in the echo area by using the Lisp printing
functions with `t' as the stream (*note Output Functions::), or
explicitly.

* Menu:

* Displaying Messages:: Explicitly displaying text in the echo area.
* Progress::            Informing user about progress of a long operation.
* Logging Messages::    Echo area messages are logged for the user.
* Echo Area Customization:: Controlling the echo area.


File: elisp,  Node: Displaying Messages,  Next: Progress,  Up: The Echo Area

38.4.1 Displaying Messages in the Echo Area
-------------------------------------------

This section describes the functions for explicitly producing echo area
messages.  Many other Emacs features display messages there, too.

 -- Function: message format-string &rest arguments
     This function displays a message in the echo area.  The argument
     FORMAT-STRING is similar to a C language `printf' format string.
     See `format' in *Note Formatting Strings::, for the details on the
     conversion specifications.  `message' returns the constructed
     string.

     In batch mode, `message' prints the message text on the standard
     error stream, followed by a newline.

     If FORMAT-STRING, or strings among the ARGUMENTS, have `face' text
     properties, these affect the way the message is displayed.

     If FORMAT-STRING is `nil' or the empty string, `message' clears
     the echo area; if the echo area has been expanded automatically,
     this brings it back to its normal size.  If the minibuffer is
     active, this brings the minibuffer contents back onto the screen
     immediately.

          (message "Minibuffer depth is %d."
                   (minibuffer-depth))
           -| Minibuffer depth is 0.
          => "Minibuffer depth is 0."

          ---------- Echo Area ----------
          Minibuffer depth is 0.
          ---------- Echo Area ----------

     To automatically display a message in the echo area or in a
     pop-buffer, depending on its size, use `display-message-or-buffer'
     (see below).

 -- Macro: with-temp-message message &rest body
     This construct displays a message in the echo area temporarily,
     during the execution of BODY.  It displays MESSAGE, executes BODY,
     then returns the value of the last body form while restoring the
     previous echo area contents.

 -- Function: message-or-box format-string &rest arguments
     This function displays a message like `message', but may display it
     in a dialog box instead of the echo area.  If this function is
     called in a command that was invoked using the mouse--more
     precisely, if `last-nonmenu-event' (*note Command Loop Info::) is
     either `nil' or a list--then it uses a dialog box or pop-up menu to
     display the message.  Otherwise, it uses the echo area.  (This is
     the same criterion that `y-or-n-p' uses to make a similar
     decision; see *Note Yes-or-No Queries::.)

     You can force use of the mouse or of the echo area by binding
     `last-nonmenu-event' to a suitable value around the call.

 -- Function: message-box format-string &rest arguments
     This function displays a message like `message', but uses a dialog
     box (or a pop-up menu) whenever that is possible.  If it is
     impossible to use a dialog box or pop-up menu, because the
     terminal does not support them, then `message-box' uses the echo
     area, like `message'.

 -- Function: display-message-or-buffer message &optional buffer-name
          not-this-window frame
     This function displays the message MESSAGE, which may be either a
     string or a buffer.  If it is shorter than the maximum height of
     the echo area, as defined by `max-mini-window-height', it is
     displayed in the echo area, using `message'.  Otherwise,
     `display-buffer' is used to show it in a pop-up buffer.

     Returns either the string shown in the echo area, or when a pop-up
     buffer is used, the window used to display it.

     If MESSAGE is a string, then the optional argument BUFFER-NAME is
     the name of the buffer used to display it when a pop-up buffer is
     used, defaulting to `*Message*'.  In the case where MESSAGE is a
     string and displayed in the echo area, it is not specified whether
     the contents are inserted into the buffer anyway.

     The optional arguments NOT-THIS-WINDOW and FRAME are as for
     `display-buffer', and only used if a buffer is displayed.

 -- Function: current-message
     This function returns the message currently being displayed in the
     echo area, or `nil' if there is none.


File: elisp,  Node: Progress,  Next: Logging Messages,  Prev: Displaying Messages,  Up: The Echo Area

38.4.2 Reporting Operation Progress
-----------------------------------

When an operation can take a while to finish, you should inform the
user about the progress it makes.  This way the user can estimate
remaining time and clearly see that Emacs is busy working, not hung.

   Functions listed in this section provide simple and efficient way of
reporting operation progress.  Here is a working example that does
nothing useful:

     (let ((progress-reporter
            (make-progress-reporter "Collecting mana for Emacs..."
                                    0  500)))
       (dotimes (k 500)
         (sit-for 0.01)
         (progress-reporter-update progress-reporter k))
       (progress-reporter-done progress-reporter))

 -- Function: make-progress-reporter message min-value max-value
          &optional current-value min-change min-time
     This function creates and returns a "progress reporter"--an object
     you will use as an argument for all other functions listed here.
     The idea is to precompute as much data as possible to make
     progress reporting very fast.

     When this progress reporter is subsequently used, it will display
     MESSAGE in the echo area, followed by progress percentage.
     MESSAGE is treated as a simple string.  If you need it to depend
     on a filename, for instance, use `format' before calling this
     function.

     MIN-VALUE and MAX-VALUE arguments stand for starting and final
     states of your operation.  For instance, if you scan a buffer,
     they should be the results of `point-min' and `point-max'
     correspondingly.  It is required that MAX-VALUE is greater than
     MIN-VALUE.  If you create progress reporter when some part of the
     operation has already been completed, then specify CURRENT-VALUE
     argument.  But normally you should omit it or set it to `nil'--it
     will default to MIN-VALUE then.

     Remaining arguments control the rate of echo area updates.
     Progress reporter will wait for at least MIN-CHANGE more percents
     of the operation to be completed before printing next message.
     MIN-TIME specifies the minimum time in seconds to pass between
     successive prints.  It can be fractional.  Depending on Emacs and
     system capabilities, progress reporter may or may not respect this
     last argument or do it with varying precision.  Default value for
     MIN-CHANGE is 1 (one percent), for MIN-TIME--0.2 (seconds.)

     This function calls `progress-reporter-update', so the first
     message is printed immediately.

 -- Function: progress-reporter-update reporter value
     This function does the main work of reporting progress of your
     operation.  It displays the message of REPORTER, followed by
     progress percentage determined by VALUE.  If percentage is zero,
     or close enough according to the MIN-CHANGE and MIN-TIME
     arguments, then it is omitted from the output.

     REPORTER must be the result of a call to `make-progress-reporter'.
     VALUE specifies the current state of your operation and must be
     between MIN-VALUE and MAX-VALUE (inclusive) as passed to
     `make-progress-reporter'.  For instance, if you scan a buffer,
     then VALUE should be the result of a call to `point'.

     This function respects MIN-CHANGE and MIN-TIME as passed to
     `make-progress-reporter' and so does not output new messages on
     every invocation.  It is thus very fast and normally you should not
     try to reduce the number of calls to it: resulting overhead will
     most likely negate your effort.

 -- Function: progress-reporter-force-update reporter value &optional
          new-message
     This function is similar to `progress-reporter-update' except that
     it prints a message in the echo area unconditionally.

     The first two arguments have the same meaning as for
     `progress-reporter-update'.  Optional NEW-MESSAGE allows you to
     change the message of the REPORTER.  Since this functions always
     updates the echo area, such a change will be immediately presented
     to the user.

 -- Function: progress-reporter-done reporter
     This function should be called when the operation is finished.  It
     prints the message of REPORTER followed by word "done" in the echo
     area.

     You should always call this function and not hope for
     `progress-reporter-update' to print "100%."  Firstly, it may never
     print it, there are many good reasons for this not to happen.
     Secondly, "done" is more explicit.

 -- Macro: dotimes-with-progress-reporter (var count [result]) message
          body...
     This is a convenience macro that works the same way as `dotimes'
     does, but also reports loop progress using the functions described
     above.  It allows you to save some typing.

     You can rewrite the example in the beginning of this node using
     this macro this way:

          (dotimes-with-progress-reporter
              (k 500)
              "Collecting some mana for Emacs..."
            (sit-for 0.01))


File: elisp,  Node: Logging Messages,  Next: Echo Area Customization,  Prev: Progress,  Up: The Echo Area

38.4.3 Logging Messages in `*Messages*'
---------------------------------------

Almost all the messages displayed in the echo area are also recorded in
the `*Messages*' buffer so that the user can refer back to them.  This
includes all the messages that are output with `message'.

 -- User Option: message-log-max
     This variable specifies how many lines to keep in the `*Messages*'
     buffer.  The value `t' means there is no limit on how many lines to
     keep.  The value `nil' disables message logging entirely.  Here's
     how to display a message and prevent it from being logged:

          (let (message-log-max)
            (message ...))

   To make `*Messages*' more convenient for the user, the logging
facility combines successive identical messages.  It also combines
successive related messages for the sake of two cases: question
followed by answer, and a series of progress messages.

   A "question followed by an answer" means two messages like the ones
produced by `y-or-n-p': the first is `QUESTION', and the second is
`QUESTION...ANSWER'.  The first message conveys no additional
information beyond what's in the second, so logging the second message
discards the first from the log.

   A "series of progress messages" means successive messages like those
produced by `make-progress-reporter'.  They have the form
`BASE...HOW-FAR', where BASE is the same each time, while HOW-FAR
varies.  Logging each message in the series discards the previous one,
provided they are consecutive.

   The functions `make-progress-reporter' and `y-or-n-p' don't have to
do anything special to activate the message log combination feature.
It operates whenever two consecutive messages are logged that share a
common prefix ending in `...'.


File: elisp,  Node: Echo Area Customization,  Prev: Logging Messages,  Up: The Echo Area

38.4.4 Echo Area Customization
------------------------------

These variables control details of how the echo area works.

 -- Variable: cursor-in-echo-area
     This variable controls where the cursor appears when a message is
     displayed in the echo area.  If it is non-`nil', then the cursor
     appears at the end of the message.  Otherwise, the cursor appears
     at point--not in the echo area at all.

     The value is normally `nil'; Lisp programs bind it to `t' for
     brief periods of time.

 -- Variable: echo-area-clear-hook
     This normal hook is run whenever the echo area is cleared--either
     by `(message nil)' or for any other reason.

 -- Variable: echo-keystrokes
     This variable determines how much time should elapse before command
     characters echo.  Its value must be an integer or floating point
     number, which specifies the number of seconds to wait before
     echoing.  If the user types a prefix key (such as `C-x') and then
     delays this many seconds before continuing, the prefix key is
     echoed in the echo area.  (Once echoing begins in a key sequence,
     all subsequent characters in the same key sequence are echoed
     immediately.)

     If the value is zero, then command input is not echoed.

 -- Variable: message-truncate-lines
     Normally, displaying a long message resizes the echo area to
     display the entire message.  But if the variable
     `message-truncate-lines' is non-`nil', the echo area does not
     resize, and the message is truncated to fit it, as in Emacs 20 and
     before.

   The variable `max-mini-window-height', which specifies the maximum
height for resizing minibuffer windows, also applies to the echo area
(which is really a special use of the minibuffer window.  *Note
Minibuffer Misc::.


File: elisp,  Node: Warnings,  Next: Invisible Text,  Prev: The Echo Area,  Up: Display

38.5 Reporting Warnings
=======================

"Warnings" are a facility for a program to inform the user of a
possible problem, but continue running.

* Menu:

* Warning Basics::      Warnings concepts and functions to report them.
* Warning Variables::   Variables programs bind to customize their warnings.
* Warning Options::     Variables users set to control display of warnings.


File: elisp,  Node: Warning Basics,  Next: Warning Variables,  Up: Warnings

38.5.1 Warning Basics
---------------------

Every warning has a textual message, which explains the problem for the
user, and a "severity level" which is a symbol.  Here are the possible
severity levels, in order of decreasing severity, and their meanings:

`:emergency'
     A problem that will seriously impair Emacs operation soon if you
     do not attend to it promptly.

`:error'
     A report of data or circumstances that are inherently wrong.

`:warning'
     A report of data or circumstances that are not inherently wrong,
     but raise suspicion of a possible problem.

`:debug'
     A report of information that may be useful if you are debugging.

   When your program encounters invalid input data, it can either
signal a Lisp error by calling `error' or `signal' or report a warning
with severity `:error'.  Signaling a Lisp error is the easiest thing to
do, but it means the program cannot continue processing.  If you want
to take the trouble to implement a way to continue processing despite
the bad data, then reporting a warning of severity `:error' is the
right way to inform the user of the problem.  For instance, the Emacs
Lisp byte compiler can report an error that way and continue compiling
other functions.  (If the program signals a Lisp error and then handles
it with `condition-case', the user won't see the error message; it could
show the message to the user by reporting it as a warning.)

   Each warning has a "warning type" to classify it.  The type is a
list of symbols.  The first symbol should be the custom group that you
use for the program's user options.  For example, byte compiler
warnings use the warning type `(bytecomp)'.  You can also subcategorize
the warnings, if you wish, by using more symbols in the list.

 -- Function: display-warning type message &optional level buffer-name
     This function reports a warning, using MESSAGE as the message and
     TYPE as the warning type.  LEVEL should be the severity level,
     with `:warning' being the default.

     BUFFER-NAME, if non-`nil', specifies the name of the buffer for
     logging the warning.  By default, it is `*Warnings*'.

 -- Function: lwarn type level message &rest args
     This function reports a warning using the value of `(format
     MESSAGE ARGS...)' as the message.  In other respects it is
     equivalent to `display-warning'.

 -- Function: warn message &rest args
     This function reports a warning using the value of `(format
     MESSAGE ARGS...)' as the message, `(emacs)' as the type, and
     `:warning' as the severity level.  It exists for compatibility
     only; we recommend not using it, because you should specify a
     specific warning type.


File: elisp,  Node: Warning Variables,  Next: Warning Options,  Prev: Warning Basics,  Up: Warnings

38.5.2 Warning Variables
------------------------

Programs can customize how their warnings appear by binding the
variables described in this section.

 -- Variable: warning-levels
     This list defines the meaning and severity order of the warning
     severity levels.  Each element defines one severity level, and
     they are arranged in order of decreasing severity.

     Each element has the form `(LEVEL STRING FUNCTION)', where LEVEL
     is the severity level it defines.  STRING specifies the textual
     description of this level.  STRING should use `%s' to specify
     where to put the warning type information, or it can omit the `%s'
     so as not to include that information.

     The optional FUNCTION, if non-`nil', is a function to call with no
     arguments, to get the user's attention.

     Normally you should not change the value of this variable.

 -- Variable: warning-prefix-function
     If non-`nil', the value is a function to generate prefix text for
     warnings.  Programs can bind the variable to a suitable function.
     `display-warning' calls this function with the warnings buffer
     current, and the function can insert text in it.  That text becomes
     the beginning of the warning message.

     The function is called with two arguments, the severity level and
     its entry in `warning-levels'.  It should return a list to use as
     the entry (this value need not be an actual member of
     `warning-levels').  By constructing this value, the function can
     change the severity of the warning, or specify different handling
     for a given severity level.

     If the variable's value is `nil' then there is no function to call.

 -- Variable: warning-series
     Programs can bind this variable to `t' to say that the next
     warning should begin a series.  When several warnings form a
     series, that means to leave point on the first warning of the
     series, rather than keep moving it for each warning so that it
     appears on the last one.  The series ends when the local binding
     is unbound and `warning-series' becomes `nil' again.

     The value can also be a symbol with a function definition.  That is
     equivalent to `t', except that the next warning will also call the
     function with no arguments with the warnings buffer current.  The
     function can insert text which will serve as a header for the
     series of warnings.

     Once a series has begun, the value is a marker which points to the
     buffer position in the warnings buffer of the start of the series.

     The variable's normal value is `nil', which means to handle each
     warning separately.

 -- Variable: warning-fill-prefix
     When this variable is non-`nil', it specifies a fill prefix to use
     for filling each warning's text.

 -- Variable: warning-type-format
     This variable specifies the format for displaying the warning type
     in the warning message.  The result of formatting the type this way
     gets included in the message under the control of the string in the
     entry in `warning-levels'.  The default value is `" (%s)"'.  If
     you bind it to `""' then the warning type won't appear at all.


File: elisp,  Node: Warning Options,  Prev: Warning Variables,  Up: Warnings

38.5.3 Warning Options
----------------------

These variables are used by users to control what happens when a Lisp
program reports a warning.

 -- User Option: warning-minimum-level
     This user option specifies the minimum severity level that should
     be shown immediately to the user.  The default is `:warning', which
     means to immediately display all warnings except `:debug' warnings.

 -- User Option: warning-minimum-log-level
     This user option specifies the minimum severity level that should
     be logged in the warnings buffer.  The default is `:warning', which
     means to log all warnings except `:debug' warnings.

 -- User Option: warning-suppress-types
     This list specifies which warning types should not be displayed
     immediately for the user.  Each element of the list should be a
     list of symbols.  If its elements match the first elements in a
     warning type, then that warning is not displayed immediately.

 -- User Option: warning-suppress-log-types
     This list specifies which warning types should not be logged in the
     warnings buffer.  Each element of the list should be a list of
     symbols.  If it matches the first few elements in a warning type,
     then that warning is not logged.


File: elisp,  Node: Invisible Text,  Next: Selective Display,  Prev: Warnings,  Up: Display

38.6 Invisible Text
===================

You can make characters "invisible", so that they do not appear on the
screen, with the `invisible' property.  This can be either a text
property (*note Text Properties::) or a property of an overlay (*note
Overlays::).  Cursor motion also partly ignores these characters; if
the command loop finds point within them, it moves point to the other
side of them.

   In the simplest case, any non-`nil' `invisible' property makes a
character invisible.  This is the default case--if you don't alter the
default value of `buffer-invisibility-spec', this is how the
`invisible' property works.  You should normally use `t' as the value
of the `invisible' property if you don't plan to set
`buffer-invisibility-spec' yourself.

   More generally, you can use the variable `buffer-invisibility-spec'
to control which values of the `invisible' property make text
invisible.  This permits you to classify the text into different subsets
in advance, by giving them different `invisible' values, and
subsequently make various subsets visible or invisible by changing the
value of `buffer-invisibility-spec'.

   Controlling visibility with `buffer-invisibility-spec' is especially
useful in a program to display the list of entries in a database.  It
permits the implementation of convenient filtering commands to view
just a part of the entries in the database.  Setting this variable is
very fast, much faster than scanning all the text in the buffer looking
for properties to change.

 -- Variable: buffer-invisibility-spec
     This variable specifies which kinds of `invisible' properties
     actually make a character invisible.  Setting this variable makes
     it buffer-local.

    `t'
          A character is invisible if its `invisible' property is
          non-`nil'.  This is the default.

    a list
          Each element of the list specifies a criterion for
          invisibility; if a character's `invisible' property fits any
          one of these criteria, the character is invisible.  The list
          can have two kinds of elements:

         `ATOM'
               A character is invisible if its `invisible' property
               value is ATOM or if it is a list with ATOM as a member.

         `(ATOM . t)'
               A character is invisible if its `invisible' property
               value is ATOM or if it is a list with ATOM as a member.
               Moreover, a sequence of such characters displays as an
               ellipsis.

   Two functions are specifically provided for adding elements to
`buffer-invisibility-spec' and removing elements from it.

 -- Function: add-to-invisibility-spec element
     This function adds the element ELEMENT to
     `buffer-invisibility-spec'.  If `buffer-invisibility-spec' was
     `t', it changes to a list, `(t)', so that text whose `invisible'
     property is `t' remains invisible.

 -- Function: remove-from-invisibility-spec element
     This removes the element ELEMENT from `buffer-invisibility-spec'.
     This does nothing if ELEMENT is not in the list.

   A convention for use of `buffer-invisibility-spec' is that a major
mode should use the mode's own name as an element of
`buffer-invisibility-spec' and as the value of the `invisible' property:

     ;; If you want to display an ellipsis:
     (add-to-invisibility-spec '(my-symbol . t))
     ;; If you don't want ellipsis:
     (add-to-invisibility-spec 'my-symbol)

     (overlay-put (make-overlay beginning end)
                  'invisible 'my-symbol)

     ;; When done with the overlays:
     (remove-from-invisibility-spec '(my-symbol . t))
     ;; Or respectively:
     (remove-from-invisibility-spec 'my-symbol)

   Ordinarily, functions that operate on text or move point do not care
whether the text is invisible.  The user-level line motion commands
explicitly ignore invisible newlines if `line-move-ignore-invisible' is
non-`nil' (the default), but only because they are explicitly
programmed to do so.

   However, if a command ends with point inside or immediately before
invisible text, the main editing loop moves point further forward or
further backward (in the same direction that the command already moved
it) until that condition is no longer true.  Thus, if the command moved
point back into an invisible range, Emacs moves point back to the
beginning of that range, and then back one more character.  If the
command moved point forward into an invisible range, Emacs moves point
forward up to the first visible character that follows the invisible
text.

   Incremental search can make invisible overlays visible temporarily
and/or permanently when a match includes invisible text.  To enable
this, the overlay should have a non-`nil' `isearch-open-invisible'
property.  The property value should be a function to be called with
the overlay as an argument.  This function should make the overlay
visible permanently; it is used when the match overlaps the overlay on
exit from the search.

   During the search, such overlays are made temporarily visible by
temporarily modifying their invisible and intangible properties.  If you
want this to be done differently for a certain overlay, give it an
`isearch-open-invisible-temporary' property which is a function.  The
function is called with two arguments: the first is the overlay, and
the second is `nil' to make the overlay visible, or `t' to make it
invisible again.


File: elisp,  Node: Selective Display,  Next: Temporary Displays,  Prev: Invisible Text,  Up: Display

38.7 Selective Display
======================

"Selective display" refers to a pair of related features for hiding
certain lines on the screen.

   The first variant, explicit selective display, is designed for use
in a Lisp program: it controls which lines are hidden by altering the
text.  This kind of hiding in some ways resembles the effect of the
`invisible' property (*note Invisible Text::), but the two features are
different and do not work the same way.

   In the second variant, the choice of lines to hide is made
automatically based on indentation.  This variant is designed to be a
user-level feature.

   The way you control explicit selective display is by replacing a
newline (control-j) with a carriage return (control-m).  The text that
was formerly a line following that newline is now hidden.  Strictly
speaking, it is temporarily no longer a line at all, since only
newlines can separate lines; it is now part of the previous line.

   Selective display does not directly affect editing commands.  For
example, `C-f' (`forward-char') moves point unhesitatingly into hidden
text.  However, the replacement of newline characters with carriage
return characters affects some editing commands.  For example,
`next-line' skips hidden lines, since it searches only for newlines.
Modes that use selective display can also define commands that take
account of the newlines, or that control which parts of the text are
hidden.

   When you write a selectively displayed buffer into a file, all the
control-m's are output as newlines.  This means that when you next read
in the file, it looks OK, with nothing hidden.  The selective display
effect is seen only within Emacs.

 -- Variable: selective-display
     This buffer-local variable enables selective display.  This means
     that lines, or portions of lines, may be made hidden.

        * If the value of `selective-display' is `t', then the character
          control-m marks the start of hidden text; the control-m, and
          the rest of the line following it, are not displayed.  This
          is explicit selective display.

        * If the value of `selective-display' is a positive integer,
          then lines that start with more than that many columns of
          indentation are not displayed.

     When some portion of a buffer is hidden, the vertical movement
     commands operate as if that portion did not exist, allowing a
     single `next-line' command to skip any number of hidden lines.
     However, character movement commands (such as `forward-char') do
     not skip the hidden portion, and it is possible (if tricky) to
     insert or delete text in an hidden portion.

     In the examples below, we show the _display appearance_ of the
     buffer `foo', which changes with the value of `selective-display'.
     The _contents_ of the buffer do not change.

          (setq selective-display nil)
               => nil

          ---------- Buffer: foo ----------
          1 on this column
           2on this column
            3n this column
            3n this column
           2on this column
          1 on this column
          ---------- Buffer: foo ----------

          (setq selective-display 2)
               => 2

          ---------- Buffer: foo ----------
          1 on this column
           2on this column
           2on this column
          1 on this column
          ---------- Buffer: foo ----------

 -- Variable: selective-display-ellipses
     If this buffer-local variable is non-`nil', then Emacs displays
     `...' at the end of a line that is followed by hidden text.  This
     example is a continuation of the previous one.

          (setq selective-display-ellipses t)
               => t

          ---------- Buffer: foo ----------
          1 on this column
           2on this column ...
           2on this column
          1 on this column
          ---------- Buffer: foo ----------

     You can use a display table to substitute other text for the
     ellipsis (`...').  *Note Display Tables::.


File: elisp,  Node: Temporary Displays,  Next: Overlays,  Prev: Selective Display,  Up: Display

38.8 Temporary Displays
=======================

Temporary displays are used by Lisp programs to put output into a
buffer and then present it to the user for perusal rather than for
editing.  Many help commands use this feature.

 -- Special Form: with-output-to-temp-buffer buffer-name forms...
     This function executes FORMS while arranging to insert any output
     they print into the buffer named BUFFER-NAME, which is first
     created if necessary, and put into Help mode.  Finally, the buffer
     is displayed in some window, but not selected.

     If the FORMS do not change the major mode in the output buffer, so
     that it is still Help mode at the end of their execution, then
     `with-output-to-temp-buffer' makes this buffer read-only at the
     end, and also scans it for function and variable names to make them
     into clickable cross-references.  *Note Tips for Documentation
     Strings: Docstring hyperlinks, in particular the item on
     hyperlinks in documentation strings, for more details.

     The string BUFFER-NAME specifies the temporary buffer, which need
     not already exist.  The argument must be a string, not a buffer.
     The buffer is erased initially (with no questions asked), and it is
     marked as unmodified after `with-output-to-temp-buffer' exits.

     `with-output-to-temp-buffer' binds `standard-output' to the
     temporary buffer, then it evaluates the forms in FORMS.  Output
     using the Lisp output functions within FORMS goes by default to
     that buffer (but screen display and messages in the echo area,
     although they are "output" in the general sense of the word, are
     not affected).  *Note Output Functions::.

     Several hooks are available for customizing the behavior of this
     construct; they are listed below.

     The value of the last form in FORMS is returned.

          ---------- Buffer: foo ----------
           This is the contents of foo.
          ---------- Buffer: foo ----------

          (with-output-to-temp-buffer "foo"
              (print 20)
              (print standard-output))
          => #<buffer foo>

          ---------- Buffer: foo ----------
          20

          #<buffer foo>

          ---------- Buffer: foo ----------

 -- Variable: temp-buffer-show-function
     If this variable is non-`nil', `with-output-to-temp-buffer' calls
     it as a function to do the job of displaying a help buffer.  The
     function gets one argument, which is the buffer it should display.

     It is a good idea for this function to run `temp-buffer-show-hook'
     just as `with-output-to-temp-buffer' normally would, inside of
     `save-selected-window' and with the chosen window and buffer
     selected.

 -- Variable: temp-buffer-setup-hook
     This normal hook is run by `with-output-to-temp-buffer' before
     evaluating BODY.  When the hook runs, the temporary buffer is
     current.  This hook is normally set up with a function to put the
     buffer in Help mode.

 -- Variable: temp-buffer-show-hook
     This normal hook is run by `with-output-to-temp-buffer' after
     displaying the temporary buffer.  When the hook runs, the
     temporary buffer is current, and the window it was displayed in is
     selected.  This hook is normally set up with a function to make
     the buffer read only, and find function names and variable names
     in it, provided the major mode is Help mode.

 -- Function: momentary-string-display string position &optional char
          message
     This function momentarily displays STRING in the current buffer at
     POSITION.  It has no effect on the undo list or on the buffer's
     modification status.

     The momentary display remains until the next input event.  If the
     next input event is CHAR, `momentary-string-display' ignores it
     and returns.  Otherwise, that event remains buffered for
     subsequent use as input.  Thus, typing CHAR will simply remove the
     string from the display, while typing (say) `C-f' will remove the
     string from the display and later (presumably) move point forward.
     The argument CHAR is a space by default.

     The return value of `momentary-string-display' is not meaningful.

     If the string STRING does not contain control characters, you can
     do the same job in a more general way by creating (and then
     subsequently deleting) an overlay with a `before-string' property.
     *Note Overlay Properties::.

     If MESSAGE is non-`nil', it is displayed in the echo area while
     STRING is displayed in the buffer.  If it is `nil', a default
     message says to type CHAR to continue.

     In this example, point is initially located at the beginning of the
     second line:

          ---------- Buffer: foo ----------
          This is the contents of foo.
          -!-Second line.
          ---------- Buffer: foo ----------

          (momentary-string-display
            "**** Important Message! ****"
            (point) ?\r
            "Type RET when done reading")
          => t

          ---------- Buffer: foo ----------
          This is the contents of foo.
          **** Important Message! ****Second line.
          ---------- Buffer: foo ----------

          ---------- Echo Area ----------
          Type RET when done reading
          ---------- Echo Area ----------


File: elisp,  Node: Overlays,  Next: Width,  Prev: Temporary Displays,  Up: Display

38.9 Overlays
=============

You can use "overlays" to alter the appearance of a buffer's text on
the screen, for the sake of presentation features.  An overlay is an
object that belongs to a particular buffer, and has a specified
beginning and end.  It also has properties that you can examine and set;
these affect the display of the text within the overlay.

   An overlay uses markers to record its beginning and end; thus,
editing the text of the buffer adjusts the beginning and end of each
overlay so that it stays with the text.  When you create the overlay,
you can specify whether text inserted at the beginning should be inside
the overlay or outside, and likewise for the end of the overlay.

* Menu:

* Managing Overlays::   Creating and moving overlays.
* Overlay Properties::  How to read and set properties.
			What properties do to the screen display.
* Finding Overlays::    Searching for overlays.


File: elisp,  Node: Managing Overlays,  Next: Overlay Properties,  Up: Overlays

38.9.1 Managing Overlays
------------------------

This section describes the functions to create, delete and move
overlays, and to examine their contents.  Overlay changes are not
recorded in the buffer's undo list, since the overlays are not part of
the buffer's contents.

 -- Function: overlayp object
     This function returns `t' if OBJECT is an overlay.

 -- Function: make-overlay start end &optional buffer front-advance
          rear-advance
     This function creates and returns an overlay that belongs to
     BUFFER and ranges from START to END.  Both START and END must
     specify buffer positions; they may be integers or markers.  If
     BUFFER is omitted, the overlay is created in the current buffer.

     The arguments FRONT-ADVANCE and REAR-ADVANCE specify the marker
     insertion type for the start of the overlay and for the end of the
     overlay, respectively.  *Note Marker Insertion Types::.  If they
     are both `nil', the default, then the overlay extends to include
     any text inserted at the beginning, but not text inserted at the
     end.  If FRONT-ADVANCE is non-`nil', text inserted at the
     beginning of the overlay is excluded from the overlay.  If
     REAR-ADVANCE is non-`nil', text inserted at the end of the overlay
     is included in the overlay.

 -- Function: overlay-start overlay
     This function returns the position at which OVERLAY starts, as an
     integer.

 -- Function: overlay-end overlay
     This function returns the position at which OVERLAY ends, as an
     integer.

 -- Function: overlay-buffer overlay
     This function returns the buffer that OVERLAY belongs to.  It
     returns `nil' if OVERLAY has been deleted.

 -- Function: delete-overlay overlay
     This function deletes OVERLAY.  The overlay continues to exist as
     a Lisp object, and its property list is unchanged, but it ceases
     to be attached to the buffer it belonged to, and ceases to have
     any effect on display.

     A deleted overlay is not permanently disconnected.  You can give
     it a position in a buffer again by calling `move-overlay'.

 -- Function: move-overlay overlay start end &optional buffer
     This function moves OVERLAY to BUFFER, and places its bounds at
     START and END.  Both arguments START and END must specify buffer
     positions; they may be integers or markers.

     If BUFFER is omitted, OVERLAY stays in the same buffer it was
     already associated with; if OVERLAY was deleted, it goes into the
     current buffer.

     The return value is OVERLAY.

     This is the only valid way to change the endpoints of an overlay.
     Do not try modifying the markers in the overlay by hand, as that
     fails to update other vital data structures and can cause some
     overlays to be "lost."

 -- Function: remove-overlays &optional start end name value
     This function removes all the overlays between START and END whose
     property NAME has the value VALUE.  It can move the endpoints of
     the overlays in the region, or split them.

     If NAME is omitted or `nil', it means to delete all overlays in
     the specified region.  If START and/or END are omitted or `nil',
     that means the beginning and end of the buffer respectively.
     Therefore, `(remove-overlays)' removes all the overlays in the
     current buffer.

   Here are some examples:

     ;; Create an overlay.
     (setq foo (make-overlay 1 10))
          => #<overlay from 1 to 10 in display.texi>
     (overlay-start foo)
          => 1
     (overlay-end foo)
          => 10
     (overlay-buffer foo)
          => #<buffer display.texi>
     ;; Give it a property we can check later.
     (overlay-put foo 'happy t)
          => t
     ;; Verify the property is present.
     (overlay-get foo 'happy)
          => t
     ;; Move the overlay.
     (move-overlay foo 5 20)
          => #<overlay from 5 to 20 in display.texi>
     (overlay-start foo)
          => 5
     (overlay-end foo)
          => 20
     ;; Delete the overlay.
     (delete-overlay foo)
          => nil
     ;; Verify it is deleted.
     foo
          => #<overlay in no buffer>
     ;; A deleted overlay has no position.
     (overlay-start foo)
          => nil
     (overlay-end foo)
          => nil
     (overlay-buffer foo)
          => nil
     ;; Undelete the overlay.
     (move-overlay foo 1 20)
          => #<overlay from 1 to 20 in display.texi>
     ;; Verify the results.
     (overlay-start foo)
          => 1
     (overlay-end foo)
          => 20
     (overlay-buffer foo)
          => #<buffer display.texi>
     ;; Moving and deleting the overlay does not change its properties.
     (overlay-get foo 'happy)
          => t

   Emacs stores the overlays of each buffer in two lists, divided
around an arbitrary "center position."  One list extends backwards
through the buffer from that center position, and the other extends
forwards from that center position.  The center position can be anywhere
in the buffer.

 -- Function: overlay-recenter pos
     This function recenters the overlays of the current buffer around
     position POS.  That makes overlay lookup faster for positions near
     POS, but slower for positions far away from POS.

   A loop that scans the buffer forwards, creating overlays, can run
faster if you do `(overlay-recenter (point-max))' first.


File: elisp,  Node: Overlay Properties,  Next: Finding Overlays,  Prev: Managing Overlays,  Up: Overlays

38.9.2 Overlay Properties
-------------------------

Overlay properties are like text properties in that the properties that
alter how a character is displayed can come from either source.  But in
most respects they are different.  *Note Text Properties::, for
comparison.

   Text properties are considered a part of the text; overlays and
their properties are specifically considered not to be part of the
text.  Thus, copying text between various buffers and strings preserves
text properties, but does not try to preserve overlays.  Changing a
buffer's text properties marks the buffer as modified, while moving an
overlay or changing its properties does not.  Unlike text property
changes, overlay property changes are not recorded in the buffer's undo
list.

   These functions read and set the properties of an overlay:

 -- Function: overlay-get overlay prop
     This function returns the value of property PROP recorded in
     OVERLAY, if any.  If OVERLAY does not record any value for that
     property, but it does have a `category' property which is a
     symbol, that symbol's PROP property is used.  Otherwise, the value
     is `nil'.

 -- Function: overlay-put overlay prop value
     This function sets the value of property PROP recorded in OVERLAY
     to VALUE.  It returns VALUE.

 -- Function: overlay-properties overlay
     This returns a copy of the property list of OVERLAY.

   See also the function `get-char-property' which checks both overlay
properties and text properties for a given character.  *Note Examining
Properties::.

   Many overlay properties have special meanings; here is a table of
them:

`priority'
     This property's value (which should be a nonnegative integer
     number) determines the priority of the overlay.  The priority
     matters when two or more overlays cover the same character and
     both specify the same property; the one whose `priority' value is
     larger takes priority over the other.  For the `face' property,
     the higher priority value does not completely replace the other;
     instead, its face attributes override the face attributes of the
     lower priority `face' property.

     Currently, all overlays take priority over text properties.  Please
     avoid using negative priority values, as we have not yet decided
     just what they should mean.

`window'
     If the `window' property is non-`nil', then the overlay applies
     only on that window.

`category'
     If an overlay has a `category' property, we call it the "category"
     of the overlay.  It should be a symbol.  The properties of the
     symbol serve as defaults for the properties of the overlay.

`face'
     This property controls the way text is displayed--for example,
     which font and which colors.  *Note Faces::, for more information.

     In the simplest case, the value is a face name.  It can also be a
     list; then each element can be any of these possibilities:

        * A face name (a symbol or string).

        * A property list of face attributes.  This has the form
          (KEYWORD VALUE ...), where each KEYWORD is a face attribute
          name and VALUE is a meaningful value for that attribute.  With
          this feature, you do not need to create a face each time you
          want to specify a particular attribute for certain text.
          *Note Face Attributes::.

        * A cons cell, either of the form `(foreground-color .
          COLOR-NAME)' or `(background-color . COLOR-NAME)'.  These
          elements specify just the foreground color or just the
          background color.

          `(foreground-color . COLOR-NAME)' has the same effect as
          `(:foreground COLOR-NAME)'; likewise for the background.

`mouse-face'
     This property is used instead of `face' when the mouse is within
     the range of the overlay.

`display'
     This property activates various features that change the way text
     is displayed.  For example, it can make text appear taller or
     shorter, higher or lower, wider or narrower, or replaced with an
     image.  *Note Display Property::.

`help-echo'
     If an overlay has a `help-echo' property, then when you move the
     mouse onto the text in the overlay, Emacs displays a help string
     in the echo area, or in the tooltip window.  For details see *Note
     Text help-echo::.

`modification-hooks'
     This property's value is a list of functions to be called if any
     character within the overlay is changed or if text is inserted
     strictly within the overlay.

     The hook functions are called both before and after each change.
     If the functions save the information they receive, and compare
     notes between calls, they can determine exactly what change has
     been made in the buffer text.

     When called before a change, each function receives four
     arguments: the overlay, `nil', and the beginning and end of the
     text range to be modified.

     When called after a change, each function receives five arguments:
     the overlay, `t', the beginning and end of the text range just
     modified, and the length of the pre-change text replaced by that
     range.  (For an insertion, the pre-change length is zero; for a
     deletion, that length is the number of characters deleted, and the
     post-change beginning and end are equal.)

     If these functions modify the buffer, they should bind
     `inhibit-modification-hooks' to `t' around doing so, to avoid
     confusing the internal mechanism that calls these hooks.

     Text properties also support the `modification-hooks' property,
     but the details are somewhat different (*note Special
     Properties::).

`insert-in-front-hooks'
     This property's value is a list of functions to be called before
     and after inserting text right at the beginning of the overlay.
     The calling conventions are the same as for the
     `modification-hooks' functions.

`insert-behind-hooks'
     This property's value is a list of functions to be called before
     and after inserting text right at the end of the overlay.  The
     calling conventions are the same as for the `modification-hooks'
     functions.

`invisible'
     The `invisible' property can make the text in the overlay
     invisible, which means that it does not appear on the screen.
     *Note Invisible Text::, for details.

`intangible'
     The `intangible' property on an overlay works just like the
     `intangible' text property.  *Note Special Properties::, for
     details.

`isearch-open-invisible'
     This property tells incremental search how to make an invisible
     overlay visible, permanently, if the final match overlaps it.
     *Note Invisible Text::.

`isearch-open-invisible-temporary'
     This property tells incremental search how to make an invisible
     overlay visible, temporarily, during the search.  *Note Invisible
     Text::.

`before-string'
     This property's value is a string to add to the display at the
     beginning of the overlay.  The string does not appear in the
     buffer in any sense--only on the screen.

`after-string'
     This property's value is a string to add to the display at the end
     of the overlay.  The string does not appear in the buffer in any
     sense--only on the screen.

`evaporate'
     If this property is non-`nil', the overlay is deleted automatically
     if it becomes empty (i.e., if its length becomes zero).  If you
     give an empty overlay a non-`nil' `evaporate' property, that
     deletes it immediately.

`local-map'
     If this property is non-`nil', it specifies a keymap for a portion
     of the text.  The property's value replaces the buffer's local
     map, when the character after point is within the overlay.  *Note
     Active Keymaps::.

`keymap'
     The `keymap' property is similar to `local-map' but overrides the
     buffer's local map (and the map specified by the `local-map'
     property) rather than replacing it.


File: elisp,  Node: Finding Overlays,  Prev: Overlay Properties,  Up: Overlays

38.9.3 Searching for Overlays
-----------------------------

 -- Function: overlays-at pos
     This function returns a list of all the overlays that cover the
     character at position POS in the current buffer.  The list is in
     no particular order.  An overlay contains position POS if it
     begins at or before POS, and ends after POS.

     To illustrate usage, here is a Lisp function that returns a list
     of the overlays that specify property PROP for the character at
     point:

          (defun find-overlays-specifying (prop)
            (let ((overlays (overlays-at (point)))
                  found)
              (while overlays
                (let ((overlay (car overlays)))
                  (if (overlay-get overlay prop)
                      (setq found (cons overlay found))))
                (setq overlays (cdr overlays)))
              found))

 -- Function: overlays-in beg end
     This function returns a list of the overlays that overlap the
     region BEG through END.  "Overlap" means that at least one
     character is contained within the overlay and also contained
     within the specified region; however, empty overlays are included
     in the result if they are located at BEG, or strictly between BEG
     and END.

 -- Function: next-overlay-change pos
     This function returns the buffer position of the next beginning or
     end of an overlay, after POS.  If there is none, it returns
     `(point-max)'.

 -- Function: previous-overlay-change pos
     This function returns the buffer position of the previous
     beginning or end of an overlay, before POS.  If there is none, it
     returns `(point-min)'.

   As an example, here's a simplified (and inefficient) version of the
primitive function `next-single-char-property-change' (*note Property
Search::).  It searches forward from position POS for the next position
where the value of a given property `prop', as obtained from either
overlays or text properties, changes.

     (defun next-single-char-property-change (position prop)
       (save-excursion
         (goto-char position)
         (let ((propval (get-char-property (point) prop)))
           (while (and (not (eobp))
                       (eq (get-char-property (point) prop) propval))
             (goto-char (min (next-overlay-change (point))
                             (next-single-property-change (point) prop)))))
         (point)))


File: elisp,  Node: Width,  Next: Line Height,  Prev: Overlays,  Up: Display

38.10 Width
===========

Since not all characters have the same width, these functions let you
check the width of a character.  *Note Primitive Indent::, and *Note
Screen Lines::, for related functions.

 -- Function: char-width char
     This function returns the width in columns of the character CHAR,
     if it were displayed in the current buffer and the selected window.

 -- Function: string-width string
     This function returns the width in columns of the string STRING,
     if it were displayed in the current buffer and the selected window.

 -- Function: truncate-string-to-width string width &optional
          start-column padding ellipsis
     This function returns the part of STRING that fits within WIDTH
     columns, as a new string.

     If STRING does not reach WIDTH, then the result ends where STRING
     ends.  If one multi-column character in STRING extends across the
     column WIDTH, that character is not included in the result.  Thus,
     the result can fall short of WIDTH but cannot go beyond it.

     The optional argument START-COLUMN specifies the starting column.
     If this is non-`nil', then the first START-COLUMN columns of the
     string are omitted from the value.  If one multi-column character
     in STRING extends across the column START-COLUMN, that character
     is not included.

     The optional argument PADDING, if non-`nil', is a padding
     character added at the beginning and end of the result string, to
     extend it to exactly WIDTH columns.  The padding character is used
     at the end of the result if it falls short of WIDTH.  It is also
     used at the beginning of the result if one multi-column character
     in STRING extends across the column START-COLUMN.

     If ELLIPSIS is non-`nil', it should be a string which will replace
     the end of STR (including any padding) if it extends beyond
     END-COLUMN, unless the display width of STR is equal to or less
     than the display width of ELLIPSIS.  If ELLIPSIS is non-`nil' and
     not a string, it stands for `"..."'.

          (truncate-string-to-width "\tab\t" 12 4)
               => "ab"
          (truncate-string-to-width "\tab\t" 12 4 ?\s)
               => "    ab  "


File: elisp,  Node: Line Height,  Next: Faces,  Prev: Width,  Up: Display

38.11 Line Height
=================

The total height of each display line consists of the height of the
contents of the line, plus optional additional vertical line spacing
above or below the display line.

   The height of the line contents is the maximum height of any
character or image on that display line, including the final newline if
there is one.  (A display line that is continued doesn't include a
final newline.)  That is the default line height, if you do nothing to
specify a greater height.  (In the most common case, this equals the
height of the default frame font.)

   There are several ways to explicitly specify a larger line height,
either by specifying an absolute height for the display line, or by
specifying vertical space.  However, no matter what you specify, the
actual line height can never be less than the default.

   A newline can have a `line-height' text or overlay property that
controls the total height of the display line ending in that newline.

   If the property value is `t', the newline character has no effect on
the displayed height of the line--the visible contents alone determine
the height.  This is useful for tiling small images (or image slices)
without adding blank areas between the images.

   If the property value is a list of the form `(HEIGHT TOTAL)', that
adds extra space _below_ the display line.  First Emacs uses HEIGHT as
a height spec to control extra space _above_ the line; then it adds
enough space _below_ the line to bring the total line height up to
TOTAL.  In this case, the other ways to specify the line spacing are
ignored.

   Any other kind of property value is a height spec, which translates
into a number--the specified line height.  There are several ways to
write a height spec; here's how each of them translates into a number:

`INTEGER'
     If the height spec is a positive integer, the height value is that
     integer.

`FLOAT'
     If the height spec is a float, FLOAT, the numeric height value is
     FLOAT times the frame's default line height.

`(FACE . RATIO)'
     If the height spec is a cons of the format shown, the numeric
     height is RATIO times the height of face FACE.  RATIO can be any
     type of number, or `nil' which means a ratio of 1.  If FACE is
     `t', it refers to the current face.

`(nil . RATIO)'
     If the height spec is a cons of the format shown, the numeric
     height is RATIO times the height of the contents of the line.

   Thus, any valid height spec determines the height in pixels, one way
or another.  If the line contents' height is less than that, Emacs adds
extra vertical space above the line to achieve the specified total
height.

   If you don't specify the `line-height' property, the line's height
consists of the contents' height plus the line spacing.  There are
several ways to specify the line spacing for different parts of Emacs
text.

   You can specify the line spacing for all lines in a frame with the
`line-spacing' frame parameter (*note Layout Parameters::).  However,
if the variable `default-line-spacing' is non-`nil', it overrides the
frame's `line-spacing' parameter.  An integer value specifies the
number of pixels put below lines on graphical displays.  A floating
point number specifies the spacing relative to the frame's default line
height.

   You can specify the line spacing for all lines in a buffer via the
buffer-local `line-spacing' variable.  An integer value specifies the
number of pixels put below lines on graphical displays.  A floating
point number specifies the spacing relative to the default frame line
height.  This overrides line spacings specified for the frame.

   Finally, a newline can have a `line-spacing' text or overlay
property that overrides the default frame line spacing and the buffer
local `line-spacing' variable, for the display line ending in that
newline.

   One way or another, these mechanisms specify a Lisp value for the
spacing of each line.  The value is a height spec, and it translates
into a Lisp value as described above.  However, in this case the
numeric height value specifies the line spacing, rather than the line
height.


File: elisp,  Node: Faces,  Next: Fringes,  Prev: Line Height,  Up: Display

38.12 Faces
===========

A "face" is a named collection of graphical attributes: font family,
foreground color, background color, optional underlining, and many
others.  Faces are used in Emacs to control the style of display of
particular parts of the text or the frame.  *Note Standard Faces:
(emacs)Standard Faces, for the list of faces Emacs normally comes with.

   Each face has its own "face number", which distinguishes faces at
low levels within Emacs.  However, for most purposes, you refer to
faces in Lisp programs by the symbols that name them.

 -- Function: facep object
     This function returns `t' if OBJECT is a face name string or
     symbol.  It returns `nil' otherwise.

   Each face name is meaningful for all frames, and by default it has
the same meaning in all frames.  But you can arrange to give a
particular face name a special meaning in one frame if you wish.

* Menu:

* Defining Faces::      How to define a face with `defface'.
* Face Attributes::     What is in a face?
* Attribute Functions::  Functions to examine and set face attributes.
* Displaying Faces::     How Emacs combines the faces specified for a character.
* Font Selection::      Finding the best available font for a face.
* Face Functions::      How to define and examine faces.
* Auto Faces::          Hook for automatic face assignment.
* Font Lookup::         Looking up the names of available fonts
                          and information about them.
* Fontsets::            A fontset is a collection of fonts
                          that handle a range of character sets.


File: elisp,  Node: Defining Faces,  Next: Face Attributes,  Up: Faces

38.12.1 Defining Faces
----------------------

The way to define a new face is with `defface'.  This creates a kind of
customization item (*note Customization::) which the user can customize
using the Customization buffer (*note Easy Customization: (emacs)Easy
Customization.).

 -- Macro: defface face spec doc [keyword value]...
     This declares FACE as a customizable face that defaults according
     to SPEC.  You should not quote the symbol FACE, and it should not
     end in `-face' (that would be redundant).  The argument DOC
     specifies the face documentation.  The keywords you can use in
     `defface' are the same as in `defgroup' and `defcustom' (*note
     Common Keywords::).

     When `defface' executes, it defines the face according to SPEC,
     then uses any customizations that were read from the init file
     (*note Init File::) to override that specification.

     When you evaluate a `defface' form with `C-M-x' in Emacs Lisp mode
     (`eval-defun'), a special feature of `eval-defun' overrides any
     customizations of the face.  This way, the face reflects exactly
     what the `defface' says.

     The purpose of SPEC is to specify how the face should appear on
     different kinds of terminals.  It should be an alist whose elements
     have the form `(DISPLAY ATTS)'.  Each element's CAR, DISPLAY,
     specifies a class of terminals.  (The first element, if its CAR is
     `default', is special--it specifies defaults for the remaining
     elements).  The element's CADR, ATTS, is a list of face attributes
     and their values; it specifies what the face should look like on
     that kind of terminal.  The possible attributes are defined in the
     value of `custom-face-attributes'.

     The DISPLAY part of an element of SPEC determines which frames the
     element matches.  If more than one element of SPEC matches a given
     frame, the first element that matches is the one used for that
     frame.  There are three possibilities for DISPLAY:

    `default'
          This element of SPEC doesn't match any frames; instead, it
          specifies defaults that apply to all frames.  This kind of
          element, if used, must be the first element of SPEC.  Each of
          the following elements can override any or all of these
          defaults.

    `t'
          This element of SPEC matches all frames.  Therefore, any
          subsequent elements of SPEC are never used.  Normally `t' is
          used in the last (or only) element of SPEC.

    a list
          If DISPLAY is a list, each element should have the form
          `(CHARACTERISTIC VALUE...)'.  Here CHARACTERISTIC specifies a
          way of classifying frames, and the VALUEs are possible
          classifications which DISPLAY should apply to.  Here are the
          possible values of CHARACTERISTIC:

         `type'
               The kind of window system the frame uses--either
               `graphic' (any graphics-capable display), `x', `pc' (for
               the MS-DOS console), `w32' (for MS Windows 9X/NT/2K/XP),
               `mac' (for the Macintosh display), or `tty' (a
               non-graphics-capable display).  *Note window-system:
               Window Systems.

         `class'
               What kinds of colors the frame supports--either `color',
               `grayscale', or `mono'.

         `background'
               The kind of background--either `light' or `dark'.

         `min-colors'
               An integer that represents the minimum number of colors
               the frame should support.  This matches a frame if its
               `display-color-cells' value is at least the specified
               integer.

         `supports'
               Whether or not the frame can display the face attributes
               given in VALUE... (*note Face Attributes::).  See the
               documentation for the function
               `display-supports-face-attributes-p' for more
               information on exactly how this testing is done.  *Note
               Display Face Attribute Testing::.

          If an element of DISPLAY specifies more than one VALUE for a
          given CHARACTERISTIC, any of those values is acceptable.  If
          DISPLAY has more than one element, each element should
          specify a different CHARACTERISTIC; then _each_
          characteristic of the frame must match one of the VALUEs
          specified for it in DISPLAY.

   Here's how the standard face `region' is defined:

     (defface region
       '((((class color) (min-colors 88) (background dark))
          :background "blue3")
         (((class color) (min-colors 88) (background light))
          :background "lightgoldenrod2")
         (((class color) (min-colors 16) (background dark))
          :background "blue3")
         (((class color) (min-colors 16) (background light))
          :background "lightgoldenrod2")
         (((class color) (min-colors 8))
          :background "blue" :foreground "white")
         (((type tty) (class mono))
          :inverse-video t)
         (t :background "gray"))
       "Basic face for highlighting the region."
       :group 'basic-faces)

   Internally, `defface' uses the symbol property `face-defface-spec'
to record the face attributes specified in `defface', `saved-face' for
the attributes saved by the user with the customization buffer,
`customized-face' for the attributes customized by the user for the
current session, but not saved, and `face-documentation' for the
documentation string.

 -- User Option: frame-background-mode
     This option, if non-`nil', specifies the background type to use for
     interpreting face definitions.  If it is `dark', then Emacs treats
     all frames as if they had a dark background, regardless of their
     actual background colors.  If it is `light', then Emacs treats all
     frames as if they had a light background.


File: elisp,  Node: Face Attributes,  Next: Attribute Functions,  Prev: Defining Faces,  Up: Faces

38.12.2 Face Attributes
-----------------------

The effect of using a face is determined by a fixed set of "face
attributes".  This table lists all the face attributes, and what they
mean.  You can specify more than one face for a given piece of text;
Emacs merges the attributes of all the faces to determine how to
display the text.  *Note Displaying Faces::.

   Any attribute in a face can have the value `unspecified'.  This
means the face doesn't specify that attribute.  In face merging, when
the first face fails to specify a particular attribute, that means the
next face gets a chance.  However, the `default' face must specify all
attributes.

   Some of these font attributes are meaningful only on certain kinds of
displays--if your display cannot handle a certain attribute, the
attribute is ignored.  (The attributes `:family', `:width', `:height',
`:weight', and `:slant' correspond to parts of an X Logical Font
Descriptor.)

`:family'
     Font family name, or fontset name (*note Fontsets::).  If you
     specify a font family name, the wild-card characters `*' and `?'
     are allowed.

`:width'
     Relative proportionate width, also known as the character set
     width or set width.  This should be one of the symbols
     `ultra-condensed', `extra-condensed', `condensed',
     `semi-condensed', `normal', `semi-expanded', `expanded',
     `extra-expanded', or `ultra-expanded'.

`:height'
     Either the font height, an integer in units of 1/10 point, a
     floating point number specifying the amount by which to scale the
     height of any underlying face, or a function, which is called with
     the old height (from the underlying face), and should return the
     new height.

`:weight'
     Font weight--a symbol from this series (from most dense to most
     faint): `ultra-bold', `extra-bold', `bold', `semi-bold', `normal',
     `semi-light', `light', `extra-light', or `ultra-light'.

     On a text-only terminal, any weight greater than normal is
     displayed as extra bright, and any weight less than normal is
     displayed as half-bright (provided the terminal supports the
     feature).

`:slant'
     Font slant--one of the symbols `italic', `oblique', `normal',
     `reverse-italic', or `reverse-oblique'.

     On a text-only terminal, slanted text is displayed as half-bright,
     if the terminal supports the feature.

`:foreground'
     Foreground color, a string.  The value can be a system-defined
     color name, or a hexadecimal color specification of the form
     `#RRGGBB'.  (`#000000' is black, `#ff0000' is red, `#00ff00' is
     green, `#0000ff' is blue, and `#ffffff' is white.)

`:background'
     Background color, a string, like the foreground color.

`:inverse-video'
     Whether or not characters should be displayed in inverse video.
     The value should be `t' (yes) or `nil' (no).

`:stipple'
     The background stipple, a bitmap.

     The value can be a string; that should be the name of a file
     containing external-format X bitmap data.  The file is found in
     the directories listed in the variable `x-bitmap-file-path'.

     Alternatively, the value can specify the bitmap directly, with a
     list of the form `(WIDTH HEIGHT DATA)'.  Here, WIDTH and HEIGHT
     specify the size in pixels, and DATA is a string containing the
     raw bits of the bitmap, row by row.  Each row occupies (WIDTH + 7)
     / 8 consecutive bytes in the string (which should be a unibyte
     string for best results).  This means that each row always
     occupies at least one whole byte.

     If the value is `nil', that means use no stipple pattern.

     Normally you do not need to set the stipple attribute, because it
     is used automatically to handle certain shades of gray.

`:underline'
     Whether or not characters should be underlined, and in what color.
     If the value is `t', underlining uses the foreground color of the
     face.  If the value is a string, underlining uses that color.  The
     value `nil' means do not underline.

`:overline'
     Whether or not characters should be overlined, and in what color.
     The value is used like that of `:underline'.

`:strike-through'
     Whether or not characters should be strike-through, and in what
     color.  The value is used like that of `:underline'.

`:inherit'
     The name of a face from which to inherit attributes, or a list of
     face names.  Attributes from inherited faces are merged into the
     face like an underlying face would be, with higher priority than
     underlying faces.  If a list of faces is used, attributes from
     faces earlier in the list override those from later faces.

`:box'
     Whether or not a box should be drawn around characters, its color,
     the width of the box lines, and 3D appearance.

   Here are the possible values of the `:box' attribute, and what they
mean:

`nil'
     Don't draw a box.

`t'
     Draw a box with lines of width 1, in the foreground color.

COLOR
     Draw a box with lines of width 1, in color COLOR.

`(:line-width WIDTH :color COLOR :style STYLE)'
     This way you can explicitly specify all aspects of the box.  The
     value WIDTH specifies the width of the lines to draw; it defaults
     to 1.

     The value COLOR specifies the color to draw with.  The default is
     the foreground color of the face for simple boxes, and the
     background color of the face for 3D boxes.

     The value STYLE specifies whether to draw a 3D box.  If it is
     `released-button', the box looks like a 3D button that is not being
     pressed.  If it is `pressed-button', the box looks like a 3D button
     that is being pressed.  If it is `nil' or omitted, a plain 2D box
     is used.

   In older versions of Emacs, before `:family', `:height', `:width',
`:weight', and `:slant' existed, these attributes were used to specify
the type face.  They are now semi-obsolete, but they still work:

`:font'
     This attribute specifies the font name.

`:bold'
     A non-`nil' value specifies a bold font.

`:italic'
     A non-`nil' value specifies an italic font.

   For compatibility, you can still set these "attributes," even though
they are not real face attributes.  Here is what that does:

`:font'
     You can specify an X font name as the "value" of this "attribute";
     that sets the `:family', `:width', `:height', `:weight', and
     `:slant' attributes according to the font name.

     If the value is a pattern with wildcards, the first font that
     matches the pattern is used to set these attributes.

`:bold'
     A non-`nil' makes the face bold; `nil' makes it normal.  This
     actually works by setting the `:weight' attribute.

`:italic'
     A non-`nil' makes the face italic; `nil' makes it normal.  This
     actually works by setting the `:slant' attribute.

 -- Variable: x-bitmap-file-path
     This variable specifies a list of directories for searching for
     bitmap files, for the `:stipple' attribute.

 -- Function: bitmap-spec-p object
     This returns `t' if OBJECT is a valid bitmap specification,
     suitable for use with `:stipple' (see above).  It returns `nil'
     otherwise.


File: elisp,  Node: Attribute Functions,  Next: Displaying Faces,  Prev: Face Attributes,  Up: Faces

38.12.3 Face Attribute Functions
--------------------------------

This section describes the functions for accessing and modifying the
attributes of an existing face.

 -- Function: set-face-attribute face frame &rest arguments
     This function sets one or more attributes of face FACE for frame
     FRAME.  The attributes you specify this way override whatever the
     `defface' says.

     The extra arguments ARGUMENTS specify the attributes to set, and
     the values for them.  They should consist of alternating attribute
     names (such as `:family' or `:underline') and corresponding values.
     Thus,

          (set-face-attribute 'foo nil
                              :width 'extended
                              :weight 'bold
                              :underline "red")

     sets the attributes `:width', `:weight' and `:underline' to the
     corresponding values.

     If FRAME is `t', this function sets the default attributes for new
     frames.  Default attribute values specified this way override the
     `defface' for newly created frames.

     If FRAME is `nil', this function sets the attributes for all
     existing frames, and the default for new frames.

 -- Function: face-attribute face attribute &optional frame inherit
     This returns the value of the ATTRIBUTE attribute of face FACE on
     FRAME.  If FRAME is `nil', that means the selected frame (*note
     Input Focus::).

     If FRAME is `t', this returns whatever new-frames default value
     you previously specified with `set-face-attribute' for the
     ATTRIBUTE attribute of FACE.  If you have not specified one, it
     returns `nil'.

     If INHERIT is `nil', only attributes directly defined by FACE are
     considered, so the return value may be `unspecified', or a
     relative value.  If INHERIT is non-`nil', FACE's definition of
     ATTRIBUTE is merged with the faces specified by its `:inherit'
     attribute; however the return value may still be `unspecified' or
     relative.  If INHERIT is a face or a list of faces, then the
     result is further merged with that face (or faces), until it
     becomes specified and absolute.

     To ensure that the return value is always specified and absolute,
     use a value of `default' for INHERIT; this will resolve any
     unspecified or relative values by merging with the `default' face
     (which is always completely specified).

     For example,

          (face-attribute 'bold :weight)
               => bold

 -- Function: face-attribute-relative-p attribute value
     This function returns non-`nil' if VALUE, when used as the value
     of the face attribute ATTRIBUTE, is relative.  This means it would
     modify, rather than completely override, any value that comes from
     a subsequent face in the face list or that is inherited from
     another face.

     `unspecified' is a relative value for all attributes.  For
     `:height', floating point values are also relative.

     For example:

          (face-attribute-relative-p :height 2.0)
               => t

 -- Function: merge-face-attribute attribute value1 value2
     If VALUE1 is a relative value for the face attribute ATTRIBUTE,
     returns it merged with the underlying value VALUE2; otherwise, if
     VALUE1 is an absolute value for the face attribute ATTRIBUTE,
     returns VALUE1 unchanged.

   The functions above did not exist before Emacs 21.  For compatibility
with older Emacs versions, you can use the following functions to set
and examine the face attributes which existed in those versions.  They
use values of `t' and `nil' for FRAME just like `set-face-attribute'
and `face-attribute'.

 -- Function: set-face-foreground face color &optional frame
 -- Function: set-face-background face color &optional frame
     These functions set the foreground (or background, respectively)
     color of face FACE to COLOR.  The argument COLOR should be a
     string, the name of a color.

     Certain shades of gray are implemented by stipple patterns on
     black-and-white screens.

 -- Function: set-face-stipple face pattern &optional frame
     This function sets the background stipple pattern of face FACE to
     PATTERN.  The argument PATTERN should be the name of a stipple
     pattern defined by the X server, or actual bitmap data (*note Face
     Attributes::), or `nil' meaning don't use stipple.

     Normally there is no need to pay attention to stipple patterns,
     because they are used automatically to handle certain shades of
     gray.

 -- Function: set-face-font face font &optional frame
     This function sets the font of face FACE.  This actually sets the
     attributes `:family', `:width', `:height', `:weight', and `:slant'
     according to the font name FONT.

 -- Function: set-face-bold-p face bold-p &optional frame
     This function specifies whether FACE should be bold.  If BOLD-P is
     non-`nil', that means yes; `nil' means no.  This actually sets the
     `:weight' attribute.

 -- Function: set-face-italic-p face italic-p &optional frame
     This function specifies whether FACE should be italic.  If
     ITALIC-P is non-`nil', that means yes; `nil' means no.  This
     actually sets the `:slant' attribute.

 -- Function: set-face-underline-p face underline &optional frame
     This function sets the underline attribute of face FACE.
     Non-`nil' means do underline; `nil' means don't.  If UNDERLINE is
     a string, underline with that color.

 -- Function: set-face-inverse-video-p face inverse-video-p &optional
          frame
     This function sets the `:inverse-video' attribute of face FACE.

 -- Function: invert-face face &optional frame
     This function swaps the foreground and background colors of face
     FACE.

   These functions examine the attributes of a face.  If you don't
specify FRAME, they refer to the selected frame; `t' refers to the
default data for new frames.  They return the symbol `unspecified' if
the face doesn't define any value for that attribute.

 -- Function: face-foreground face &optional frame inherit
 -- Function: face-background face &optional frame inherit
     These functions return the foreground color (or background color,
     respectively) of face FACE, as a string.

     If INHERIT is `nil', only a color directly defined by the face is
     returned.  If INHERIT is non-`nil', any faces specified by its
     `:inherit' attribute are considered as well, and if INHERIT is a
     face or a list of faces, then they are also considered, until a
     specified color is found.  To ensure that the return value is
     always specified, use a value of `default' for INHERIT.

 -- Function: face-stipple face &optional frame inherit
     This function returns the name of the background stipple pattern
     of face FACE, or `nil' if it doesn't have one.

     If INHERIT is `nil', only a stipple directly defined by the face
     is returned.  If INHERIT is non-`nil', any faces specified by its
     `:inherit' attribute are considered as well, and if INHERIT is a
     face or a list of faces, then they are also considered, until a
     specified stipple is found.  To ensure that the return value is
     always specified, use a value of `default' for INHERIT.

 -- Function: face-font face &optional frame
     This function returns the name of the font of face FACE.

 -- Function: face-bold-p face &optional frame
     This function returns `t' if FACE is bold--that is, if it is
     bolder than normal.  It returns `nil' otherwise.

 -- Function: face-italic-p face &optional frame
     This function returns `t' if FACE is italic or oblique, `nil'
     otherwise.

 -- Function: face-underline-p face &optional frame
     This function returns the `:underline' attribute of face FACE.

 -- Function: face-inverse-video-p face &optional frame
     This function returns the `:inverse-video' attribute of face FACE.


File: elisp,  Node: Displaying Faces,  Next: Font Selection,  Prev: Attribute Functions,  Up: Faces

38.12.4 Displaying Faces
------------------------

Here are the ways to specify which faces to use for display of text:

   * With defaults.  The `default' face is used as the ultimate default
     for all text.  (In Emacs 19 and 20, the `default' face is used
     only when no other face is specified.)

   * For a mode line or header line, the face `mode-line' or
     `mode-line-inactive', or `header-line', is merged in just before
     `default'.

   * With text properties.  A character can have a `face' property; if
     so, the faces and face attributes specified there apply.  *Note
     Special Properties::.

     If the character has a `mouse-face' property, that is used instead
     of the `face' property when the mouse is "near enough" to the
     character.

   * With overlays.  An overlay can have `face' and `mouse-face'
     properties too; they apply to all the text covered by the overlay.

   * With a region that is active.  In Transient Mark mode, the region
     is highlighted with the face `region' (*note Standard Faces:
     (emacs)Standard Faces.).

   * With special glyphs.  Each glyph can specify a particular face
     number.  *Note Glyphs::.

   If these various sources together specify more than one face for a
particular character, Emacs merges the attributes of the various faces
specified.  For each attribute, Emacs tries first the face of any
special glyph; then the face for region highlighting, if appropriate;
then the faces specified by overlays, followed by those specified by
text properties, then the `mode-line' or `mode-line-inactive' or
`header-line' face (if in a mode line or a header line), and last the
`default' face.

   When multiple overlays cover one character, an overlay with higher
priority overrides those with lower priority.  *Note Overlays::.


File: elisp,  Node: Font Selection,  Next: Face Functions,  Prev: Displaying Faces,  Up: Faces

38.12.5 Font Selection
----------------------

"Selecting a font" means mapping the specified face attributes for a
character to a font that is available on a particular display.  The
face attributes, as determined by face merging, specify most of the
font choice, but not all.  Part of the choice depends on what character
it is.

   If the face specifies a fontset name, that fontset determines a
pattern for fonts of the given charset.  If the face specifies a font
family, a font pattern is constructed.

   Emacs tries to find an available font for the given face attributes
and character's registry and encoding.  If there is a font that matches
exactly, it is used, of course.  The hard case is when no available font
exactly fits the specification.  Then Emacs looks for one that is
"close"--one attribute at a time.  You can specify the order to
consider the attributes.  In the case where a specified font family is
not available, you can specify a set of mappings for alternatives to
try.

 -- Variable: face-font-selection-order
     This variable specifies the order of importance of the face
     attributes `:width', `:height', `:weight', and `:slant'.  The
     value should be a list containing those four symbols, in order of
     decreasing importance.

     Font selection first finds the best available matches for the first
     attribute listed; then, among the fonts which are best in that
     way, it searches for the best matches in the second attribute, and
     so on.

     The attributes `:weight' and `:width' have symbolic values in a
     range centered around `normal'.  Matches that are more extreme
     (farther from `normal') are somewhat preferred to matches that are
     less extreme (closer to `normal'); this is designed to ensure that
     non-normal faces contrast with normal ones, whenever possible.

     The default is `(:width :height :weight :slant)', which means first
     find the fonts closest to the specified `:width', then--among the
     fonts with that width--find a best match for the specified font
     height, and so on.

     One example of a case where this variable makes a difference is
     when the default font has no italic equivalent.  With the default
     ordering, the `italic' face will use a non-italic font that is
     similar to the default one.  But if you put `:slant' before
     `:height', the `italic' face will use an italic font, even if its
     height is not quite right.

 -- Variable: face-font-family-alternatives
     This variable lets you specify alternative font families to try,
     if a given family is specified and doesn't exist.  Each element
     should have this form:

          (FAMILY ALTERNATE-FAMILIES...)

     If FAMILY is specified but not available, Emacs will try the other
     families given in ALTERNATE-FAMILIES, one by one, until it finds a
     family that does exist.

 -- Variable: face-font-registry-alternatives
     This variable lets you specify alternative font registries to try,
     if a given registry is specified and doesn't exist.  Each element
     should have this form:

          (REGISTRY ALTERNATE-REGISTRIES...)

     If REGISTRY is specified but not available, Emacs will try the
     other registries given in ALTERNATE-REGISTRIES, one by one, until
     it finds a registry that does exist.

   Emacs can make use of scalable fonts, but by default it does not use
them, since the use of too many or too big scalable fonts can crash
XFree86 servers.

 -- Variable: scalable-fonts-allowed
     This variable controls which scalable fonts to use.  A value of
     `nil', the default, means do not use scalable fonts.  `t' means to
     use any scalable font that seems appropriate for the text.

     Otherwise, the value must be a list of regular expressions.  Then a
     scalable font is enabled for use if its name matches any regular
     expression in the list.  For example,

          (setq scalable-fonts-allowed '("muleindian-2$"))

     allows the use of scalable fonts with registry `muleindian-2'.

 -- Variable: face-font-rescale-alist
     This variable specifies scaling for certain faces.  Its value
     should be a list of elements of the form

          (FONTNAME-REGEXP . SCALE-FACTOR)

     If FONTNAME-REGEXP matches the font name that is about to be used,
     this says to choose a larger similar font according to the factor
     SCALE-FACTOR.  You would use this feature to normalize the font
     size if certain fonts are bigger or smaller than their nominal
     heights and widths would suggest.


File: elisp,  Node: Face Functions,  Next: Auto Faces,  Prev: Font Selection,  Up: Faces

38.12.6 Functions for Working with Faces
----------------------------------------

Here are additional functions for creating and working with faces.

 -- Function: make-face name
     This function defines a new face named NAME, initially with all
     attributes `nil'.  It does nothing if there is already a face named
     NAME.

 -- Function: face-list
     This function returns a list of all defined face names.

 -- Function: copy-face old-face new-name &optional frame new-frame
     This function defines a face named NEW-NAME as a copy of the
     existing face named OLD-FACE.  It creates the face NEW-NAME if that
     doesn't already exist.

     If the optional argument FRAME is given, this function applies
     only to that frame.  Otherwise it applies to each frame
     individually, copying attributes from OLD-FACE in each frame to
     NEW-FACE in the same frame.

     If the optional argument NEW-FRAME is given, then `copy-face'
     copies the attributes of OLD-FACE in FRAME to NEW-NAME in
     NEW-FRAME.

 -- Function: face-id face
     This function returns the face number of face FACE.

 -- Function: face-documentation face
     This function returns the documentation string of face FACE, or
     `nil' if none was specified for it.

 -- Function: face-equal face1 face2 &optional frame
     This returns `t' if the faces FACE1 and FACE2 have the same
     attributes for display.

 -- Function: face-differs-from-default-p face &optional frame
     This returns non-`nil' if the face FACE displays differently from
     the default face.

   A "face alias" provides an equivalent name for a face.  You can
define a face alias by giving the alias symbol the `face-alias'
property, with a value of the target face name.  The following example
makes `modeline' an alias for the `mode-line' face.

     (put 'modeline 'face-alias 'mode-line)


File: elisp,  Node: Auto Faces,  Next: Font Lookup,  Prev: Face Functions,  Up: Faces

38.12.7 Automatic Face Assignment
---------------------------------

This hook is used for automatically assigning faces to text in the
buffer.  It is part of the implementation of Jit-Lock mode, used by
Font-Lock.

 -- Variable: fontification-functions
     This variable holds a list of functions that are called by Emacs
     redisplay as needed to assign faces automatically to text in the
     buffer.

     The functions are called in the order listed, with one argument, a
     buffer position POS.  Each function should attempt to assign faces
     to the text in the current buffer starting at POS.

     Each function should record the faces they assign by setting the
     `face' property.  It should also add a non-`nil' `fontified'
     property for all the text it has assigned faces to.  That property
     tells redisplay that faces have been assigned to that text already.

     It is probably a good idea for each function to do nothing if the
     character after POS already has a non-`nil' `fontified' property,
     but this is not required.  If one function overrides the
     assignments made by a previous one, the properties as they are
     after the last function finishes are the ones that really matter.

     For efficiency, we recommend writing these functions so that they
     usually assign faces to around 400 to 600 characters at each call.


File: elisp,  Node: Font Lookup,  Next: Fontsets,  Prev: Auto Faces,  Up: Faces

38.12.8 Looking Up Fonts
------------------------

 -- Function: x-list-fonts pattern &optional face frame maximum
     This function returns a list of available font names that match
     PATTERN.  If the optional arguments FACE and FRAME are specified,
     then the list is limited to fonts that are the same size as FACE
     currently is on FRAME.

     The argument PATTERN should be a string, perhaps with wildcard
     characters: the `*' character matches any substring, and the `?'
     character matches any single character.  Pattern matching of font
     names ignores case.

     If you specify FACE and FRAME, FACE should be a face name (a
     symbol) and FRAME should be a frame.

     The optional argument MAXIMUM sets a limit on how many fonts to
     return.  If this is non-`nil', then the return value is truncated
     after the first MAXIMUM matching fonts.  Specifying a small value
     for MAXIMUM can make this function much faster, in cases where
     many fonts match the pattern.

 -- Function: x-family-fonts &optional family frame
     This function returns a list describing the available fonts for
     family FAMILY on FRAME.  If FAMILY is omitted or `nil', this list
     applies to all families, and therefore, it contains all available
     fonts.  Otherwise, FAMILY must be a string; it may contain the
     wildcards `?' and `*'.

     The list describes the display that FRAME is on; if FRAME is
     omitted or `nil', it applies to the selected frame's display
     (*note Input Focus::).

     The list contains a vector of the following form for each font:

          [FAMILY WIDTH POINT-SIZE WEIGHT SLANT
           FIXED-P FULL REGISTRY-AND-ENCODING]

     The first five elements correspond to face attributes; if you
     specify these attributes for a face, it will use this font.

     The last three elements give additional information about the font.
     FIXED-P is non-`nil' if the font is fixed-pitch.  FULL is the full
     name of the font, and REGISTRY-AND-ENCODING is a string giving the
     registry and encoding of the font.

     The result list is sorted according to the current face font sort
     order.

 -- Function: x-font-family-list &optional frame
     This function returns a list of the font families available for
     FRAME's display.  If FRAME is omitted or `nil', it describes the
     selected frame's display (*note Input Focus::).

     The value is a list of elements of this form:

          (FAMILY . FIXED-P)

     Here FAMILY is a font family, and FIXED-P is non-`nil' if fonts of
     that family are fixed-pitch.

 -- Variable: font-list-limit
     This variable specifies maximum number of fonts to consider in font
     matching.  The function `x-family-fonts' will not return more than
     that many fonts, and font selection will consider only that many
     fonts when searching a matching font for face attributes.  The
     default is currently 100.


File: elisp,  Node: Fontsets,  Prev: Font Lookup,  Up: Faces

38.12.9 Fontsets
----------------

A "fontset" is a list of fonts, each assigned to a range of character
codes.  An individual font cannot display the whole range of characters
that Emacs supports, but a fontset can.  Fontsets have names, just as
fonts do, and you can use a fontset name in place of a font name when
you specify the "font" for a frame or a face.  Here is information
about defining a fontset under Lisp program control.

 -- Function: create-fontset-from-fontset-spec fontset-spec &optional
          style-variant-p noerror
     This function defines a new fontset according to the specification
     string FONTSET-SPEC.  The string should have this format:

          FONTPATTERN, [CHARSETNAME:FONTNAME]...

     Whitespace characters before and after the commas are ignored.

     The first part of the string, FONTPATTERN, should have the form of
     a standard X font name, except that the last two fields should be
     `fontset-ALIAS'.

     The new fontset has two names, one long and one short.  The long
     name is FONTPATTERN in its entirety.  The short name is
     `fontset-ALIAS'.  You can refer to the fontset by either name.  If
     a fontset with the same name already exists, an error is signaled,
     unless NOERROR is non-`nil', in which case this function does
     nothing.

     If optional argument STYLE-VARIANT-P is non-`nil', that says to
     create bold, italic and bold-italic variants of the fontset as
     well.  These variant fontsets do not have a short name, only a
     long one, which is made by altering FONTPATTERN to indicate the
     bold or italic status.

     The specification string also says which fonts to use in the
     fontset.  See below for the details.

   The construct `CHARSET:FONT' specifies which font to use (in this
fontset) for one particular character set.  Here, CHARSET is the name
of a character set, and FONT is the font to use for that character set.
You can use this construct any number of times in the specification
string.

   For the remaining character sets, those that you don't specify
explicitly, Emacs chooses a font based on FONTPATTERN: it replaces
`fontset-ALIAS' with a value that names one character set.  For the
ASCII character set, `fontset-ALIAS' is replaced with `ISO8859-1'.

   In addition, when several consecutive fields are wildcards, Emacs
collapses them into a single wildcard.  This is to prevent use of
auto-scaled fonts.  Fonts made by scaling larger fonts are not usable
for editing, and scaling a smaller font is not useful because it is
better to use the smaller font in its own size, which Emacs does.

   Thus if FONTPATTERN is this,

     -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24

the font specification for ASCII characters would be this:

     -*-fixed-medium-r-normal-*-24-*-ISO8859-1

and the font specification for Chinese GB2312 characters would be this:

     -*-fixed-medium-r-normal-*-24-*-gb2312*-*

   You may not have any Chinese font matching the above font
specification.  Most X distributions include only Chinese fonts that
have `song ti' or `fangsong ti' in the FAMILY field.  In such a case,
`Fontset-N' can be specified as below:

     Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
             chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*

Then, the font specifications for all but Chinese GB2312 characters have
`fixed' in the FAMILY field, and the font specification for Chinese
GB2312 characters has a wild card `*' in the FAMILY field.

 -- Function: set-fontset-font name character fontname &optional frame
     This function modifies the existing fontset NAME to use the font
     name FONTNAME for the character CHARACTER.

     If NAME is `nil', this function modifies the default fontset,
     whose short name is `fontset-default'.

     CHARACTER may be a cons; `(FROM . TO)', where FROM and TO are
     non-generic characters.  In that case, use FONTNAME for all
     characters in the range FROM and TO (inclusive).

     CHARACTER may be a charset.  In that case, use FONTNAME for all
     character in the charsets.

     FONTNAME may be a cons; `(FAMILY . REGISTRY)', where FAMILY is a
     family name of a font (possibly including a foundry name at the
     head), REGISTRY is a registry name of a font (possibly including
     an encoding name at the tail).

     For instance, this changes the default fontset to use a font of
     which registry name is `JISX0208.1983' for all characters
     belonging to the charset `japanese-jisx0208'.

          (set-fontset-font nil 'japanese-jisx0208 '(nil . "JISX0208.1983"))

 -- Function: char-displayable-p char
     This function returns `t' if Emacs ought to be able to display
     CHAR.  More precisely, if the selected frame's fontset has a font
     to display the character set that CHAR belongs to.

     Fontsets can specify a font on a per-character basis; when the
     fontset does that, this function's value may not be accurate.


File: elisp,  Node: Fringes,  Next: Scroll Bars,  Prev: Faces,  Up: Display

38.13 Fringes
=============

The "fringes" of a window are thin vertical strips down the sides that
are used for displaying bitmaps that indicate truncation, continuation,
horizontal scrolling, and the overlay arrow.

* Menu:

* Fringe Size/Pos::     Specifying where to put the window fringes.
* Fringe Indicators::   Displaying indicator icons in the window fringes.
* Fringe Cursors::      Displaying cursors in the right fringe.
* Fringe Bitmaps::      Specifying bitmaps for fringe indicators.
* Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
* Overlay Arrow::       Display of an arrow to indicate position.


File: elisp,  Node: Fringe Size/Pos,  Next: Fringe Indicators,  Up: Fringes

38.13.1 Fringe Size and Position
--------------------------------

The following buffer-local variables control the position and width of
the window fringes.

 -- Variable: fringes-outside-margins
     The fringes normally appear between the display margins and the
     window text.  If the value is non-`nil', they appear outside the
     display margins.  *Note Display Margins::.

 -- Variable: left-fringe-width
     This variable, if non-`nil', specifies the width of the left
     fringe in pixels.  A value of `nil' means to use the left fringe
     width from the window's frame.

 -- Variable: right-fringe-width
     This variable, if non-`nil', specifies the width of the right
     fringe in pixels.  A value of `nil' means to use the right fringe
     width from the window's frame.

   The values of these variables take effect when you display the
buffer in a window.  If you change them while the buffer is visible,
you can call `set-window-buffer' to display it once again in the same
window, to make the changes take effect.

 -- Function: set-window-fringes window left &optional right
          outside-margins
     This function sets the fringe widths of window WINDOW.  If WINDOW
     is `nil', the selected window is used.

     The argument LEFT specifies the width in pixels of the left
     fringe, and likewise RIGHT for the right fringe.  A value of `nil'
     for either one stands for the default width.  If OUTSIDE-MARGINS
     is non-`nil', that specifies that fringes should appear outside of
     the display margins.

 -- Function: window-fringes &optional window
     This function returns information about the fringes of a window
     WINDOW.  If WINDOW is omitted or `nil', the selected window is
     used.  The value has the form `(LEFT-WIDTH RIGHT-WIDTH
     OUTSIDE-MARGINS)'.


File: elisp,  Node: Fringe Indicators,  Next: Fringe Cursors,  Prev: Fringe Size/Pos,  Up: Fringes

38.13.2 Fringe Indicators
-------------------------

The "fringe indicators" are tiny icons Emacs displays in the window
fringe (on a graphic display) to indicate truncated or continued lines,
buffer boundaries, overlay arrow, etc.

 -- User Option: indicate-empty-lines
     When this is non-`nil', Emacs displays a special glyph in the
     fringe of each empty line at the end of the buffer, on graphical
     displays.  *Note Fringes::.  This variable is automatically
     buffer-local in every buffer.

 -- Variable: indicate-buffer-boundaries
     This buffer-local variable controls how the buffer boundaries and
     window scrolling are indicated in the window fringes.

     Emacs can indicate the buffer boundaries--that is, the first and
     last line in the buffer--with angle icons when they appear on the
     screen.  In addition, Emacs can display an up-arrow in the fringe
     to show that there is text above the screen, and a down-arrow to
     show there is text below the screen.

     There are three kinds of basic values:

    `nil'
          Don't display any of these fringe icons.

    `left'
          Display the angle icons and arrows in the left fringe.

    `right'
          Display the angle icons and arrows in the right fringe.

    any non-alist
          Display the angle icons in the left fringe and don't display
          the arrows.

     Otherwise the value should be an alist that specifies which fringe
     indicators to display and where.  Each element of the alist should
     have the form `(INDICATOR . POSITION)'.  Here, INDICATOR is one of
     `top', `bottom', `up', `down', and `t' (which covers all the icons
     not yet specified), while POSITION is one of `left', `right' and
     `nil'.

     For example, `((top . left) (t . right))' places the top angle
     bitmap in left fringe, and the bottom angle bitmap as well as both
     arrow bitmaps in right fringe.  To show the angle bitmaps in the
     left fringe, and no arrow bitmaps, use `((top .  left) (bottom .
     left))'.

 -- Variable: default-indicate-buffer-boundaries
     The value of this variable is the default value for
     `indicate-buffer-boundaries' in buffers that do not override it.

 -- Variable: fringe-indicator-alist
     This buffer-local variable specifies the mapping from logical
     fringe indicators to the actual bitmaps displayed in the window
     fringes.

     These symbols identify the logical fringe indicators:

    Truncation and continuation line indicators:
          `truncation', `continuation'.

    Buffer position indicators:
          `up', `down', `top', `bottom', `top-bottom'.

    Empty line indicator:
          `empty-line'.

    Overlay arrow indicator:
          `overlay-arrow'.

    Unknown bitmap indicator:
          `unknown'.

     The value is an alist where each element `(INDICATOR . BITMAPS)'
     specifies the fringe bitmaps used to display a specific logical
     fringe indicator.

     Here, INDICATOR specifies the logical indicator type, and BITMAPS
     is list of symbols `(LEFT RIGHT [LEFT1 RIGHT1])' which specifies
     the actual bitmap shown in the left or right fringe for the
     logical indicator.

     The LEFT and RIGHT symbols specify the bitmaps shown in the left
     and/or right fringe for the specific indicator.  The LEFT1 or
     RIGHT1 bitmaps are used only for the `bottom' and `top-bottom
     indicators when the last (only) line in has no final newline.
     Alternatively, BITMAPS may be a single symbol which is used in
     both left and right fringes.

     When `fringe-indicator-alist' has a buffer-local value, and there
     is no bitmap defined for a logical indicator, or the bitmap is
     `t', the corresponding value from the (non-local)
     `default-fringe-indicator-alist' is used.

     To completely hide a specific indicator, set the bitmap to `nil'.

 -- Variable: default-fringe-indicator-alist
     The value of this variable is the default value for
     `fringe-indicator-alist' in buffers that do not override it.

   Standard fringe bitmaps for indicators:
     left-arrow right-arrow up-arrow down-arrow
     left-curly-arrow right-curly-arrow
     left-triangle right-triangle
     top-left-angle top-right-angle
     bottom-left-angle bottom-right-angle
     left-bracket right-bracket
     filled-rectangle hollow-rectangle
     filled-square hollow-square
     vertical-bar horizontal-bar
     empty-line question-mark


File: elisp,  Node: Fringe Cursors,  Next: Fringe Bitmaps,  Prev: Fringe Indicators,  Up: Fringes

38.13.3 Fringe Cursors
----------------------

When a line is exactly as wide as the window, Emacs displays the cursor
in the right fringe instead of using two lines.  Different bitmaps are
used to represent the cursor in the fringe depending on the current
buffer's cursor type.

Logical cursor types:
     `box' , `hollow', `bar', `hbar', `hollow-small'.

   The `hollow-small' type is used instead of `hollow' when the normal
`hollow-rectangle' bitmap is too tall to fit on a specific display line.

 -- Variable: overflow-newline-into-fringe
     If this is non-`nil', lines exactly as wide as the window (not
     counting the final newline character) are not continued.  Instead,
     when point is at the end of the line, the cursor appears in the
     right fringe.

 -- Variable: fringe-cursor-alist
     This variable specifies the mapping from logical cursor type to the
     actual fringe bitmaps displayed in the right fringe.  The value is
     an alist where each element `(CURSOR . BITMAP)' specifies the
     fringe bitmaps used to display a specific logical cursor type in
     the fringe.  Here, CURSOR specifies the logical cursor type and
     BITMAP is a symbol specifying the fringe bitmap to be displayed
     for that logical cursor type.

     When `fringe-cursor-alist' has a buffer-local value, and there is
     no bitmap defined for a cursor type, the corresponding value from
     the (non-local) `default-fringes-indicator-alist' is used.

 -- Variable: default-fringes-cursor-alist
     The value of this variable is the default value for
     `fringe-cursor-alist' in buffers that do not override it.

   Standard bitmaps for displaying the cursor in right fringe:
     filled-rectangle hollow-rectangle filled-square hollow-square
     vertical-bar horizontal-bar


File: elisp,  Node: Fringe Bitmaps,  Next: Customizing Bitmaps,  Prev: Fringe Cursors,  Up: Fringes

38.13.4 Fringe Bitmaps
----------------------

The "fringe bitmaps" are the actual bitmaps which represent the logical
fringe indicators for truncated or continued lines, buffer boundaries,
overlay arrow, etc.  Fringe bitmap symbols have their own name space.
The fringe bitmaps are shared by all frames and windows.  You can
redefine the built-in fringe bitmaps, and you can define new fringe
bitmaps.

   The way to display a bitmap in the left or right fringes for a given
line in a window is by specifying the `display' property for one of the
characters that appears in it.  Use a display specification of the form
`(left-fringe BITMAP [FACE])' or `(right-fringe BITMAP [FACE])' (*note
Display Property::).  Here, BITMAP is a symbol identifying the bitmap
you want, and FACE (which is optional) is the name of the face whose
colors should be used for displaying the bitmap, instead of the default
`fringe' face.  FACE is automatically merged with the `fringe' face, so
normally FACE need only specify the foreground color for the bitmap.

 -- Function: fringe-bitmaps-at-pos &optional pos window
     This function returns the fringe bitmaps of the display line
     containing position POS in window WINDOW.  The return value has
     the form `(LEFT RIGHT OV)', where LEFT is the symbol for the
     fringe bitmap in the left fringe (or `nil' if no bitmap), RIGHT is
     similar for the right fringe, and OV is non-`nil' if there is an
     overlay arrow in the left fringe.

     The value is `nil' if POS is not visible in WINDOW.  If WINDOW is
     `nil', that stands for the selected window.  If POS is `nil', that
     stands for the value of point in WINDOW.


File: elisp,  Node: Customizing Bitmaps,  Next: Overlay Arrow,  Prev: Fringe Bitmaps,  Up: Fringes

38.13.5 Customizing Fringe Bitmaps
----------------------------------

 -- Function: define-fringe-bitmap bitmap bits &optional height width
          align
     This function defines the symbol BITMAP as a new fringe bitmap, or
     replaces an existing bitmap with that name.

     The argument BITS specifies the image to use.  It should be either
     a string or a vector of integers, where each element (an integer)
     corresponds to one row of the bitmap.  Each bit of an integer
     corresponds to one pixel of the bitmap, where the low bit
     corresponds to the rightmost pixel of the bitmap.

     The height is normally the length of BITS.  However, you can
     specify a different height with non-`nil' HEIGHT.  The width is
     normally 8, but you can specify a different width with non-`nil'
     WIDTH.  The width must be an integer between 1 and 16.

     The argument ALIGN specifies the positioning of the bitmap
     relative to the range of rows where it is used; the default is to
     center the bitmap.  The allowed values are `top', `center', or
     `bottom'.

     The ALIGN argument may also be a list `(ALIGN PERIODIC)' where
     ALIGN is interpreted as described above.  If PERIODIC is
     non-`nil', it specifies that the rows in `bits' should be repeated
     enough times to reach the specified height.

 -- Function: destroy-fringe-bitmap bitmap
     This function destroy the fringe bitmap identified by BITMAP.  If
     BITMAP identifies a standard fringe bitmap, it actually restores
     the standard definition of that bitmap, instead of eliminating it
     entirely.

 -- Function: set-fringe-bitmap-face bitmap &optional face
     This sets the face for the fringe bitmap BITMAP to FACE.  If FACE
     is `nil', it selects the `fringe' face.  The bitmap's face
     controls the color to draw it in.

     FACE is merged with the `fringe' face, so normally FACE should
     specify only the foreground color.


File: elisp,  Node: Overlay Arrow,  Prev: Customizing Bitmaps,  Up: Fringes

38.13.6 The Overlay Arrow
-------------------------

The "overlay arrow" is useful for directing the user's attention to a
particular line in a buffer.  For example, in the modes used for
interface to debuggers, the overlay arrow indicates the line of code
about to be executed.  This feature has nothing to do with "overlays"
(*note Overlays::).

 -- Variable: overlay-arrow-string
     This variable holds the string to display to call attention to a
     particular line, or `nil' if the arrow feature is not in use.  On
     a graphical display the contents of the string are ignored;
     instead a glyph is displayed in the fringe area to the left of the
     display area.

 -- Variable: overlay-arrow-position
     This variable holds a marker that indicates where to display the
     overlay arrow.  It should point at the beginning of a line.  On a
     non-graphical display the arrow text appears at the beginning of
     that line, overlaying any text that would otherwise appear.  Since
     the arrow is usually short, and the line usually begins with
     indentation, normally nothing significant is overwritten.

     The overlay-arrow string is displayed in any given buffer if the
     value of `overlay-arrow-position' in that buffer points into that
     buffer.  Thus, it works to can display multiple overlay arrow
     strings by creating buffer-local bindings of
     `overlay-arrow-position'.  However, it is usually cleaner to use
     `overlay-arrow-variable-list' to achieve this result.

   You can do a similar job by creating an overlay with a
`before-string' property.  *Note Overlay Properties::.

   You can define multiple overlay arrows via the variable
`overlay-arrow-variable-list'.

 -- Variable: overlay-arrow-variable-list
     This variable's value is a list of variables, each of which
     specifies the position of an overlay arrow.  The variable
     `overlay-arrow-position' has its normal meaning because it is on
     this list.

   Each variable on this list can have properties
`overlay-arrow-string' and `overlay-arrow-bitmap' that specify an
overlay arrow string (for text-only terminals) or fringe bitmap (for
graphical terminals) to display at the corresponding overlay arrow
position.  If either property is not set, the default
`overlay-arrow-string' or `overlay-arrow' fringe indicator is used.


File: elisp,  Node: Scroll Bars,  Next: Display Property,  Prev: Fringes,  Up: Display

38.14 Scroll Bars
=================

Normally the frame parameter `vertical-scroll-bars' controls whether
the windows in the frame have vertical scroll bars, and whether they
are on the left or right.  The frame parameter `scroll-bar-width'
specifies how wide they are (`nil' meaning the default).  *Note Layout
Parameters::.

 -- Function: frame-current-scroll-bars &optional frame
     This function reports the scroll bar type settings for frame
     FRAME.  The value is a cons cell `(VERTICAL-TYPE .
     HORIZONTAL-TYPE)', where VERTICAL-TYPE is either `left', `right',
     or `nil' (which means no scroll bar.)  HORIZONTAL-TYPE is meant to
     specify the horizontal scroll bar type, but since they are not
     implemented, it is always `nil'.

   You can enable or disable scroll bars for a particular buffer, by
setting the variable `vertical-scroll-bar'.  This variable
automatically becomes buffer-local when set.  The possible values are
`left', `right', `t', which means to use the frame's default, and `nil'
for no scroll bar.

   You can also control this for individual windows.  Call the function
`set-window-scroll-bars' to specify what to do for a specific window:

 -- Function: set-window-scroll-bars window width &optional
          vertical-type horizontal-type
     This function sets the width and type of scroll bars for window
     WINDOW.

     WIDTH specifies the scroll bar width in pixels (`nil' means use
     the width specified for the frame).  VERTICAL-TYPE specifies
     whether to have a vertical scroll bar and, if so, where.  The
     possible values are `left', `right' and `nil', just like the
     values of the `vertical-scroll-bars' frame parameter.

     The argument HORIZONTAL-TYPE is meant to specify whether and where
     to have horizontal scroll bars, but since they are not
     implemented, it has no effect.  If WINDOW is `nil', the selected
     window is used.

 -- Function: window-scroll-bars &optional window
     Report the width and type of scroll bars specified for WINDOW.  If
     WINDOW is omitted or `nil', the selected window is used.  The
     value is a list of the form `(WIDTH COLS VERTICAL-TYPE
     HORIZONTAL-TYPE)'.  The value WIDTH is the value that was
     specified for the width (which may be `nil'); COLS is the number
     of columns that the scroll bar actually occupies.

     HORIZONTAL-TYPE is not actually meaningful.

   If you don't specify these values for a window with
`set-window-scroll-bars', the buffer-local variables `scroll-bar-mode'
and `scroll-bar-width' in the buffer being displayed control the
window's vertical scroll bars.  The function `set-window-buffer'
examines these variables.  If you change them in a buffer that is
already visible in a window, you can make the window take note of the
new values by calling `set-window-buffer' specifying the same buffer
that is already displayed.

 -- Variable: scroll-bar-mode
     This variable, always local in all buffers, controls whether and
     where to put scroll bars in windows displaying the buffer.  The
     possible values are `nil' for no scroll bar, `left' to put a
     scroll bar on the left, and `right' to put a scroll bar on the
     right.

 -- Function: window-current-scroll-bars &optional window
     This function reports the scroll bar type for window WINDOW.  If
     WINDOW is omitted or `nil', the selected window is used.  The
     value is a cons cell `(VERTICAL-TYPE . HORIZONTAL-TYPE)'.  Unlike
     `window-scroll-bars', this reports the scroll bar type actually
     used, once frame defaults and `scroll-bar-mode' are taken into
     account.

 -- Variable: scroll-bar-width
     This variable, always local in all buffers, specifies the width of
     the buffer's scroll bars, measured in pixels.  A value of `nil'
     means to use the value specified by the frame.


File: elisp,  Node: Display Property,  Next: Images,  Prev: Scroll Bars,  Up: Display

38.15 The `display' Property
============================

The `display' text property (or overlay property) is used to insert
images into text, and also control other aspects of how text displays.
The value of the `display' property should be a display specification,
or a list or vector containing several display specifications.  Display
specifications in the same `display' property value generally apply in
parallel to the text they cover.

   If several sources (overlays and/or a text property) specify values
for the `display' property, only one of the values takes effect,
following the rules of `get-char-property'.  *Note Examining
Properties::.

   The rest of this section describes several kinds of display
specifications and what they mean.

* Menu:

* Replacing Specs::      Display specs that replace the text.
* Specified Space::      Displaying one space with a specified width.
* Pixel Specification::  Specifying space width or height in pixels.
* Other Display Specs::  Displaying an image; magnifying text; moving it
                          up or down on the page; adjusting the width
                          of spaces within text.
* Display Margins::     Displaying text or images to the side of the main text.


File: elisp,  Node: Replacing Specs,  Next: Specified Space,  Up: Display Property

38.15.1 Display Specs That Replace The Text
-------------------------------------------

Some kinds of `display' specifications specify something to display
instead of the text that has the property.  These are called
"replacing" display specifications.  Emacs does not allow the user to
interactively move point into the middle of buffer text that is
replaced in this way.

   If a list of display specifications includes more than one replacing
display specification, the first overrides the rest.  Replacing display
specifications make most other display specifications irrelevant, since
those don't apply to the replacement.

   For replacing display specifications, "the text that has the
property" means all the consecutive characters that have the same Lisp
object as their `display' property; these characters are replaced as a
single unit.  By contrast, characters that have similar but distinct
Lisp objects as their `display' properties are handled separately.
Here's a function that illustrates this point:

     (defun foo ()
       (goto-char (point-min))
       (dotimes (i 5)
         (let ((string (concat "A")))
           (put-text-property (point) (1+ (point)) 'display string)
           (forward-char 1)
           (put-text-property (point) (1+ (point)) 'display string)
           (forward-char 1))))

It gives each of the first ten characters in the buffer string `"A"' as
the `display' property, but they don't all get the same string.  The
first two characters get the same string, so they together are replaced
with one `A'.  The next two characters get a second string, so they
together are replaced with one `A'.  Likewise for each following pair
of characters.  Thus, the ten characters appear as five A's.  This
function would have the same results:

     (defun foo ()
       (goto-char (point-min))
       (dotimes (i 5)
         (let ((string (concat "A")))
           (put-text-property (point) (+ 2 (point)) 'display string)
           (put-text-property (point) (1+ (point)) 'display string)
           (forward-char 2))))

This illustrates that what matters is the property value for each
character.  If two consecutive characters have the same object as the
`display' property value, it's irrelevant whether they got this
property from a single call to `put-text-property' or from two
different calls.


File: elisp,  Node: Specified Space,  Next: Pixel Specification,  Prev: Replacing Specs,  Up: Display Property

38.15.2 Specified Spaces
------------------------

To display a space of specified width and/or height, use a display
specification of the form `(space . PROPS)', where PROPS is a property
list (a list of alternating properties and values).  You can put this
property on one or more consecutive characters; a space of the
specified height and width is displayed in place of _all_ of those
characters.  These are the properties you can use in PROPS to specify
the weight of the space:

`:width WIDTH'
     If WIDTH is an integer or floating point number, it specifies that
     the space width should be WIDTH times the normal character width.
     WIDTH can also be a "pixel width" specification (*note Pixel
     Specification::).

`:relative-width FACTOR'
     Specifies that the width of the stretch should be computed from the
     first character in the group of consecutive characters that have
     the same `display' property.  The space width is the width of that
     character, multiplied by FACTOR.

`:align-to HPOS'
     Specifies that the space should be wide enough to reach HPOS.  If
     HPOS is a number, it is measured in units of the normal character
     width.  HPOS can also be a "pixel width" specification (*note
     Pixel Specification::).

   You should use one and only one of the above properties.  You can
also specify the height of the space, with these properties:

`:height HEIGHT'
     Specifies the height of the space.  If HEIGHT is an integer or
     floating point number, it specifies that the space height should
     be HEIGHT times the normal character height.  The HEIGHT may also
     be a "pixel height" specification (*note Pixel Specification::).

`:relative-height FACTOR'
     Specifies the height of the space, multiplying the ordinary height
     of the text having this display specification by FACTOR.

`:ascent ASCENT'
     If the value of ASCENT is a non-negative number no greater than
     100, it specifies that ASCENT percent of the height of the space
     should be considered as the ascent of the space--that is, the part
     above the baseline.  The ascent may also be specified in pixel
     units with a "pixel ascent" specification (*note Pixel
     Specification::).


   Don't use both `:height' and `:relative-height' together.

   The `:width' and `:align-to' properties are supported on non-graphic
terminals, but the other space properties in this section are not.


File: elisp,  Node: Pixel Specification,  Next: Other Display Specs,  Prev: Specified Space,  Up: Display Property

38.15.3 Pixel Specification for Spaces
--------------------------------------

The value of the `:width', `:align-to', `:height', and `:ascent'
properties can be a special kind of expression that is evaluated during
redisplay.  The result of the evaluation is used as an absolute number
of pixels.

   The following expressions are supported:

       EXPR ::= NUM | (NUM) | UNIT | ELEM | POS | IMAGE | FORM
       NUM  ::= INTEGER | FLOAT | SYMBOL
       UNIT ::= in | mm | cm | width | height
       ELEM ::= left-fringe | right-fringe | left-margin | right-margin
             |  scroll-bar | text
       POS  ::= left | center | right
       FORM ::= (NUM . EXPR) | (OP EXPR ...)
       OP   ::= + | -

   The form NUM specifies a fraction of the default frame font height
or width.  The form `(NUM)' specifies an absolute number of pixels.  If
NUM is a symbol, SYMBOL, its buffer-local variable binding is used.

   The `in', `mm', and `cm' units specify the number of pixels per
inch, millimeter, and centimeter, respectively.  The `width' and
`height' units correspond to the default width and height of the
current face.  An image specification `image' corresponds to the width
or height of the image.

   The `left-fringe', `right-fringe', `left-margin', `right-margin',
`scroll-bar', and `text' elements specify to the width of the
corresponding area of the window.

   The `left', `center', and `right' positions can be used with
`:align-to' to specify a position relative to the left edge, center, or
right edge of the text area.

   Any of the above window elements (except `text') can also be used
with `:align-to' to specify that the position is relative to the left
edge of the given area.  Once the base offset for a relative position
has been set (by the first occurrence of one of these symbols), further
occurrences of these symbols are interpreted as the width of the
specified area.  For example, to align to the center of the
left-margin, use

     :align-to (+ left-margin (0.5 . left-margin))

   If no specific base offset is set for alignment, it is always
relative to the left edge of the text area.  For example, `:align-to 0'
in a header-line aligns with the first text column in the text area.

   A value of the form `(NUM . EXPR)' stands for the product of the
values of NUM and EXPR.  For example, `(2 . in)' specifies a width of 2
inches, while `(0.5 .  IMAGE)' specifies half the width (or height) of
the specified image.

   The form `(+ EXPR ...)' adds up the value of the expressions.  The
form `(- EXPR ...)' negates or subtracts the value of the expressions.


File: elisp,  Node: Other Display Specs,  Next: Display Margins,  Prev: Pixel Specification,  Up: Display Property

38.15.4 Other Display Specifications
------------------------------------

Here are the other sorts of display specifications that you can use in
the `display' text property.

`STRING'
     Display STRING instead of the text that has this property.

     Recursive display specifications are not supported--STRING's
     `display' properties, if any, are not used.

`(image . IMAGE-PROPS)'
     This kind of display specification is an image descriptor (*note
     Images::).  When used as a display specification, it means to
     display the image instead of the text that has the display
     specification.

`(slice X Y WIDTH HEIGHT)'
     This specification together with `image' specifies a "slice" (a
     partial area) of the image to display.  The elements Y and X
     specify the top left corner of the slice, within the image; WIDTH
     and HEIGHT specify the width and height of the slice.  Integer
     values are numbers of pixels.  A floating point number in the
     range 0.0-1.0 stands for that fraction of the width or height of
     the entire image.

`((margin nil) STRING)'
     A display specification of this form means to display STRING
     instead of the text that has the display specification, at the same
     position as that text.  It is equivalent to using just STRING, but
     it is done as a special case of marginal display (*note Display
     Margins::).

`(space-width FACTOR)'
     This display specification affects all the space characters within
     the text that has the specification.  It displays all of these
     spaces FACTOR times as wide as normal.  The element FACTOR should
     be an integer or float.  Characters other than spaces are not
     affected at all; in particular, this has no effect on tab
     characters.

`(height HEIGHT)'
     This display specification makes the text taller or shorter.  Here
     are the possibilities for HEIGHT:

    `(+ N)'
          This means to use a font that is N steps larger.  A "step" is
          defined by the set of available fonts--specifically, those
          that match what was otherwise specified for this text, in all
          attributes except height.  Each size for which a suitable
          font is available counts as another step.  N should be an
          integer.

    `(- N)'
          This means to use a font that is N steps smaller.

    a number, FACTOR
          A number, FACTOR, means to use a font that is FACTOR times as
          tall as the default font.

    a symbol, FUNCTION
          A symbol is a function to compute the height.  It is called
          with the current height as argument, and should return the
          new height to use.

    anything else, FORM
          If the HEIGHT value doesn't fit the previous possibilities,
          it is a form.  Emacs evaluates it to get the new height, with
          the symbol `height' bound to the current specified font
          height.

`(raise FACTOR)'
     This kind of display specification raises or lowers the text it
     applies to, relative to the baseline of the line.

     FACTOR must be a number, which is interpreted as a multiple of the
     height of the affected text.  If it is positive, that means to
     display the characters raised.  If it is negative, that means to
     display them lower down.

     If the text also has a `height' display specification, that does
     not affect the amount of raising or lowering, which is based on the
     faces used for the text.

   You can make any display specification conditional.  To do that,
package it in another list of the form `(when CONDITION . SPEC)'.  Then
the specification SPEC applies only when CONDITION evaluates to a
non-`nil' value.  During the evaluation, `object' is bound to the
string or buffer having the conditional `display' property.  `position'
and `buffer-position' are bound to the position within `object' and the
buffer position where the `display' property was found, respectively.
Both positions can be different when `object' is a string.


File: elisp,  Node: Display Margins,  Prev: Other Display Specs,  Up: Display Property

38.15.5 Displaying in the Margins
---------------------------------

A buffer can have blank areas called "display margins" on the left and
on the right.  Ordinary text never appears in these areas, but you can
put things into the display margins using the `display' property.
There is currently no way to make text or images in the margin
mouse-sensitive.

   The way to display something in the margins is to specify it in a
margin display specification in the `display' property of some text.
This is a replacing display specification, meaning that the text you
put it on does not get displayed; the margin display appears, but that
text does not.

   A margin display specification looks like `((margin right-margin)
SPEC' or `((margin left-margin) SPEC)'.  Here, SPEC is another display
specification that says what to display in the margin.  Typically it is
a string of text to display, or an image descriptor.

   To display something in the margin _in association with_ certain
buffer text, without altering or preventing the display of that text,
put a `before-string' property on the text and put the margin display
specification on the contents of the before-string.

   Before the display margins can display anything, you must give them
a nonzero width.  The usual way to do that is to set these variables:

 -- Variable: left-margin-width
     This variable specifies the width of the left margin.  It is
     buffer-local in all buffers.

 -- Variable: right-margin-width
     This variable specifies the width of the right margin.  It is
     buffer-local in all buffers.

   Setting these variables does not immediately affect the window.
These variables are checked when a new buffer is displayed in the
window.  Thus, you can make changes take effect by calling
`set-window-buffer'.

   You can also set the margin widths immediately.

 -- Function: set-window-margins window left &optional right
     This function specifies the margin widths for window WINDOW.  The
     argument LEFT controls the left margin and RIGHT controls the
     right margin (default `0').

 -- Function: window-margins &optional window
     This function returns the left and right margins of WINDOW as a
     cons cell of the form `(LEFT . RIGHT)'.  If WINDOW is `nil', the
     selected window is used.


File: elisp,  Node: Images,  Next: Buttons,  Prev: Display Property,  Up: Display

38.16 Images
============

To display an image in an Emacs buffer, you must first create an image
descriptor, then use it as a display specifier in the `display'
property of text that is displayed (*note Display Property::).

   Emacs is usually able to display images when it is run on a
graphical terminal.  Images cannot be displayed in a text terminal, on
certain graphical terminals that lack the support for this, or if Emacs
is compiled without image support.  You can use the function
`display-images-p' to determine if images can in principle be displayed
(*note Display Feature Testing::).

   Emacs can display a number of different image formats; some of them
are supported only if particular support libraries are installed on
your machine.  In some environments, Emacs can load image libraries on
demand; if so, the variable `image-library-alist' can be used to modify
the set of known names for these dynamic libraries (though it is not
possible to add new image formats).

   The supported image formats include XBM, XPM (this requires the
libraries `libXpm' version 3.4k and `libz'), GIF (requiring `libungif'
4.1.0), PostScript, PBM, JPEG (requiring the `libjpeg' library version
v6a), TIFF (requiring `libtiff' v3.4), and PNG (requiring `libpng'
1.0.2).

   You specify one of these formats with an image type symbol.  The
image type symbols are `xbm', `xpm', `gif', `postscript', `pbm',
`jpeg', `tiff', and `png'.

 -- Variable: image-types
     This variable contains a list of those image type symbols that are
     potentially supported in the current configuration.  _Potentially_
     here means that Emacs knows about the image types, not necessarily
     that they can be loaded (they could depend on unavailable dynamic
     libraries, for example).

     To know which image types are really available, use
     `image-type-available-p'.

 -- Variable: image-library-alist
     This in an alist of image types vs external libraries needed to
     display them.

     Each element is a list `(IMAGE-TYPE LIBRARY...)', where the car is
     a supported image format from `image-types', and the rest are
     strings giving alternate filenames for the corresponding external
     libraries to load.

     Emacs tries to load the libraries in the order they appear on the
     list; if none is loaded, the running session of Emacs won't support
     the image type.  `pbm' and `xbm' don't need to be listed; they're
     always supported.

     This variable is ignored if the image libraries are statically
     linked into Emacs.

 -- Function: image-type-available-p type
     This function returns non-`nil' if image type TYPE is available,
     i.e., if images of this type can be loaded and displayed in Emacs.
     TYPE should be one of the types contained in `image-types'.

     For image types whose support libraries are statically linked, this
     function always returns `t'; for other image types, it returns `t'
     if the dynamic library could be loaded, `nil' otherwise.

* Menu:

* Image Descriptors::   How to specify an image for use in `:display'.
* XBM Images::          Special features for XBM format.
* XPM Images::          Special features for XPM format.
* GIF Images::          Special features for GIF format.
* PostScript Images::   Special features for PostScript format.
* Other Image Types::   Various other formats are supported.
* Defining Images::     Convenient ways to define an image for later use.
* Showing Images::      Convenient ways to display an image once it is defined.
* Image Cache::         Internal mechanisms of image display.


File: elisp,  Node: Image Descriptors,  Next: XBM Images,  Up: Images

38.16.1 Image Descriptors
-------------------------

An image description is a list of the form `(image . PROPS)', where
PROPS is a property list containing alternating keyword symbols
(symbols whose names start with a colon) and their values.  You can use
any Lisp object as a property, but the only properties that have any
special meaning are certain symbols, all of them keywords.

   Every image descriptor must contain the property `:type TYPE' to
specify the format of the image.  The value of TYPE should be an image
type symbol; for example, `xpm' for an image in XPM format.

   Here is a list of other properties that are meaningful for all image
types:

`:file FILE'
     The `:file' property says to load the image from file FILE.  If
     FILE is not an absolute file name, it is expanded in
     `data-directory'.

`:data DATA'
     The `:data' property says the actual contents of the image.  Each
     image must use either `:data' or `:file', but not both.  For most
     image types, the value of the `:data' property should be a string
     containing the image data; we recommend using a unibyte string.

     Before using `:data', look for further information in the section
     below describing the specific image format.  For some image types,
     `:data' may not be supported; for some, it allows other data types;
     for some, `:data' alone is not enough, so you need to use other
     image properties along with `:data'.

`:margin MARGIN'
     The `:margin' property specifies how many pixels to add as an
     extra margin around the image.  The value, MARGIN, must be a
     non-negative number, or a pair `(X . Y)' of such numbers.  If it
     is a pair, X specifies how many pixels to add horizontally, and Y
     specifies how many pixels to add vertically.  If `:margin' is not
     specified, the default is zero.

`:ascent ASCENT'
     The `:ascent' property specifies the amount of the image's height
     to use for its ascent--that is, the part above the baseline.  The
     value, ASCENT, must be a number in the range 0 to 100, or the
     symbol `center'.

     If ASCENT is a number, that percentage of the image's height is
     used for its ascent.

     If ASCENT is `center', the image is vertically centered around a
     centerline which would be the vertical centerline of text drawn at
     the position of the image, in the manner specified by the text
     properties and overlays that apply to the image.

     If this property is omitted, it defaults to 50.

`:relief RELIEF'
     The `:relief' property, if non-`nil', adds a shadow rectangle
     around the image.  The value, RELIEF, specifies the width of the
     shadow lines, in pixels.  If RELIEF is negative, shadows are drawn
     so that the image appears as a pressed button; otherwise, it
     appears as an unpressed button.

`:conversion ALGORITHM'
     The `:conversion' property, if non-`nil', specifies a conversion
     algorithm that should be applied to the image before it is
     displayed; the value, ALGORITHM, specifies which algorithm.

    `laplace'
    `emboss'
          Specifies the Laplace edge detection algorithm, which blurs
          out small differences in color while highlighting larger
          differences.  People sometimes consider this useful for
          displaying the image for a "disabled" button.

    `(edge-detection :matrix MATRIX :color-adjust ADJUST)'
          Specifies a general edge-detection algorithm.  MATRIX must be
          either a nine-element list or a nine-element vector of
          numbers.  A pixel at position x/y in the transformed image is
          computed from original pixels around that position.  MATRIX
          specifies, for each pixel in the neighborhood of x/y, a
          factor with which that pixel will influence the transformed
          pixel; element 0 specifies the factor for the pixel at
          x-1/y-1, element 1 the factor for the pixel at x/y-1 etc., as
          shown below:
                 (x-1/y-1  x/y-1  x+1/y-1
                  x-1/y    x/y    x+1/y
                  x-1/y+1  x/y+1  x+1/y+1)

          The resulting pixel is computed from the color intensity of
          the color resulting from summing up the RGB values of
          surrounding pixels, multiplied by the specified factors, and
          dividing that sum by the sum of the factors' absolute values.

          Laplace edge-detection currently uses a matrix of
                 (1  0  0
                  0  0  0
                  9  9 -1)

          Emboss edge-detection uses a matrix of
                 ( 2 -1  0
                  -1  0  1
                   0  1 -2)

    `disabled'
          Specifies transforming the image so that it looks "disabled."

`:mask MASK'
     If MASK is `heuristic' or `(heuristic BG)', build a clipping mask
     for the image, so that the background of a frame is visible behind
     the image.  If BG is not specified, or if BG is `t', determine the
     background color of the image by looking at the four corners of
     the image, assuming the most frequently occurring color from the
     corners is the background color of the image.  Otherwise, BG must
     be a list `(RED GREEN BLUE)' specifying the color to assume for
     the background of the image.

     If MASK is `nil', remove a mask from the image, if it has one.
     Images in some formats include a mask which can be removed by
     specifying `:mask nil'.

`:pointer SHAPE'
     This specifies the pointer shape when the mouse pointer is over
     this image.  *Note Pointer Shape::, for available pointer shapes.

`:map MAP'
     This associates an image map of "hot spots" with this image.

     An image map is an alist where each element has the format `(AREA
     ID PLIST)'.  An AREA is specified as either a rectangle, a circle,
     or a polygon.

     A rectangle is a cons `(rect . ((X0 . Y0) . (X1 . Y1)))' which
     specifies the pixel coordinates of the upper left and bottom right
     corners of the rectangle area.

     A circle is a cons `(circle . ((X0 . Y0) . R))' which specifies
     the center and the radius of the circle; R may be a float or
     integer.

     A polygon is a cons `(poly . [X0 Y0 X1 Y1 ...])' where each pair
     in the vector describes one corner in the polygon.

     When the mouse pointer lies on a hot-spot area of an image, the
     PLIST of that hot-spot is consulted; if it contains a `help-echo'
     property, that defines a tool-tip for the hot-spot, and if it
     contains a `pointer' property, that defines the shape of the mouse
     cursor when it is on the hot-spot.  *Note Pointer Shape::, for
     available pointer shapes.

     When you click the mouse when the mouse pointer is over a
     hot-spot, an event is composed by combining the ID of the hot-spot
     with the mouse event; for instance, `[area4 mouse-1]' if the
     hot-spot's ID is `area4'.

 -- Function: image-mask-p spec &optional frame
     This function returns `t' if image SPEC has a mask bitmap.  FRAME
     is the frame on which the image will be displayed.  FRAME `nil' or
     omitted means to use the selected frame (*note Input Focus::).


File: elisp,  Node: XBM Images,  Next: XPM Images,  Prev: Image Descriptors,  Up: Images

38.16.2 XBM Images
------------------

To use XBM format, specify `xbm' as the image type.  This image format
doesn't require an external library, so images of this type are always
supported.

   Additional image properties supported for the `xbm' image type are:

`:foreground FOREGROUND'
     The value, FOREGROUND, should be a string specifying the image
     foreground color, or `nil' for the default color.  This color is
     used for each pixel in the XBM that is 1.  The default is the
     frame's foreground color.

`:background BACKGROUND'
     The value, BACKGROUND, should be a string specifying the image
     background color, or `nil' for the default color.  This color is
     used for each pixel in the XBM that is 0.  The default is the
     frame's background color.

   If you specify an XBM image using data within Emacs instead of an
external file, use the following three properties:

`:data DATA'
     The value, DATA, specifies the contents of the image.  There are
     three formats you can use for DATA:

        * A vector of strings or bool-vectors, each specifying one line
          of the image.  Do specify `:height' and `:width'.

        * A string containing the same byte sequence as an XBM file
          would contain.  You must not specify `:height' and `:width'
          in this case, because omitting them is what indicates the
          data has the format of an XBM file.  The file contents
          specify the height and width of the image.

        * A string or a bool-vector containing the bits of the image
          (plus perhaps some extra bits at the end that will not be
          used).  It should contain at least WIDTH * `height' bits.  In
          this case, you must specify `:height' and `:width', both to
          indicate that the string contains just the bits rather than a
          whole XBM file, and to specify the size of the image.

`:width WIDTH'
     The value, WIDTH, specifies the width of the image, in pixels.

`:height HEIGHT'
     The value, HEIGHT, specifies the height of the image, in pixels.


File: elisp,  Node: XPM Images,  Next: GIF Images,  Prev: XBM Images,  Up: Images

38.16.3 XPM Images
------------------

To use XPM format, specify `xpm' as the image type.  The additional
image property `:color-symbols' is also meaningful with the `xpm' image
type:

`:color-symbols SYMBOLS'
     The value, SYMBOLS, should be an alist whose elements have the
     form `(NAME . COLOR)'.  In each element, NAME is the name of a
     color as it appears in the image file, and COLOR specifies the
     actual color to use for displaying that name.


File: elisp,  Node: GIF Images,  Next: PostScript Images,  Prev: XPM Images,  Up: Images

38.16.4 GIF Images
------------------

For GIF images, specify image type `gif'.

`:index INDEX'
     You can use `:index' to specify one image from a GIF file that
     contains more than one image.  This property specifies use of image
     number INDEX from the file.  If the GIF file doesn't contain an
     image with index INDEX, the image displays as a hollow box.


File: elisp,  Node: PostScript Images,  Next: Other Image Types,  Prev: GIF Images,  Up: Images

38.16.5 PostScript Images
-------------------------

To use PostScript for an image, specify image type `postscript'.  This
works only if you have Ghostscript installed.  You must always use
these three properties:

`:pt-width WIDTH'
     The value, WIDTH, specifies the width of the image measured in
     points (1/72 inch).  WIDTH must be an integer.

`:pt-height HEIGHT'
     The value, HEIGHT, specifies the height of the image in points
     (1/72 inch).  HEIGHT must be an integer.

`:bounding-box BOX'
     The value, BOX, must be a list or vector of four integers, which
     specifying the bounding box of the PostScript image, analogous to
     the `BoundingBox' comment found in PostScript files.

          %%BoundingBox: 22 171 567 738

   Displaying PostScript images from Lisp data is not currently
implemented, but it may be implemented by the time you read this.  See
the `etc/NEWS' file to make sure.


File: elisp,  Node: Other Image Types,  Next: Defining Images,  Prev: PostScript Images,  Up: Images

38.16.6 Other Image Types
-------------------------

For PBM images, specify image type `pbm'.  Color, gray-scale and
monochromatic images are supported.   For mono PBM images, two
additional image properties are supported.

`:foreground FOREGROUND'
     The value, FOREGROUND, should be a string specifying the image
     foreground color, or `nil' for the default color.  This color is
     used for each pixel in the XBM that is 1.  The default is the
     frame's foreground color.

`:background BACKGROUND'
     The value, BACKGROUND, should be a string specifying the image
     background color, or `nil' for the default color.  This color is
     used for each pixel in the XBM that is 0.  The default is the
     frame's background color.

   For JPEG images, specify image type `jpeg'.

   For TIFF images, specify image type `tiff'.

   For PNG images, specify image type `png'.


File: elisp,  Node: Defining Images,  Next: Showing Images,  Prev: Other Image Types,  Up: Images

38.16.7 Defining Images
-----------------------

The functions `create-image', `defimage' and `find-image' provide
convenient ways to create image descriptors.

 -- Function: create-image file-or-data &optional type data-p &rest
          props
     This function creates and returns an image descriptor which uses
     the data in FILE-OR-DATA.  FILE-OR-DATA can be a file name or a
     string containing the image data; DATA-P should be `nil' for the
     former case, non-`nil' for the latter case.

     The optional argument TYPE is a symbol specifying the image type.
     If TYPE is omitted or `nil', `create-image' tries to determine the
     image type from the file's first few bytes, or else from the
     file's name.

     The remaining arguments, PROPS, specify additional image
     properties--for example,

          (create-image "foo.xpm" 'xpm nil :heuristic-mask t)

     The function returns `nil' if images of this type are not
     supported.  Otherwise it returns an image descriptor.

 -- Macro: defimage symbol specs &optional doc
     This macro defines SYMBOL as an image name.  The arguments SPECS
     is a list which specifies how to display the image.  The third
     argument, DOC, is an optional documentation string.

     Each argument in SPECS has the form of a property list, and each
     one should specify at least the `:type' property and either the
     `:file' or the `:data' property.  The value of `:type' should be a
     symbol specifying the image type, the value of `:file' is the file
     to load the image from, and the value of `:data' is a string
     containing the actual image data.  Here is an example:

          (defimage test-image
            ((:type xpm :file "~/test1.xpm")
             (:type xbm :file "~/test1.xbm")))

     `defimage' tests each argument, one by one, to see if it is
     usable--that is, if the type is supported and the file exists.  The
     first usable argument is used to make an image descriptor which is
     stored in SYMBOL.

     If none of the alternatives will work, then SYMBOL is defined as
     `nil'.

 -- Function: find-image specs
     This function provides a convenient way to find an image
     satisfying one of a list of image specifications SPECS.

     Each specification in SPECS is a property list with contents
     depending on image type.  All specifications must at least contain
     the properties `:type TYPE' and either `:file FILE' or
     `:data DATA', where TYPE is a symbol specifying the image type,
     e.g. `xbm', FILE is the file to load the image from, and DATA is a
     string containing the actual image data.  The first specification
     in the list whose TYPE is supported, and FILE exists, is used to
     construct the image specification to be returned.  If no
     specification is satisfied, `nil' is returned.

     The image is looked for in `image-load-path'.

 -- Variable: image-load-path
     This variable's value is a list of locations in which to search for
     image files.  If an element is a string or a variable symbol whose
     value is a string, the string is taken to be the name of a
     directory to search.  If an element is a variable symbol whose
     value is a list, that is taken to be a list of directory names to
     search.

     The default is to search in the `images' subdirectory of the
     directory specified by `data-directory', then the directory
     specified by `data-directory', and finally in the directories in
     `load-path'.  Subdirectories are not automatically included in the
     search, so if you put an image file in a subdirectory, you have to
     supply the subdirectory name explicitly.  For example, to find the
     image `images/foo/bar.xpm' within `data-directory', you should
     specify the image as follows:

          (defimage foo-image '((:type xpm :file "foo/bar.xpm")))

 -- Function: image-load-path-for-library library image &optional path
          no-error
     This function returns a suitable search path for images used by the
     Lisp package LIBRARY.

     The function searches for IMAGE first using `image-load-path',
     excluding ``data-directory'/images', and then in `load-path',
     followed by a path suitable for LIBRARY, which includes
     `../../etc/images' and `../etc/images' relative to the library
     file itself, and finally in ``data-directory'/images'.

     Then this function returns a list of directories which contains
     first the directory in which IMAGE was found, followed by the
     value of `load-path'.  If PATH is given, it is used instead of
     `load-path'.

     If NO-ERROR is non-`nil' and a suitable path can't be found, don't
     signal an error.  Instead, return a list of directories as before,
     except that `nil' appears in place of the image directory.

     Here is an example that uses a common idiom to provide
     compatibility with versions of Emacs that lack the variable
     `image-load-path':

          (defvar image-load-path) ; shush compiler
          (let* ((load-path (image-load-path-for-library
                                  "mh-e" "mh-logo.xpm"))
                 (image-load-path (cons (car load-path)
                                        (when (boundp 'image-load-path)
                                          image-load-path))))
            (mh-tool-bar-folder-buttons-init))


File: elisp,  Node: Showing Images,  Next: Image Cache,  Prev: Defining Images,  Up: Images

38.16.8 Showing Images
----------------------

You can use an image descriptor by setting up the `display' property
yourself, but it is easier to use the functions in this section.

 -- Function: insert-image image &optional string area slice
     This function inserts IMAGE in the current buffer at point.  The
     value IMAGE should be an image descriptor; it could be a value
     returned by `create-image', or the value of a symbol defined with
     `defimage'.  The argument STRING specifies the text to put in the
     buffer to hold the image.  If it is omitted or `nil',
     `insert-image' uses `" "' by default.

     The argument AREA specifies whether to put the image in a margin.
     If it is `left-margin', the image appears in the left margin;
     `right-margin' specifies the right margin.  If AREA is `nil' or
     omitted, the image is displayed at point within the buffer's text.

     The argument SLICE specifies a slice of the image to insert.  If
     SLICE is `nil' or omitted the whole image is inserted.  Otherwise,
     SLICE is a list `(X Y WIDTH HEIGHT)' which specifies the X and Y
     positions and WIDTH and HEIGHT of the image area to insert.
     Integer values are in units of pixels.  A floating point number in
     the range 0.0-1.0 stands for that fraction of the width or height
     of the entire image.

     Internally, this function inserts STRING in the buffer, and gives
     it a `display' property which specifies IMAGE.  *Note Display
     Property::.

 -- Function: insert-sliced-image image &optional string area rows cols
     This function inserts IMAGE in the current buffer at point, like
     `insert-image', but splits the image into ROWSxCOLS equally sized
     slices.

 -- Function: put-image image pos &optional string area
     This function puts image IMAGE in front of POS in the current
     buffer.  The argument POS should be an integer or a marker.  It
     specifies the buffer position where the image should appear.  The
     argument STRING specifies the text that should hold the image as
     an alternative to the default.

     The argument IMAGE must be an image descriptor, perhaps returned
     by `create-image' or stored by `defimage'.

     The argument AREA specifies whether to put the image in a margin.
     If it is `left-margin', the image appears in the left margin;
     `right-margin' specifies the right margin.  If AREA is `nil' or
     omitted, the image is displayed at point within the buffer's text.

     Internally, this function creates an overlay, and gives it a
     `before-string' property containing text that has a `display'
     property whose value is the image.  (Whew!)

 -- Function: remove-images start end &optional buffer
     This function removes images in BUFFER between positions START and
     END.  If BUFFER is omitted or `nil', images are removed from the
     current buffer.

     This removes only images that were put into BUFFER the way
     `put-image' does it, not images that were inserted with
     `insert-image' or in other ways.

 -- Function: image-size spec &optional pixels frame
     This function returns the size of an image as a pair
     `(WIDTH . HEIGHT)'.  SPEC is an image specification.  PIXELS
     non-`nil' means return sizes measured in pixels, otherwise return
     sizes measured in canonical character units (fractions of the
     width/height of the frame's default font).  FRAME is the frame on
     which the image will be displayed.  FRAME null or omitted means
     use the selected frame (*note Input Focus::).

 -- Variable: max-image-size
     This variable is used to define the maximum size of image that
     Emacs will load.  Emacs will refuse to load (and display) any
     image that is larger than this limit.

     If the value is an integer, it directly specifies the maximum
     image height and width, measured in pixels.  If it is a floating
     point number, it specifies the maximum image height and width as a
     ratio to the frame height and width.  If the value is non-numeric,
     there is no explicit limit on the size of images.

     The purpose of this variable is to prevent unreasonably large
     images from accidentally being loaded into Emacs.  It only takes
     effect the first time an image is loaded.  Once an image is placed
     in the image cache, it can always be displayed, even if the value
     of MAX-IMAGE-SIZE is subsequently changed (*note Image Cache::).


File: elisp,  Node: Image Cache,  Prev: Showing Images,  Up: Images

38.16.9 Image Cache
-------------------

Emacs stores images in an image cache so that it can display them again
more efficiently.  When Emacs displays an image, it searches the image
cache for an existing image specification `equal' to the desired
specification.  If a match is found, the image is displayed from the
cache; otherwise, Emacs loads the image normally.

   Occasionally, you may need to tell Emacs to refresh the images
associated with a given image specification.  For example, suppose you
display an image using a specification that contains a `:file'
property.  The image is loaded from the given file and stored in the
image cache.  If you later display the image again, using the same
image specification, the image is displayed from the image cache.
Normally, this is not a problem.  However, if the image file has
changed in the meantime, Emacs would be displaying the old version of
the image.  In such a situation, it is necessary to "refresh" the image
using `image-refresh'.

 -- Function: image-refresh spec &optional frame
     This function refreshes any images having image specifications
     `equal' to SPEC on frame FRAME.  If FRAME is `nil', the selected
     frame is used.  If FRAME is `t', the refresh is applied to all
     existing frames.

     This works by removing all image with image specifications matching
     SPEC from the image cache.  Thus, the next time the image is
     displayed, Emacs will load the image again.

 -- Function: clear-image-cache &optional frame
     This function clears the entire image cache.  If FRAME is
     non-`nil', only the cache for that frame is cleared.  Otherwise,
     all frames' caches are cleared.

   If an image in the image cache has not been displayed for a specified
period of time, Emacs removes it from the cache and frees the
associated memory.

 -- Variable: image-cache-eviction-delay
     This variable specifies the number of seconds an image can remain
     in the cache without being displayed.  When an image is not
     displayed for this length of time, Emacs removes it from the image
     cache.

     If the value is `nil', Emacs does not remove images from the cache
     except when you explicitly clear it.  This mode can be useful for
     debugging.


File: elisp,  Node: Buttons,  Next: Abstract Display,  Prev: Images,  Up: Display

38.17 Buttons
=============

The _button_ package defines functions for inserting and manipulating
clickable (with the mouse, or via keyboard commands) buttons in Emacs
buffers, such as might be used for help hyper-links, etc.  Emacs uses
buttons for the hyper-links in help text and the like.

   A button is essentially a set of properties attached (via text
properties or overlays) to a region of text in an Emacs buffer.  These
properties are called "button properties".

   One of these properties (`action') is a function, which will be
called when the user invokes it using the keyboard or the mouse.  The
invoked function may then examine the button and use its other
properties as desired.

   In some ways the Emacs button package duplicates functionality
offered by the widget package (*note Introduction: (widget)Top.), but
the button package has the advantage that it is much faster, much
smaller, and much simpler to use (for elisp programmers--for users, the
result is about the same).  The extra speed and space savings are
useful mainly if you need to create many buttons in a buffer (for
instance an `*Apropos*' buffer uses buttons to make entries clickable,
and may contain many thousands of entries).

* Menu:

* Button Properties::      Button properties with special meanings.
* Button Types::           Defining common properties for classes of buttons.
* Making Buttons::         Adding buttons to Emacs buffers.
* Manipulating Buttons::   Getting and setting properties of buttons.
* Button Buffer Commands:: Buffer-wide commands and bindings for buttons.


File: elisp,  Node: Button Properties,  Next: Button Types,  Up: Buttons

38.17.1 Button Properties
-------------------------

Buttons have an associated list of properties defining their appearance
and behavior, and other arbitrary properties may be used for
application specific purposes.  Some properties that have special
meaning to the button package include:

`action'
     The function to call when the user invokes the button, which is
     passed the single argument BUTTON.  By default this is `ignore',
     which does nothing.

`mouse-action'
     This is similar to `action', and when present, will be used
     instead of `action' for button invocations resulting from
     mouse-clicks (instead of the user hitting <RET>).  If not present,
     mouse-clicks use `action' instead.

`face'
     This is an Emacs face controlling how buttons of this type are
     displayed; by default this is the `button' face.

`mouse-face'
     This is an additional face which controls appearance during
     mouse-overs (merged with the usual button face); by default this is
     the usual Emacs `highlight' face.

`keymap'
     The button's keymap, defining bindings active within the button
     region.  By default this is the usual button region keymap, stored
     in the variable `button-map', which defines <RET> and <mouse-2> to
     invoke the button.

`type'
     The button-type of the button.  When creating a button, this is
     usually specified using the `:type' keyword argument.  *Note
     Button Types::.

`help-echo'
     A string displayed by the Emacs tool-tip help system; by default,
     `"mouse-2, RET: Push this button"'.

`follow-link'
     The follow-link property, defining how a <Mouse-1> click behaves
     on this button, *Note Links and Mouse-1::.

`button'
     All buttons have a non-`nil' `button' property, which may be useful
     in finding regions of text that comprise buttons (which is what the
     standard button functions do).

   There are other properties defined for the regions of text in a
button, but these are not generally interesting for typical uses.


File: elisp,  Node: Button Types,  Next: Making Buttons,  Prev: Button Properties,  Up: Buttons

38.17.2 Button Types
--------------------

Every button has a button _type_, which defines default values for the
button's properties.  Button types are arranged in a hierarchy, with
specialized types inheriting from more general types, so that it's easy
to define special-purpose types of buttons for specific tasks.

 -- Function: define-button-type name &rest properties
     Define a `button type' called NAME.  The remaining arguments form
     a sequence of PROPERTY VALUE pairs, specifying default property
     values for buttons with this type (a button's type may be set by
     giving it a `type' property when creating the button, using the
     `:type' keyword argument).

     In addition, the keyword argument `:supertype' may be used to
     specify a button-type from which NAME inherits its default
     property values.  Note that this inheritance happens only when
     NAME is defined; subsequent changes to a supertype are not
     reflected in its subtypes.

   Using `define-button-type' to define default properties for buttons
is not necessary--buttons without any specified type use the built-in
button-type `button'--but it is encouraged, since doing so usually
makes the resulting code clearer and more efficient.


File: elisp,  Node: Making Buttons,  Next: Manipulating Buttons,  Prev: Button Types,  Up: Buttons

38.17.3 Making Buttons
----------------------

Buttons are associated with a region of text, using an overlay or text
properties to hold button-specific information, all of which are
initialized from the button's type (which defaults to the built-in
button type `button').  Like all Emacs text, the appearance of the
button is governed by the `face' property; by default (via the `face'
property inherited from the `button' button-type) this is a simple
underline, like a typical web-page link.

   For convenience, there are two sorts of button-creation functions,
those that add button properties to an existing region of a buffer,
called `make-...button', and those that also insert the button text,
called `insert-...button'.

   The button-creation functions all take the `&rest' argument
PROPERTIES, which should be a sequence of PROPERTY VALUE pairs,
specifying properties to add to the button; see *Note Button
Properties::.  In addition, the keyword argument `:type' may be used to
specify a button-type from which to inherit other properties; see *Note
Button Types::.  Any properties not explicitly specified during
creation will be inherited from the button's type (if the type defines
such a property).

   The following functions add a button using an overlay (*note
Overlays::) to hold the button properties:

 -- Function: make-button beg end &rest properties
     This makes a button from BEG to END in the current buffer, and
     returns it.

 -- Function: insert-button label &rest properties
     This insert a button with the label LABEL at point, and returns it.

   The following functions are similar, but use Emacs text properties
(*note Text Properties::) to hold the button properties, making the
button actually part of the text instead of being a property of the
buffer.  Buttons using text properties do not create markers into the
buffer, which is important for speed when you use extremely large
numbers of buttons.  Both functions return the position of the start of
the new button:

 -- Function: make-text-button beg end &rest properties
     This makes a button from BEG to END in the current buffer, using
     text properties.

 -- Function: insert-text-button label &rest properties
     This inserts a button with the label LABEL at point, using text
     properties.


File: elisp,  Node: Manipulating Buttons,  Next: Button Buffer Commands,  Prev: Making Buttons,  Up: Buttons

38.17.4 Manipulating Buttons
----------------------------

These are functions for getting and setting properties of buttons.
Often these are used by a button's invocation function to determine
what to do.

   Where a BUTTON parameter is specified, it means an object referring
to a specific button, either an overlay (for overlay buttons), or a
buffer-position or marker (for text property buttons).  Such an object
is passed as the first argument to a button's invocation function when
it is invoked.

 -- Function: button-start button
     Return the position at which BUTTON starts.

 -- Function: button-end button
     Return the position at which BUTTON ends.

 -- Function: button-get button prop
     Get the property of button BUTTON named PROP.

 -- Function: button-put button prop val
     Set BUTTON's PROP property to VAL.

 -- Function: button-activate button &optional use-mouse-action
     Call BUTTON's `action' property (i.e., invoke it).  If
     USE-MOUSE-ACTION is non-`nil', try to invoke the button's
     `mouse-action' property instead of `action'; if the button has no
     `mouse-action' property, use `action' as normal.

 -- Function: button-label button
     Return BUTTON's text label.

 -- Function: button-type button
     Return BUTTON's button-type.

 -- Function: button-has-type-p button type
     Return `t' if BUTTON has button-type TYPE, or one of TYPE's
     subtypes.

 -- Function: button-at pos
     Return the button at position POS in the current buffer, or `nil'.

 -- Function: button-type-put type prop val
     Set the button-type TYPE's PROP property to VAL.

 -- Function: button-type-get type prop
     Get the property of button-type TYPE named PROP.

 -- Function: button-type-subtype-p type supertype
     Return `t' if button-type TYPE is a subtype of SUPERTYPE.


File: elisp,  Node: Button Buffer Commands,  Prev: Manipulating Buttons,  Up: Buttons

38.17.5 Button Buffer Commands
------------------------------

These are commands and functions for locating and operating on buttons
in an Emacs buffer.

   `push-button' is the command that a user uses to actually `push' a
button, and is bound by default in the button itself to <RET> and to
<mouse-2> using a region-specific keymap.  Commands that are useful
outside the buttons itself, such as `forward-button' and
`backward-button' are additionally available in the keymap stored in
`button-buffer-map'; a mode which uses buttons may want to use
`button-buffer-map' as a parent keymap for its keymap.

   If the button has a non-`nil' `follow-link' property, and
MOUSE-1-CLICK-FOLLOWS-LINK is set, a quick <Mouse-1> click will also
activate the `push-button' command.  *Note Links and Mouse-1::.

 -- Command: push-button &optional pos use-mouse-action
     Perform the action specified by a button at location POS.  POS may
     be either a buffer position or a mouse-event.  If USE-MOUSE-ACTION
     is non-`nil', or POS is a mouse-event (*note Mouse Events::), try
     to invoke the button's `mouse-action' property instead of
     `action'; if the button has no `mouse-action' property, use
     `action' as normal.  POS defaults to point, except when
     `push-button' is invoked interactively as the result of a
     mouse-event, in which case, the mouse event's position is used.
     If there's no button at POS, do nothing and return `nil',
     otherwise return `t'.

 -- Command: forward-button n &optional wrap display-message
     Move to the Nth next button, or Nth previous button if N is
     negative.  If N is zero, move to the start of any button at point.
     If WRAP is non-`nil', moving past either end of the buffer
     continues from the other end.  If DISPLAY-MESSAGE is non-`nil',
     the button's help-echo string is displayed.  Any button with a
     non-`nil' `skip' property is skipped over.  Returns the button
     found.

 -- Command: backward-button n &optional wrap display-message
     Move to the Nth previous button, or Nth next button if N is
     negative.  If N is zero, move to the start of any button at point.
     If WRAP is non-`nil', moving past either end of the buffer
     continues from the other end.  If DISPLAY-MESSAGE is non-`nil',
     the button's help-echo string is displayed.  Any button with a
     non-`nil' `skip' property is skipped over.  Returns the button
     found.

 -- Function: next-button pos &optional count-current
 -- Function: previous-button pos &optional count-current
     Return the next button after (for `next-button' or before (for
     `previous-button') position POS in the current buffer.  If
     COUNT-CURRENT is non-`nil', count any button at POS in the search,
     instead of starting at the next button.


File: elisp,  Node: Abstract Display,  Next: Blinking,  Prev: Buttons,  Up: Display

38.18 Abstract Display
======================

The Ewoc package constructs buffer text that represents a structure of
Lisp objects, and updates the text to follow changes in that structure.
This is like the "view" component in the "model/view/controller"
design paradigm.

   An "ewoc" is a structure that organizes information required to
construct buffer text that represents certain Lisp data.  The buffer
text of the ewoc has three parts, in order: first, fixed "header" text;
next, textual descriptions of a series of data elements (Lisp objects
that you specify); and last, fixed "footer" text.  Specifically, an
ewoc contains information on:

   * The buffer which its text is generated in.

   * The text's start position in the buffer.

   * The header and footer strings.

   * A doubly-linked chain of "nodes", each of which contains:

        * A "data element", a single Lisp object.

        * Links to the preceding and following nodes in the chain.

   * A "pretty-printer" function which is responsible for inserting the
     textual representation of a data element value into the current
     buffer.

   Typically, you define an ewoc with `ewoc-create', and then pass the
resulting ewoc structure to other functions in the Ewoc package to
build nodes within it, and display it in the buffer.  Once it is
displayed in the buffer, other functions determine the correspondance
between buffer positions and nodes, move point from one node's textual
representation to another, and so forth.  *Note Abstract Display
Functions::.

   A node "encapsulates" a data element much the way a variable holds a
value.  Normally, encapsulation occurs as a part of adding a node to
the ewoc.  You can retrieve the data element value and place a new
value in its place, like so:

     (ewoc-data NODE)
     => value

     (ewoc-set-data NODE NEW-VALUE)
     => NEW-VALUE

You can also use, as the data element value, a Lisp object (list or
vector) that is a container for the "real" value, or an index into some
other structure.  The example (*note Abstract Display Example::) uses
the latter approach.

   When the data changes, you will want to update the text in the
buffer.  You can update all nodes by calling `ewoc-refresh', or just
specific nodes using `ewoc-invalidate', or all nodes satisfying a
predicate using `ewoc-map'.  Alternatively, you can delete invalid
nodes using `ewoc-delete' or `ewoc-filter', and add new nodes in their
place.  Deleting a node from an ewoc deletes its associated textual
description from buffer, as well.

* Menu:

* Abstract Display Functions::
* Abstract Display Example::


File: elisp,  Node: Abstract Display Functions,  Next: Abstract Display Example,  Up: Abstract Display

38.18.1 Abstract Display Functions
----------------------------------

In this subsection, EWOC and NODE stand for the structures described
above (*note Abstract Display::), while DATA stands for an arbitrary
Lisp object used as a data element.

 -- Function: ewoc-create pretty-printer &optional header footer nosep
     This constructs and returns a new ewoc, with no nodes (and thus no
     data elements).  PRETTY-PRINTER should be a function that takes one
     argument, a data element of the sort you plan to use in this ewoc,
     and inserts its textual description at point using `insert' (and
     never `insert-before-markers', because that would interfere with
     the Ewoc package's internal mechanisms).

     Normally, a newline is automatically inserted after the header,
     the footer and every node's textual description.  If NOSEP is
     non-`nil', no newline is inserted.  This may be useful for
     displaying an entire ewoc on a single line, for example, or for
     making nodes "invisible" by arranging for PRETTY-PRINTER to do
     nothing for those nodes.

     An ewoc maintains its text in the buffer that is current when you
     create it, so switch to the intended buffer before calling
     `ewoc-create'.

 -- Function: ewoc-buffer ewoc
     This returns the buffer where EWOC maintains its text.

 -- Function: ewoc-get-hf ewoc
     This returns a cons cell `(HEADER . FOOTER)' made from EWOC's
     header and footer.

 -- Function: ewoc-set-hf ewoc header footer
     This sets the header and footer of EWOC to the strings HEADER and
     FOOTER, respectively.

 -- Function: ewoc-enter-first ewoc data
 -- Function: ewoc-enter-last ewoc data
     These add a new node encapsulating DATA, putting it, respectively,
     at the beginning or end of EWOC's chain of nodes.

 -- Function: ewoc-enter-before ewoc node data
 -- Function: ewoc-enter-after ewoc node data
     These add a new node encapsulating DATA, adding it to EWOC before
     or after NODE, respectively.

 -- Function: ewoc-prev ewoc node
 -- Function: ewoc-next ewoc node
     These return, respectively, the previous node and the next node of
     NODE in EWOC.

 -- Function: ewoc-nth ewoc n
     This returns the node in EWOC found at zero-based index N.  A
     negative N means count from the end.  `ewoc-nth' returns `nil' if
     N is out of range.

 -- Function: ewoc-data node
     This extracts the data encapsulated by NODE and returns it.

 -- Function: ewoc-set-data node data
     This sets the data encapsulated by NODE to DATA.

 -- Function: ewoc-locate ewoc &optional pos guess
     This determines the node in EWOC which contains point (or POS if
     specified), and returns that node.  If EWOC has no nodes, it
     returns `nil'.  If POS is before the first node, it returns the
     first node; if POS is after the last node, it returns the last
     node.  The optional third arg GUESS should be a node that is
     likely to be near POS; this doesn't alter the result, but makes
     the function run faster.

 -- Function: ewoc-location node
     This returns the start position of NODE.

 -- Function: ewoc-goto-prev ewoc arg
 -- Function: ewoc-goto-next ewoc arg
     These move point to the previous or next, respectively, ARGth node
     in EWOC.  `ewoc-goto-prev' does not move if it is already at the
     first node or if EWOC is empty, whereas `ewoc-goto-next' moves
     past the last node, returning `nil'.  Excepting this special case,
     these functions return the node moved to.

 -- Function: ewoc-goto-node ewoc node
     This moves point to the start of NODE in EWOC.

 -- Function: ewoc-refresh ewoc
     This function regenerates the text of EWOC.  It works by deleting
     the text between the header and the footer, i.e., all the data
     elements' representations, and then calling the pretty-printer
     function for each node, one by one, in order.

 -- Function: ewoc-invalidate ewoc &rest nodes
     This is similar to `ewoc-refresh', except that only NODES in EWOC
     are updated instead of the entire set.

 -- Function: ewoc-delete ewoc &rest nodes
     This deletes each node in NODES from EWOC.

 -- Function: ewoc-filter ewoc predicate &rest args
     This calls PREDICATE for each data element in EWOC and deletes
     those nodes for which PREDICATE returns `nil'.  Any ARGS are
     passed to PREDICATE.

 -- Function: ewoc-collect ewoc predicate &rest args
     This calls PREDICATE for each data element in EWOC and returns a
     list of those elements for which PREDICATE returns non-`nil'.  The
     elements in the list are ordered as in the buffer.  Any ARGS are
     passed to PREDICATE.

 -- Function: ewoc-map map-function ewoc &rest args
     This calls MAP-FUNCTION for each data element in EWOC and updates
     those nodes for which MAP-FUNCTION returns non-`nil'.  Any ARGS
     are passed to MAP-FUNCTION.


File: elisp,  Node: Abstract Display Example,  Prev: Abstract Display Functions,  Up: Abstract Display

38.18.2 Abstract Display Example
--------------------------------

Here is a simple example using functions of the ewoc package to
implement a "color components display," an area in a buffer that
represents a vector of three integers (itself representing a 24-bit RGB
value) in various ways.

     (setq colorcomp-ewoc nil
           colorcomp-data nil
           colorcomp-mode-map nil
           colorcomp-labels ["Red" "Green" "Blue"])

     (defun colorcomp-pp (data)
       (if data
           (let ((comp (aref colorcomp-data data)))
             (insert (aref colorcomp-labels data) "\t: #x"
                     (format "%02X" comp) " "
                     (make-string (ash comp -2) ?#) "\n"))
         (let ((cstr (format "#%02X%02X%02X"
                             (aref colorcomp-data 0)
                             (aref colorcomp-data 1)
                             (aref colorcomp-data 2)))
               (samp " (sample text) "))
           (insert "Color\t: "
                   (propertize samp 'face `(foreground-color . ,cstr))
                   (propertize samp 'face `(background-color . ,cstr))
                   "\n"))))

     (defun colorcomp (color)
       "Allow fiddling with COLOR in a new buffer.
     The buffer is in Color Components mode."
       (interactive "sColor (name or #RGB or #RRGGBB): ")
       (when (string= "" color)
         (setq color "green"))
       (unless (color-values color)
         (error "No such color: %S" color))
       (switch-to-buffer
        (generate-new-buffer (format "originally: %s" color)))
       (kill-all-local-variables)
       (setq major-mode 'colorcomp-mode
             mode-name "Color Components")
       (use-local-map colorcomp-mode-map)
       (erase-buffer)
       (buffer-disable-undo)
       (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
                                          (color-values color))))
             (ewoc (ewoc-create 'colorcomp-pp
                                "\nColor Components\n\n"
                                (substitute-command-keys
                                 "\n\\{colorcomp-mode-map}"))))
         (set (make-local-variable 'colorcomp-data) data)
         (set (make-local-variable 'colorcomp-ewoc) ewoc)
         (ewoc-enter-last ewoc 0)
         (ewoc-enter-last ewoc 1)
         (ewoc-enter-last ewoc 2)
         (ewoc-enter-last ewoc nil)))

   This example can be extended to be a "color selection widget" (in
other words, the controller part of the "model/view/controller" design
paradigm) by defining commands to modify `colorcomp-data' and to
"finish" the selection process, and a keymap to tie it all together
conveniently.

     (defun colorcomp-mod (index limit delta)
       (let ((cur (aref colorcomp-data index)))
         (unless (= limit cur)
           (aset colorcomp-data index (+ cur delta)))
         (ewoc-invalidate
          colorcomp-ewoc
          (ewoc-nth colorcomp-ewoc index)
          (ewoc-nth colorcomp-ewoc -1))))

     (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
     (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
     (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
     (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
     (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
     (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))

     (defun colorcomp-copy-as-kill-and-exit ()
       "Copy the color components into the kill ring and kill the buffer.
     The string is formatted #RRGGBB (hash followed by six hex digits)."
       (interactive)
       (kill-new (format "#%02X%02X%02X"
                         (aref colorcomp-data 0)
                         (aref colorcomp-data 1)
                         (aref colorcomp-data 2)))
       (kill-buffer nil))

     (setq colorcomp-mode-map
           (let ((m (make-sparse-keymap)))
             (suppress-keymap m)
             (define-key m "i" 'colorcomp-R-less)
             (define-key m "o" 'colorcomp-R-more)
             (define-key m "k" 'colorcomp-G-less)
             (define-key m "l" 'colorcomp-G-more)
             (define-key m "," 'colorcomp-B-less)
             (define-key m "." 'colorcomp-B-more)
             (define-key m " " 'colorcomp-copy-as-kill-and-exit)
             m))

   Note that we never modify the data in each node, which is fixed when
the ewoc is created to be either `nil' or an index into the vector
`colorcomp-data', the actual color components.


File: elisp,  Node: Blinking,  Next: Usual Display,  Prev: Abstract Display,  Up: Display

38.19 Blinking Parentheses
==========================

This section describes the mechanism by which Emacs shows a matching
open parenthesis when the user inserts a close parenthesis.

 -- Variable: blink-paren-function
     The value of this variable should be a function (of no arguments)
     to be called whenever a character with close parenthesis syntax is
     inserted.  The value of `blink-paren-function' may be `nil', in
     which case nothing is done.

 -- User Option: blink-matching-paren
     If this variable is `nil', then `blink-matching-open' does nothing.

 -- User Option: blink-matching-paren-distance
     This variable specifies the maximum distance to scan for a matching
     parenthesis before giving up.

 -- User Option: blink-matching-delay
     This variable specifies the number of seconds for the cursor to
     remain at the matching parenthesis.  A fraction of a second often
     gives good results, but the default is 1, which works on all
     systems.

 -- Command: blink-matching-open
     This function is the default value of `blink-paren-function'.  It
     assumes that point follows a character with close parenthesis
     syntax and moves the cursor momentarily to the matching opening
     character.  If that character is not already on the screen, it
     displays the character's context in the echo area.  To avoid long
     delays, this function does not search farther than
     `blink-matching-paren-distance' characters.

     Here is an example of calling this function explicitly.

          (defun interactive-blink-matching-open ()
            "Indicate momentarily the start of sexp before point."
            (interactive)
            (let ((blink-matching-paren-distance
                   (buffer-size))
                  (blink-matching-paren t))
              (blink-matching-open)))


File: elisp,  Node: Usual Display,  Next: Display Tables,  Prev: Blinking,  Up: Display

38.20 Usual Display Conventions
===============================

The usual display conventions define how to display each character
code.  You can override these conventions by setting up a display table
(*note Display Tables::).  Here are the usual display conventions:

   * Character codes 32 through 126 map to glyph codes 32 through 126.
     Normally this means they display as themselves.

   * Character code 9 is a horizontal tab.  It displays as whitespace
     up to a position determined by `tab-width'.

   * Character code 10 is a newline.

   * All other codes in the range 0 through 31, and code 127, display
     in one of two ways according to the value of `ctl-arrow'.  If it is
     non-`nil', these codes map to sequences of two glyphs, where the
     first glyph is the ASCII code for `^'.  (A display table can
     specify a glyph to use instead of `^'.)  Otherwise, these codes map
     just like the codes in the range 128 to 255.

     On MS-DOS terminals, Emacs arranges by default for the character
     code 127 to be mapped to the glyph code 127, which normally
     displays as an empty polygon.  This glyph is used to display
     non-ASCII characters that the MS-DOS terminal doesn't support.
     *Note MS-DOS and MULE: (emacs)MS-DOS and MULE.

   * Character codes 128 through 255 map to sequences of four glyphs,
     where the first glyph is the ASCII code for `\', and the others are
     digit characters representing the character code in octal.  (A
     display table can specify a glyph to use instead of `\'.)

   * Multibyte character codes above 256 are displayed as themselves,
     or as a question mark or empty box if the terminal cannot display
     that character.

   The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
`nil'.  Thus, when you set up a display table, you need only specify
the characters for which you want special behavior.

   These display rules apply to carriage return (character code 13),
when it appears in the buffer.  But that character may not appear in the
buffer where you expect it, if it was eliminated as part of end-of-line
conversion (*note Coding System Basics::).

   These variables affect the way certain characters are displayed on
the screen.  Since they change the number of columns the characters
occupy, they also affect the indentation functions.  These variables
also affect how the mode line is displayed; if you want to force
redisplay of the mode line using the new values, call the function
`force-mode-line-update' (*note Mode Line Format::).

 -- User Option: ctl-arrow
     This buffer-local variable controls how control characters are
     displayed.  If it is non-`nil', they are displayed as a caret
     followed by the character: `^A'.  If it is `nil', they are
     displayed as a backslash followed by three octal digits: `\001'.

 -- Variable: default-ctl-arrow
     The value of this variable is the default value for `ctl-arrow' in
     buffers that do not override it.  *Note Default Value::.

 -- User Option: tab-width
     The value of this buffer-local variable is the spacing between tab
     stops used for displaying tab characters in Emacs buffers.  The
     value is in units of columns, and the default is 8.  Note that
     this feature is completely independent of the user-settable tab
     stops used by the command `tab-to-tab-stop'.  *Note Indent Tabs::.


File: elisp,  Node: Display Tables,  Next: Beeping,  Prev: Usual Display,  Up: Display

38.21 Display Tables
====================

You can use the "display table" feature to control how all possible
character codes display on the screen.  This is useful for displaying
European languages that have letters not in the ASCII character set.

   The display table maps each character code into a sequence of
"glyphs", each glyph being a graphic that takes up one character
position on the screen.  You can also define how to display each glyph
on your terminal, using the "glyph table".

   Display tables affect how the mode line is displayed; if you want to
force redisplay of the mode line using a new display table, call
`force-mode-line-update' (*note Mode Line Format::).

* Menu:

* Display Table Format::  What a display table consists of.
* Active Display Table::  How Emacs selects a display table to use.
* Glyphs::              How to define a glyph, and what glyphs mean.


File: elisp,  Node: Display Table Format,  Next: Active Display Table,  Up: Display Tables

38.21.1 Display Table Format
----------------------------

A display table is actually a char-table (*note Char-Tables::) with
`display-table' as its subtype.

 -- Function: make-display-table
     This creates and returns a display table.  The table initially has
     `nil' in all elements.

   The ordinary elements of the display table are indexed by character
codes; the element at index C says how to display the character code C.
The value should be `nil' or a vector of the glyphs to be output
(*note Glyphs::).  `nil' says to display the character C according to
the usual display conventions (*note Usual Display::).

   *Warning:* if you use the display table to change the display of
newline characters, the whole buffer will be displayed as one long
"line."

   The display table also has six "extra slots" which serve special
purposes.  Here is a table of their meanings; `nil' in any slot means
to use the default for that slot, as stated below.

0
     The glyph for the end of a truncated screen line (the default for
     this is `$').  *Note Glyphs::.  On graphical terminals, Emacs uses
     arrows in the fringes to indicate truncation, so the display table
     has no effect.

1
     The glyph for the end of a continued line (the default is `\').
     On graphical terminals, Emacs uses curved arrows in the fringes to
     indicate continuation, so the display table has no effect.

2
     The glyph for indicating a character displayed as an octal
     character code (the default is `\').

3
     The glyph for indicating a control character (the default is `^').

4
     A vector of glyphs for indicating the presence of invisible lines
     (the default is `...').  *Note Selective Display::.

5
     The glyph used to draw the border between side-by-side windows (the
     default is `|').  *Note Splitting Windows::.  This takes effect
     only when there are no scroll bars; if scroll bars are supported
     and in use, a scroll bar separates the two windows.

   For example, here is how to construct a display table that mimics the
effect of setting `ctl-arrow' to a non-`nil' value:

     (setq disptab (make-display-table))
     (let ((i 0))
       (while (< i 32)
         (or (= i ?\t) (= i ?\n)
             (aset disptab i (vector ?^ (+ i 64))))
         (setq i (1+ i)))
       (aset disptab 127 (vector ?^ ??)))

 -- Function: display-table-slot display-table slot
     This function returns the value of the extra slot SLOT of
     DISPLAY-TABLE.  The argument SLOT may be a number from 0 to 5
     inclusive, or a slot name (symbol).  Valid symbols are
     `truncation', `wrap', `escape', `control', `selective-display',
     and `vertical-border'.

 -- Function: set-display-table-slot display-table slot value
     This function stores VALUE in the extra slot SLOT of
     DISPLAY-TABLE.  The argument SLOT may be a number from 0 to 5
     inclusive, or a slot name (symbol).  Valid symbols are
     `truncation', `wrap', `escape', `control', `selective-display',
     and `vertical-border'.

 -- Function: describe-display-table display-table
     This function displays a description of the display table
     DISPLAY-TABLE in a help buffer.

 -- Command: describe-current-display-table
     This command displays a description of the current display table
     in a help buffer.


File: elisp,  Node: Active Display Table,  Next: Glyphs,  Prev: Display Table Format,  Up: Display Tables

38.21.2 Active Display Table
----------------------------

Each window can specify a display table, and so can each buffer.  When
a buffer B is displayed in window W, display uses the display table for
window W if it has one; otherwise, the display table for buffer B if it
has one; otherwise, the standard display table if any.  The display
table chosen is called the "active" display table.

 -- Function: window-display-table &optional window
     This function returns WINDOW's display table, or `nil' if WINDOW
     does not have an assigned display table.  The default for WINDOW
     is the selected window.

 -- Function: set-window-display-table window table
     This function sets the display table of WINDOW to TABLE.  The
     argument TABLE should be either a display table or `nil'.

 -- Variable: buffer-display-table
     This variable is automatically buffer-local in all buffers; its
     value in a particular buffer specifies the display table for that
     buffer.  If it is `nil', that means the buffer does not have an
     assigned display table.

 -- Variable: standard-display-table
     This variable's value is the default display table, used whenever a
     window has no display table and neither does the buffer displayed
     in that window.  This variable is `nil' by default.

   If there is no display table to use for a particular window--that is,
if the window specifies none, its buffer specifies none, and
`standard-display-table' is `nil'--then Emacs uses the usual display
conventions for all character codes in that window.  *Note Usual
Display::.

   A number of functions for changing the standard display table are
defined in the library `disp-table'.


File: elisp,  Node: Glyphs,  Prev: Active Display Table,  Up: Display Tables

38.21.3 Glyphs
--------------

A "glyph" is a generalization of a character; it stands for an image
that takes up a single character position on the screen.  Normally
glyphs come from vectors in the display table (*note Display Tables::).

   A glyph is represented in Lisp as a "glyph code".  A glyph code can
be "simple" or it can be defined by the "glyph table".  A simple glyph
code is just a way of specifying a character and a face to output it
in.  *Note Faces::.

   The following functions are used to manipulate simple glyph codes:

 -- Function: make-glyph-code char &optional face
     This function returns a simple glyph code representing char CHAR
     with face FACE.

 -- Function: glyph-char glyph
     This function returns the character of simple glyph code GLYPH.

 -- Function: glyph-face glyph
     This function returns face of simple glyph code GLYPH, or `nil' if
     GLYPH has the default face (face-id 0).

   On character terminals, you can set up a "glyph table" to define the
meaning of glyph codes (represented as small integers).

 -- Variable: glyph-table
     The value of this variable is the current glyph table.  It should
     be `nil' or a vector whose Gth element defines glyph code G.

     If a glyph code is greater than or equal to the length of the glyph
     table, that code is automatically simple.  If `glyph-table' is
     `nil' then all glyph codes are simple.

     The glyph table is used only on character terminals.  On graphical
     displays, all glyph codes are simple.

   Here are the meaningful types of elements in the glyph table:

STRING
     Send the characters in STRING to the terminal to output this glyph
     code.

CODE
     Define this glyph code as an alias for glyph code CODE created by
     `make-glyph-code'.  You can use such an alias to define a
     small-numbered glyph code which specifies a character with a face.

`nil'
     This glyph code is simple.

 -- Function: create-glyph string
     This function returns a newly-allocated glyph code which is set up
     to display by sending STRING to the terminal.


File: elisp,  Node: Beeping,  Next: Window Systems,  Prev: Display Tables,  Up: Display

38.22 Beeping
=============

This section describes how to make Emacs ring the bell (or blink the
screen) to attract the user's attention.  Be conservative about how
often you do this; frequent bells can become irritating.  Also be
careful not to use just beeping when signaling an error is more
appropriate.  (*Note Errors::.)

 -- Function: ding &optional do-not-terminate
     This function beeps, or flashes the screen (see `visible-bell'
     below).  It also terminates any keyboard macro currently executing
     unless DO-NOT-TERMINATE is non-`nil'.

 -- Function: beep &optional do-not-terminate
     This is a synonym for `ding'.

 -- User Option: visible-bell
     This variable determines whether Emacs should flash the screen to
     represent a bell.  Non-`nil' means yes, `nil' means no.  This is
     effective on graphical displays, and on text-only terminals
     provided the terminal's Termcap entry defines the visible bell
     capability (`vb').

 -- Variable: ring-bell-function
     If this is non-`nil', it specifies how Emacs should "ring the
     bell."  Its value should be a function of no arguments.  If this is
     non-`nil', it takes precedence over the `visible-bell' variable.


File: elisp,  Node: Window Systems,  Prev: Beeping,  Up: Display

38.23 Window Systems
====================

Emacs works with several window systems, most notably the X Window
System.  Both Emacs and X use the term "window," but use it
differently.  An Emacs frame is a single window as far as X is
concerned; the individual Emacs windows are not known to X at all.

 -- Variable: window-system
     This variable tells Lisp programs what window system Emacs is
     running under.  The possible values are

    `x'
          Emacs is displaying using X.

    `pc'
          Emacs is displaying using MS-DOS.

    `w32'
          Emacs is displaying using Windows.

    `mac'
          Emacs is displaying using a Macintosh.

    `nil'
          Emacs is using a character-based terminal.

 -- Variable: window-setup-hook
     This variable is a normal hook which Emacs runs after handling the
     initialization files.  Emacs runs this hook after it has completed
     loading your init file, the default initialization file (if any),
     and the terminal-specific Lisp code, and running the hook
     `term-setup-hook'.

     This hook is used for internal purposes: setting up communication
     with the window system, and creating the initial window.  Users
     should not interfere with it.


File: elisp,  Node: System Interface,  Next: Antinews,  Prev: Display,  Up: Top

39 Operating System Interface
*****************************

This chapter is about starting and getting out of Emacs, access to
values in the operating system environment, and terminal input, output,
and flow control.

   *Note Building Emacs::, for related information.  See also *Note
Display::, for additional operating system status information
pertaining to the terminal and the screen.

* Menu:

* Starting Up::         Customizing Emacs startup processing.
* Getting Out::         How exiting works (permanent or temporary).
* System Environment::  Distinguish the name and kind of system.
* User Identification:: Finding the name and user id of the user.
* Time of Day::		Getting the current time.
* Time Conversion::     Converting a time from numeric form
                          to calendrical data, and vice versa).
* Time Parsing::        Converting a time from numeric form to text
                          and vice versa.
* Processor Run Time::  Getting the run time used by Emacs.
* Time Calculations::   Adding, subtracting, comparing times, etc.
* Timers::		Setting a timer to call a function at a certain time.
* Idle Timers::         Setting a timer to call a function when Emacs has
                          been idle for a certain length of time.
* Terminal Input::      Accessing and recording terminal input.
* Terminal Output::     Controlling and recording terminal output.
* Sound Output::        Playing sounds on the computer's speaker.
* X11 Keysyms::         Operating on key symbols for X Windows
* Batch Mode::          Running Emacs without terminal interaction.
* Session Management::  Saving and restoring state with X Session Management.


File: elisp,  Node: Starting Up,  Next: Getting Out,  Up: System Interface

39.1 Starting Up Emacs
======================

This section describes what Emacs does when it is started, and how you
can customize these actions.

* Menu:

* Startup Summary::         Sequence of actions Emacs performs at startup.
* Init File::               Details on reading the init file (`.emacs').
* Terminal-Specific::       How the terminal-specific Lisp file is read.
* Command-Line Arguments::  How command-line arguments are processed,
                              and how you can customize them.


File: elisp,  Node: Startup Summary,  Next: Init File,  Up: Starting Up

39.1.1 Summary: Sequence of Actions at Startup
----------------------------------------------

The order of operations performed (in `startup.el') by Emacs when it is
started up is as follows:

  1. It adds subdirectories to `load-path', by running the file named
     `subdirs.el' in each directory in the list.  Normally this file
     adds the directory's subdirectories to the list, and these will be
     scanned in their turn.  The files `subdirs.el' are normally
     generated automatically by Emacs installation.

  2. It sets the language environment and the terminal coding system,
     if requested by environment variables such as `LANG'.

  3. It loads the initialization library for the window system, if you
     are using a window system.  This library's name is
     `term/WINDOWSYSTEM-win.el'.

  4. It processes the initial options.  (Some of them are handled even
     earlier than this.)

  5. It initializes the window frame and faces, if appropriate.

  6. It runs the normal hook `before-init-hook'.

  7. It loads the library `site-start' (if any), unless the option `-Q'
     (or `--no-site-file') was specified.  The library's file name is
     usually `site-start.el'.  

  8. It loads your init file (usually `~/.emacs'), unless the option
     `-q' (or `--no-init-file'), `-Q', or `--batch' was specified on
     the command line.  The `-u' option can specify another user whose
     home directory should be used instead of `~'.

  9. It loads the library `default' (if any), unless
     `inhibit-default-init' is non-`nil'.  (This is not done in
     `-batch' mode, or if `-Q' or `-q' was specified on the command
     line.)  The library's file name is usually `default.el'.  

 10. It runs the normal hook `after-init-hook'.

 11. It sets the major mode according to `initial-major-mode', provided
     the buffer `*scratch*' is still current and still in Fundamental
     mode.

 12. It loads the terminal-specific Lisp file, if any, except when in
     batch mode or using a window system.

 13. It displays the initial echo area message, unless you have
     suppressed that with `inhibit-startup-echo-area-message'.

 14. It processes the action arguments from the command line.

 15. It runs `emacs-startup-hook' and then `term-setup-hook'.

 16. It calls `frame-notice-user-settings', which modifies the
     parameters of the selected frame according to whatever the init
     files specify.

 17. It runs `window-setup-hook'.  *Note Window Systems::.

 18. It displays copyleft, nonwarranty, and basic use information,
     provided the value of `inhibit-startup-message' is `nil', you
     didn't specify `--no-splash' or `-Q'.

 -- User Option: inhibit-startup-message
     This variable inhibits the initial startup messages (the
     nonwarranty, etc.).  If it is non-`nil', then the messages are not
     printed.

     This variable exists so you can set it in your personal init file,
     once you are familiar with the contents of the startup message.
     Do not set this variable in the init file of a new user, or in a
     way that affects more than one user, because that would prevent
     new users from receiving the information they are supposed to see.

 -- User Option: inhibit-startup-echo-area-message
     This variable controls the display of the startup echo area
     message.  You can suppress the startup echo area message by adding
     text with this form to your init file:

          (setq inhibit-startup-echo-area-message
                "YOUR-LOGIN-NAME")

     Emacs explicitly checks for an expression as shown above in your
     init file; your login name must appear in the expression as a Lisp
     string constant.  Other methods of setting
     `inhibit-startup-echo-area-message' to the same value do not
     inhibit the startup message.

     This way, you can easily inhibit the message for yourself if you
     wish, but thoughtless copying of your init file will not inhibit
     the message for someone else.


File: elisp,  Node: Init File,  Next: Terminal-Specific,  Prev: Startup Summary,  Up: Starting Up

39.1.2 The Init File, `.emacs'
------------------------------

When you start Emacs, it normally attempts to load your "init file", a
file in your home directory.  Its normal name is `.emacs', but you can
also call it `.emacs.el'.  Alternatively, you can use a file named
`init.el' in a subdirectory `.emacs.d'.  Whichever place you use, you
can also compile the file (*note Byte Compilation::); then the actual
file loaded will be `.emacs.elc' or `init.elc'.

   The command-line switches `-q', `-Q', and `-u' control whether and
where to find the init file; `-q' (and the stronger `-Q') says not to
load an init file, while `-u USER' says to load USER's init file
instead of yours.  *Note Entering Emacs: (emacs)Entering Emacs.  If
neither option is specified, Emacs uses the `LOGNAME' environment
variable, or the `USER' (most systems) or `USERNAME' (MS systems)
variable, to find your home directory and thus your init file; this
way, even if you have su'd, Emacs still loads your own init file.  If
those environment variables are absent, though, Emacs uses your user-id
to find your home directory.

   A site may have a "default init file", which is the library named
`default.el'.  Emacs finds the `default.el' file through the standard
search path for libraries (*note How Programs Do Loading::).  The Emacs
distribution does not come with this file; sites may provide one for
local customizations.  If the default init file exists, it is loaded
whenever you start Emacs, except in batch mode or if `-q' (or `-Q') is
specified.  But your own personal init file, if any, is loaded first;
if it sets `inhibit-default-init' to a non-`nil' value, then Emacs does
not subsequently load the `default.el' file.

   Another file for site-customization is `site-start.el'.  Emacs loads
this _before_ the user's init file.  You can inhibit the loading of
this file with the option `--no-site-file'.

 -- Variable: site-run-file
     This variable specifies the site-customization file to load before
     the user's init file.  Its normal value is `"site-start"'.  The
     only way you can change it with real effect is to do so before
     dumping Emacs.

   *Note Init File Examples: (emacs)Init Examples, for examples of how
to make various commonly desired customizations in your `.emacs' file.

 -- User Option: inhibit-default-init
     This variable prevents Emacs from loading the default
     initialization library file for your session of Emacs.  If its
     value is non-`nil', then the default library is not loaded.  The
     default value is `nil'.

 -- Variable: before-init-hook
     This normal hook is run, once, just before loading all the init
     files (the user's init file, `default.el', and/or `site-start.el').
     (The only way to change it with real effect is before dumping
     Emacs.)

 -- Variable: after-init-hook
     This normal hook is run, once, just after loading all the init
     files (the user's init file, `default.el', and/or `site-start.el'),
     before loading the terminal-specific library and processing the
     command-line action arguments.

 -- Variable: emacs-startup-hook
     This normal hook is run, once, just after handling the command line
     arguments, just before `term-setup-hook'.

 -- Variable: user-init-file
     This variable holds the absolute file name of the user's init
     file.  If the actual init file loaded is a compiled file, such as
     `.emacs.elc', the value refers to the corresponding source file.


File: elisp,  Node: Terminal-Specific,  Next: Command-Line Arguments,  Prev: Init File,  Up: Starting Up

39.1.3 Terminal-Specific Initialization
---------------------------------------

Each terminal type can have its own Lisp library that Emacs loads when
run on that type of terminal.  The library's name is constructed by
concatenating the value of the variable `term-file-prefix' and the
terminal type (specified by the environment variable `TERM').
Normally, `term-file-prefix' has the value `"term/"'; changing this is
not recommended.  Emacs finds the file in the normal manner, by
searching the `load-path' directories, and trying the `.elc' and `.el'
suffixes.

   The usual function of a terminal-specific library is to enable
special keys to send sequences that Emacs can recognize.  It may also
need to set or add to `function-key-map' if the Termcap or Terminfo
entry does not specify all the terminal's function keys.  *Note
Terminal Input::.

   When the name of the terminal type contains a hyphen, and no library
is found whose name is identical to the terminal's name, Emacs strips
from the terminal's name the last hyphen and everything that follows
it, and tries again.  This process is repeated until Emacs finds a
matching library or until there are no more hyphens in the name (the
latter means the terminal doesn't have any library specific to it).
Thus, for example, if there are no `aaa-48' and `aaa-30' libraries,
Emacs will try the same library `term/aaa.el' for terminal types
`aaa-48' and `aaa-30-rv'.  If necessary, the library can evaluate
`(getenv "TERM")' to find the full name of the terminal type.

   Your init file can prevent the loading of the terminal-specific
library by setting the variable `term-file-prefix' to `nil'.  This
feature is useful when experimenting with your own peculiar
customizations.

   You can also arrange to override some of the actions of the
terminal-specific library by setting the variable `term-setup-hook'.
This is a normal hook which Emacs runs using `run-hooks' at the end of
Emacs initialization, after loading both your init file and any
terminal-specific libraries.  You can use this variable to define
initializations for terminals that do not have their own libraries.
*Note Hooks::.

 -- Variable: term-file-prefix
     If the `term-file-prefix' variable is non-`nil', Emacs loads a
     terminal-specific initialization file as follows:

          (load (concat term-file-prefix (getenv "TERM")))

     You may set the `term-file-prefix' variable to `nil' in your init
     file if you do not wish to load the terminal-initialization file.
     To do this, put the following in your init file: `(setq
     term-file-prefix nil)'.

     On MS-DOS, if the environment variable `TERM' is not set, Emacs
     uses `internal' as the terminal type.

 -- Variable: term-setup-hook
     This variable is a normal hook that Emacs runs after loading your
     init file, the default initialization file (if any) and the
     terminal-specific Lisp file.

     You can use `term-setup-hook' to override the definitions made by a
     terminal-specific file.

   See `window-setup-hook' in *Note Window Systems::, for a related
feature.


File: elisp,  Node: Command-Line Arguments,  Prev: Terminal-Specific,  Up: Starting Up

39.1.4 Command-Line Arguments
-----------------------------

You can use command-line arguments to request various actions when you
start Emacs.  Since you do not need to start Emacs more than once per
day, and will often leave your Emacs session running longer than that,
command-line arguments are hardly ever used.  As a practical matter, it
is best to avoid making the habit of using them, since this habit would
encourage you to kill and restart Emacs unnecessarily often.  These
options exist for two reasons: to be compatible with other editors (for
invocation by other programs) and to enable shell scripts to run
specific Lisp programs.

   This section describes how Emacs processes command-line arguments,
and how you can customize them.

 -- Function: command-line
     This function parses the command line that Emacs was called with,
     processes it, loads the user's init file and displays the startup
     messages.

 -- Variable: command-line-processed
     The value of this variable is `t' once the command line has been
     processed.

     If you redump Emacs by calling `dump-emacs', you may wish to set
     this variable to `nil' first in order to cause the new dumped Emacs
     to process its new command-line arguments.

 -- Variable: command-switch-alist
     The value of this variable is an alist of user-defined command-line
     options and associated handler functions.  This variable exists so
     you can add elements to it.

     A "command-line option" is an argument on the command line, which
     has the form:

          -OPTION

     The elements of the `command-switch-alist' look like this:

          (OPTION . HANDLER-FUNCTION)

     The CAR, OPTION, is a string, the name of a command-line option
     (not including the initial hyphen).  The HANDLER-FUNCTION is
     called to handle OPTION, and receives the option name as its sole
     argument.

     In some cases, the option is followed in the command line by an
     argument.  In these cases, the HANDLER-FUNCTION can find all the
     remaining command-line arguments in the variable
     `command-line-args-left'.  (The entire list of command-line
     arguments is in `command-line-args'.)

     The command-line arguments are parsed by the `command-line-1'
     function in the `startup.el' file.  See also *Note Command Line
     Arguments for Emacs Invocation: (emacs)Emacs Invocation.

 -- Variable: command-line-args
     The value of this variable is the list of command-line arguments
     passed to Emacs.

 -- Variable: command-line-functions
     This variable's value is a list of functions for handling an
     unrecognized command-line argument.  Each time the next argument
     to be processed has no special meaning, the functions in this list
     are called, in order of appearance, until one of them returns a
     non-`nil' value.

     These functions are called with no arguments.  They can access the
     command-line argument under consideration through the variable
     `argi', which is bound temporarily at this point.  The remaining
     arguments (not including the current one) are in the variable
     `command-line-args-left'.

     When a function recognizes and processes the argument in `argi', it
     should return a non-`nil' value to say it has dealt with that
     argument.  If it has also dealt with some of the following
     arguments, it can indicate that by deleting them from
     `command-line-args-left'.

     If all of these functions return `nil', then the argument is used
     as a file name to visit.


File: elisp,  Node: Getting Out,  Next: System Environment,  Prev: Starting Up,  Up: System Interface

39.2 Getting Out of Emacs
=========================

There are two ways to get out of Emacs: you can kill the Emacs job,
which exits permanently, or you can suspend it, which permits you to
reenter the Emacs process later.  As a practical matter, you seldom kill
Emacs--only when you are about to log out.  Suspending is much more
common.

* Menu:

* Killing Emacs::        Exiting Emacs irreversibly.
* Suspending Emacs::     Exiting Emacs reversibly.


File: elisp,  Node: Killing Emacs,  Next: Suspending Emacs,  Up: Getting Out

39.2.1 Killing Emacs
--------------------

Killing Emacs means ending the execution of the Emacs process.  The
parent process normally resumes control.  The low-level primitive for
killing Emacs is `kill-emacs'.

 -- Function: kill-emacs &optional exit-data
     This function exits the Emacs process and kills it.

     If EXIT-DATA is an integer, then it is used as the exit status of
     the Emacs process.  (This is useful primarily in batch operation;
     see *Note Batch Mode::.)

     If EXIT-DATA is a string, its contents are stuffed into the
     terminal input buffer so that the shell (or whatever program next
     reads input) can read them.

   All the information in the Emacs process, aside from files that have
been saved, is lost when the Emacs process is killed.  Because killing
Emacs inadvertently can lose a lot of work, Emacs queries for
confirmation before actually terminating if you have buffers that need
saving or subprocesses that are running.  This is done in the function
`save-buffers-kill-emacs', the higher level function from which
`kill-emacs' is usually called.

 -- Variable: kill-emacs-query-functions
     After asking the standard questions, `save-buffers-kill-emacs'
     calls the functions in the list `kill-emacs-query-functions', in
     order of appearance, with no arguments.  These functions can ask
     for additional confirmation from the user.  If any of them returns
     `nil', `save-buffers-kill-emacs' does not kill Emacs, and does not
     run the remaining functions in this hook.  Calling `kill-emacs'
     directly does not run this hook.

 -- Variable: kill-emacs-hook
     This variable is a normal hook; once `save-buffers-kill-emacs' is
     finished with all file saving and confirmation, it calls
     `kill-emacs' which runs the functions in this hook.  `kill-emacs'
     does not run this hook in batch mode.

     `kill-emacs' may be invoked directly (that is not via
     `save-buffers-kill-emacs') if the terminal is disconnected, or in
     similar situations where interaction with the user is not possible.
     Thus, if your hook needs to interact with the user, put it on
     `kill-emacs-query-functions'; if it needs to run regardless of how
     Emacs is killed, put it on `kill-emacs-hook'.


File: elisp,  Node: Suspending Emacs,  Prev: Killing Emacs,  Up: Getting Out

39.2.2 Suspending Emacs
-----------------------

"Suspending Emacs" means stopping Emacs temporarily and returning
control to its superior process, which is usually the shell.  This
allows you to resume editing later in the same Emacs process, with the
same buffers, the same kill ring, the same undo history, and so on.  To
resume Emacs, use the appropriate command in the parent shell--most
likely `fg'.

   Some operating systems do not support suspension of jobs; on these
systems, "suspension" actually creates a new shell temporarily as a
subprocess of Emacs.  Then you would exit the shell to return to Emacs.

   Suspension is not useful with window systems, because the Emacs job
may not have a parent that can resume it again, and in any case you can
give input to some other job such as a shell merely by moving to a
different window.  Therefore, suspending is not allowed when Emacs is
using a window system (X, MS Windows, or Mac).

 -- Function: suspend-emacs &optional string
     This function stops Emacs and returns control to the superior
     process.  If and when the superior process resumes Emacs,
     `suspend-emacs' returns `nil' to its caller in Lisp.

     If STRING is non-`nil', its characters are sent to be read as
     terminal input by Emacs's superior shell.  The characters in
     STRING are not echoed by the superior shell; only the results
     appear.

     Before suspending, `suspend-emacs' runs the normal hook
     `suspend-hook'.

     After the user resumes Emacs, `suspend-emacs' runs the normal hook
     `suspend-resume-hook'.  *Note Hooks::.

     The next redisplay after resumption will redraw the entire screen,
     unless the variable `no-redraw-on-reenter' is non-`nil' (*note
     Refresh Screen::).

     In the following example, note that `pwd' is not echoed after
     Emacs is suspended.  But it is read and executed by the shell.

          (suspend-emacs)
               => nil

          (add-hook 'suspend-hook
                    (function (lambda ()
                                (or (y-or-n-p
                                      "Really suspend? ")
                                    (error "Suspend canceled")))))
               => (lambda nil
                    (or (y-or-n-p "Really suspend? ")
                        (error "Suspend canceled")))
          (add-hook 'suspend-resume-hook
                    (function (lambda () (message "Resumed!"))))
               => (lambda nil (message "Resumed!"))
          (suspend-emacs "pwd")
               => nil
          ---------- Buffer: Minibuffer ----------
          Really suspend? y
          ---------- Buffer: Minibuffer ----------

          ---------- Parent Shell ----------
          lewis@slug[23] % /user/lewis/manual
          lewis@slug[24] % fg

          ---------- Echo Area ----------
          Resumed!

 -- Variable: suspend-hook
     This variable is a normal hook that Emacs runs before suspending.

 -- Variable: suspend-resume-hook
     This variable is a normal hook that Emacs runs on resuming after a
     suspension.


File: elisp,  Node: System Environment,  Next: User Identification,  Prev: Getting Out,  Up: System Interface

39.3 Operating System Environment
=================================

Emacs provides access to variables in the operating system environment
through various functions.  These variables include the name of the
system, the user's UID, and so on.

 -- Variable: system-configuration
     This variable holds the standard GNU configuration name for the
     hardware/software configuration of your system, as a string.  The
     convenient way to test parts of this string is with `string-match'.

 -- Variable: system-type
     The value of this variable is a symbol indicating the type of
     operating system Emacs is operating on.  Here is a table of the
     possible values:

    `alpha-vms'
          VMS on the Alpha.

    `aix-v3'
          AIX.

    `berkeley-unix'
          Berkeley BSD.

    `cygwin'
          Cygwin.

    `dgux'
          Data General DGUX operating system.

    `gnu'
          the GNU system (using the GNU kernel, which consists of the
          HURD and Mach).

    `gnu/linux'
          A GNU/Linux system--that is, a variant GNU system, using the
          Linux kernel.  (These systems are the ones people often call
          "Linux," but actually Linux is just the kernel, not the whole
          system.)

    `hpux'
          Hewlett-Packard HPUX operating system.

    `irix'
          Silicon Graphics Irix system.

    `ms-dos'
          Microsoft MS-DOS "operating system."  Emacs compiled with
          DJGPP for MS-DOS binds `system-type' to `ms-dos' even when
          you run it on MS-Windows.

    `next-mach'
          NeXT Mach-based system.

    `rtu'
          Masscomp RTU, UCB universe.

    `unisoft-unix'
          UniSoft UniPlus.

    `usg-unix-v'
          AT&T System V.

    `vax-vms'
          VAX VMS.

    `windows-nt'
          Microsoft windows NT.  The same executable supports Windows
          9X, but the value of `system-type' is `windows-nt' in either
          case.

    `xenix'
          SCO Xenix 386.

     We do not wish to add new symbols to make finer distinctions
     unless it is absolutely necessary!  In fact, we hope to eliminate
     some of these alternatives in the future.  We recommend using
     `system-configuration' to distinguish between different operating
     systems.

 -- Function: system-name
     This function returns the name of the machine you are running on.
          (system-name)
               => "www.gnu.org"

   The symbol `system-name' is a variable as well as a function.  In
fact, the function returns whatever value the variable `system-name'
currently holds.  Thus, you can set the variable `system-name' in case
Emacs is confused about the name of your system.  The variable is also
useful for constructing frame titles (*note Frame Titles::).

 -- Variable: mail-host-address
     If this variable is non-`nil', it is used instead of `system-name'
     for purposes of generating email addresses.  For example, it is
     used when constructing the default value of `user-mail-address'.
     *Note User Identification::.  (Since this is done when Emacs
     starts up, the value actually used is the one saved when Emacs was
     dumped.  *Note Building Emacs::.)

 -- Command: getenv var
     This function returns the value of the environment variable VAR,
     as a string.  VAR should be a string.  If VAR is undefined in the
     environment, `getenv' returns `nil'.  If returns `""' if VAR is
     set but null.  Within Emacs, the environment variable values are
     kept in the Lisp variable `process-environment'.

          (getenv "USER")
               => "lewis"

          lewis@slug[10] % printenv
          PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
          USER=lewis
          TERM=ibmapa16
          SHELL=/bin/csh
          HOME=/user/lewis

 -- Command: setenv variable &optional value
     This command sets the value of the environment variable named
     VARIABLE to VALUE.  VARIABLE should be a string.  Internally,
     Emacs Lisp can handle any string.  However, normally VARIABLE
     should be a valid shell identifier, that is, a sequence of
     letters, digits and underscores, starting with a letter or
     underscore.  Otherwise, errors may occur if subprocesses of Emacs
     try to access the value of VARIABLE.  If VALUE is omitted or
     `nil', `setenv' removes VARIABLE from the environment.  Otherwise,
     VALUE should be a string.

     `setenv' works by modifying `process-environment'; binding that
     variable with `let' is also reasonable practice.

     `setenv' returns the new value of VARIABLE, or `nil' if it removed
     VARIABLE from the environment.

 -- Variable: process-environment
     This variable is a list of strings, each describing one environment
     variable.  The functions `getenv' and `setenv' work by means of
     this variable.

          process-environment
          => ("l=/usr/stanford/lib/gnuemacs/lisp"
              "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
              "USER=lewis"
              "TERM=ibmapa16"
              "SHELL=/bin/csh"
              "HOME=/user/lewis")

     If `process-environment' contains "duplicate" elements that
     specify the same environment variable, the first of these elements
     specifies the variable, and the other "duplicates" are ignored.

 -- Variable: path-separator
     This variable holds a string which says which character separates
     directories in a search path (as found in an environment
     variable).  Its value is `":"' for Unix and GNU systems, and `";"'
     for MS-DOS and MS-Windows.

 -- Function: parse-colon-path path
     This function takes a search path string such as would be the
     value of the `PATH' environment variable, and splits it at the
     separators, returning a list of directory names.  `nil' in this
     list stands for "use the current directory."  Although the
     function's name says "colon," it actually uses the value of
     `path-separator'.

          (parse-colon-path ":/foo:/bar")
               => (nil "/foo/" "/bar/")

 -- Variable: invocation-name
     This variable holds the program name under which Emacs was
     invoked.  The value is a string, and does not include a directory
     name.

 -- Variable: invocation-directory
     This variable holds the directory from which the Emacs executable
     was invoked, or perhaps `nil' if that directory cannot be
     determined.

 -- Variable: installation-directory
     If non-`nil', this is a directory within which to look for the
     `lib-src' and `etc' subdirectories.  This is non-`nil' when Emacs
     can't find those directories in their standard installed
     locations, but can find them in a directory related somehow to the
     one containing the Emacs executable.

 -- Function: load-average &optional use-float
     This function returns the current 1-minute, 5-minute, and
     15-minute load averages, in a list.

     By default, the values are integers that are 100 times the system
     load averages, which indicate the average number of processes
     trying to run.  If USE-FLOAT is non-`nil', then they are returned
     as floating point numbers and without multiplying by 100.

     If it is impossible to obtain the load average, this function
     signals an error.  On some platforms, access to load averages
     requires installing Emacs as setuid or setgid so that it can read
     kernel information, and that usually isn't advisable.

     If the 1-minute load average is available, but the 5- or 15-minute
     averages are not, this function returns a shortened list containing
     the available averages.

          (load-average)
               => (169 48 36)
          (load-average t)
               => (1.69 0.48 0.36)

          lewis@rocky[5] % uptime
           11:55am  up 1 day, 19:37,  3 users,
           load average: 1.69, 0.48, 0.36

 -- Function: emacs-pid
     This function returns the process ID of the Emacs process, as an
     integer.

 -- Variable: tty-erase-char
     This variable holds the erase character that was selected in the
     system's terminal driver, before Emacs was started.  The value is
     `nil' if Emacs is running under a window system.

 -- Function: setprv privilege-name &optional setp getprv
     This function sets or resets a VMS privilege.  (It does not exist
     on other systems.)  The first argument is the privilege name, as a
     string.  The second argument, SETP, is `t' or `nil', indicating
     whether the privilege is to be turned on or off.  Its default is
     `nil'.  The function returns `t' if successful, `nil' otherwise.

     If the third argument, GETPRV, is non-`nil', `setprv' does not
     change the privilege, but returns `t' or `nil' indicating whether
     the privilege is currently enabled.


File: elisp,  Node: User Identification,  Next: Time of Day,  Prev: System Environment,  Up: System Interface

39.4 User Identification
========================

 -- Variable: init-file-user
     This variable says which user's init files should be used by
     Emacs--or `nil' if none.  `""' stands for the user who originally
     logged in.  The value reflects command-line options such as `-q'
     or `-u USER'.

     Lisp packages that load files of customizations, or any other sort
     of user profile, should obey this variable in deciding where to
     find it.  They should load the profile of the user name found in
     this variable.  If `init-file-user' is `nil', meaning that the `-q'
     option was used, then Lisp packages should not load any
     customization files or user profile.

 -- Variable: user-mail-address
     This holds the nominal email address of the user who is using
     Emacs.  Emacs normally sets this variable to a default value after
     reading your init files, but not if you have already set it.  So
     you can set the variable to some other value in your init file if
     you do not want to use the default value.

 -- Function: user-login-name &optional uid
     If you don't specify UID, this function returns the name under
     which the user is logged in.  If the environment variable `LOGNAME'
     is set, that value is used.  Otherwise, if the environment variable
     `USER' is set, that value is used.  Otherwise, the value is based
     on the effective UID, not the real UID.

     If you specify UID, the value is the user name that corresponds to
     UID (which should be an integer), or `nil' if there is no such
     user.

          (user-login-name)
               => "lewis"

 -- Function: user-real-login-name
     This function returns the user name corresponding to Emacs's real
     UID.  This ignores the effective UID and ignores the environment
     variables `LOGNAME' and `USER'.

 -- Function: user-full-name &optional uid
     This function returns the full name of the logged-in user--or the
     value of the environment variable `NAME', if that is set.

          (user-full-name)
               => "Bil Lewis"

     If the Emacs job's user-id does not correspond to any known user
     (and provided `NAME' is not set), the value is `"unknown"'.

     If UID is non-`nil', then it should be a number (a user-id) or a
     string (a login name).  Then `user-full-name' returns the full
     name corresponding to that user-id or login name.  If you specify a
     user-id or login name that isn't defined, it returns `nil'.

   The symbols `user-login-name', `user-real-login-name' and
`user-full-name' are variables as well as functions.  The functions
return the same values that the variables hold.  These variables allow
you to "fake out" Emacs by telling the functions what to return.  The
variables are also useful for constructing frame titles (*note Frame
Titles::).

 -- Function: user-real-uid
     This function returns the real UID of the user.  The value may be
     a floating point number.

          (user-real-uid)
               => 19

 -- Function: user-uid
     This function returns the effective UID of the user.  The value
     may be a floating point number.


File: elisp,  Node: Time of Day,  Next: Time Conversion,  Prev: User Identification,  Up: System Interface

39.5 Time of Day
================

This section explains how to determine the current time and the time
zone.

 -- Function: current-time-string &optional time-value
     This function returns the current time and date as a human-readable
     string.  The format of the string is unvarying; the number of
     characters used for each part is always the same, so you can
     reliably use `substring' to extract pieces of it.  It is wise to
     count the characters from the beginning of the string rather than
     from the end, as additional information may some day be added at
     the end.

     The argument TIME-VALUE, if given, specifies a time to format
     instead of the current time.  The argument should be a list whose
     first two elements are integers.  Thus, you can use times obtained
     from `current-time' (see below) and from `file-attributes' (*note
     Definition of file-attributes::).  TIME-VALUE can also be a cons
     of two integers, but this is considered obsolete.

          (current-time-string)
               => "Wed Oct 14 22:21:05 1987"

 -- Function: current-time
     This function returns the system's time value as a list of three
     integers: `(HIGH LOW MICROSEC)'.  The integers HIGH and LOW
     combine to give the number of seconds since 0:00 January 1, 1970
     UTC (Coordinated Universal Time), which is HIGH * 2**16 + LOW.

     The third element, MICROSEC, gives the microseconds since the
     start of the current second (or 0 for systems that return time with
     the resolution of only one second).

     The first two elements can be compared with file time values such
     as you get with the function `file-attributes'.  *Note Definition
     of file-attributes::.

 -- Function: current-time-zone &optional time-value
     This function returns a list describing the time zone that the
     user is in.

     The value has the form `(OFFSET NAME)'.  Here OFFSET is an integer
     giving the number of seconds ahead of UTC (east of Greenwich).  A
     negative value means west of Greenwich.  The second element, NAME,
     is a string giving the name of the time zone.  Both elements
     change when daylight saving time begins or ends; if the user has
     specified a time zone that does not use a seasonal time
     adjustment, then the value is constant through time.

     If the operating system doesn't supply all the information
     necessary to compute the value, the unknown elements of the list
     are `nil'.

     The argument TIME-VALUE, if given, specifies a time to analyze
     instead of the current time.  The argument should have the same
     form as for `current-time-string' (see above).  Thus, you can use
     times obtained from `current-time' (see above) and from
     `file-attributes'.  *Note Definition of file-attributes::.

 -- Function: set-time-zone-rule tz
     This function specifies the local time zone according to TZ.  If
     TZ is `nil', that means to use an implementation-defined default
     time zone.  If TZ is `t', that means to use Universal Time.
     Otherwise, TZ should be a string specifying a time zone rule.

 -- Function: float-time &optional time-value
     This function returns the current time as a floating-point number
     of seconds since the epoch.  The argument TIME-VALUE, if given,
     specifies a time to convert instead of the current time.  The
     argument should have the same form as for `current-time-string'
     (see above).  Thus, it accepts the output of `current-time' and
     `file-attributes'.

     _Warning_: Since the result is floating point, it may not be
     exact.  Do not use this function if precise time stamps are
     required.


File: elisp,  Node: Time Conversion,  Next: Time Parsing,  Prev: Time of Day,  Up: System Interface

39.6 Time Conversion
====================

These functions convert time values (lists of two or three integers) to
calendrical information and vice versa.  You can get time values from
the functions `current-time' (*note Time of Day::) and
`file-attributes' (*note Definition of file-attributes::).

   Many operating systems are limited to time values that contain 32
bits of information; these systems typically handle only the times from
1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC.  However, some
operating systems have larger time values, and can represent times far
in the past or future.

   Time conversion functions always use the Gregorian calendar, even
for dates before the Gregorian calendar was introduced.  Year numbers
count the number of years since the year 1 B.C., and do not skip zero
as traditional Gregorian years do; for example, the year number -37
represents the Gregorian year 38 B.C.

 -- Function: decode-time &optional time
     This function converts a time value into calendrical information.
     If you don't specify TIME, it decodes the current time.  The return
     value is a list of nine elements, as follows:

          (SECONDS MINUTES HOUR DAY MONTH YEAR DOW DST ZONE)

     Here is what the elements mean:

    SECONDS
          The number of seconds past the minute, as an integer between
          0 and 59.  On some operating systems, this is 60 for leap
          seconds.

    MINUTES
          The number of minutes past the hour, as an integer between 0
          and 59.

    HOUR
          The hour of the day, as an integer between 0 and 23.

    DAY
          The day of the month, as an integer between 1 and 31.

    MONTH
          The month of the year, as an integer between 1 and 12.

    YEAR
          The year, an integer typically greater than 1900.

    DOW
          The day of week, as an integer between 0 and 6, where 0
          stands for Sunday.

    DST
          `t' if daylight saving time is effect, otherwise `nil'.

    ZONE
          An integer indicating the time zone, as the number of seconds
          east of Greenwich.

     *Common Lisp Note:* Common Lisp has different meanings for DOW and
     ZONE.

 -- Function: encode-time seconds minutes hour day month year &optional
          zone
     This function is the inverse of `decode-time'.  It converts seven
     items of calendrical data into a time value.  For the meanings of
     the arguments, see the table above under `decode-time'.

     Year numbers less than 100 are not treated specially.  If you want
     them to stand for years above 1900, or years above 2000, you must
     alter them yourself before you call `encode-time'.

     The optional argument ZONE defaults to the current time zone and
     its daylight saving time rules.  If specified, it can be either a
     list (as you would get from `current-time-zone'), a string as in
     the `TZ' environment variable, `t' for Universal Time, or an
     integer (as you would get from `decode-time').  The specified zone
     is used without any further alteration for daylight saving time.

     If you pass more than seven arguments to `encode-time', the first
     six are used as SECONDS through YEAR, the last argument is used as
     ZONE, and the arguments in between are ignored.  This feature
     makes it possible to use the elements of a list returned by
     `decode-time' as the arguments to `encode-time', like this:

          (apply 'encode-time (decode-time ...))

     You can perform simple date arithmetic by using out-of-range
     values for the SECONDS, MINUTES, HOUR, DAY, and MONTH arguments;
     for example, day 0 means the day preceding the given month.

     The operating system puts limits on the range of possible time
     values; if you try to encode a time that is out of range, an error
     results.  For instance, years before 1970 do not work on some
     systems; on others, years as early as 1901 do work.


File: elisp,  Node: Time Parsing,  Next: Processor Run Time,  Prev: Time Conversion,  Up: System Interface

39.7 Parsing and Formatting Times
=================================

These functions convert time values (lists of two or three integers) to
text in a string, and vice versa.

 -- Function: date-to-time string
     This function parses the time-string STRING and returns the
     corresponding time value.

 -- Function: format-time-string format-string &optional time universal
     This function converts TIME (or the current time, if TIME is
     omitted) to a string according to FORMAT-STRING.  The argument
     FORMAT-STRING may contain `%'-sequences which say to substitute
     parts of the time.  Here is a table of what the `%'-sequences mean:

    `%a'
          This stands for the abbreviated name of the day of week.

    `%A'
          This stands for the full name of the day of week.

    `%b'
          This stands for the abbreviated name of the month.

    `%B'
          This stands for the full name of the month.

    `%c'
          This is a synonym for `%x %X'.

    `%C'
          This has a locale-specific meaning.  In the default locale
          (named C), it is equivalent to `%A, %B %e, %Y'.

    `%d'
          This stands for the day of month, zero-padded.

    `%D'
          This is a synonym for `%m/%d/%y'.

    `%e'
          This stands for the day of month, blank-padded.

    `%h'
          This is a synonym for `%b'.

    `%H'
          This stands for the hour (00-23).

    `%I'
          This stands for the hour (01-12).

    `%j'
          This stands for the day of the year (001-366).

    `%k'
          This stands for the hour (0-23), blank padded.

    `%l'
          This stands for the hour (1-12), blank padded.

    `%m'
          This stands for the month (01-12).

    `%M'
          This stands for the minute (00-59).

    `%n'
          This stands for a newline.

    `%p'
          This stands for `AM' or `PM', as appropriate.

    `%r'
          This is a synonym for `%I:%M:%S %p'.

    `%R'
          This is a synonym for `%H:%M'.

    `%S'
          This stands for the seconds (00-59).

    `%t'
          This stands for a tab character.

    `%T'
          This is a synonym for `%H:%M:%S'.

    `%U'
          This stands for the week of the year (01-52), assuming that
          weeks start on Sunday.

    `%w'
          This stands for the numeric day of week (0-6).  Sunday is day
          0.

    `%W'
          This stands for the week of the year (01-52), assuming that
          weeks start on Monday.

    `%x'
          This has a locale-specific meaning.  In the default locale
          (named `C'), it is equivalent to `%D'.

    `%X'
          This has a locale-specific meaning.  In the default locale
          (named `C'), it is equivalent to `%T'.

    `%y'
          This stands for the year without century (00-99).

    `%Y'
          This stands for the year with century.

    `%Z'
          This stands for the time zone abbreviation (e.g., `EST').

    `%z'
          This stands for the time zone numerical offset (e.g.,
          `-0500').

     You can also specify the field width and type of padding for any of
     these `%'-sequences.  This works as in `printf': you write the
     field width as digits in the middle of a `%'-sequences.  If you
     start the field width with `0', it means to pad with zeros.  If you
     start the field width with `_', it means to pad with spaces.

     For example, `%S' specifies the number of seconds since the minute;
     `%03S' means to pad this with zeros to 3 positions, `%_3S' to pad
     with spaces to 3 positions.  Plain `%3S' pads with zeros, because
     that is how `%S' normally pads to two positions.

     The characters `E' and `O' act as modifiers when used between `%'
     and one of the letters in the table above.  `E' specifies using
     the current locale's "alternative" version of the date and time.
     In a Japanese locale, for example, `%Ex' might yield a date format
     based on the Japanese Emperors' reigns.  `E' is allowed in `%Ec',
     `%EC', `%Ex', `%EX', `%Ey', and `%EY'.

     `O' means to use the current locale's "alternative" representation
     of numbers, instead of the ordinary decimal digits.  This is
     allowed with most letters, all the ones that output numbers.

     If UNIVERSAL is non-`nil', that means to describe the time as
     Universal Time; `nil' means describe it using what Emacs believes
     is the local time zone (see `current-time-zone').

     This function uses the C library function `strftime' (*note
     Formatting Calendar Time: (libc)Formatting Calendar Time.) to do
     most of the work.  In order to communicate with that function, it
     first encodes its argument using the coding system specified by
     `locale-coding-system' (*note Locales::); after `strftime' returns
     the resulting string, `format-time-string' decodes the string
     using that same coding system.

 -- Function: seconds-to-time seconds
     This function converts SECONDS, a floating point number of seconds
     since the epoch, to a time value and returns that.  To perform the
     inverse conversion, use `float-time'.


File: elisp,  Node: Processor Run Time,  Next: Time Calculations,  Prev: Time Parsing,  Up: System Interface

39.8 Processor Run time
=======================

 -- Function: get-internal-run-time
     This function returns the processor run time used by Emacs as a
     list of three integers: `(HIGH LOW MICROSEC)'.  The integers HIGH
     and LOW combine to give the number of seconds, which is HIGH *
     2**16 + LOW.

     The third element, MICROSEC, gives the microseconds (or 0 for
     systems that return time with the resolution of only one second).

     If the system doesn't provide a way to determine the processor run
     time, get-internal-run-time returns the same time as current-time.


File: elisp,  Node: Time Calculations,  Next: Timers,  Prev: Processor Run Time,  Up: System Interface

39.9 Time Calculations
======================

These functions perform calendrical computations using time values (the
kind of list that `current-time' returns).

 -- Function: time-less-p t1 t2
     This returns `t' if time value T1 is less than time value T2.

 -- Function: time-subtract t1 t2
     This returns the time difference T1 - T2 between two time values,
     in the same format as a time value.

 -- Function: time-add t1 t2
     This returns the sum of two time values, one of which ought to
     represent a time difference rather than a point in time.  Here is
     how to add a number of seconds to a time value:

          (time-add TIME (seconds-to-time SECONDS))

 -- Function: time-to-days time
     This function returns the number of days between the beginning of
     year 1 and TIME.

 -- Function: time-to-day-in-year time
     This returns the day number within the year corresponding to TIME.

 -- Function: date-leap-year-p year
     This function returns `t' if YEAR is a leap year.


File: elisp,  Node: Timers,  Next: Idle Timers,  Prev: Time Calculations,  Up: System Interface

39.10 Timers for Delayed Execution
==================================

You can set up a "timer" to call a function at a specified future time
or after a certain length of idleness.

   Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
`sit-for' or `read-event' which _can_ wait.  Therefore, a timer's
execution may be delayed if Emacs is busy.  However, the time of
execution is very precise if Emacs is idle.

   Emacs binds `inhibit-quit' to `t' before calling the timer function,
because quitting out of many timer functions can leave things in an
inconsistent state.  This is normally unproblematical because most
timer functions don't do a lot of work.  Indeed, for a timer to call a
function that takes substantial time to run is likely to be annoying.
If a timer function needs to allow quitting, it should use
`with-local-quit' (*note Quitting::).  For example, if a timer function
calls `accept-process-output' to receive output from an external
process, that call should be wrapped inside `with-local-quit', to
ensure that `C-g' works if the external process hangs.

   It is usually a bad idea for timer functions to alter buffer
contents.  When they do, they usually should call `undo-boundary' both
before and after changing the buffer, to separate the timer's changes
from user commands' changes and prevent a single undo entry from
growing to be quite large.

   Timer functions should also avoid calling functions that cause Emacs
to wait, such as `sit-for' (*note Waiting::).  This can lead to
unpredictable effects, since other timers (or even the same timer) can
run while waiting.  If a timer function needs to perform an action
after a certain time has elapsed, it can do this by scheduling a new
timer.

   If a timer function calls functions that can change the match data,
it should save and restore the match data.  *Note Saving Match Data::.

 -- Command: run-at-time time repeat function &rest args
     This sets up a timer that calls the function FUNCTION with
     arguments ARGS at time TIME.  If REPEAT is a number (integer or
     floating point), the timer is scheduled to run again every REPEAT
     seconds after TIME.  If REPEAT is `nil', the timer runs only once.

     TIME may specify an absolute or a relative time.

     Absolute times may be specified using a string with a limited
     variety of formats, and are taken to be times _today_, even if
     already in the past.  The recognized forms are `XXXX', `X:XX', or
     `XX:XX' (military time), and `XXam', `XXAM', `XXpm', `XXPM',
     `XX:XXam', `XX:XXAM', `XX:XXpm', or `XX:XXPM'.  A period can be
     used instead of a colon to separate the hour and minute parts.

     To specify a relative time as a string, use numbers followed by
     units.  For example:

    `1 min'
          denotes 1 minute from now.

    `1 min 5 sec'
          denotes 65 seconds from now.

    `1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year'
          denotes exactly 103 months, 123 days, and 10862 seconds from
          now.

     For relative time values, Emacs considers a month to be exactly
     thirty days, and a year to be exactly 365.25 days.

     Not all convenient formats are strings.  If TIME is a number
     (integer or floating point), that specifies a relative time
     measured in seconds.  The result of `encode-time' can also be used
     to specify an absolute value for TIME.

     In most cases, REPEAT has no effect on when _first_ call takes
     place--TIME alone specifies that.  There is one exception: if TIME
     is `t', then the timer runs whenever the time is a multiple of
     REPEAT seconds after the epoch.  This is useful for functions like
     `display-time'.

     The function `run-at-time' returns a timer value that identifies
     the particular scheduled future action.  You can use this value to
     call `cancel-timer' (see below).

   A repeating timer nominally ought to run every REPEAT seconds, but
remember that any invocation of a timer can be late.  Lateness of one
repetition has no effect on the scheduled time of the next repetition.
For instance, if Emacs is busy computing for long enough to cover three
scheduled repetitions of the timer, and then starts to wait, it will
immediately call the timer function three times in immediate succession
(presuming no other timers trigger before or between them).  If you
want a timer to run again no less than N seconds after the last
invocation, don't use the REPEAT argument.  Instead, the timer function
should explicitly reschedule the timer.

 -- Variable: timer-max-repeats
     This variable's value specifies the maximum number of times to
     repeat calling a timer function in a row, when many previously
     scheduled calls were unavoidably delayed.

 -- Macro: with-timeout (seconds timeout-forms...) body...
     Execute BODY, but give up after SECONDS seconds.  If BODY finishes
     before the time is up, `with-timeout' returns the value of the
     last form in BODY.  If, however, the execution of BODY is cut
     short by the timeout, then `with-timeout' executes all the
     TIMEOUT-FORMS and returns the value of the last of them.

     This macro works by setting a timer to run after SECONDS seconds.
     If BODY finishes before that time, it cancels the timer.  If the
     timer actually runs, it terminates execution of BODY, then
     executes TIMEOUT-FORMS.

     Since timers can run within a Lisp program only when the program
     calls a primitive that can wait, `with-timeout' cannot stop
     executing BODY while it is in the midst of a computation--only
     when it calls one of those primitives.  So use `with-timeout' only
     with a BODY that waits for input, not one that does a long
     computation.

   The function `y-or-n-p-with-timeout' provides a simple way to use a
timer to avoid waiting too long for an answer.  *Note Yes-or-No
Queries::.

 -- Function: cancel-timer timer
     This cancels the requested action for TIMER, which should be a
     timer--usually, one previously returned by `run-at-time' or
     `run-with-idle-timer'.  This cancels the effect of that call to
     one of these functions; the arrival of the specified time will not
     cause anything special to happen.


File: elisp,  Node: Idle Timers,  Next: Terminal Input,  Prev: Timers,  Up: System Interface

39.11 Idle Timers
=================

Here is how to set up a timer that runs when Emacs is idle for a
certain length of time.  Aside from how to set them up, idle timers
work just like ordinary timers.

 -- Command: run-with-idle-timer secs repeat function &rest args
     Set up a timer which runs when Emacs has been idle for SECS
     seconds.  The value of SECS may be an integer or a floating point
     number; a value of the type returned by `current-idle-time' is
     also allowed.

     If REPEAT is `nil', the timer runs just once, the first time Emacs
     remains idle for a long enough time.  More often REPEAT is
     non-`nil', which means to run the timer _each time_ Emacs remains
     idle for SECS seconds.

     The function `run-with-idle-timer' returns a timer value which you
     can use in calling `cancel-timer' (*note Timers::).

   Emacs becomes "idle" when it starts waiting for user input, and it
remains idle until the user provides some input.  If a timer is set for
five seconds of idleness, it runs approximately five seconds after Emacs
first becomes idle.  Even if REPEAT is non-`nil', this timer will not
run again as long as Emacs remains idle, because the duration of
idleness will continue to increase and will not go down to five seconds
again.

   Emacs can do various things while idle: garbage collect, autosave or
handle data from a subprocess.  But these interludes during idleness do
not interfere with idle timers, because they do not reset the clock of
idleness to zero.  An idle timer set for 600 seconds will run when ten
minutes have elapsed since the last user command was finished, even if
subprocess output has been accepted thousands of times within those ten
minutes, and even if there have been garbage collections and autosaves.

   When the user supplies input, Emacs becomes non-idle while executing
the input.  Then it becomes idle again, and all the idle timers that are
set up to repeat will subsequently run another time, one by one.

 -- Function: current-idle-time
     If Emacs is idle, this function returns the length of time Emacs
     has been idle, as a list of three integers: `(HIGH LOW MICROSEC)'.
     The integers HIGH and LOW combine to give the number of seconds
     of idleness, which is HIGH * 2**16 + LOW.

     The third element, MICROSEC, gives the microseconds since the
     start of the current second (or 0 for systems that return time with
     the resolution of only one second).

     When Emacs is not idle, `current-idle-time' returns `nil'.  This
     is a convenient way to test whether Emacs is idle.

     The main use of this function is when an idle timer function wants
     to "take a break" for a while.  It can set up another idle timer to
     call the same function again, after a few seconds more idleness.
     Here's an example:

          (defvar resume-timer nil
            "Timer that `timer-function' used to reschedule itself, or nil.")

          (defun timer-function ()
            ;; If the user types a command while `resume-timer'
            ;; is active, the next time this function is called from
            ;; its main idle timer, deactivate `resume-timer'.
            (when resume-timer
              (cancel-timer resume-timer))
            ...DO THE WORK FOR A WHILE...
            (when TAKING-A-BREAK
              (setq resume-timer
                    (run-with-idle-timer
                      ;; Compute an idle time BREAK-LENGTH
                      ;; more than the current value.
                      (time-add (current-idle-time)
                                (seconds-to-time BREAK-LENGTH))
                      nil
                      'timer-function))))

   Some idle timer functions in user Lisp packages have a loop that
does a certain amount of processing each time around, and exits when
`(input-pending-p)' is non-`nil'.  That approach seems very natural but
has two problems:

   * It blocks out all process output (since Emacs accepts process
     output only while waiting).

   * It blocks out any idle timers that ought to run during that time.

To avoid these problems, don't use that technique.  Instead, write such
idle timers to reschedule themselves after a brief pause, using the
method in the `timer-function' example above.


File: elisp,  Node: Terminal Input,  Next: Terminal Output,  Prev: Idle Timers,  Up: System Interface

39.12 Terminal Input
====================

This section describes functions and variables for recording or
manipulating terminal input.  See *Note Display::, for related
functions.

* Menu:

* Input Modes::		Options for how input is processed.
* Recording Input::	Saving histories of recent or all input events.


File: elisp,  Node: Input Modes,  Next: Recording Input,  Up: Terminal Input

39.12.1 Input Modes
-------------------

 -- Function: set-input-mode interrupt flow meta &optional quit-char
     This function sets the mode for reading keyboard input.  If
     INTERRUPT is non-null, then Emacs uses input interrupts.  If it is
     `nil', then it uses CBREAK mode.  The default setting is
     system-dependent.  Some systems always use CBREAK mode regardless
     of what is specified.

     When Emacs communicates directly with X, it ignores this argument
     and uses interrupts if that is the way it knows how to communicate.

     If FLOW is non-`nil', then Emacs uses XON/XOFF (`C-q', `C-s') flow
     control for output to the terminal.  This has no effect except in
     CBREAK mode.

     The argument META controls support for input character codes above
     127.  If META is `t', Emacs converts characters with the 8th bit
     set into Meta characters.  If META is `nil', Emacs disregards the
     8th bit; this is necessary when the terminal uses it as a parity
     bit.  If META is neither `t' nor `nil', Emacs uses all 8 bits of
     input unchanged.  This is good for terminals that use 8-bit
     character sets.

     If QUIT-CHAR is non-`nil', it specifies the character to use for
     quitting.  Normally this character is `C-g'.  *Note Quitting::.

   The `current-input-mode' function returns the input mode settings
Emacs is currently using.

 -- Function: current-input-mode
     This function returns the current mode for reading keyboard input.
     It returns a list, corresponding to the arguments of
     `set-input-mode', of the form `(INTERRUPT FLOW META QUIT)' in
     which:
    INTERRUPT
          is non-`nil' when Emacs is using interrupt-driven input.  If
          `nil', Emacs is using CBREAK mode.

    FLOW
          is non-`nil' if Emacs uses XON/XOFF (`C-q', `C-s') flow
          control for output to the terminal.  This value is meaningful
          only when INTERRUPT is `nil'.

    META
          is `t' if Emacs treats the eighth bit of input characters as
          the meta bit; `nil' means Emacs clears the eighth bit of every
          input character; any other value means Emacs uses all eight
          bits as the basic character code.

    QUIT
          is the character Emacs currently uses for quitting, usually
          `C-g'.


File: elisp,  Node: Recording Input,  Prev: Input Modes,  Up: Terminal Input

39.12.2 Recording Input
-----------------------

 -- Function: recent-keys
     This function returns a vector containing the last 300 input
     events from the keyboard or mouse.  All input events are included,
     whether or not they were used as parts of key sequences.  Thus,
     you always get the last 100 input events, not counting events
     generated by keyboard macros.  (These are excluded because they
     are less interesting for debugging; it should be enough to see the
     events that invoked the macros.)

     A call to `clear-this-command-keys' (*note Command Loop Info::)
     causes this function to return an empty vector immediately
     afterward.

 -- Command: open-dribble-file filename
     This function opens a "dribble file" named FILENAME.  When a
     dribble file is open, each input event from the keyboard or mouse
     (but not those from keyboard macros) is written in that file.  A
     non-character event is expressed using its printed representation
     surrounded by `<...>'.

     You close the dribble file by calling this function with an
     argument of `nil'.

     This function is normally used to record the input necessary to
     trigger an Emacs bug, for the sake of a bug report.

          (open-dribble-file "~/dribble")
               => nil

   See also the `open-termscript' function (*note Terminal Output::).


File: elisp,  Node: Terminal Output,  Next: Sound Output,  Prev: Terminal Input,  Up: System Interface

39.13 Terminal Output
=====================

The terminal output functions send output to a text terminal, or keep
track of output sent to the terminal.  The variable `baud-rate' tells
you what Emacs thinks is the output speed of the terminal.

 -- Variable: baud-rate
     This variable's value is the output speed of the terminal, as far
     as Emacs knows.  Setting this variable does not change the speed
     of actual data transmission, but the value is used for
     calculations such as padding.

     It also affects decisions about whether to scroll part of the
     screen or repaint on text terminals.  *Note Forcing Redisplay::,
     for the corresponding functionality on graphical terminals.

     The value is measured in baud.

   If you are running across a network, and different parts of the
network work at different baud rates, the value returned by Emacs may be
different from the value used by your local terminal.  Some network
protocols communicate the local terminal speed to the remote machine, so
that Emacs and other programs can get the proper value, but others do
not.  If Emacs has the wrong value, it makes decisions that are less
than optimal.  To fix the problem, set `baud-rate'.

 -- Function: baud-rate
     This obsolete function returns the value of the variable
     `baud-rate'.

 -- Function: send-string-to-terminal string
     This function sends STRING to the terminal without alteration.
     Control characters in STRING have terminal-dependent effects.
     This function operates only on text terminals.

     One use of this function is to define function keys on terminals
     that have downloadable function key definitions.  For example,
     this is how (on certain terminals) to define function key 4 to
     move forward four characters (by transmitting the characters `C-u
     C-f' to the computer):

          (send-string-to-terminal "\eF4\^U\^F")
               => nil

 -- Command: open-termscript filename
     This function is used to open a "termscript file" that will record
     all the characters sent by Emacs to the terminal.  It returns
     `nil'.  Termscript files are useful for investigating problems
     where Emacs garbles the screen, problems that are due to incorrect
     Termcap entries or to undesirable settings of terminal options more
     often than to actual Emacs bugs.  Once you are certain which
     characters were actually output, you can determine reliably
     whether they correspond to the Termcap specifications in use.

     You close the termscript file by calling this function with an
     argument of `nil'.

     See also `open-dribble-file' in *Note Recording Input::.

          (open-termscript "../junk/termscript")
               => nil


File: elisp,  Node: Sound Output,  Next: X11 Keysyms,  Prev: Terminal Output,  Up: System Interface

39.14 Sound Output
==================

To play sound using Emacs, use the function `play-sound'.  Only certain
systems are supported; if you call `play-sound' on a system which
cannot really do the job, it gives an error.  Emacs version 20 and
earlier did not support sound at all.

   The sound must be stored as a file in RIFF-WAVE format (`.wav') or
Sun Audio format (`.au').

 -- Function: play-sound sound
     This function plays a specified sound.  The argument, SOUND, has
     the form `(sound PROPERTIES...)', where the PROPERTIES consist of
     alternating keywords (particular symbols recognized specially) and
     values corresponding to them.

     Here is a table of the keywords that are currently meaningful in
     SOUND, and their meanings:

    `:file FILE'
          This specifies the file containing the sound to play.  If the
          file name is not absolute, it is expanded against the
          directory `data-directory'.

    `:data DATA'
          This specifies the sound to play without need to refer to a
          file.  The value, DATA, should be a string containing the
          same bytes as a sound file.  We recommend using a unibyte
          string.

    `:volume VOLUME'
          This specifies how loud to play the sound.  It should be a
          number in the range of 0 to 1.  The default is to use
          whatever volume has been specified before.

    `:device DEVICE'
          This specifies the system device on which to play the sound,
          as a string.  The default device is system-dependent.

     Before actually playing the sound, `play-sound' calls the
     functions in the list `play-sound-functions'.  Each function is
     called with one argument, SOUND.

 -- Function: play-sound-file file &optional volume device
     This function is an alternative interface to playing a sound FILE
     specifying an optional VOLUME and DEVICE.

 -- Variable: play-sound-functions
     A list of functions to be called before playing a sound.  Each
     function is called with one argument, a property list that
     describes the sound.


File: elisp,  Node: X11 Keysyms,  Next: Batch Mode,  Prev: Sound Output,  Up: System Interface

39.15 Operating on X11 Keysyms
==============================

To define system-specific X11 keysyms, set the variable
`system-key-alist'.

 -- Variable: system-key-alist
     This variable's value should be an alist with one element for each
     system-specific keysym.  Each element has the form `(CODE .
     SYMBOL)', where CODE is the numeric keysym code (not including the
     "vendor specific" bit, -2**28), and SYMBOL is the name for the
     function key.

     For example `(168 . mute-acute)' defines a system-specific key
     (used by HP X servers) whose numeric code is -2**28 + 168.

     It is not crucial to exclude from the alist the keysyms of other X
     servers; those do no harm, as long as they don't conflict with the
     ones used by the X server actually in use.

     The variable is always local to the current terminal, and cannot be
     buffer-local.  *Note Multiple Displays::.

   You can specify which keysyms Emacs should use for the Meta, Alt,
Hyper, and Super modifiers by setting these variables:

 -- Variable: x-alt-keysym
 -- Variable: x-meta-keysym
 -- Variable: x-hyper-keysym
 -- Variable: x-super-keysym
     The name of the keysym that should stand for the Alt modifier
     (respectively, for Meta, Hyper, and Super).  For example, here is
     how to swap the Meta and Alt modifiers within Emacs:
          (setq x-alt-keysym 'meta)
          (setq x-meta-keysym 'alt)


File: elisp,  Node: Batch Mode,  Next: Session Management,  Prev: X11 Keysyms,  Up: System Interface

39.16 Batch Mode
================

The command-line option `-batch' causes Emacs to run noninteractively.
In this mode, Emacs does not read commands from the terminal, it does
not alter the terminal modes, and it does not expect to be outputting
to an erasable screen.  The idea is that you specify Lisp programs to
run; when they are finished, Emacs should exit.  The way to specify the
programs to run is with `-l FILE', which loads the library named FILE,
or `-f FUNCTION', which calls FUNCTION with no arguments, or `--eval
FORM'.

   Any Lisp program output that would normally go to the echo area,
either using `message', or using `prin1', etc., with `t' as the stream,
goes instead to Emacs's standard error descriptor when in batch mode.
Similarly, input that would normally come from the minibuffer is read
from the standard input descriptor.  Thus, Emacs behaves much like a
noninteractive application program.  (The echo area output that Emacs
itself normally generates, such as command echoing, is suppressed
entirely.)

 -- Variable: noninteractive
     This variable is non-`nil' when Emacs is running in batch mode.


File: elisp,  Node: Session Management,  Prev: Batch Mode,  Up: System Interface

39.17 Session Management
========================

Emacs supports the X Session Management Protocol for suspension and
restart of applications.  In the X Window System, a program called the
"session manager" has the responsibility to keep track of the
applications that are running.  During shutdown, the session manager
asks applications to save their state, and delays the actual shutdown
until they respond.  An application can also cancel the shutdown.

   When the session manager restarts a suspended session, it directs
these applications to individually reload their saved state.  It does
this by specifying a special command-line argument that says what saved
session to restore.  For Emacs, this argument is `--smid SESSION'.

 -- Variable: emacs-save-session-functions
     Emacs supports saving state by using a hook called
     `emacs-save-session-functions'.  Each function in this hook is
     called when the session manager tells Emacs that the window system
     is shutting down.  The functions are called with no arguments and
     with the current buffer set to a temporary buffer.  Each function
     can use `insert' to add Lisp code to this buffer.  At the end,
     Emacs saves the buffer in a file that a subsequent Emacs
     invocation will load in order to restart the saved session.

     If a function in `emacs-save-session-functions' returns non-`nil',
     Emacs tells the session manager to cancel the shutdown.

   Here is an example that just inserts some text into `*scratch*' when
Emacs is restarted by the session manager.

     (add-hook 'emacs-save-session-functions 'save-yourself-test)

     (defun save-yourself-test ()
       (insert "(save-excursion
       (switch-to-buffer \"*scratch*\")
       (insert \"I am restored\"))")
       nil)


File: elisp,  Node: Antinews,  Next: GNU Free Documentation License,  Prev: System Interface,  Up: Top

Appendix A Emacs 21 Antinews
****************************

For those users who live backwards in time, here is information about
downgrading to Emacs version 21.4.  We hope you will enjoy the greater
simplicity that results from the absence of many Emacs 22.3 features.

A.1 Old Lisp Features in Emacs 21
=================================

   * Many unnecessary features of redisplay have been eliminated.  (The
     earlier major release, Emacs 20, will have a completely rewritten
     redisplay engine, which will be even simpler.)

        - The function `redisplay' has been removed.  To update the
          display without delay, call `(sit-for 0)'.  Since it is
          generally considered wasteful to update the display if there
          are any pending input events, no replacement for `(redisplay
          t)' is provided.

        - The function `force-window-update' has been removed.  It
          shouldn't be needed, since changes in window contents are
          detected automatically.  In case they aren't, call
          `redraw-display' to redraw everything.

        - Point no longer moves out from underneath invisible text at
          the end of each command.  This allows the user to detect
          invisible text by moving the cursor around--if the cursor
          gets stuck, there is something invisible in the way.  If you
          really want cursor motion to ignore the text, try marking it
          as intangible.

        - Support for image maps and image slices has been removed.
          Emacs was always meant for editing text, anyway.

        - The mode line now accepts all text properties, as well as
          `:propertize' and `:eval' forms, regardless of the
          `risky-local-variable' property.

        - The `line-height' and `line-spacing' properties no longer
          have any meaning for newline characters.  Such properties
          wouldn't make sense, since newlines are not really
          characters; they just tell you where to break a line.

        - Considerable simplifications have been made to the display
          specification `(space . PROPS)', which is used for displaying
          a space of specified width and height.  Pixel-based
          specifications and Lisp expressions are no longer accepted.

        - Many features associated with the fringe areas have been
          removed, to encourage people to concentrate on the main
          editing area (the fringe will be completely removed in Emacs
          20.)  Arbitrary bitmaps can no longer be displayed in the
          fringe; an overlay arrow can still be displayed, but there
          can only be one overlay arrow at a time (any more would be
          confusing.)  The fringe widths cannot be adjusted, and
          individual windows cannot have their own fringe settings.  A
          mouse click on the fringe no longer generates a special event.

        - Individual windows cannot have their own scroll-bar settings.

        - You can no longer use `default' in a `defface' to specify
          defaults for subsequent faces.

        - The function `display-supports-face-attributes-p' has been
          removed.  In `defface' specifications, the `supports'
          predicate is no longer supported.

        - The functions `merge-face-attribute' and
          `face-attribute-relative-p' have been removed.

        - The priority of faces in a list supplied by the `:inherit'
          face attribute has been reversed.  We like to make changes
          like this once in a while, to keep Emacs Lisp programmers on
          their toes.

        - The `min-colors' face attribute, used for tailoring faces to
          limited-color displays, does not exist.  If in doubt, use
          colors like "white" and "black," which ought to be defined
          everywhere.

        - The `tty-color-mode' frame parameter does not exist.  You
          should just trust the terminal capabilities database.

   * Several simplifications have been made to mouse support:

        - Clicking `mouse-1' won't follow links, as that is alien to the
          spirit of Emacs.  Therefore, the `follow-link' property
          doesn't have any special meaning, and the function
          `mouse-on-link-p' has been removed.

        - The variable `void-text-area-pointer' has been removed, so the
          mouse pointer shape remains unchanged when moving between
          valid text areas and void text areas.  The `pointer' image
          and text properties are no longer supported.

        - Mouse events will no longer specify the timestamp, the object
          clicked, equivalent buffer positions (for marginal or fringe
          areas), glyph coordinates, or relative pixel coordinates.

   * Simplifications have also been made to the way Emacs handles
     keymaps and key sequences:

        - The `kbd' macro is now obsolete and is no longer documented.
          It isn't that difficult to write key sequences using the
          string and vector representations, and we want to encourage
          users to learn.

        - Emacs no longer supports key remapping.  You can do pretty
          much the same thing with `substitute-key-definition', or by
          advising the relevant command.

        - The `keymap' text and overlay property is now overridden by
          minor mode keymaps, and will not work at the ends of text
          properties and overlays.

        - The functions `map-keymap', `keymap-prompt', and
          `current-active-maps' have been removed.

   * Process support has been pared down to a functional minimum.  The
     functions `call-process-shell-command' and `process-file' have
     been deleted.  Processes no longer maintain property lists, and
     they won't ask any questions when the user tries to exit Emacs
     (which would simply be rude.)  The function `signal-process' won't
     accept a process object, only the process id; determining the
     process id from a process object is left as an exercise to the
     programmer.

   * Networking has also been simplified: `make-network-process' and
     its various associated function have all been replaced with a
     single easy-to-use function, `open-network-stream', which can't
     use UDP, can't act as a server, and can't set up non-blocking
     connections.  Also, deleting a network process with
     `delete-process' won't call the sentinel.

   * Many programming shortcuts have been deleted, to provide you with
     the enjoyment of "rolling your own."  The macros `while-no-input',
     `with-local-quit', and `with-selected-window', along with
     `dynamic-completion-table' and `lazy-completion-table' no longer
     exist.  Also, there are no built-in progress reporters; with
     Emacs, you can take progress for granted.

   * Variable aliases are no longer supported.  Aliases are for
     functions, not for variables.

   * The variables `most-positive-fixnum' and `most-negative-fixnum' do
     not exist.  On 32 bit machines, the most positive integer is
     probably 134217727, and the most negative integer is probably
     -134217728.

   * The functions `eql' and `macroexpand-all' are no longer available.
     However, you can find similar functions in the `cl' package.

   * The list returned by `split-string' won't include null substrings
     for separators at the beginning or end of a string.  If you want to
     check for such separators, do it separately.

   * The function `assoc-string' has been removed.  Use
     `assoc-ignore-case' or `assoc-ignore-representation' (which are no
     longer obsolete.)

   * The escape sequence `\s' is always interpreted as a super
     modifier, never a space.

   * The variable `buffer-save-without-query' has been removed, to
     prevent Emacs from sneakily saving buffers.  Also, the hook
     `before-save-hook' has been removed, so if you want something to
     be done before saving, advise or redefine `basic-save-buffer'.

   * The variable `buffer-auto-save-file-format' has been renamed to
     `auto-save-file-format', and is no longer a permanent local.

   * The function `visited-file-modtime' now returns a cons, instead of
     a list of two integers.  The primitive `set-file-times' has been
     eliminated.

   * The function `file-remote-p' is no longer available.

   * When determining the filename extension, a leading dot in a
     filename is no longer ignored.  Thus, `.emacs' is considered to
     have extension `emacs', rather than being extensionless.

   * Emacs looks for special file handlers in a more efficient manner:
     it will choose the first matching handler in
     `file-name-handler-alist', rather than trying to figure out which
     provides the closest match.

   * The `predicate' argument for `read-file-name' has been removed,
     and so have the variables `read-file-name-function' and
     `read-file-name-completion-ignore-case'.  The function
     `read-directory-name' has also been removed.

   * The functions `all-completions' and `try-completion' will no
     longer accept lists of strings or hash tables (it will still accept
     alists, obarrays, and functions.)  In addition, the function
     `test-completion' is no longer available.

   * The `G' interactive code character is no longer supported.  Use
     `F' instead.

   * Arbitrary Lisp functions can no longer be recorded into
     `buffer-undo-list'.  As a consequence, `yank-undo-function' is
     obsolete, and has been removed.

   * Emacs will never complain about commands that accumulate too much
     undo information, so you no longer have to worry about binding
     `buffer-undo-list' to `t' for such commands (though you may want
     to do that anyway, to avoid taking up unnecessary memory space.)

   * Atomic change groups are no longer supported.

   * The list returned by `(match-data t)' no longer records the buffer
     as a final element.

   * The function `looking-back' has been removed, so we no longer have
     the benefit of hindsight.

   * The variable `search-spaces-regexp' does not exist.  Spaces always
     stand for themselves in regular expression searches.

   * The functions `skip-chars-forward' and `skip-chars-backward' no
     longer accepts character classes such as `[:alpha:]'.  All
     characters are created equal.

   * The `yank-handler' text property no longer has any meaning.  Also,
     `yank-excluded-properties', `insert-for-yank', and
     `insert-buffer-substring-as-yank' have all been removed.

   * The variable `char-property-alias-alist' has been deleted.
     Aliases are for functions, not for properties.

   * The function `get-char-property-and-overlay' has been deleted.  If
     you want the properties at a point, find the text properties at the
     point; then, find the overlays at the point, and find the
     properties on those overlays.

   * Font Lock mode only manages `face' properties; you can't use
     font-lock keywords to specify arbitrary text properties for it to
     manage.  After all, it is called Font Lock mode, not Arbitrary
     Properties Lock mode.

   * The arguments to `remove-overlays' are no longer optional.

   * In `replace-match', the replacement text now inherits properties
     from the surrounding text.

   * The variable `mode-line-format' no longer supports the
     `:propertize', `%i', and `%I' constructs.  The function
     `format-mode-line' has been removed.

   * The functions `window-inside-edges' and `window-body-height' have
     been removed.  You should do the relevant calculations yourself,
     starting with `window-width' and `window-height'.

   * The functions `window-pixel-edges' and `window-inside-pixel-edges'
     have been removed.  We prefer to think in terms of lines and
     columns, not pixel coordinates.  (Sometime in the distant past, we
     will do away with graphical terminals entirely, in favor of text
     terminals.)  For similar reasons, the functions `posn-at-point',
     `posn-at-x-y', and `window-line-height' have been removed, and
     `pos-visible-in-window-p' no longer worries about partially
     visible rows.

   * The macro `save-selected-window' only saves the selected window of
     the selected frame, so don't try selecting windows in other frames.

   * The function `minibufferp' is no longer available.

   * The function `modify-all-frames-parameters' has been removed (we
     always suspected the name was ungrammatical, anyway.)

   * The `line-spacing' variable no longer accepts float values.

   * The function `tool-bar-local-item-from-menu' has been deleted.  If
     you need to make an entry in the tool bar, you can still use
     `tool-bar-add-item-from-menu', but that modifies the binding in
     the source keymap instead of copying it into the local keymap.

   * When determining the major mode, the file name takes precedence
     over the interpreter magic line.  The variable `magic-mode-alist',
     which associates certain buffer beginnings with major modes, has
     been eliminated.

   * The hook `after-change-major-mode-hook' is not defined, and
     neither are `run-mode-hooks' and `delay-mode-hooks'.

   * The variable `minor-mode-list' has been removed.

   * `define-derived-mode' will copy abbrevs from the parent mode's
     abbrev table, instead of creating a new, empty abbrev table.

   * There are no "system" abbrevs.  When the user saves into the
     abbrevs file, all abbrevs are saved.

   * The Warnings facility has been removed.  Just use `error'.

   * Several hook variables have been renamed to flout the Emacs naming
     conventions.  We feel that consistency is boring, and having
     non-standard hook names encourages users to check the documentation
     before using a hook.  For instance, the normal hook
     `find-file-hook' has been renamed to `find-file-hooks', and the
     abnormal hook `delete-frame-functions' has been renamed to
     `delete-frame-hook'.

   * The function `symbol-file' does not exist.  If you want to know
     which file defined a function or variable, try grepping for it.

   * The variable `load-history' records function definitions just like
     variable definitions, instead of indicating which functions were
     previously autoloaded.

   * There is a new variable, `recursive-load-depth-limit', which
     specifies how many times files can recursively load themselves; it
     is 50 by default, and `nil' means infinity.  Previously, Emacs
     signaled an error after just 3 recursive loads, which was boring.

   * Byte-compiler warnings and error messages will leave out the line
     and character positions, in order to exercise your debugging
     skills.  Also, there is no `with-no-warnings' macro--instead of
     suppressing compiler warnings, fix your code to avoid them!

   * The function `unsafep' has been removed.

   * File local variables can now specify a string with text properties.
     Since arbitrary Lisp expressions can be embedded in text
     properties, this can provide you with a great deal of flexibility
     and power.  On the other hand, `safe-local-eval-forms' and the
     `safe-local-eval-function' function property have no special
     meaning.

   * You can no longer use `char-displayable-p' to test if Emacs can
     display a certain character.

   * The function `string-to-multibyte' is no longer available.

   * The `translation-table-for-input' translation table has been
     removed.  Also, translation hash tables are no longer available,
     so we don't need the functions `lookup-character' and
     `lookup-integer'.

   * The `table' argument to `translate-region' can no longer be a
     char-table; it has to be a string.

   * The variable `auto-coding-functions' and the two functions
     `merge-coding-systems' and `decode-coding-inserted-region' have
     been deleted.  The coding system property `mime-text-unsuitable'
     no longer has any special meaning.

   * If pure storage overflows while dumping, Emacs won't tell you how
     much additional pure storage it needs.  Try adding in increments
     of 20000, until you have enough.

   * The variables `gc-elapsed', `gcs-done', and `post-gc-hook' have
     been garbage-collected.


File: elisp,  Node: GNU Free Documentation License,  Next: GPL,  Prev: Antinews,  Up: Top

Appendix B GNU Free Documentation License
*****************************************

                      Version 1.2, November 2002

     Copyright (C) 2000,2001,2002  Free Software Foundation, Inc.
     51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.


  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft," which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.
     We recommend this License principally for works whose purpose is
     instruction or reference.


  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it
     can be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document," below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you."  You
     accept the license if you copy, modify or distribute the work in a
     way requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter
     section of the Document that deals exclusively with the
     relationship of the publishers or authors of the Document to the
     Document's overall subject (or to related matters) and contains
     nothing that could fall directly within that overall subject.
     (Thus, if the Document is in part a textbook of mathematics, a
     Secondary Section may not explain any mathematics.)  The
     relationship could be a matter of historical connection with the
     subject or with related matters, or of legal, commercial,
     philosophical, ethical or political position regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in
     the notice that says that the Document is released under this
     License.  If a section does not fit the above definition of
     Secondary then it is not allowed to be designated as Invariant.
     The Document may contain zero Invariant Sections.  If the Document
     does not identify any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images
     composed of pixels) generic paint programs or (for drawings) some
     widely available drawing editor, and that is suitable for input to
     text formatters or for automatic translation to a variety of
     formats suitable for input to text formatters.  A copy made in an
     otherwise Transparent file format whose markup, or absence of
     markup, has been arranged to thwart or discourage subsequent
     modification by readers is not Transparent.  An image format is
     not Transparent if used for any substantial amount of text.  A
     copy that is not "Transparent" is called "Opaque."

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and
     standard-conforming simple HTML, PostScript or PDF designed for
     human modification.  Examples of transparent image formats include
     PNG, XCF and JPG.  Opaque formats include proprietary formats that
     can be read and edited only by proprietary word processors, SGML
     or XML for which the DTD and/or processing tools are not generally
     available, and the machine-generated HTML, PostScript or PDF
     produced by some word processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements," "Dedications," "Endorsements," or "History.")
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
     covers, as long as they preserve the title of the Document and
     satisfy these conditions, can be treated as verbatim copying in
     other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy a computer-network location from
     which the general network-using public has access to download
     using public-standard network protocols a complete Transparent
     copy of the Document, free of added material.  If you use the
     latter option, you must take reasonably prudent steps, when you
     begin distribution of Opaque copies in quantity, to ensure that
     this Transparent copy will remain thus accessible at the stated
     location until at least one year after the last time you
     distribute an Opaque copy (directly or through your agents or
     retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
     copies, to give them a chance to provide you with an updated
     version of the Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

     A. Use in the Title Page (and on the covers, if any) a title
     distinct    from that of the Document, and from those of previous
     versions    (which should, if there were any, be listed in the
     History section    of the Document).  You may use the same title
     as a previous version    if the original publisher of that version
     gives permission.
     B. List on the Title Page, as authors, one or more persons or
     entities    responsible for authorship of the modifications in the
     Modified    Version, together with at least five of the principal
     authors of the    Document (all of its principal authors, if it
     has fewer than five),    unless they release you from this
     requirement.
     C. State on the Title page the name of the publisher of the
     Modified Version, as the publisher.
     D. Preserve all the copyright notices of the Document.
     E. Add an appropriate copyright notice for your modifications
     adjacent to the other copyright notices.
     F. Include, immediately after the copyright notices, a license
     notice    giving the public permission to use the Modified Version
     under the    terms of this License, in the form shown in the
     Addendum below.
     G. Preserve in that license notice the full lists of Invariant
     Sections    and required Cover Texts given in the Document's
     license notice.
     H. Include an unaltered copy of this License.
     I. Preserve the section Entitled "History," Preserve its Title,
     and add    to it an item stating at least the title, year, new
     authors, and    publisher of the Modified Version as given on the
     Title Page.  If    there is no section Entitled "History" in the
     Document, create one    stating the title, year, authors, and
     publisher of the Document as    given on its Title Page, then add
     an item describing the Modified    Version as stated in the
     previous sentence.
     J. Preserve the network location, if any, given in the Document for
       public access to a Transparent copy of the Document, and
     likewise    the network locations given in the Document for
     previous versions    it was based on.  These may be placed in the
     "History" section.     You may omit a network location for a work
     that was published at    least four years before the Document
     itself, or if the original    publisher of the version it refers
     to gives permission.
     K. For any section Entitled "Acknowledgements" or "Dedications,"
     Preserve the Title of the section, and preserve in the section all
       the substance and tone of each of the contributor
     acknowledgements    and/or dedications given therein.
     L. Preserve all the Invariant Sections of the Document,
     unaltered in their text and in their titles.  Section numbers
     or the equivalent are not considered part of the section titles.
     M. Delete any section Entitled "Endorsements."  Such a section
     may not be included in the Modified Version.
     N. Do not retitle any existing section to be Entitled
     "Endorsements"    or to conflict in title with any Invariant
     Section.
     O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option
     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section Entitled "Endorsements," provided it contains
     nothing but endorsements of your Modified Version by various
     parties-for example, statements of peer review or that the text has
     been approved by an organization as the authoritative definition
     of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
     passage of Front-Cover Text and one of Back-Cover Text may be
     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
     previously added by you or by arrangement made by the same entity
     you are acting on behalf of, you may not add another; but you may
     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements," and any sections Entitled "Dedications."  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements,"
     "Dedications," or "History," the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     http://www.gnu.org/copyleft/.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.


ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

     Copyright (C)  YEAR  YOUR NAME.
     Permission is granted to copy, distribute and/or modify this document
     under the terms of the GNU Free Documentation License, Version 1.2
     or any later version published by the Free Software Foundation;
     with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
     A copy of the license is included in the section entitled ``GNU
     Free Documentation License.''

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

     with the Invariant Sections being LIST THEIR TITLES, with the
     Front-Cover Texts being LIST, and with the Back-Cover Texts being
     LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


File: elisp,  Node: GPL,  Next: Tips,  Prev: GNU Free Documentation License,  Up: Top

Appendix C GNU General Public License
*************************************

                        Version 3, 29 June 2007

     Copyright (C) 2007 Free Software Foundation, Inc. `http://fsf.org/'

     Everyone is permitted to copy and distribute verbatim copies of this
     license document, but changing it is not allowed.

Preamble
========

The GNU General Public License is a free, copyleft license for software
and other kinds of works.

   The licenses for most software and other practical works are designed
to take away your freedom to share and change the works.  By contrast,
the GNU General Public License is intended to guarantee your freedom to
share and change all versions of a program--to make sure it remains
free software for all its users.  We, the Free Software Foundation, use
the GNU General Public License for most of our software; it applies
also to any other work released this way by its authors.  You can apply
it to your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs, and that you know you can do these things.

   To protect your rights, we need to prevent others from denying you
these rights or asking you to surrender the rights.  Therefore, you
have certain responsibilities if you distribute copies of the software,
or if you modify it: responsibilities to respect the freedom of others.

   For example, if you distribute copies of such a program, whether
gratis or for a fee, you must pass on to the recipients the same
freedoms that you received.  You must make sure that they, too, receive
or can get the source code.  And you must show them these terms so they
know their rights.

   Developers that use the GNU GPL protect your rights with two steps:
(1) assert copyright on the software, and (2) offer you this License
giving you legal permission to copy, distribute and/or modify it.

   For the developers' and authors' protection, the GPL clearly explains
that there is no warranty for this free software.  For both users' and
authors' sake, the GPL requires that modified versions be marked as
changed, so that their problems will not be attributed erroneously to
authors of previous versions.

   Some devices are designed to deny users access to install or run
modified versions of the software inside them, although the
manufacturer can do so.  This is fundamentally incompatible with the
aim of protecting users' freedom to change the software.  The
systematic pattern of such abuse occurs in the area of products for
individuals to use, which is precisely where it is most unacceptable.
Therefore, we have designed this version of the GPL to prohibit the
practice for those products.  If such problems arise substantially in
other domains, we stand ready to extend this provision to those domains
in future versions of the GPL, as needed to protect the freedom of
users.

   Finally, every program is threatened constantly by software patents.
States should not allow patents to restrict development and use of
software on general-purpose computers, but in those that do, we wish to
avoid the special danger that patents applied to a free program could
make it effectively proprietary.  To prevent this, the GPL assures that
patents cannot be used to render the program non-free.

   The precise terms and conditions for copying, distribution and
modification follow.

TERMS AND CONDITIONS
====================

  0. Definitions.

     "This License" refers to version 3 of the GNU General Public
     License.

     "Copyright" also means copyright-like laws that apply to other
     kinds of works, such as semiconductor masks.

     "The Program" refers to any copyrightable work licensed under this
     License.  Each licensee is addressed as "you".  "Licensees" and
     "recipients" may be individuals or organizations.

     To "modify" a work means to copy from or adapt all or part of the
     work in a fashion requiring copyright permission, other than the
     making of an exact copy.  The resulting work is called a "modified
     version" of the earlier work or a work "based on" the earlier work.

     A "covered work" means either the unmodified Program or a work
     based on the Program.

     To "propagate" a work means to do anything with it that, without
     permission, would make you directly or secondarily liable for
     infringement under applicable copyright law, except executing it
     on a computer or modifying a private copy.  Propagation includes
     copying, distribution (with or without modification), making
     available to the public, and in some countries other activities as
     well.

     To "convey" a work means any kind of propagation that enables other
     parties to make or receive copies.  Mere interaction with a user
     through a computer network, with no transfer of a copy, is not
     conveying.

     An interactive user interface displays "Appropriate Legal Notices"
     to the extent that it includes a convenient and prominently visible
     feature that (1) displays an appropriate copyright notice, and (2)
     tells the user that there is no warranty for the work (except to
     the extent that warranties are provided), that licensees may
     convey the work under this License, and how to view a copy of this
     License.  If the interface presents a list of user commands or
     options, such as a menu, a prominent item in the list meets this
     criterion.

  1. Source Code.

     The "source code" for a work means the preferred form of the work
     for making modifications to it.  "Object code" means any
     non-source form of a work.

     A "Standard Interface" means an interface that either is an
     official standard defined by a recognized standards body, or, in
     the case of interfaces specified for a particular programming
     language, one that is widely used among developers working in that
     language.

     The "System Libraries" of an executable work include anything,
     other than the work as a whole, that (a) is included in the normal
     form of packaging a Major Component, but which is not part of that
     Major Component, and (b) serves only to enable use of the work
     with that Major Component, or to implement a Standard Interface
     for which an implementation is available to the public in source
     code form.  A "Major Component", in this context, means a major
     essential component (kernel, window system, and so on) of the
     specific operating system (if any) on which the executable work
     runs, or a compiler used to produce the work, or an object code
     interpreter used to run it.

     The "Corresponding Source" for a work in object code form means all
     the source code needed to generate, install, and (for an executable
     work) run the object code and to modify the work, including
     scripts to control those activities.  However, it does not include
     the work's System Libraries, or general-purpose tools or generally
     available free programs which are used unmodified in performing
     those activities but which are not part of the work.  For example,
     Corresponding Source includes interface definition files
     associated with source files for the work, and the source code for
     shared libraries and dynamically linked subprograms that the work
     is specifically designed to require, such as by intimate data
     communication or control flow between those subprograms and other
     parts of the work.

     The Corresponding Source need not include anything that users can
     regenerate automatically from other parts of the Corresponding
     Source.

     The Corresponding Source for a work in source code form is that
     same work.

  2. Basic Permissions.

     All rights granted under this License are granted for the term of
     copyright on the Program, and are irrevocable provided the stated
     conditions are met.  This License explicitly affirms your unlimited
     permission to run the unmodified Program.  The output from running
     a covered work is covered by this License only if the output,
     given its content, constitutes a covered work.  This License
     acknowledges your rights of fair use or other equivalent, as
     provided by copyright law.

     You may make, run and propagate covered works that you do not
     convey, without conditions so long as your license otherwise
     remains in force.  You may convey covered works to others for the
     sole purpose of having them make modifications exclusively for
     you, or provide you with facilities for running those works,
     provided that you comply with the terms of this License in
     conveying all material for which you do not control copyright.
     Those thus making or running the covered works for you must do so
     exclusively on your behalf, under your direction and control, on
     terms that prohibit them from making any copies of your
     copyrighted material outside their relationship with you.

     Conveying under any other circumstances is permitted solely under
     the conditions stated below.  Sublicensing is not allowed; section
     10 makes it unnecessary.

  3. Protecting Users' Legal Rights From Anti-Circumvention Law.

     No covered work shall be deemed part of an effective technological
     measure under any applicable law fulfilling obligations under
     article 11 of the WIPO copyright treaty adopted on 20 December
     1996, or similar laws prohibiting or restricting circumvention of
     such measures.

     When you convey a covered work, you waive any legal power to forbid
     circumvention of technological measures to the extent such
     circumvention is effected by exercising rights under this License
     with respect to the covered work, and you disclaim any intention
     to limit operation or modification of the work as a means of
     enforcing, against the work's users, your or third parties' legal
     rights to forbid circumvention of technological measures.

  4. Conveying Verbatim Copies.

     You may convey verbatim copies of the Program's source code as you
     receive it, in any medium, provided that you conspicuously and
     appropriately publish on each copy an appropriate copyright notice;
     keep intact all notices stating that this License and any
     non-permissive terms added in accord with section 7 apply to the
     code; keep intact all notices of the absence of any warranty; and
     give all recipients a copy of this License along with the Program.

     You may charge any price or no price for each copy that you convey,
     and you may offer support or warranty protection for a fee.

  5. Conveying Modified Source Versions.

     You may convey a work based on the Program, or the modifications to
     produce it from the Program, in the form of source code under the
     terms of section 4, provided that you also meet all of these
     conditions:

       a. The work must carry prominent notices stating that you
          modified it, and giving a relevant date.

       b. The work must carry prominent notices stating that it is
          released under this License and any conditions added under
          section 7.  This requirement modifies the requirement in
          section 4 to "keep intact all notices".

       c. You must license the entire work, as a whole, under this
          License to anyone who comes into possession of a copy.  This
          License will therefore apply, along with any applicable
          section 7 additional terms, to the whole of the work, and all
          its parts, regardless of how they are packaged.  This License
          gives no permission to license the work in any other way, but
          it does not invalidate such permission if you have separately
          received it.

       d. If the work has interactive user interfaces, each must display
          Appropriate Legal Notices; however, if the Program has
          interactive interfaces that do not display Appropriate Legal
          Notices, your work need not make them do so.

     A compilation of a covered work with other separate and independent
     works, which are not by their nature extensions of the covered
     work, and which are not combined with it such as to form a larger
     program, in or on a volume of a storage or distribution medium, is
     called an "aggregate" if the compilation and its resulting
     copyright are not used to limit the access or legal rights of the
     compilation's users beyond what the individual works permit.
     Inclusion of a covered work in an aggregate does not cause this
     License to apply to the other parts of the aggregate.

  6. Conveying Non-Source Forms.

     You may convey a covered work in object code form under the terms
     of sections 4 and 5, provided that you also convey the
     machine-readable Corresponding Source under the terms of this
     License, in one of these ways:

       a. Convey the object code in, or embodied in, a physical product
          (including a physical distribution medium), accompanied by the
          Corresponding Source fixed on a durable physical medium
          customarily used for software interchange.

       b. Convey the object code in, or embodied in, a physical product
          (including a physical distribution medium), accompanied by a
          written offer, valid for at least three years and valid for
          as long as you offer spare parts or customer support for that
          product model, to give anyone who possesses the object code
          either (1) a copy of the Corresponding Source for all the
          software in the product that is covered by this License, on a
          durable physical medium customarily used for software
          interchange, for a price no more than your reasonable cost of
          physically performing this conveying of source, or (2) access
          to copy the Corresponding Source from a network server at no
          charge.

       c. Convey individual copies of the object code with a copy of
          the written offer to provide the Corresponding Source.  This
          alternative is allowed only occasionally and noncommercially,
          and only if you received the object code with such an offer,
          in accord with subsection 6b.

       d. Convey the object code by offering access from a designated
          place (gratis or for a charge), and offer equivalent access
          to the Corresponding Source in the same way through the same
          place at no further charge.  You need not require recipients
          to copy the Corresponding Source along with the object code.
          If the place to copy the object code is a network server, the
          Corresponding Source may be on a different server (operated
          by you or a third party) that supports equivalent copying
          facilities, provided you maintain clear directions next to
          the object code saying where to find the Corresponding Source.
          Regardless of what server hosts the Corresponding Source, you
          remain obligated to ensure that it is available for as long
          as needed to satisfy these requirements.

       e. Convey the object code using peer-to-peer transmission,
          provided you inform other peers where the object code and
          Corresponding Source of the work are being offered to the
          general public at no charge under subsection 6d.


     A separable portion of the object code, whose source code is
     excluded from the Corresponding Source as a System Library, need
     not be included in conveying the object code work.

     A "User Product" is either (1) a "consumer product", which means
     any tangible personal property which is normally used for personal,
     family, or household purposes, or (2) anything designed or sold for
     incorporation into a dwelling.  In determining whether a product
     is a consumer product, doubtful cases shall be resolved in favor of
     coverage.  For a particular product received by a particular user,
     "normally used" refers to a typical or common use of that class of
     product, regardless of the status of the particular user or of the
     way in which the particular user actually uses, or expects or is
     expected to use, the product.  A product is a consumer product
     regardless of whether the product has substantial commercial,
     industrial or non-consumer uses, unless such uses represent the
     only significant mode of use of the product.

     "Installation Information" for a User Product means any methods,
     procedures, authorization keys, or other information required to
     install and execute modified versions of a covered work in that
     User Product from a modified version of its Corresponding Source.
     The information must suffice to ensure that the continued
     functioning of the modified object code is in no case prevented or
     interfered with solely because modification has been made.

     If you convey an object code work under this section in, or with,
     or specifically for use in, a User Product, and the conveying
     occurs as part of a transaction in which the right of possession
     and use of the User Product is transferred to the recipient in
     perpetuity or for a fixed term (regardless of how the transaction
     is characterized), the Corresponding Source conveyed under this
     section must be accompanied by the Installation Information.  But
     this requirement does not apply if neither you nor any third party
     retains the ability to install modified object code on the User
     Product (for example, the work has been installed in ROM).

     The requirement to provide Installation Information does not
     include a requirement to continue to provide support service,
     warranty, or updates for a work that has been modified or
     installed by the recipient, or for the User Product in which it
     has been modified or installed.  Access to a network may be denied
     when the modification itself materially and adversely affects the
     operation of the network or violates the rules and protocols for
     communication across the network.

     Corresponding Source conveyed, and Installation Information
     provided, in accord with this section must be in a format that is
     publicly documented (and with an implementation available to the
     public in source code form), and must require no special password
     or key for unpacking, reading or copying.

  7. Additional Terms.

     "Additional permissions" are terms that supplement the terms of
     this License by making exceptions from one or more of its
     conditions.  Additional permissions that are applicable to the
     entire Program shall be treated as though they were included in
     this License, to the extent that they are valid under applicable
     law.  If additional permissions apply only to part of the Program,
     that part may be used separately under those permissions, but the
     entire Program remains governed by this License without regard to
     the additional permissions.

     When you convey a copy of a covered work, you may at your option
     remove any additional permissions from that copy, or from any part
     of it.  (Additional permissions may be written to require their own
     removal in certain cases when you modify the work.)  You may place
     additional permissions on material, added by you to a covered work,
     for which you have or can give appropriate copyright permission.

     Notwithstanding any other provision of this License, for material
     you add to a covered work, you may (if authorized by the copyright
     holders of that material) supplement the terms of this License
     with terms:

       a. Disclaiming warranty or limiting liability differently from
          the terms of sections 15 and 16 of this License; or

       b. Requiring preservation of specified reasonable legal notices
          or author attributions in that material or in the Appropriate
          Legal Notices displayed by works containing it; or

       c. Prohibiting misrepresentation of the origin of that material,
          or requiring that modified versions of such material be
          marked in reasonable ways as different from the original
          version; or

       d. Limiting the use for publicity purposes of names of licensors
          or authors of the material; or

       e. Declining to grant rights under trademark law for use of some
          trade names, trademarks, or service marks; or

       f. Requiring indemnification of licensors and authors of that
          material by anyone who conveys the material (or modified
          versions of it) with contractual assumptions of liability to
          the recipient, for any liability that these contractual
          assumptions directly impose on those licensors and authors.

     All other non-permissive additional terms are considered "further
     restrictions" within the meaning of section 10.  If the Program as
     you received it, or any part of it, contains a notice stating that
     it is governed by this License along with a term that is a further
     restriction, you may remove that term.  If a license document
     contains a further restriction but permits relicensing or
     conveying under this License, you may add to a covered work
     material governed by the terms of that license document, provided
     that the further restriction does not survive such relicensing or
     conveying.

     If you add terms to a covered work in accord with this section, you
     must place, in the relevant source files, a statement of the
     additional terms that apply to those files, or a notice indicating
     where to find the applicable terms.

     Additional terms, permissive or non-permissive, may be stated in
     the form of a separately written license, or stated as exceptions;
     the above requirements apply either way.

  8. Termination.

     You may not propagate or modify a covered work except as expressly
     provided under this License.  Any attempt otherwise to propagate or
     modify it is void, and will automatically terminate your rights
     under this License (including any patent licenses granted under
     the third paragraph of section 11).

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly
     and finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from
     you under this License.  If your rights have been terminated and
     not permanently reinstated, you do not qualify to receive new
     licenses for the same material under section 10.

  9. Acceptance Not Required for Having Copies.

     You are not required to accept this License in order to receive or
     run a copy of the Program.  Ancillary propagation of a covered work
     occurring solely as a consequence of using peer-to-peer
     transmission to receive a copy likewise does not require
     acceptance.  However, nothing other than this License grants you
     permission to propagate or modify any covered work.  These actions
     infringe copyright if you do not accept this License.  Therefore,
     by modifying or propagating a covered work, you indicate your
     acceptance of this License to do so.

 10. Automatic Licensing of Downstream Recipients.

     Each time you convey a covered work, the recipient automatically
     receives a license from the original licensors, to run, modify and
     propagate that work, subject to this License.  You are not
     responsible for enforcing compliance by third parties with this
     License.

     An "entity transaction" is a transaction transferring control of an
     organization, or substantially all assets of one, or subdividing an
     organization, or merging organizations.  If propagation of a
     covered work results from an entity transaction, each party to that
     transaction who receives a copy of the work also receives whatever
     licenses to the work the party's predecessor in interest had or
     could give under the previous paragraph, plus a right to
     possession of the Corresponding Source of the work from the
     predecessor in interest, if the predecessor has it or can get it
     with reasonable efforts.

     You may not impose any further restrictions on the exercise of the
     rights granted or affirmed under this License.  For example, you
     may not impose a license fee, royalty, or other charge for
     exercise of rights granted under this License, and you may not
     initiate litigation (including a cross-claim or counterclaim in a
     lawsuit) alleging that any patent claim is infringed by making,
     using, selling, offering for sale, or importing the Program or any
     portion of it.

 11. Patents.

     A "contributor" is a copyright holder who authorizes use under this
     License of the Program or a work on which the Program is based.
     The work thus licensed is called the contributor's "contributor
     version".

     A contributor's "essential patent claims" are all patent claims
     owned or controlled by the contributor, whether already acquired or
     hereafter acquired, that would be infringed by some manner,
     permitted by this License, of making, using, or selling its
     contributor version, but do not include claims that would be
     infringed only as a consequence of further modification of the
     contributor version.  For purposes of this definition, "control"
     includes the right to grant patent sublicenses in a manner
     consistent with the requirements of this License.

     Each contributor grants you a non-exclusive, worldwide,
     royalty-free patent license under the contributor's essential
     patent claims, to make, use, sell, offer for sale, import and
     otherwise run, modify and propagate the contents of its
     contributor version.

     In the following three paragraphs, a "patent license" is any
     express agreement or commitment, however denominated, not to
     enforce a patent (such as an express permission to practice a
     patent or covenant not to sue for patent infringement).  To
     "grant" such a patent license to a party means to make such an
     agreement or commitment not to enforce a patent against the party.

     If you convey a covered work, knowingly relying on a patent
     license, and the Corresponding Source of the work is not available
     for anyone to copy, free of charge and under the terms of this
     License, through a publicly available network server or other
     readily accessible means, then you must either (1) cause the
     Corresponding Source to be so available, or (2) arrange to deprive
     yourself of the benefit of the patent license for this particular
     work, or (3) arrange, in a manner consistent with the requirements
     of this License, to extend the patent license to downstream
     recipients.  "Knowingly relying" means you have actual knowledge
     that, but for the patent license, your conveying the covered work
     in a country, or your recipient's use of the covered work in a
     country, would infringe one or more identifiable patents in that
     country that you have reason to believe are valid.

     If, pursuant to or in connection with a single transaction or
     arrangement, you convey, or propagate by procuring conveyance of, a
     covered work, and grant a patent license to some of the parties
     receiving the covered work authorizing them to use, propagate,
     modify or convey a specific copy of the covered work, then the
     patent license you grant is automatically extended to all
     recipients of the covered work and works based on it.

     A patent license is "discriminatory" if it does not include within
     the scope of its coverage, prohibits the exercise of, or is
     conditioned on the non-exercise of one or more of the rights that
     are specifically granted under this License.  You may not convey a
     covered work if you are a party to an arrangement with a third
     party that is in the business of distributing software, under
     which you make payment to the third party based on the extent of
     your activity of conveying the work, and under which the third
     party grants, to any of the parties who would receive the covered
     work from you, a discriminatory patent license (a) in connection
     with copies of the covered work conveyed by you (or copies made
     from those copies), or (b) primarily for and in connection with
     specific products or compilations that contain the covered work,
     unless you entered into that arrangement, or that patent license
     was granted, prior to 28 March 2007.

     Nothing in this License shall be construed as excluding or limiting
     any implied license or other defenses to infringement that may
     otherwise be available to you under applicable patent law.

 12. No Surrender of Others' Freedom.

     If conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot convey a covered work so as to satisfy
     simultaneously your obligations under this License and any other
     pertinent obligations, then as a consequence you may not convey it
     at all.  For example, if you agree to terms that obligate you to
     collect a royalty for further conveying from those to whom you
     convey the Program, the only way you could satisfy both those
     terms and this License would be to refrain entirely from conveying
     the Program.

 13. Use with the GNU Affero General Public License.

     Notwithstanding any other provision of this License, you have
     permission to link or combine any covered work with a work licensed
     under version 3 of the GNU Affero General Public License into a
     single combined work, and to convey the resulting work.  The terms
     of this License will continue to apply to the part which is the
     covered work, but the special requirements of the GNU Affero
     General Public License, section 13, concerning interaction through
     a network will apply to the combination as such.

 14. Revised Versions of this License.

     The Free Software Foundation may publish revised and/or new
     versions of the GNU General Public License from time to time.
     Such new versions will be similar in spirit to the present
     version, but may differ in detail to address new problems or
     concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies that a certain numbered version of the GNU
     General Public License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that numbered version or of any later version published by the
     Free Software Foundation.  If the Program does not specify a
     version number of the GNU General Public License, you may choose
     any version ever published by the Free Software Foundation.

     If the Program specifies that a proxy can decide which future
     versions of the GNU General Public License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Program.

     Later license versions may give you additional or different
     permissions.  However, no additional obligations are imposed on any
     author or copyright holder as a result of your choosing to follow a
     later version.

 15. Disclaimer of Warranty.

     THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
     APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE
     COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
     WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE
     RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.
     SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
     NECESSARY SERVICING, REPAIR OR CORRECTION.

 16. Limitation of Liability.

     IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
     AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU
     FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
     CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
     THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
     BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
     PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
     PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
     THE POSSIBILITY OF SUCH DAMAGES.

 17. Interpretation of Sections 15 and 16.

     If the disclaimer of warranty and limitation of liability provided
     above cannot be given local legal effect according to their terms,
     reviewing courts shall apply local law that most closely
     approximates an absolute waiver of all civil liability in
     connection with the Program, unless a warranty or assumption of
     liability accompanies a copy of the Program in return for a fee.


END OF TERMS AND CONDITIONS
===========================

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR NAME OF AUTHOR

     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation, either version 3 of the License, or (at
     your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program.  If not, see `http://www.gnu.org/licenses/'.

   Also add information on how to contact you by electronic and paper
mail.

   If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

     PROGRAM Copyright (C) YEAR NAME OF AUTHOR
     This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".

   You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  For more information on this, and how to apply and follow
the GNU GPL, see `http://www.gnu.org/licenses/'.

   The GNU General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Lesser General Public License instead of this License.  But first,
please read `http://www.gnu.org/philosophy/why-not-lgpl.html'.


File: elisp,  Node: Tips,  Next: GNU Emacs Internals,  Prev: GPL,  Up: Top

Appendix D Tips and Conventions
*******************************

This chapter describes no additional features of Emacs Lisp.  Instead
it gives advice on making effective use of the features described in the
previous chapters, and describes conventions Emacs Lisp programmers
should follow.

   You can automatically check some of the conventions described below
by running the command `M-x checkdoc RET' when visiting a Lisp file.
It cannot check all of the conventions, and not all the warnings it
gives necessarily correspond to problems, but it is worth examining them
all.

* Menu:

* Coding Conventions::        Conventions for clean and robust programs.
* Key Binding Conventions::   Which keys should be bound by which programs.
* Programming Tips::          Making Emacs code fit smoothly in Emacs.
* Compilation Tips::          Making compiled code run fast.
* Warning Tips::              Turning off compiler warnings.
* Documentation Tips::        Writing readable documentation strings.
* Comment Tips::	      Conventions for writing comments.
* Library Headers::           Standard headers for library packages.


File: elisp,  Node: Coding Conventions,  Next: Key Binding Conventions,  Up: Tips

D.1 Emacs Lisp Coding Conventions
=================================

Here are conventions that you should follow when writing Emacs Lisp
code intended for widespread use:

   * Simply loading the package should not change Emacs's editing
     behavior.  Include a command or commands to enable and disable the
     feature, or to invoke it.

     This convention is mandatory for any file that includes custom
     definitions.  If fixing such a file to follow this convention
     requires an incompatible change, go ahead and make the
     incompatible change; don't postpone it.

   * Since all global variables share the same name space, and all
     functions share another name space, you should choose a short word
     to distinguish your program from other Lisp programs(1).  Then
     take care to begin the names of all global variables, constants,
     and functions in your program with the chosen prefix.  This helps
     avoid name conflicts.

     Occasionally, for a command name intended for users to use, it is
     more convenient if some words come before the package's name
     prefix.  And constructs that define functions, variables, etc.,
     work better if they start with `defun' or `defvar', so put the
     name prefix later on in the name.

     This recommendation applies even to names for traditional Lisp
     primitives that are not primitives in Emacs Lisp--such as
     `copy-list'.  Believe it or not, there is more than one plausible
     way to define `copy-list'.  Play it safe; append your name prefix
     to produce a name like `foo-copy-list' or `mylib-copy-list'
     instead.

     If you write a function that you think ought to be added to Emacs
     under a certain name, such as `twiddle-files', don't call it by
     that name in your program.  Call it `mylib-twiddle-files' in your
     program, and send mail to `bug-gnu-emacs@gnu.org' suggesting we add
     it to Emacs.  If and when we do, we can change the name easily
     enough.

     If one prefix is insufficient, your package can use two or three
     alternative common prefixes, so long as they make sense.

     Separate the prefix from the rest of the symbol name with a hyphen,
     `-'.  This will be consistent with Emacs itself and with most Emacs
     Lisp programs.

   * Put a call to `provide' at the end of each separate Lisp file.

   * If a file requires certain other Lisp programs to be loaded
     beforehand, then the comments at the beginning of the file should
     say so.  Also, use `require' to make sure they are loaded.

   * If one file FOO uses a macro defined in another file BAR, FOO
     should contain this expression before the first use of the macro:

          (eval-when-compile (require 'BAR))

     (And the library BAR should contain `(provide 'BAR)', to make the
     `require' work.)  This will cause BAR to be loaded when you
     byte-compile FOO.  Otherwise, you risk compiling FOO without the
     necessary macro loaded, and that would produce compiled code that
     won't work right.  *Note Compiling Macros::.

     Using `eval-when-compile' avoids loading BAR when the compiled
     version of FOO is _used_.

   * Please don't require the `cl' package of Common Lisp extensions at
     run time.  Use of this package is optional, and it is not part of
     the standard Emacs namespace.  If your package loads `cl' at run
     time, that could cause name clashes for users who don't use that
     package.

     However, there is no problem with using the `cl' package at
     compile time, with `(eval-when-compile (require 'cl))'.  That's
     sufficient for using the macros in the `cl' package, because the
     compiler expands them before generating the byte-code.

   * When defining a major mode, please follow the major mode
     conventions.  *Note Major Mode Conventions::.

   * When defining a minor mode, please follow the minor mode
     conventions.  *Note Minor Mode Conventions::.

   * If the purpose of a function is to tell you whether a certain
     condition is true or false, give the function a name that ends in
     `p'.  If the name is one word, add just `p'; if the name is
     multiple words, add `-p'.  Examples are `framep' and
     `frame-live-p'.

   * If a user option variable records a true-or-false condition, give
     it a name that ends in `-flag'.

   * If the purpose of a variable is to store a single function, give
     it a name that ends in `-function'.  If the purpose of a variable
     is to store a list of functions (i.e., the variable is a hook),
     please follow the naming conventions for hooks.  *Note Hooks::.

   * If loading the file adds functions to hooks, define a function
     `FEATURE-unload-hook', where FEATURE is the name of the feature
     the package provides, and make it undo any such changes.  Using
     `unload-feature' to unload the file will run this function.  *Note
     Unloading::.

   * It is a bad idea to define aliases for the Emacs primitives.
     Normally you should use the standard names instead.  The case
     where an alias may be useful is where it facilitates backwards
     compatibility or portability.

   * If a package needs to define an alias or a new function for
     compatibility with some other version of Emacs, name it with the
     package prefix, not with the raw name with which it occurs in the
     other version.  Here is an example from Gnus, which provides many
     examples of such compatibility issues.

          (defalias 'gnus-point-at-bol
            (if (fboundp 'point-at-bol)
                'point-at-bol
              'line-beginning-position))

   * Redefining (or advising) an Emacs primitive is a bad idea.  It may
     do the right thing for a particular program, but there is no
     telling what other programs might break as a result.  In any case,
     it is a problem for debugging, because the advised function
     doesn't do what its source code says it does.  If the programmer
     investigating the problem is unaware that there is advice on the
     function, the experience can be very frustrating.

     We hope to remove all the places in Emacs that advise primitives.
     In the mean time, please don't add any more.

   * It is likewise a bad idea for one Lisp package to advise a function
     in another Lisp package.

   * Likewise, avoid using `eval-after-load' (*note Hooks for
     Loading::) in libraries and packages.  This feature is meant for
     personal customizations; using it in a Lisp program is unclean,
     because it modifies the behavior of another Lisp file in a way
     that's not visible in that file.  This is an obstacle for
     debugging, much like advising a function in the other package.

   * If a file does replace any of the functions or library programs of
     standard Emacs, prominent comments at the beginning of the file
     should say which functions are replaced, and how the behavior of
     the replacements differs from that of the originals.

   * Constructs that define a function or variable should be macros,
     not functions, and their names should start with `def'.

   * A macro that defines a function or variable should have a name that
     starts with `define-'.  The macro should receive the name to be
     defined as the first argument.  That will help various tools find
     the definition automatically.  Avoid constructing the names in the
     macro itself, since that would confuse these tools.

   * Please keep the names of your Emacs Lisp source files to 13
     characters or less.  This way, if the files are compiled, the
     compiled files' names will be 14 characters or less, which is
     short enough to fit on all kinds of Unix systems.

   * In some other systems there is a convention of choosing variable
     names that begin and end with `*'.  We don't use that convention
     in Emacs Lisp, so please don't use it in your programs.  (Emacs
     uses such names only for special-purpose buffers.)  The users will
     find Emacs more coherent if all libraries use the same conventions.

   * If your program contains non-ASCII characters in string or
     character constants, you should make sure Emacs always decodes
     these characters the same way, regardless of the user's settings.
     There are two ways to do that:

        - Use coding system `emacs-mule', and specify that for `coding'
          in the `-*-' line or the local variables list.

               ;; XXX.el  -*- coding: emacs-mule; -*-

        - Use one of the coding systems based on ISO 2022 (such as
          iso-8859-N and iso-2022-7bit), and specify it with `!' at the
          end for `coding'.  (The `!' turns off any possible character
          translation.)

               ;; XXX.el -*- coding: iso-latin-2!; -*-

   * Indent each function with `C-M-q' (`indent-sexp') using the
     default indentation parameters.

   * Don't make a habit of putting close-parentheses on lines by
     themselves; Lisp programmers find this disconcerting.  Once in a
     while, when there is a sequence of many consecutive
     close-parentheses, it may make sense to split the sequence in one
     or two significant places.

   * Please put a copyright notice and copying permission notice on the
     file if you distribute copies.  Use a notice like this one:

          ;; Copyright (C) YEAR NAME

          ;; This program is free software; you can redistribute it and/or
          ;; modify it under the terms of the GNU General Public License as
          ;; published by the Free Software Foundation; either version 3 of
          ;; the License, or (at your option) any later version.

          ;; This program is distributed in the hope that it will be
          ;; useful, but WITHOUT ANY WARRANTY; without even the implied
          ;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
          ;; PURPOSE.  See the GNU General Public License for more details.

          ;; You should have received a copy of the GNU General Public
          ;; License along with this program; if not, write to the Free
          ;; Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
          ;; Boston, MA 02110-1301 USA

     If you have signed papers to assign the copyright to the
     Foundation, then use `Free Software Foundation, Inc.' as NAME.
     Otherwise, use your name.  See also *Note Library Headers::.

   ---------- Footnotes ----------

   (1) The benefits of a Common Lisp-style package system are
considered not to outweigh the costs.


File: elisp,  Node: Key Binding Conventions,  Next: Programming Tips,  Prev: Coding Conventions,  Up: Tips

D.2 Key Binding Conventions
===========================

   * Special major modes used for read-only text should usually redefine
     `mouse-2' and <RET> to trace some sort of reference in the text.
     Modes such as Dired, Info, Compilation, and Occur redefine it in
     this way.

     In addition, they should mark the text as a kind of "link" so that
     `mouse-1' will follow it also.  *Note Links and Mouse-1::.

   * Please do not define `C-c LETTER' as a key in Lisp programs.
     Sequences consisting of `C-c' and a letter (either upper or lower
     case) are reserved for users; they are the *only* sequences
     reserved for users, so do not block them.

     Changing all the Emacs major modes to respect this convention was a
     lot of work; abandoning this convention would make that work go to
     waste, and inconvenience users.  Please comply with it.

   * Function keys <F5> through <F9> without modifier keys are also
     reserved for users to define.

   * Applications should not bind mouse events based on button 1 with
     the shift key held down.  These events include `S-mouse-1',
     `M-S-mouse-1', `C-S-mouse-1', and so on.  They are reserved for
     users.

   * Sequences consisting of `C-c' followed by a control character or a
     digit are reserved for major modes.

   * Sequences consisting of `C-c' followed by `{', `}', `<', `>', `:'
     or `;' are also reserved for major modes.

   * Sequences consisting of `C-c' followed by any other punctuation
     character are allocated for minor modes.  Using them in a major
     mode is not absolutely prohibited, but if you do that, the major
     mode binding may be shadowed from time to time by minor modes.

   * Do not bind `C-h' following any prefix character (including
     `C-c').  If you don't bind `C-h', it is automatically available as
     a help character for listing the subcommands of the prefix
     character.

   * Do not bind a key sequence ending in <ESC> except following
     another <ESC>.  (That is, it is OK to bind a sequence ending in
     `<ESC> <ESC>'.)

     The reason for this rule is that a non-prefix binding for <ESC> in
     any context prevents recognition of escape sequences as function
     keys in that context.

   * Anything which acts like a temporary mode or state which the user
     can enter and leave should define `<ESC> <ESC>' or `<ESC> <ESC>
     <ESC>' as a way to escape.

     For a state which accepts ordinary Emacs commands, or more
     generally any kind of state in which <ESC> followed by a function
     key or arrow key is potentially meaningful, then you must not
     define `<ESC> <ESC>', since that would preclude recognizing an
     escape sequence after <ESC>.  In these states, you should define
     `<ESC> <ESC> <ESC>' as the way to escape.  Otherwise, define
     `<ESC> <ESC>' instead.


File: elisp,  Node: Programming Tips,  Next: Compilation Tips,  Prev: Key Binding Conventions,  Up: Tips

D.3 Emacs Programming Tips
==========================

Following these conventions will make your program fit better into
Emacs when it runs.

   * Don't use `next-line' or `previous-line' in programs; nearly
     always, `forward-line' is more convenient as well as more
     predictable and robust.  *Note Text Lines::.

   * Don't call functions that set the mark, unless setting the mark is
     one of the intended features of your program.  The mark is a
     user-level feature, so it is incorrect to change the mark except
     to supply a value for the user's benefit.  *Note The Mark::.

     In particular, don't use any of these functions:

        * `beginning-of-buffer', `end-of-buffer'

        * `replace-string', `replace-regexp'

        * `insert-file', `insert-buffer'

     If you just want to move point, or replace a certain string, or
     insert a file or buffer's contents, without any of the other
     features intended for interactive users, you can replace these
     functions with one or two lines of simple Lisp code.

   * Use lists rather than vectors, except when there is a particular
     reason to use a vector.  Lisp has more facilities for manipulating
     lists than for vectors, and working with lists is usually more
     convenient.

     Vectors are advantageous for tables that are substantial in size
     and are accessed in random order (not searched front to back),
     provided there is no need to insert or delete elements (only lists
     allow that).

   * The recommended way to show a message in the echo area is with the
     `message' function, not `princ'.  *Note The Echo Area::.

   * When you encounter an error condition, call the function `error'
     (or `signal').  The function `error' does not return.  *Note
     Signaling Errors::.

     Do not use `message', `throw', `sleep-for', or `beep' to report
     errors.

   * An error message should start with a capital letter but should not
     end with a period.

   * A question asked in the minibuffer with `y-or-n-p' or
     `yes-or-no-p' should start with a capital letter and end with `? '.

   * When you mention a default value in a minibuffer prompt, put it
     and the word `default' inside parentheses.  It should look like
     this:

          Enter the answer (default 42):

   * In `interactive', if you use a Lisp expression to produce a list
     of arguments, don't try to provide the "correct" default values for
     region or position arguments.  Instead, provide `nil' for those
     arguments if they were not specified, and have the function body
     compute the default value when the argument is `nil'.  For
     instance, write this:

          (defun foo (pos)
            (interactive
             (list (if SPECIFIED SPECIFIED-POS)))
            (unless pos (setq pos DEFAULT-POS))
            ...)

     rather than this:

          (defun foo (pos)
            (interactive
             (list (if SPECIFIED SPECIFIED-POS
                       DEFAULT-POS)))
            ...)

     This is so that repetition of the command will recompute these
     defaults based on the current circumstances.

     You do not need to take such precautions when you use interactive
     specs `d', `m' and `r', because they make special arrangements to
     recompute the argument values on repetition of the command.

   * Many commands that take a long time to execute display a message
     that says something like `Operating...' when they start, and
     change it to `Operating...done' when they finish.  Please keep the
     style of these messages uniform: _no_ space around the ellipsis,
     and _no_ period after `done'.

   * Try to avoid using recursive edits.  Instead, do what the Rmail `e'
     command does: use a new local keymap that contains one command
     defined to switch back to the old local keymap.  Or do what the
     `edit-options' command does: switch to another buffer and let the
     user switch back at will.  *Note Recursive Editing::.


File: elisp,  Node: Compilation Tips,  Next: Warning Tips,  Prev: Programming Tips,  Up: Tips

D.4 Tips for Making Compiled Code Fast
======================================

Here are ways of improving the execution speed of byte-compiled Lisp
programs.

   * Profile your program with the `elp' library.  See the file
     `elp.el' for instructions.

   * Check the speed of individual Emacs Lisp forms using the
     `benchmark' library.  See the functions `benchmark-run' and
     `benchmark-run-compiled' in `benchmark.el'.

   * Use iteration rather than recursion whenever possible.  Function
     calls are slow in Emacs Lisp even when a compiled function is
     calling another compiled function.

   * Using the primitive list-searching functions `memq', `member',
     `assq', or `assoc' is even faster than explicit iteration.  It can
     be worth rearranging a data structure so that one of these
     primitive search functions can be used.

   * Certain built-in functions are handled specially in byte-compiled
     code, avoiding the need for an ordinary function call.  It is a
     good idea to use these functions rather than alternatives.  To see
     whether a function is handled specially by the compiler, examine
     its `byte-compile' property.  If the property is non-`nil', then
     the function is handled specially.

     For example, the following input will show you that `aref' is
     compiled specially (*note Array Functions::):

          (get 'aref 'byte-compile)
               => byte-compile-two-args

   * If calling a small function accounts for a substantial part of your
     program's running time, make the function inline.  This eliminates
     the function call overhead.  Since making a function inline reduces
     the flexibility of changing the program, don't do it unless it
     gives a noticeable speedup in something slow enough that users
     care about the speed.  *Note Inline Functions::.


File: elisp,  Node: Warning Tips,  Next: Documentation Tips,  Prev: Compilation Tips,  Up: Tips

D.5 Tips for Avoiding Compiler Warnings
=======================================

   * Try to avoid compiler warnings about undefined free variables, by
     adding dummy `defvar' definitions for these variables, like this:

          (defvar foo)

     Such a definition has no effect except to tell the compiler not to
     warn about uses of the variable `foo' in this file.

   * If you use many functions and variables from a certain file, you
     can add a `require' for that package to avoid compilation warnings
     for them.  For instance,

          (eval-when-compile
            (require 'foo))

   * If you bind a variable in one function, and use it or set it in
     another function, the compiler warns about the latter function
     unless the variable has a definition.  But adding a definition
     would be unclean if the variable has a short name, since Lisp
     packages should not define short variable names.  The right thing
     to do is to rename this variable to start with the name prefix
     used for the other functions and variables in your package.

   * The last resort for avoiding a warning, when you want to do
     something that usually is a mistake but it's not a mistake in this
     one case, is to put a call to `with-no-warnings' around it.


File: elisp,  Node: Documentation Tips,  Next: Comment Tips,  Prev: Warning Tips,  Up: Tips

D.6 Tips for Documentation Strings
==================================

Here are some tips and conventions for the writing of documentation
strings.  You can check many of these conventions by running the command
`M-x checkdoc-minor-mode'.

   * Every command, function, or variable intended for users to know
     about should have a documentation string.

   * An internal variable or subroutine of a Lisp program might as well
     have a documentation string.  In earlier Emacs versions, you could
     save space by using a comment instead of a documentation string,
     but that is no longer the case--documentation strings now take up
     very little space in a running Emacs.

   * Format the documentation string so that it fits in an Emacs window
     on an 80-column screen.  It is a good idea for most lines to be no
     wider than 60 characters.  The first line should not be wider than
     67 characters or it will look bad in the output of `apropos'.

     You can fill the text if that looks good.  However, rather than
     blindly filling the entire documentation string, you can often
     make it much more readable by choosing certain line breaks with
     care.  Use blank lines between topics if the documentation string
     is long.

   * The first line of the documentation string should consist of one
     or two complete sentences that stand on their own as a summary.
     `M-x apropos' displays just the first line, and if that line's
     contents don't stand on their own, the result looks bad.  In
     particular, start the first line with a capital letter and end
     with a period.

     For a function, the first line should briefly answer the question,
     "What does this function do?"  For a variable, the first line
     should briefly answer the question, "What does this value mean?"

     Don't limit the documentation string to one line; use as many
     lines as you need to explain the details of how to use the
     function or variable.  Please use complete sentences for the rest
     of the text too.

   * When the user tries to use a disabled command, Emacs displays just
     the first paragraph of its documentation string--everything
     through the first blank line.  If you wish, you can choose which
     information to include before the first blank line so as to make
     this display useful.

   * The first line should mention all the important arguments of the
     function, and should mention them in the order that they are
     written in a function call.  If the function has many arguments,
     then it is not feasible to mention them all in the first line; in
     that case, the first line should mention the first few arguments,
     including the most important arguments.

   * When a function's documentation string mentions the value of an
     argument of the function, use the argument name in capital letters
     as if it were a name for that value.  Thus, the documentation
     string of the function `eval' refers to its second argument as
     `FORM', because the actual argument name is `form':

          Evaluate FORM and return its value.

     Also write metasyntactic variables in capital letters, such as
     when you show the decomposition of a list or vector into subunits,
     some of which may vary.  `KEY' and `VALUE' in the following example
     illustrate this practice:

          The argument TABLE should be an alist whose elements
          have the form (KEY . VALUE).  Here, KEY is ...

   * Never change the case of a Lisp symbol when you mention it in a doc
     string.  If the symbol's name is `foo', write "foo," not "Foo"
     (which is a different symbol).

     This might appear to contradict the policy of writing function
     argument values, but there is no real contradiction; the argument
     _value_ is not the same thing as the _symbol_ which the function
     uses to hold the value.

     If this puts a lower-case letter at the beginning of a sentence
     and that annoys you, rewrite the sentence so that the symbol is
     not at the start of it.

   * Do not start or end a documentation string with whitespace.

   * *Do not* indent subsequent lines of a documentation string so that
     the text is lined up in the source code with the text of the first
     line.  This looks nice in the source code, but looks bizarre when
     users view the documentation.  Remember that the indentation
     before the starting double-quote is not part of the string!

   * When a documentation string refers to a Lisp symbol, write it as it
     would be printed (which usually means in lower case), with
     single-quotes around it.  For example: `lambda'.  There are two
     exceptions: write t and nil without single-quotes.  (In this
     manual, we use a different convention, with single-quotes for all
     symbols.)

     Help mode automatically creates a hyperlink when a documentation
     string uses a symbol name inside single quotes, if the symbol has
     either a function or a variable definition.  You do not need to do
     anything special to make use of this feature.  However, when a
     symbol has both a function definition and a variable definition,
     and you want to refer to just one of them, you can specify which
     one by writing one of the words `variable', `option', `function',
     or `command', immediately before the symbol name.  (Case makes no
     difference in recognizing these indicator words.)  For example, if
     you write

          This function sets the variable `buffer-file-name'.

     then the hyperlink will refer only to the variable documentation of
     `buffer-file-name', and not to its function documentation.

     If a symbol has a function definition and/or a variable
     definition, but those are irrelevant to the use of the symbol that
     you are documenting, you can write the words `symbol' or `program'
     before the symbol name to prevent making any hyperlink.  For
     example,

          If the argument KIND-OF-RESULT is the symbol `list',
          this function returns a list of all the objects
          that satisfy the criterion.

     does not make a hyperlink to the documentation, irrelevant here,
     of the function `list'.

     Normally, no hyperlink is made for a variable without variable
     documentation.  You can force a hyperlink for such variables by
     preceding them with one of the words `variable' or `option'.

     Hyperlinks for faces are only made if the face name is preceded or
     followed by the word `face'.  In that case, only the face
     documentation will be shown, even if the symbol is also defined as
     a variable or as a function.

     To make a hyperlink to Info documentation, write the name of the
     Info node (or anchor) in single quotes, preceded by `info node',
     `Info node', `info anchor' or `Info anchor'.  The Info file name
     defaults to `emacs'.  For example,

          See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.

     Finally, to create a hyperlink to URLs, write the URL in single
     quotes, preceded by `URL'. For example,

          The home page for the GNU project has more information (see URL
          `http://www.gnu.org/').

   * Don't write key sequences directly in documentation strings.
     Instead, use the `\\[...]' construct to stand for them.  For
     example, instead of writing `C-f', write the construct
     `\\[forward-char]'.  When Emacs displays the documentation string,
     it substitutes whatever key is currently bound to `forward-char'.
     (This is normally `C-f', but it may be some other character if the
     user has moved key bindings.)  *Note Keys in Documentation::.

   * In documentation strings for a major mode, you will want to refer
     to the key bindings of that mode's local map, rather than global
     ones.  Therefore, use the construct `\\<...>' once in the
     documentation string to specify which key map to use.  Do this
     before the first use of `\\[...]'.  The text inside the `\\<...>'
     should be the name of the variable containing the local keymap for
     the major mode.

     It is not practical to use `\\[...]' very many times, because
     display of the documentation string will become slow.  So use this
     to describe the most important commands in your major mode, and
     then use `\\{...}' to display the rest of the mode's keymap.

   * For consistency, phrase the verb in the first sentence of a
     function's documentation string as an imperative--for instance,
     use "Return the cons of A and B." in preference to "Returns the
     cons of A and B."  Usually it looks good to do likewise for the
     rest of the first paragraph.  Subsequent paragraphs usually look
     better if each sentence is indicative and has a proper subject.

   * The documentation string for a function that is a yes-or-no
     predicate should start with words such as "Return t if," to
     indicate explicitly what constitutes "truth."  The word "return"
     avoids starting the sentence with lower-case "t," which could be
     somewhat distracting.

   * If a line in a documentation string begins with an
     open-parenthesis, write a backslash before the open-parenthesis,
     like this:

          The argument FOO can be either a number
          \(a buffer position) or a string (a file name).

     This prevents the open-parenthesis from being treated as the start
     of a defun (*note Defuns: (emacs)Defuns.).

   * Write documentation strings in the active voice, not the passive,
     and in the present tense, not the future.  For instance, use
     "Return a list containing A and B." instead of "A list containing
     A and B will be returned."

   * Avoid using the word "cause" (or its equivalents) unnecessarily.
     Instead of, "Cause Emacs to display text in boldface," write just
     "Display text in boldface."

   * Avoid using "iff" (a mathematics term meaning "if and only if"),
     since many people are unfamiliar with it and mistake it for a
     typo.  In most cases, the meaning is clear with just "if".
     Otherwise, try to find an alternate phrasing that conveys the
     meaning.

   * When a command is meaningful only in a certain mode or situation,
     do mention that in the documentation string.  For example, the
     documentation of `dired-find-file' is:

          In Dired, visit the file or directory named on this line.

   * When you define a variable that users ought to set interactively,
     you normally should use `defcustom'.  However, if for some reason
     you use `defvar' instead, start the doc string with a `*'.  *Note
     Defining Variables::.

   * The documentation string for a variable that is a yes-or-no flag
     should start with words such as "Non-nil means," to make it clear
     that all non-`nil' values are equivalent and indicate explicitly
     what `nil' and non-`nil' mean.


File: elisp,  Node: Comment Tips,  Next: Library Headers,  Prev: Documentation Tips,  Up: Tips

D.7 Tips on Writing Comments
============================

We recommend these conventions for where to put comments and how to
indent them:

`;'
     Comments that start with a single semicolon, `;', should all be
     aligned to the same column on the right of the source code.  Such
     comments usually explain how the code on the same line does its
     job.  In Lisp mode and related modes, the `M-;'
     (`indent-for-comment') command automatically inserts such a `;' in
     the right place, or aligns such a comment if it is already present.

     This and following examples are taken from the Emacs sources.

          (setq base-version-list                 ; there was a base
                (assoc (substring fn 0 start-vn)  ; version to which
                       file-version-assoc-list))  ; this looks like
                                                  ; a subversion

`;;'
     Comments that start with two semicolons, `;;', should be aligned to
     the same level of indentation as the code.  Such comments usually
     describe the purpose of the following lines or the state of the
     program at that point.  For example:

          (prog1 (setq auto-fill-function
                       ...
                       ...
            ;; update mode line
            (force-mode-line-update)))

     We also normally use two semicolons for comments outside functions.

          ;; This Lisp code is run in Emacs
          ;; when it is to operate as a server
          ;; for other processes.

     Every function that has no documentation string (presumably one
     that is used only internally within the package it belongs to),
     should instead have a two-semicolon comment right before the
     function, explaining what the function does and how to call it
     properly.  Explain precisely what each argument means and how the
     function interprets its possible values.

`;;;'
     Comments that start with three semicolons, `;;;', should start at
     the left margin.  These are used, occasionally, for comments within
     functions that should start at the margin.  We also use them
     sometimes for comments that are between functions--whether to use
     two or three semicolons depends on whether the comment should be
     considered a "heading" by Outline minor mode.  By default,
     comments starting with at least three semicolons (followed by a
     single space and a non-whitespace character) are considered
     headings, comments starting with two or less are not.

     Another use for triple-semicolon comments is for commenting out
     lines within a function.  We use three semicolons for this
     precisely so that they remain at the left margin.  By default,
     Outline minor mode does not consider a comment to be a heading
     (even if it starts with at least three semicolons) if the
     semicolons are followed by at least two spaces.  Thus, if you add
     an introductory comment to the commented out code, make sure to
     indent it by at least two spaces after the three semicolons.

          (defun foo (a)
          ;;;  This is no longer necessary.
          ;;;  (force-mode-line-update)
            (message "Finished with %s" a))

     When commenting out entire functions, use two semicolons.

`;;;;'
     Comments that start with four semicolons, `;;;;', should be aligned
     to the left margin and are used for headings of major sections of a
     program.  For example:

          ;;;; The kill ring

The indentation commands of the Lisp modes in Emacs, such as `M-;'
(`indent-for-comment') and <TAB> (`lisp-indent-line'), automatically
indent comments according to these conventions, depending on the number
of semicolons.  *Note Manipulating Comments: (emacs)Comments.


File: elisp,  Node: Library Headers,  Prev: Comment Tips,  Up: Tips

D.8 Conventional Headers for Emacs Libraries
============================================

Emacs has conventions for using special comments in Lisp libraries to
divide them into sections and give information such as who wrote them.
This section explains these conventions.

   We'll start with an example, a package that is included in the Emacs
distribution.

   Parts of this example reflect its status as part of Emacs; for
example, the copyright notice lists the Free Software Foundation as the
copyright holder, and the copying permission says the file is part of
Emacs.  When you write a package and post it, the copyright holder would
be you (unless your employer claims to own it instead), and you should
get the suggested copying permission from the end of the GNU General
Public License itself.  Don't say your file is part of Emacs if we
haven't installed it in Emacs yet!

   With that warning out of the way, on to the example:

     ;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers

     ;; Copyright (C) 1992 Free Software Foundation, Inc.

     ;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
     ;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com>
     ;; Created: 14 Jul 1992
     ;; Version: 1.2
     ;; Keywords: docs

     ;; This file is part of GNU Emacs.
     ...
     ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
     ;; Boston, MA 02110-1301, USA.

   The very first line should have this format:

     ;;; FILENAME --- DESCRIPTION

The description should be complete in one line.  If the file needs a
`-*-' specification, put it after DESCRIPTION.

   After the copyright notice come several "header comment" lines, each
beginning with `;; HEADER-NAME:'.  Here is a table of the conventional
possibilities for HEADER-NAME:

`Author'
     This line states the name and net address of at least the principal
     author of the library.

     If there are multiple authors, you can list them on continuation
     lines led by `;;' and a tab character, like this:

          ;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu>
          ;;      Dave Sill <de5@ornl.gov>
          ;;      Dave Brennan <brennan@hal.com>
          ;;      Eric Raymond <esr@snark.thyrsus.com>

`Maintainer'
     This line should contain a single name/address as in the Author
     line, or an address only, or the string `FSF'.  If there is no
     maintainer line, the person(s) in the Author field are presumed to
     be the maintainers.  The example above is mildly bogus because the
     maintainer line is redundant.

     The idea behind the `Author' and `Maintainer' lines is to make
     possible a Lisp function to "send mail to the maintainer" without
     having to mine the name out by hand.

     Be sure to surround the network address with `<...>' if you
     include the person's full name as well as the network address.

`Created'
     This optional line gives the original creation date of the file.
     For historical interest only.

`Version'
     If you wish to record version numbers for the individual Lisp
     program, put them in this line.

`Adapted-By'
     In this header line, place the name of the person who adapted the
     library for installation (to make it fit the style conventions, for
     example).

`Keywords'
     This line lists keywords for the `finder-by-keyword' help command.
     Please use that command to see a list of the meaningful keywords.

     This field is important; it's how people will find your package
     when they're looking for things by topic area.  To separate the
     keywords, you can use spaces, commas, or both.

   Just about every Lisp library ought to have the `Author' and
`Keywords' header comment lines.  Use the others if they are
appropriate.  You can also put in header lines with other header
names--they have no standard meanings, so they can't do any harm.

   We use additional stylized comments to subdivide the contents of the
library file.  These should be separated by blank lines from anything
else.  Here is a table of them:

`;;; Commentary:'
     This begins introductory comments that explain how the library
     works.  It should come right after the copying permissions,
     terminated by a `Change Log', `History' or `Code' comment line.
     This text is used by the Finder package, so it should make sense
     in that context.

`;;; Documentation:'
     This was used in some files in place of `;;; Commentary:', but it
     is deprecated.

`;;; Change Log:'
     This begins change log information stored in the library file (if
     you store the change history there).  For Lisp files distributed
     with Emacs, the change history is kept in the file `ChangeLog' and
     not in the source file at all; these files generally do not have a
     `;;; Change Log:' line.  `History' is an alternative to `Change
     Log'.

`;;; Code:'
     This begins the actual code of the program.

`;;; FILENAME ends here'
     This is the "footer line"; it appears at the very end of the file.
     Its purpose is to enable people to detect truncated versions of
     the file from the lack of a footer line.


File: elisp,  Node: GNU Emacs Internals,  Next: Standard Errors,  Prev: Tips,  Up: Top

Appendix E GNU Emacs Internals
******************************

This chapter describes how the runnable Emacs executable is dumped with
the preloaded Lisp libraries in it, how storage is allocated, and some
internal aspects of GNU Emacs that may be of interest to C programmers.

* Menu:

* Building Emacs::      How the dumped Emacs is made.
* Pure Storage::        A kludge to make preloaded Lisp functions sharable.
* Garbage Collection::  Reclaiming space for Lisp objects no longer used.
* Memory Usage::        Info about total size of Lisp objects made so far.
* Writing Emacs Primitives::   Writing C code for Emacs.
* Object Internals::    Data formats of buffers, windows, processes.


File: elisp,  Node: Building Emacs,  Next: Pure Storage,  Up: GNU Emacs Internals

E.1 Building Emacs
==================

This section explains the steps involved in building the Emacs
executable.  You don't have to know this material to build and install
Emacs, since the makefiles do all these things automatically.  This
information is pertinent to Emacs maintenance.

   Compilation of the C source files in the `src' directory produces an
executable file called `temacs', also called a "bare impure Emacs".  It
contains the Emacs Lisp interpreter and I/O routines, but not the
editing commands.

   The command `temacs -l loadup' uses `temacs' to create the real
runnable Emacs executable.  These arguments direct `temacs' to evaluate
the Lisp files specified in the file `loadup.el'.  These files set up
the normal Emacs editing environment, resulting in an Emacs that is
still impure but no longer bare.

   It takes a substantial time to load the standard Lisp files.
Luckily, you don't have to do this each time you run Emacs; `temacs' can
dump out an executable program called `emacs' that has these files
preloaded.  `emacs' starts more quickly because it does not need to
load the files.  This is the Emacs executable that is normally
installed.

   To create `emacs', use the command `temacs -batch -l loadup dump'.
The purpose of `-batch' here is to prevent `temacs' from trying to
initialize any of its data on the terminal; this ensures that the
tables of terminal information are empty in the dumped Emacs.  The
argument `dump' tells `loadup.el' to dump a new executable named
`emacs'.

   Some operating systems don't support dumping.  On those systems, you
must start Emacs with the `temacs -l loadup' command each time you use
it.  This takes a substantial time, but since you need to start Emacs
once a day at most--or once a week if you never log out--the extra time
is not too severe a problem.

   You can specify additional files to preload by writing a library
named `site-load.el' that loads them.  You may need to add a definition

     #define SITELOAD_PURESIZE_EXTRA N

to make N added bytes of pure space to hold the additional files.  (Try
adding increments of 20000 until it is big enough.)  However, the
advantage of preloading additional files decreases as machines get
faster.  On modern machines, it is usually not advisable.

   After `loadup.el' reads `site-load.el', it finds the documentation
strings for primitive and preloaded functions (and variables) in the
file `etc/DOC' where they are stored, by calling `Snarf-documentation'
(*note Accessing Documentation: Definition of Snarf-documentation.).

   You can specify other Lisp expressions to execute just before dumping
by putting them in a library named `site-init.el'.  This file is
executed after the documentation strings are found.

   If you want to preload function or variable definitions, there are
three ways you can do this and make their documentation strings
accessible when you subsequently run Emacs:

   * Arrange to scan these files when producing the `etc/DOC' file, and
     load them with `site-load.el'.

   * Load the files with `site-init.el', then copy the files into the
     installation directory for Lisp files when you install Emacs.

   * Specify a non-`nil' value for `byte-compile-dynamic-docstrings' as
     a local variable in each of these files, and load them with either
     `site-load.el' or `site-init.el'.  (This method has the drawback
     that the documentation strings take up space in Emacs all the
     time.)

   It is not advisable to put anything in `site-load.el' or
`site-init.el' that would alter any of the features that users expect
in an ordinary unmodified Emacs.  If you feel you must override normal
features for your site, do it with `default.el', so that users can
override your changes if they wish.  *Note Startup Summary::.

   In a package that can be preloaded, it is sometimes useful to
specify a computation to be done when Emacs subsequently starts up.
For this, use `eval-at-startup':

 -- Macro: eval-at-startup body...
     This evaluates the BODY forms, either immediately if running in an
     Emacs that has already started up, or later when Emacs does start
     up.  Since the value of the BODY forms is not necessarily
     available when the `eval-at-startup' form is run, that form always
     returns `nil'.

 -- Function: dump-emacs to-file from-file
     This function dumps the current state of Emacs into an executable
     file TO-FILE.  It takes symbols from FROM-FILE (this is normally
     the executable file `temacs').

     If you want to use this function in an Emacs that was already
     dumped, you must run Emacs with `-batch'.


File: elisp,  Node: Pure Storage,  Next: Garbage Collection,  Prev: Building Emacs,  Up: GNU Emacs Internals

E.2 Pure Storage
================

Emacs Lisp uses two kinds of storage for user-created Lisp objects:
"normal storage" and "pure storage".  Normal storage is where all the
new data created during an Emacs session are kept; see the following
section for information on normal storage.  Pure storage is used for
certain data in the preloaded standard Lisp files--data that should
never change during actual use of Emacs.

   Pure storage is allocated only while `temacs' is loading the
standard preloaded Lisp libraries.  In the file `emacs', it is marked
as read-only (on operating systems that permit this), so that the
memory space can be shared by all the Emacs jobs running on the machine
at once.  Pure storage is not expandable; a fixed amount is allocated
when Emacs is compiled, and if that is not sufficient for the preloaded
libraries, `temacs' allocates dynamic memory for the part that didn't
fit.  If that happens, you should increase the compilation parameter
`PURESIZE' in the file `src/puresize.h' and rebuild Emacs, even though
the resulting image will work: garbage collection is disabled in this
situation, causing a memory leak.  Such an overflow normally won't
happen unless you try to preload additional libraries or add features
to the standard ones.  Emacs will display a warning about the overflow
when it starts.

 -- Function: purecopy object
     This function makes a copy in pure storage of OBJECT, and returns
     it.  It copies a string by simply making a new string with the same
     characters, but without text properties, in pure storage.  It
     recursively copies the contents of vectors and cons cells.  It does
     not make copies of other objects such as symbols, but just returns
     them unchanged.  It signals an error if asked to copy markers.

     This function is a no-op except while Emacs is being built and
     dumped; it is usually called only in the file
     `emacs/lisp/loaddefs.el', but a few packages call it just in case
     you decide to preload them.

 -- Variable: pure-bytes-used
     The value of this variable is the number of bytes of pure storage
     allocated so far.  Typically, in a dumped Emacs, this number is
     very close to the total amount of pure storage available--if it
     were not, we would preallocate less.

 -- Variable: purify-flag
     This variable determines whether `defun' should make a copy of the
     function definition in pure storage.  If it is non-`nil', then the
     function definition is copied into pure storage.

     This flag is `t' while loading all of the basic functions for
     building Emacs initially (allowing those functions to be sharable
     and non-collectible).  Dumping Emacs as an executable always writes
     `nil' in this variable, regardless of the value it actually has
     before and after dumping.

     You should not change this flag in a running Emacs.


File: elisp,  Node: Garbage Collection,  Next: Memory Usage,  Prev: Pure Storage,  Up: GNU Emacs Internals

E.3 Garbage Collection
======================

When a program creates a list or the user defines a new function (such
as by loading a library), that data is placed in normal storage.  If
normal storage runs low, then Emacs asks the operating system to
allocate more memory in blocks of 1k bytes.  Each block is used for one
type of Lisp object, so symbols, cons cells, markers, etc., are
segregated in distinct blocks in memory.  (Vectors, long strings,
buffers and certain other editing types, which are fairly large, are
allocated in individual blocks, one per object, while small strings are
packed into blocks of 8k bytes.)

   It is quite common to use some storage for a while, then release it
by (for example) killing a buffer or deleting the last pointer to an
object.  Emacs provides a "garbage collector" to reclaim this abandoned
storage.  (This name is traditional, but "garbage recycler" might be a
more intuitive metaphor for this facility.)

   The garbage collector operates by finding and marking all Lisp
objects that are still accessible to Lisp programs.  To begin with, it
assumes all the symbols, their values and associated function
definitions, and any data presently on the stack, are accessible.  Any
objects that can be reached indirectly through other accessible objects
are also accessible.

   When marking is finished, all objects still unmarked are garbage.  No
matter what the Lisp program or the user does, it is impossible to refer
to them, since there is no longer a way to reach them.  Their space
might as well be reused, since no one will miss them.  The second
("sweep") phase of the garbage collector arranges to reuse them.

   The sweep phase puts unused cons cells onto a "free list" for future
allocation; likewise for symbols and markers.  It compacts the
accessible strings so they occupy fewer 8k blocks; then it frees the
other 8k blocks.  Vectors, buffers, windows, and other large objects are
individually allocated and freed using `malloc' and `free'.

     Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call
     the garbage collector when the free list is empty.  Instead, it
     simply requests the operating system to allocate more storage, and
     processing continues until `gc-cons-threshold' bytes have been
     used.

     This means that you can make sure that the garbage collector will
     not run during a certain portion of a Lisp program by calling the
     garbage collector explicitly just before it (provided that portion
     of the program does not use so much space as to force a second
     garbage collection).

 -- Command: garbage-collect
     This command runs a garbage collection, and returns information on
     the amount of space in use.  (Garbage collection can also occur
     spontaneously if you use more than `gc-cons-threshold' bytes of
     Lisp data since the previous garbage collection.)

     `garbage-collect' returns a list containing the following
     information:

          ((USED-CONSES . FREE-CONSES)
           (USED-SYMS . FREE-SYMS)
           (USED-MISCS . FREE-MISCS)
           USED-STRING-CHARS
           USED-VECTOR-SLOTS
           (USED-FLOATS . FREE-FLOATS)
           (USED-INTERVALS . FREE-INTERVALS)
           (USED-STRINGS . FREE-STRINGS))

     Here is an example:

          (garbage-collect)
               => ((106886 . 13184) (9769 . 0)
                          (7731 . 4651) 347543 121628
                          (31 . 94) (1273 . 168)
                          (25474 . 3569))

     Here is a table explaining each element:

    USED-CONSES
          The number of cons cells in use.

    FREE-CONSES
          The number of cons cells for which space has been obtained
          from the operating system, but that are not currently being
          used.

    USED-SYMS
          The number of symbols in use.

    FREE-SYMS
          The number of symbols for which space has been obtained from
          the operating system, but that are not currently being used.

    USED-MISCS
          The number of miscellaneous objects in use.  These include
          markers and overlays, plus certain objects not visible to
          users.

    FREE-MISCS
          The number of miscellaneous objects for which space has been
          obtained from the operating system, but that are not
          currently being used.

    USED-STRING-CHARS
          The total size of all strings, in characters.

    USED-VECTOR-SLOTS
          The total number of elements of existing vectors.

    USED-FLOATS
          The number of floats in use.

    FREE-FLOATS
          The number of floats for which space has been obtained from
          the operating system, but that are not currently being used.

    USED-INTERVALS
          The number of intervals in use.  Intervals are an internal
          data structure used for representing text properties.

    FREE-INTERVALS
          The number of intervals for which space has been obtained
          from the operating system, but that are not currently being
          used.

    USED-STRINGS
          The number of strings in use.

    FREE-STRINGS
          The number of string headers for which the space was obtained
          from the operating system, but which are currently not in
          use.  (A string object consists of a header and the storage
          for the string text itself; the latter is only allocated when
          the string is created.)

     If there was overflow in pure space (see the previous section),
     `garbage-collect' returns `nil', because a real garbage collection
     can not be done in this situation.

 -- User Option: garbage-collection-messages
     If this variable is non-`nil', Emacs displays a message at the
     beginning and end of garbage collection.  The default value is
     `nil', meaning there are no such messages.

 -- Variable: post-gc-hook
     This is a normal hook that is run at the end of garbage collection.
     Garbage collection is inhibited while the hook functions run, so be
     careful writing them.

 -- User Option: gc-cons-threshold
     The value of this variable is the number of bytes of storage that
     must be allocated for Lisp objects after one garbage collection in
     order to trigger another garbage collection.  A cons cell counts
     as eight bytes, a string as one byte per character plus a few
     bytes of overhead, and so on; space allocated to the contents of
     buffers does not count.  Note that the subsequent garbage
     collection does not happen immediately when the threshold is
     exhausted, but only the next time the Lisp evaluator is called.

     The initial threshold value is 400,000.  If you specify a larger
     value, garbage collection will happen less often.  This reduces the
     amount of time spent garbage collecting, but increases total
     memory use.  You may want to do this when running a program that
     creates lots of Lisp data.

     You can make collections more frequent by specifying a smaller
     value, down to 10,000.  A value less than 10,000 will remain in
     effect only until the subsequent garbage collection, at which time
     `garbage-collect' will set the threshold back to 10,000.

 -- User Option: gc-cons-percentage
     The value of this variable specifies the amount of consing before a
     garbage collection occurs, as a fraction of the current heap size.
     This criterion and `gc-cons-threshold' apply in parallel, and
     garbage collection occurs only when both criteria are satisfied.

     As the heap size increases, the time to perform a garbage
     collection increases.  Thus, it can be desirable to do them less
     frequently in proportion.

   The value returned by `garbage-collect' describes the amount of
memory used by Lisp data, broken down by data type.  By contrast, the
function `memory-limit' provides information on the total amount of
memory Emacs is currently using.

 -- Function: memory-limit
     This function returns the address of the last byte Emacs has
     allocated, divided by 1024.  We divide the value by 1024 to make
     sure it fits in a Lisp integer.

     You can use this to get a general idea of how your actions affect
     the memory usage.

 -- Variable: memory-full
     This variable is `t' if Emacs is close to out of memory for Lisp
     objects, and `nil' otherwise.

 -- Function: memory-use-counts
     This returns a list of numbers that count the number of objects
     created in this Emacs session.  Each of these counters increments
     for a certain kind of object.  See the documentation string for
     details.

 -- Variable: gcs-done
     This variable contains the total number of garbage collections
     done so far in this Emacs session.

 -- Variable: gc-elapsed
     This variable contains the total number of seconds of elapsed time
     during garbage collection so far in this Emacs session, as a
     floating point number.


File: elisp,  Node: Memory Usage,  Next: Writing Emacs Primitives,  Prev: Garbage Collection,  Up: GNU Emacs Internals

E.4 Memory Usage
================

These functions and variables give information about the total amount
of memory allocation that Emacs has done, broken down by data type.
Note the difference between these and the values returned by
`(garbage-collect)'; those count objects that currently exist, but
these count the number or size of all allocations, including those for
objects that have since been freed.

 -- Variable: cons-cells-consed
     The total number of cons cells that have been allocated so far in
     this Emacs session.

 -- Variable: floats-consed
     The total number of floats that have been allocated so far in this
     Emacs session.

 -- Variable: vector-cells-consed
     The total number of vector cells that have been allocated so far
     in this Emacs session.

 -- Variable: symbols-consed
     The total number of symbols that have been allocated so far in
     this Emacs session.

 -- Variable: string-chars-consed
     The total number of string characters that have been allocated so
     far in this Emacs session.

 -- Variable: misc-objects-consed
     The total number of miscellaneous objects that have been allocated
     so far in this Emacs session.  These include markers and overlays,
     plus certain objects not visible to users.

 -- Variable: intervals-consed
     The total number of intervals that have been allocated so far in
     this Emacs session.

 -- Variable: strings-consed
     The total number of strings that have been allocated so far in this
     Emacs session.


File: elisp,  Node: Writing Emacs Primitives,  Next: Object Internals,  Prev: Memory Usage,  Up: GNU Emacs Internals

E.5 Writing Emacs Primitives
============================

Lisp primitives are Lisp functions implemented in C.  The details of
interfacing the C function so that Lisp can call it are handled by a few
C macros.  The only way to really understand how to write new C code is
to read the source, but we can explain some things here.

   An example of a special form is the definition of `or', from
`eval.c'.  (An ordinary function would have the same general
appearance.)

     DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
       doc: /* Eval args until one of them yields non-nil, then return that
     value. The remaining args are not evalled at all.
     If all args return nil, return nil.
     usage: (or CONDITIONS ...)  */)
       (args)
          Lisp_Object args;
     {
       register Lisp_Object val = Qnil;
       struct gcpro gcpro1;

       GCPRO1 (args);

       while (CONSP (args))
         {
           val = Feval (XCAR (args));
           if (!NILP (val))
             break;
           args = XCDR (args);
         }

       UNGCPRO;
       return val;
     }

   Let's start with a precise explanation of the arguments to the
`DEFUN' macro.  Here is a template for them:

     DEFUN (LNAME, FNAME, SNAME, MIN, MAX, INTERACTIVE, DOC)

LNAME
     This is the name of the Lisp symbol to define as the function
     name; in the example above, it is `or'.

FNAME
     This is the C function name for this function.  This is the name
     that is used in C code for calling the function.  The name is, by
     convention, `F' prepended to the Lisp name, with all dashes (`-')
     in the Lisp name changed to underscores.  Thus, to call this
     function from C code, call `For'.  Remember that the arguments must
     be of type `Lisp_Object'; various macros and functions for creating
     values of type `Lisp_Object' are declared in the file `lisp.h'.

SNAME
     This is a C variable name to use for a structure that holds the
     data for the subr object that represents the function in Lisp.
     This structure conveys the Lisp symbol name to the initialization
     routine that will create the symbol and store the subr object as
     its definition.  By convention, this name is always FNAME with `F'
     replaced with `S'.

MIN
     This is the minimum number of arguments that the function
     requires.  The function `or' allows a minimum of zero arguments.

MAX
     This is the maximum number of arguments that the function accepts,
     if there is a fixed maximum.  Alternatively, it can be `UNEVALLED',
     indicating a special form that receives unevaluated arguments, or
     `MANY', indicating an unlimited number of evaluated arguments (the
     equivalent of `&rest').  Both `UNEVALLED' and `MANY' are macros.
     If MAX is a number, it may not be less than MIN and it may not be
     greater than eight.

INTERACTIVE
     This is an interactive specification, a string such as might be
     used as the argument of `interactive' in a Lisp function.  In the
     case of `or', it is 0 (a null pointer), indicating that `or'
     cannot be called interactively.  A value of `""' indicates a
     function that should receive no arguments when called
     interactively.

DOC
     This is the documentation string.  It uses C comment syntax rather
     than C string syntax because comment syntax requires nothing
     special to include multiple lines.  The `doc:' identifies the
     comment that follows as the documentation string.  The `/*' and
     `*/' delimiters that begin and end the comment are not part of the
     documentation string.

     If the last line of the documentation string begins with the
     keyword `usage:', the rest of the line is treated as the argument
     list for documentation purposes.  This way, you can use different
     argument names in the documentation string from the ones used in
     the C code.  `usage:' is required if the function has an unlimited
     number of arguments.

     All the usual rules for documentation strings in Lisp code (*note
     Documentation Tips::) apply to C code documentation strings too.

   After the call to the `DEFUN' macro, you must write the argument
name list that every C function must have, followed by ordinary C
declarations for the arguments.  For a function with a fixed maximum
number of arguments, declare a C argument for each Lisp argument, and
give them all type `Lisp_Object'.  When a Lisp function has no upper
limit on the number of arguments, its implementation in C actually
receives exactly two arguments: the first is the number of Lisp
arguments, and the second is the address of a block containing their
values.  They have types `int' and `Lisp_Object *'.

   Within the function `For' itself, note the use of the macros
`GCPRO1' and `UNGCPRO'.  `GCPRO1' is used to "protect" a variable from
garbage collection--to inform the garbage collector that it must look
in that variable and regard its contents as an accessible object.  GC
protection is necessary whenever you call `Feval' or anything that can
directly or indirectly call `Feval'.  At such a time, any Lisp object
that this function may refer to again must be protected somehow.

   It suffices to ensure that at least one pointer to each object is
GC-protected; that way, the object cannot be recycled, so all pointers
to it remain valid.  Thus, a particular local variable can do without
protection if it is certain that the object it points to will be
preserved by some other pointer (such as another local variable which
has a `GCPRO')(1).  Otherwise, the local variable needs a `GCPRO'.

   The macro `GCPRO1' protects just one local variable.  If you want to
protect two variables, use `GCPRO2' instead; repeating `GCPRO1' will
not work.  Macros `GCPRO3', `GCPRO4', `GCPRO5', and `GCPRO6' also
exist.  All these macros implicitly use local variables such as
`gcpro1'; you must declare these explicitly, with type `struct gcpro'.
Thus, if you use `GCPRO2', you must declare `gcpro1' and `gcpro2'.
Alas, we can't explain all the tricky details here.

   `UNGCPRO' cancels the protection of the variables that are protected
in the current function.  It is necessary to do this explicitly.

   Built-in functions that take a variable number of arguments actually
accept two arguments at the C level: the number of Lisp arguments, and
a `Lisp_Object *' pointer to a C vector containing those Lisp
arguments.  This C vector may be part of a Lisp vector, but it need not
be.  The responsibility for using `GCPRO' to protect the Lisp arguments
from GC if necessary rests with the caller in this case, since the
caller allocated or found the storage for them.

   You must not use C initializers for static or global variables unless
the variables are never written once Emacs is dumped.  These variables
with initializers are allocated in an area of memory that becomes
read-only (on certain operating systems) as a result of dumping Emacs.
*Note Pure Storage::.

   Do not use static variables within functions--place all static
variables at top level in the file.  This is necessary because Emacs on
some operating systems defines the keyword `static' as a null macro.
(This definition is used because those systems put all variables
declared static in a place that becomes read-only after dumping, whether
they have initializers or not.)

   Defining the C function is not enough to make a Lisp primitive
available; you must also create the Lisp symbol for the primitive and
store a suitable subr object in its function cell.  The code looks like
this:

     defsubr (&SUBR-STRUCTURE-NAME);

Here SUBR-STRUCTURE-NAME is the name you used as the third argument to
`DEFUN'.

   If you add a new primitive to a file that already has Lisp primitives
defined in it, find the function (near the end of the file) named
`syms_of_SOMETHING', and add the call to `defsubr' there.  If the file
doesn't have this function, or if you create a new file, add to it a
`syms_of_FILENAME' (e.g., `syms_of_myfile').  Then find the spot in
`emacs.c' where all of these functions are called, and add a call to
`syms_of_FILENAME' there.

   The function `syms_of_FILENAME' is also the place to define any C
variables that are to be visible as Lisp variables.  `DEFVAR_LISP'
makes a C variable of type `Lisp_Object' visible in Lisp.  `DEFVAR_INT'
makes a C variable of type `int' visible in Lisp with a value that is
always an integer.  `DEFVAR_BOOL' makes a C variable of type `int'
visible in Lisp with a value that is either `t' or `nil'.  Note that
variables defined with `DEFVAR_BOOL' are automatically added to the list
`byte-boolean-vars' used by the byte compiler.

   If you define a file-scope C variable of type `Lisp_Object', you
must protect it from garbage-collection by calling `staticpro' in
`syms_of_FILENAME', like this:

     staticpro (&VARIABLE);

   Here is another example function, with more complicated arguments.
This comes from the code in `window.c', and it demonstrates the use of
macros and functions to manipulate Lisp objects.

     DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
       Scoordinates_in_window_p, 2, 2,
       "xSpecify coordinate pair: \nXExpression which evals to window: ",
       "Return non-nil if COORDINATES is in WINDOW.\n\
     COORDINATES is a cons of the form (X . Y), X and Y being distances\n\
     ...
     If they are on the border between WINDOW and its right sibling,\n\
        `vertical-line' is returned.")
       (coordinates, window)
          register Lisp_Object coordinates, window;
     {
       int x, y;

       CHECK_LIVE_WINDOW (window, 0);
       CHECK_CONS (coordinates, 1);
       x = XINT (Fcar (coordinates));
       y = XINT (Fcdr (coordinates));

       switch (coordinates_in_window (XWINDOW (window), &x, &y))
         {
         case 0:			/* NOT in window at all. */
           return Qnil;

         case 1:			/* In text part of window. */
           return Fcons (make_number (x), make_number (y));

         case 2:			/* In mode line of window. */
           return Qmode_line;

         case 3:			/* On right border of window.  */
           return Qvertical_line;

         default:
           abort ();
         }
     }

   Note that C code cannot call functions by name unless they are
defined in C.  The way to call a function written in Lisp is to use
`Ffuncall', which embodies the Lisp function `funcall'.  Since the Lisp
function `funcall' accepts an unlimited number of arguments, in C it
takes two: the number of Lisp-level arguments, and a one-dimensional
array containing their values.  The first Lisp-level argument is the
Lisp function to call, and the rest are the arguments to pass to it.
Since `Ffuncall' can call the evaluator, you must protect pointers from
garbage collection around the call to `Ffuncall'.

   The C functions `call0', `call1', `call2', and so on, provide handy
ways to call a Lisp function conveniently with a fixed number of
arguments.  They work by calling `Ffuncall'.

   `eval.c' is a very good file to look through for examples; `lisp.h'
contains the definitions for some important macros and functions.

   If you define a function which is side-effect free, update the code
in `byte-opt.el' which binds `side-effect-free-fns' and
`side-effect-and-error-free-fns' so that the compiler optimizer knows
about it.

   ---------- Footnotes ----------

   (1) Formerly, strings were a special exception; in older Emacs
versions, every local variable that might point to a string needed a
`GCPRO'.


File: elisp,  Node: Object Internals,  Prev: Writing Emacs Primitives,  Up: GNU Emacs Internals

E.6 Object Internals
====================

GNU Emacs Lisp manipulates many different types of data.  The actual
data are stored in a heap and the only access that programs have to it
is through pointers.  Pointers are thirty-two bits wide in most
implementations.  Depending on the operating system and type of machine
for which you compile Emacs, twenty-nine bits are used to address the
object, and the remaining three bits are used for the tag that
identifies the object's type.

   Because Lisp objects are represented as tagged pointers, it is always
possible to determine the Lisp data type of any object.  The C data type
`Lisp_Object' can hold any Lisp object of any data type.  Ordinary
variables have type `Lisp_Object', which means they can hold any type
of Lisp value; you can determine the actual data type only at run time.
The same is true for function arguments; if you want a function to
accept only a certain type of argument, you must check the type
explicitly using a suitable predicate (*note Type Predicates::).  

* Menu:

* Buffer Internals::    Components of a buffer structure.
* Window Internals::    Components of a window structure.
* Process Internals::   Components of a process structure.


File: elisp,  Node: Buffer Internals,  Next: Window Internals,  Up: Object Internals

E.6.1 Buffer Internals
----------------------

Buffers contain fields not directly accessible by the Lisp programmer.
We describe them here, naming them by the names used in the C code.
Many are accessible indirectly in Lisp programs via Lisp primitives.

   Two structures are used to represent buffers in C.  The
`buffer_text' structure contains fields describing the text of a
buffer; the `buffer' structure holds other fields.  In the case of
indirect buffers, two or more `buffer' structures reference the same
`buffer_text' structure.

   Here is a list of the `struct buffer_text' fields:

`beg'
     This field contains the actual address of the buffer contents.

`gpt'
     This holds the character position of the gap in the buffer.  *Note
     Buffer Gap::.

`z'
     This field contains the character position of the end of the buffer
     text.

`gpt_byte'
     Contains the byte position of the gap.

`z_byte'
     Holds the byte position of the end of the buffer text.

`gap_size'
     Contains the size of buffer's gap.  *Note Buffer Gap::.

`modiff'
     This field counts buffer-modification events for this buffer.  It
     is incremented for each such event, and never otherwise changed.

`save_modiff'
     Contains the previous value of `modiff', as of the last time a
     buffer was visited or saved in a file.

`overlay_modiff'
     Counts modifications to overlays analogous to `modiff'.

`beg_unchanged'
     Holds the number of characters at the start of the text that are
     known to be unchanged since the last redisplay that finished.

`end_unchanged'
     Holds the number of characters at the end of the text that are
     known to be unchanged since the last redisplay that finished.

`unchanged_modified'
     Contains the value of `modiff' at the time of the last redisplay
     that finished.  If this value matches `modiff', `beg_unchanged'
     and `end_unchanged' contain no useful information.

`overlay_unchanged_modified'
     Contains the value of `overlay_modiff' at the time of the last
     redisplay that finished.  If this value matches `overlay_modiff',
     `beg_unchanged' and `end_unchanged' contain no useful information.

`markers'
     The markers that refer to this buffer.  This is actually a single
     marker, and successive elements in its marker `chain' are the other
     markers referring to this buffer text.

`intervals'
     Contains the interval tree which records the text properties of
     this buffer.

   The fields of `struct buffer' are:

`next'
     Points to the next buffer, in the chain of all buffers including
     killed buffers.  This chain is used only for garbage collection,
     in order to collect killed buffers properly.  Note that vectors,
     and most kinds of objects allocated as vectors, are all on one
     chain, but buffers are on a separate chain of their own.

`own_text'
     This is a `struct buffer_text' structure.  In an ordinary buffer,
     it holds the buffer contents.  In indirect buffers, this field is
     not used.

`text'
     This points to the `buffer_text' structure that is used for this
     buffer.  In an ordinary buffer, this is the `own_text' field above.
     In an indirect buffer, this is the `own_text' field of the base
     buffer.

`pt'
     Contains the character position of point in a buffer.

`pt_byte'
     Contains the byte position of point in a buffer.

`begv'
     This field contains the character position of the beginning of the
     accessible range of text in the buffer.

`begv_byte'
     This field contains the byte position of the beginning of the
     accessible range of text in the buffer.

`zv'
     This field contains the character position of the end of the
     accessible range of text in the buffer.

`zv_byte'
     This field contains the byte position of the end of the accessible
     range of text in the buffer.

`base_buffer'
     In an indirect buffer, this points to the base buffer.  In an
     ordinary buffer, it is null.

`local_var_flags'
     This field contains flags indicating that certain variables are
     local in this buffer.  Such variables are declared in the C code
     using `DEFVAR_PER_BUFFER', and their buffer-local bindings are
     stored in fields in the buffer structure itself.  (Some of these
     fields are described in this table.)

`modtime'
     This field contains the modification time of the visited file.  It
     is set when the file is written or read.  Before writing the
     buffer into a file, this field is compared to the modification
     time of the file to see if the file has changed on disk.  *Note
     Buffer Modification::.

`auto_save_modified'
     This field contains the time when the buffer was last auto-saved.

`auto_save_failure_time'
     The time at which we detected a failure to auto-save, or -1 if we
     didn't have a failure.

`last_window_start'
     This field contains the `window-start' position in the buffer as of
     the last time the buffer was displayed in a window.

`clip_changed'
     This flag is set when narrowing changes in a buffer.

`prevent_redisplay_optimizations_p'
     this flag indicates that redisplay optimizations should not be used
     to display this buffer.

`undo_list'
     This field points to the buffer's undo list.  *Note Undo::.

`name'
     The buffer name is a string that names the buffer.  It is
     guaranteed to be unique.  *Note Buffer Names::.

`filename'
     The name of the file visited in this buffer, or `nil'.

`directory'
     The directory for expanding relative file names.

`save_length'
     Length of the file this buffer is visiting, when last read or
     saved.  This and other fields concerned with saving are not kept
     in the `buffer_text' structure because indirect buffers are never
     saved.

`auto_save_file_name'
     File name used for auto-saving this buffer.  This is not in the
     `buffer_text' because it's not used in indirect buffers at all.

`read_only'
     Non-`nil' means this buffer is read-only.

`mark'
     This field contains the mark for the buffer.  The mark is a marker,
     hence it is also included on the list `markers'.  *Note The Mark::.

`local_var_alist'
     This field contains the association list describing the
     buffer-local variable bindings of this buffer, not including the
     built-in buffer-local bindings that have special slots in the
     buffer object.  (Those slots are omitted from this table.)  *Note
     Buffer-Local Variables::.

`major_mode'
     Symbol naming the major mode of this buffer, e.g., `lisp-mode'.

`mode_name'
     Pretty name of major mode, e.g., `"Lisp"'.

`mode_line_format'
     Mode line element that controls the format of the mode line.  If
     this is `nil', no mode line will be displayed.

`header_line_format'
     This field is analogous to `mode_line_format' for the mode line
     displayed at the top of windows.

`keymap'
     This field holds the buffer's local keymap.  *Note Keymaps::.

`abbrev_table'
     This buffer's local abbrevs.

`syntax_table'
     This field contains the syntax table for the buffer.  *Note Syntax
     Tables::.

`category_table'
     This field contains the category table for the buffer.

`case_fold_search'
     The value of `case-fold-search' in this buffer.

`tab_width'
     The value of `tab-width' in this buffer.

`fill_column'
     The value of `fill-column' in this buffer.

`left_margin'
     The value of `left-margin' in this buffer.

`auto_fill_function'
     The value of `auto-fill-function' in this buffer.

`downcase_table'
     This field contains the conversion table for converting text to
     lower case.  *Note Case Tables::.

`upcase_table'
     This field contains the conversion table for converting text to
     upper case.  *Note Case Tables::.

`case_canon_table'
     This field contains the conversion table for canonicalizing text
     for case-folding search.  *Note Case Tables::.

`case_eqv_table'
     This field contains the equivalence table for case-folding search.
     *Note Case Tables::.

`truncate_lines'
     The value of `truncate-lines' in this buffer.

`ctl_arrow'
     The value of `ctl-arrow' in this buffer.

`selective_display'
     The value of `selective-display' in this buffer.

`selective_display_ellipsis'
     The value of `selective-display-ellipsis' in this buffer.

`minor_modes'
     An alist of the minor modes of this buffer.

`overwrite_mode'
     The value of `overwrite_mode' in this buffer.

`abbrev_mode'
     The value of `abbrev-mode' in this buffer.

`display_table'
     This field contains the buffer's display table, or `nil' if it
     doesn't have one.  *Note Display Tables::.

`save_modified'
     This field contains the time when the buffer was last saved, as an
     integer.  *Note Buffer Modification::.

`mark_active'
     This field is non-`nil' if the buffer's mark is active.

`overlays_before'
     This field holds a list of the overlays in this buffer that end at
     or before the current overlay center position.  They are sorted in
     order of decreasing end position.

`overlays_after'
     This field holds a list of the overlays in this buffer that end
     after the current overlay center position.  They are sorted in
     order of increasing beginning position.

`overlay_center'
     This field holds the current overlay center position.  *Note
     Overlays::.

`enable_multibyte_characters'
     This field holds the buffer's local value of
     `enable-multibyte-characters'--either `t' or `nil'.

`buffer_file_coding_system'
     The value of `buffer-file-coding-system' in this buffer.

`file_format'
     The value of `buffer-file-format' in this buffer.

`auto_save_file_format'
     The value of `buffer-auto-save-file-format' in this buffer.

`pt_marker'
     In an indirect buffer, or a buffer that is the base of an indirect
     buffer, this holds a marker that records point for this buffer
     when the buffer is not current.

`begv_marker'
     In an indirect buffer, or a buffer that is the base of an indirect
     buffer, this holds a marker that records `begv' for this buffer
     when the buffer is not current.

`zv_marker'
     In an indirect buffer, or a buffer that is the base of an indirect
     buffer, this holds a marker that records `zv' for this buffer when
     the buffer is not current.

`file_truename'
     The truename of the visited file, or `nil'.

`invisibility_spec'
     The value of `buffer-invisibility-spec' in this buffer.

`last_selected_window'
     This is the last window that was selected with this buffer in it,
     or `nil' if that window no longer displays this buffer.

`display_count'
     This field is incremented each time the buffer is displayed in a
     window.

`left_margin_width'
     The value of `left-margin-width' in this buffer.

`right_margin_width'
     The value of `right-margin-width' in this buffer.

`indicate_empty_lines'
     Non-`nil' means indicate empty lines (lines with no text) with a
     small bitmap in the fringe, when using a window system that can do
     it.

`display_time'
     This holds a time stamp that is updated each time this buffer is
     displayed in a window.

`scroll_up_aggressively'
     The value of `scroll-up-aggressively' in this buffer.

`scroll_down_aggressively'
     The value of `scroll-down-aggressively' in this buffer.


File: elisp,  Node: Window Internals,  Next: Process Internals,  Prev: Buffer Internals,  Up: Object Internals

E.6.2 Window Internals
----------------------

Windows have the following accessible fields:

`frame'
     The frame that this window is on.

`mini_p'
     Non-`nil' if this window is a minibuffer window.

`parent'
     Internally, Emacs arranges windows in a tree; each group of
     siblings has a parent window whose area includes all the siblings.
     This field points to a window's parent.

     Parent windows do not display buffers, and play little role in
     display except to shape their child windows.  Emacs Lisp programs
     usually have no access to the parent windows; they operate on the
     windows at the leaves of the tree, which actually display buffers.

     The following four fields also describe the window tree structure.

`hchild'
     In a window subdivided horizontally by child windows, the leftmost
     child.  Otherwise, `nil'.

`vchild'
     In a window subdivided vertically by child windows, the topmost
     child.  Otherwise, `nil'.

`next'
     The next sibling of this window.  It is `nil' in a window that is
     the rightmost or bottommost of a group of siblings.

`prev'
     The previous sibling of this window.  It is `nil' in a window that
     is the leftmost or topmost of a group of siblings.

`left'
     This is the left-hand edge of the window, measured in columns.
     (The leftmost column on the screen is column 0.)

`top'
     This is the top edge of the window, measured in lines.  (The top
     line on the screen is line 0.)

`height'
     The height of the window, measured in lines.

`width'
     The width of the window, measured in columns.  This width includes
     the scroll bar and fringes, and/or the separator line on the right
     of the window (if any).

`buffer'
     The buffer that the window is displaying.  This may change often
     during the life of the window.

`start'
     The position in the buffer that is the first character to be
     displayed in the window.

`pointm'
     This is the value of point in the current buffer when this window
     is selected; when it is not selected, it retains its previous
     value.

`force_start'
     If this flag is non-`nil', it says that the window has been
     scrolled explicitly by the Lisp program.  This affects what the
     next redisplay does if point is off the screen: instead of
     scrolling the window to show the text around point, it moves point
     to a location that is on the screen.

`frozen_window_start_p'
     This field is set temporarily to 1 to indicate to redisplay that
     `start' of this window should not be changed, even if point gets
     invisible.

`start_at_line_beg'
     Non-`nil' means current value of `start' was the beginning of a
     line when it was chosen.

`too_small_ok'
     Non-`nil' means don't delete this window for becoming "too small."

`height_fixed_p'
     This field is temporarily set to 1 to fix the height of the
     selected window when the echo area is resized.

`use_time'
     This is the last time that the window was selected.  The function
     `get-lru-window' uses this field.

`sequence_number'
     A unique number assigned to this window when it was created.

`last_modified'
     The `modiff' field of the window's buffer, as of the last time a
     redisplay completed in this window.

`last_overlay_modified'
     The `overlay_modiff' field of the window's buffer, as of the last
     time a redisplay completed in this window.

`last_point'
     The buffer's value of point, as of the last time a redisplay
     completed in this window.

`last_had_star'
     A non-`nil' value means the window's buffer was "modified" when the
     window was last updated.

`vertical_scroll_bar'
     This window's vertical scroll bar.

`left_margin_width'
     The width of the left margin in this window, or `nil' not to
     specify it (in which case the buffer's value of `left-margin-width'
     is used.

`right_margin_width'
     Likewise for the right margin.

`window_end_pos'
     This is computed as `z' minus the buffer position of the last glyph
     in the current matrix of the window.  The value is only valid if
     `window_end_valid' is not `nil'.

`window_end_bytepos'
     The byte position corresponding to `window_end_pos'.

`window_end_vpos'
     The window-relative vertical position of the line containing
     `window_end_pos'.

`window_end_valid'
     This field is set to a non-`nil' value if `window_end_pos' is truly
     valid.  This is `nil' if nontrivial redisplay is preempted since
     in that case the display that `window_end_pos' was computed for
     did not get onto the screen.

`redisplay_end_trigger'
     If redisplay in this window goes beyond this buffer position, it
     runs the `redisplay-end-trigger-hook'.

`cursor'
     A structure describing where the cursor is in this window.

`last_cursor'
     The value of `cursor' as of the last redisplay that finished.

`phys_cursor'
     A structure describing where the cursor of this window physically
     is.

`phys_cursor_type'
     The type of cursor that was last displayed on this window.

`phys_cursor_on_p'
     This field is non-zero if the cursor is physically on.

`cursor_off_p'
     Non-zero means the cursor in this window is logically on.

`last_cursor_off_p'
     This field contains the value of `cursor_off_p' as of the time of
     the last redisplay.

`must_be_updated_p'
     This is set to 1 during redisplay when this window must be updated.

`hscroll'
     This is the number of columns that the display in the window is
     scrolled horizontally to the left.  Normally, this is 0.

`vscroll'
     Vertical scroll amount, in pixels.  Normally, this is 0.

`dedicated'
     Non-`nil' if this window is dedicated to its buffer.

`display_table'
     The window's display table, or `nil' if none is specified for it.

`update_mode_line'
     Non-`nil' means this window's mode line needs to be updated.

`base_line_number'
     The line number of a certain position in the buffer, or `nil'.
     This is used for displaying the line number of point in the mode
     line.

`base_line_pos'
     The position in the buffer for which the line number is known, or
     `nil' meaning none is known.

`region_showing'
     If the region (or part of it) is highlighted in this window, this
     field holds the mark position that made one end of that region.
     Otherwise, this field is `nil'.

`column_number_displayed'
     The column number currently displayed in this window's mode line,
     or `nil' if column numbers are not being displayed.

`current_matrix'
     A glyph matrix describing the current display of this window.

`desired_matrix'
     A glyph matrix describing the desired display of this window.


File: elisp,  Node: Process Internals,  Prev: Window Internals,  Up: Object Internals

E.6.3 Process Internals
-----------------------

The fields of a process are:

`name'
     A string, the name of the process.

`command'
     A list containing the command arguments that were used to start
     this process.

`filter'
     A function used to accept output from the process instead of a
     buffer, or `nil'.

`sentinel'
     A function called whenever the process receives a signal, or `nil'.

`buffer'
     The associated buffer of the process.

`pid'
     An integer, the operating system's process ID.

`childp'
     A flag, non-`nil' if this is really a child process.  It is `nil'
     for a network connection.

`mark'
     A marker indicating the position of the end of the last output
     from this process inserted into the buffer.  This is often but not
     always the end of the buffer.

`kill_without_query'
     If this is non-`nil', killing Emacs while this process is still
     running does not ask for confirmation about killing the process.

`raw_status_low'
`raw_status_high'
     These two fields record 16 bits each of the process status
     returned by the `wait' system call.

`status'
     The process status, as `process-status' should return it.

`tick'
`update_tick'
     If these two fields are not equal, a change in the status of the
     process needs to be reported, either by running the sentinel or by
     inserting a message in the process buffer.

`pty_flag'
     Non-`nil' if communication with the subprocess uses a PTY; `nil'
     if it uses a pipe.

`infd'
     The file descriptor for input from the process.

`outfd'
     The file descriptor for output to the process.

`subtty'
     The file descriptor for the terminal that the subprocess is using.
     (On some systems, there is no need to record this, so the value is
     `nil'.)

`tty_name'
     The name of the terminal that the subprocess is using, or `nil' if
     it is using pipes.

`decode_coding_system'
     Coding-system for decoding the input from this process.

`decoding_buf'
     A working buffer for decoding.

`decoding_carryover'
     Size of carryover in decoding.

`encode_coding_system'
     Coding-system for encoding the output to this process.

`encoding_buf'
     A working buffer for encoding.

`encoding_carryover'
     Size of carryover in encoding.

`inherit_coding_system_flag'
     Flag to set `coding-system' of the process buffer from the coding
     system used to decode process output.


File: elisp,  Node: Standard Errors,  Next: Standard Buffer-Local Variables,  Prev: GNU Emacs Internals,  Up: Top

Appendix F Standard Errors
**************************

Here is the complete list of the error symbols in standard Emacs,
grouped by concept.  The list includes each symbol's message (on the
`error-message' property of the symbol) and a cross reference to a
description of how the error can occur.

   Each error symbol has an `error-conditions' property that is a list
of symbols.  Normally this list includes the error symbol itself and
the symbol `error'.  Occasionally it includes additional symbols, which
are intermediate classifications, narrower than `error' but broader
than a single error symbol.  For example, all the errors in accessing
files have the condition `file-error'.  If we do not say here that a
certain error symbol has additional error conditions, that means it has
none.

   As a special exception, the error symbol `quit' does not have the
condition `error', because quitting is not considered an error.

   *Note Errors::, for an explanation of how errors are generated and
handled.

`SYMBOL'
     STRING; REFERENCE.

`error'
     `"error"'
     *Note Errors::.

`quit'
     `"Quit"'
     *Note Quitting::.

`args-out-of-range'
     `"Args out of range"'
     This happens when trying to access an element beyond the range of a
     sequence or buffer.
     *Note Sequences Arrays Vectors::, *Note Text::.

`arith-error'
     `"Arithmetic error"'
     *Note Arithmetic Operations::.

`beginning-of-buffer'
     `"Beginning of buffer"'
     *Note Character Motion::.

`buffer-read-only'
     `"Buffer is read-only"'
     *Note Read Only Buffers::.

`coding-system-error'
     `"Invalid coding system"'
     *Note Lisp and Coding Systems::.

`cyclic-function-indirection'
     `"Symbol's chain of function indirections\
     contains a loop"'
     *Note Function Indirection::.

`cyclic-variable-indirection'
     `"Symbol's chain of variable indirections\
     contains a loop"'
     *Note Variable Aliases::.

`end-of-buffer'
     `"End of buffer"'
     *Note Character Motion::.

`end-of-file'
     `"End of file during parsing"'
     Note that this is not a subcategory of `file-error', because it
     pertains to the Lisp reader, not to file I/O.
     *Note Input Functions::.

`file-already-exists'
     This is a subcategory of `file-error'.
     *Note Writing to Files::.

`file-date-error'
     This is a subcategory of `file-error'.  It occurs when `copy-file'
     tries and fails to set the last-modification time of the output
     file.
     *Note Changing Files::.

`file-error'
     We do not list the error-strings of this error and its
     subcategories, because the error message is normally constructed
     from the data items alone when the error condition `file-error' is
     present.  Thus, the error-strings are not very relevant.  However,
     these error symbols do have `error-message' properties, and if no
     data is provided, the `error-message' property _is_ used.
     *Note Files::.

`file-locked'
     This is a subcategory of `file-error'.
     *Note File Locks::.

`file-supersession'
     This is a subcategory of `file-error'.
     *Note Modification Time::.

`ftp-error'
     This is a subcategory of `file-error', which results from problems
     in accessing a remote file using ftp.
     *Note Remote Files: (emacs)Remote Files.

`invalid-function'
     `"Invalid function"'
     *Note Function Indirection::.

`invalid-read-syntax'
     `"Invalid read syntax"'
     *Note Printed Representation::.

`invalid-regexp'
     `"Invalid regexp"'
     *Note Regular Expressions::.

`mark-inactive'
     `"The mark is not active now"'
     *Note The Mark::.

`no-catch'
     `"No catch for tag"'
     *Note Catch and Throw::.

`scan-error'
     `"Scan error"'
     This happens when certain syntax-parsing functions find invalid
     syntax or mismatched parentheses.
     *Note List Motion::, and *Note Parsing Expressions::.

`search-failed'
     `"Search failed"'
     *Note Searching and Matching::.

`setting-constant'
     `"Attempt to set a constant symbol"'
     The values of the symbols `nil' and `t', and any symbols that
     start with `:', may not be changed.
     *Note Variables that Never Change: Constant Variables.

`text-read-only'
     `"Text is read-only"'
     This is a subcategory of `buffer-read-only'.
     *Note Special Properties::.

`undefined-color'
     `"Undefined color"'
     *Note Color Names::.

`void-function'
     `"Symbol's function definition is void"'
     *Note Function Cells::.

`void-variable'
     `"Symbol's value as variable is void"'
     *Note Accessing Variables::.

`wrong-number-of-arguments'
     `"Wrong number of arguments"'
     *Note Classifying Lists::.

`wrong-type-argument'
     `"Wrong type argument"'
     *Note Type Predicates::.

   These kinds of error, which are classified as special cases of
`arith-error', can occur on certain systems for invalid use of
mathematical functions.

`domain-error'
     `"Arithmetic domain error"'
     *Note Math Functions::.

`overflow-error'
     `"Arithmetic overflow error"'
     This is a subcategory of `domain-error'.
     *Note Math Functions::.

`range-error'
     `"Arithmetic range error"'
     *Note Math Functions::.

`singularity-error'
     `"Arithmetic singularity error"'
     This is a subcategory of `domain-error'.
     *Note Math Functions::.

`underflow-error'
     `"Arithmetic underflow error"'
     This is a subcategory of `domain-error'.
     *Note Math Functions::.


File: elisp,  Node: Standard Buffer-Local Variables,  Next: Standard Keymaps,  Prev: Standard Errors,  Up: Top

Appendix G Buffer-Local Variables
*********************************

The table below lists the general-purpose Emacs variables that
automatically become buffer-local in each buffer.  Most become
buffer-local only when set; a few of them are always local in every
buffer.  Many Lisp packages define such variables for their internal
use, but we don't try to list them all here.

   Every buffer-specific minor mode defines a buffer-local variable
named `MODENAME-mode'.  *Note Minor Mode Conventions::.  Minor mode
variables will not be listed here.

`auto-fill-function'
     *Note Auto Filling::.

`buffer-auto-save-file-format'
     *Note Format Conversion::.

`buffer-auto-save-file-name'
     *Note Auto-Saving::.

`buffer-backed-up'
     *Note Making Backups::.

`buffer-display-count'
     *Note Buffers and Windows::.

`buffer-display-table'
     *Note Active Display Table::.

`buffer-display-time'
     *Note Buffers and Windows::.

`buffer-file-coding-system'
     *Note Encoding and I/O::.

`buffer-file-format'
     *Note Format Conversion::.

`buffer-file-name'
     *Note Buffer File Name::.

`buffer-file-number'
     *Note Buffer File Name::.

`buffer-file-truename'
     *Note Buffer File Name::.

`buffer-file-type'
     *Note MS-DOS File Types::.

`buffer-invisibility-spec'
     *Note Invisible Text::.

`buffer-offer-save'
     *Note Killing Buffers::.

`buffer-save-without-query'
     *Note Killing Buffers::.

`buffer-read-only'
     *Note Read Only Buffers::.

`buffer-saved-size'
     *Note Auto-Saving::.

`buffer-undo-list'
     *Note Undo::.

`cache-long-line-scans'
     *Note Truncation::.

`case-fold-search'
     *Note Searching and Case::.

`ctl-arrow'
     *Note Usual Display::.

`cursor-type'
     *Note Cursor Parameters::.

`cursor-in-non-selected-windows'
     *Note Basic Windows::.

`comment-column'
     *Note Comments: (emacs)Comments.

`default-directory'
     *Note File Name Expansion::.

`defun-prompt-regexp'
     *Note List Motion::.

`desktop-save-buffer'
     *Note Desktop Save Mode::.

`enable-multibyte-characters'
     *Note Text Representations::.

`fill-column'
     *Note Margins::.

`fill-prefix'
     *Note Margins::.

`font-lock-defaults'
     *Note Font Lock Basics::.

`fringe-cursor-alist'
     *Note Fringe Cursors::.

`fringe-indicator-alist'
     *Note Fringe Indicators::.

`fringes-outside-margins'
     *Note Fringes::.

`goal-column'
     *Note Moving Point: (emacs)Moving Point.

`header-line-format'
     *Note Header Lines::.

`indicate-buffer-boundaries'
     *Note Usual Display::.

`indicate-empty-lines'
     *Note Usual Display::.

`left-fringe-width'
     *Note Fringe Size/Pos::.

`left-margin'
     *Note Margins::.

`left-margin-width'
     *Note Display Margins::.

`line-spacing'
     *Note Line Height::.

`local-abbrev-table'
     *Note Standard Abbrev Tables::.

`major-mode'
     *Note Mode Help::.

`mark-active'
     *Note The Mark::.

`mark-ring'
     *Note The Mark::.

`mode-line-buffer-identification'
     *Note Mode Line Variables::.

`mode-line-format'
     *Note Mode Line Data::.

`mode-line-modified'
     *Note Mode Line Variables::.

`mode-line-process'
     *Note Mode Line Variables::.

`mode-name'
     *Note Mode Line Variables::.

`point-before-scroll'
     Used for communication between mouse commands and scroll-bar
     commands.

`right-fringe-width'
     *Note Fringe Size/Pos::.

`right-margin-width'
     *Note Display Margins::.

`save-buffer-coding-system'
     *Note Encoding and I/O::.

`scroll-bar-width'
     *Note Scroll Bars::.

`scroll-down-aggressively'
     *Note Textual Scrolling::.

`scroll-up-aggressively'
     *Note Textual Scrolling::.

`selective-display'
     *Note Selective Display::.

`selective-display-ellipses'
     *Note Selective Display::.

`tab-width'
     *Note Usual Display::.

`truncate-lines'
     *Note Truncation::.

`vertical-scroll-bar'
     *Note Scroll Bars::.

`window-size-fixed'
     *Note Resizing Windows::.

`write-contents-functions'
     *Note Saving Buffers::.


File: elisp,  Node: Standard Keymaps,  Next: Standard Hooks,  Prev: Standard Buffer-Local Variables,  Up: Top

Appendix H Standard Keymaps
***************************

The following symbols are used as the names for various keymaps.  Some
of these exist when Emacs is first started, others are loaded only when
their respective mode is used.  This is not an exhaustive list.

   Several keymaps are used in the minibuffer.  *Note Completion
Commands::.

   Almost all of these maps are used as local maps.  Indeed, of the
modes that presently exist, only Vip mode and Terminal mode ever change
the global keymap.

`apropos-mode-map'
     A sparse keymap for `apropos' buffers.

`Buffer-menu-mode-map'
     A full keymap used by Buffer Menu mode.

`c-mode-map'
     A sparse keymap used by C mode.

`command-history-map'
     A full keymap used by Command History mode.

`ctl-x-4-map'
     A sparse keymap for subcommands of the prefix `C-x 4'.

`ctl-x-5-map'
     A sparse keymap for subcommands of the prefix `C-x 5'.

`ctl-x-map'
     A full keymap for `C-x' commands.

`custom-mode-map'
     A full keymap for Custom mode.

`debugger-mode-map'
     A full keymap used by Debugger mode.

`dired-mode-map'
     A full keymap for `dired-mode' buffers.

`edit-abbrevs-map'
     A sparse keymap used in `edit-abbrevs'.

`edit-tab-stops-map'
     A sparse keymap used in `edit-tab-stops'.

`electric-buffer-menu-mode-map'
     A full keymap used by Electric Buffer Menu mode.

`electric-history-map'
     A full keymap used by Electric Command History mode.

`emacs-lisp-mode-map'
     A sparse keymap used by Emacs Lisp mode.

`esc-map'
     A full keymap for `ESC' (or `Meta') commands.

`facemenu-menu'
     The sparse keymap that displays the Text Properties menu.

`facemenu-background-menu'
     The sparse keymap that displays the Background Color submenu of
     the Text Properties menu.

`facemenu-face-menu'
     The sparse keymap that displays the Face submenu of the Text
     Properties menu.

`facemenu-foreground-menu'
     The sparse keymap that displays the Foreground Color submenu of
     the Text Properties menu.

`facemenu-indentation-menu'
     The sparse keymap that displays the Indentation submenu of the Text
     Properties menu.

`facemenu-justification-menu'
     The sparse keymap that displays the Justification submenu of the
     Text Properties menu.

`facemenu-special-menu'
     The sparse keymap that displays the Special Props submenu of the
     Text Properties menu.

`function-key-map'
     The keymap for translating keypad and function keys.
     If there are none, then it contains an empty sparse keymap.  *Note
     Translation Keymaps::.

`fundamental-mode-map'
     The sparse keymap for Fundamental mode.
     It is empty and should not be changed.

`global-map'
     The full keymap containing default global key bindings.
     Modes should not modify the Global map.

`grep-mode-map'
     The keymap for `grep-mode' buffers.

`help-map'
     The sparse keymap for the keys that follow the help character
     `C-h'.

`help-mode-map'
     The sparse keymap for Help mode.

`Helper-help-map'
     A full keymap used by the help utility package.
     It has the same keymap in its value cell and in its function cell.

`Info-edit-map'
     A sparse keymap used by the `e' command of Info.

`Info-mode-map'
     A sparse keymap containing Info commands.

`isearch-mode-map'
     A keymap that defines the characters you can type within
     incremental search.

`key-translation-map'
     A keymap for translating keys.  This one overrides ordinary key
     bindings, unlike `function-key-map'.  *Note Translation Keymaps::.

`kmacro-map'
     A sparse keymap for keys that follows the `C-x C-k' prefix search.

`lisp-interaction-mode-map'
     A sparse keymap used by Lisp Interaction mode.

`lisp-mode-map'
     A sparse keymap used by Lisp mode.

`menu-bar-edit-menu'
     The keymap which displays the Edit menu in the menu bar.

`menu-bar-files-menu'
     The keymap which displays the Files menu in the menu bar.

`menu-bar-help-menu'
     The keymap which displays the Help menu in the menu bar.

`menu-bar-mule-menu'
     The keymap which displays the Mule menu in the menu bar.

`menu-bar-search-menu'
     The keymap which displays the Search menu in the menu bar.

`menu-bar-tools-menu'
     The keymap which displays the Tools menu in the menu bar.

`mode-specific-map'
     The keymap for characters following `C-c'.  Note, this is in the
     global map.  This map is not actually mode specific: its name was
     chosen to be informative for the user in `C-h b'
     (`display-bindings'), where it describes the main use of the `C-c'
     prefix key.

`occur-mode-map'
     A sparse keymap used by Occur mode.

`query-replace-map'
     A sparse keymap used for responses in `query-replace' and related
     commands; also for `y-or-n-p' and `map-y-or-n-p'.  The functions
     that use this map do not support prefix keys; they look up one
     event at a time.

`text-mode-map'
     A sparse keymap used by Text mode.

`tool-bar-map'
     The keymap defining the contents of the tool bar.

`view-mode-map'
     A full keymap used by View mode.


File: elisp,  Node: Standard Hooks,  Next: Index,  Prev: Standard Keymaps,  Up: Top

Appendix I Standard Hooks
*************************

The following is a list of hook variables that let you provide
functions to be called from within Emacs on suitable occasions.

   Most of these variables have names ending with `-hook'.  They are
"normal hooks", run by means of `run-hooks'.  The value of such a hook
is a list of functions; the functions are called with no arguments and
their values are completely ignored.  The recommended way to put a new
function on such a hook is to call `add-hook'.  *Note Hooks::, for more
information about using hooks.

   Every major mode defines a mode hook named `MODENAME-mode-hook'.
The major mode command runs this normal hook with `run-mode-hooks' as
the very last thing it does.  *Note Mode Hooks::.  Most minor modes
have mode hooks too.  Mode hooks are omitted in the list below.

   The variables whose names end in `-hooks' or `-functions' are
usually "abnormal hooks"; their values are lists of functions, but
these functions are called in a special way (they are passed arguments,
or their values are used). The variables whose names end in `-function'
have single functions as their values.

   A special feature allows you to specify expressions to evaluate if
and when a file is loaded (*note Hooks for Loading::).  That feature is
not exactly a hook, but does a similar job.

`activate-mark-hook'
     *Note The Mark::.

`after-change-functions'
     *Note Change Hooks::.

`after-change-major-mode-hook'
     *Note Mode Hooks::.

`after-init-hook'
     *Note Init File::.

`after-insert-file-functions'
     *Note Saving Properties::.

`after-make-frame-functions'
     *Note Creating Frames::.

`after-revert-hook'
     *Note Reverting::.

`after-save-hook'
     *Note Saving Buffers::.

`auto-fill-function'
     *Note Auto Filling::.

`auto-save-hook'
     *Note Auto-Saving::.

`before-change-functions'
     *Note Change Hooks::.

`before-init-hook'
     *Note Init File::.

`before-make-frame-hook'
     *Note Creating Frames::.

`before-revert-hook'
     *Note Reverting::.

`before-save-hook'
     *Note Saving Buffers::.

`blink-paren-function'
     *Note Blinking::.

`buffer-access-fontify-functions'
     *Note Lazy Properties::.

`calendar-load-hook'
     *Note Calendar Customizing: (emacs)Calendar Customizing.

`change-major-mode-hook'
     *Note Creating Buffer-Local::.

`command-line-functions'
     *Note Command-Line Arguments::.

`comment-indent-function'
     *Note Options Controlling Comments: (emacs)Options for Comments.

`compilation-finish-functions'
     Functions to call when a compilation process finishes.

`custom-define-hook'
     Hook called after defining each customize option.

`deactivate-mark-hook'
     *Note The Mark::.

`desktop-after-read-hook'
     Normal hook run after a successful `desktop-read'.  May be used to
     show a buffer list.  *Note Saving Emacs Sessions: (emacs)Saving
     Emacs Sessions.

`desktop-no-desktop-file-hook'
     Normal hook run when `desktop-read' can't find a desktop file.
     May be used to show a dired buffer.  *Note Saving Emacs Sessions:
     (emacs)Saving Emacs Sessions.

`desktop-save-hook'
     Normal hook run before the desktop is saved in a desktop file.
     This is useful for truncating history lists, for example.  *Note
     Saving Emacs Sessions: (emacs)Saving Emacs Sessions.

`diary-display-hook'
     *Note Fancy Diary Display: (emacs)Fancy Diary Display.

`diary-hook'
     List of functions called after the display of the diary.  Can be
     used for appointment notification.

`disabled-command-function'
     *Note Disabling Commands::.

`echo-area-clear-hook'
     *Note Echo Area Customization::.

`emacs-startup-hook'
     *Note Init File::.

`find-file-hook'
     *Note Visiting Functions::.

`find-file-not-found-functions'
     *Note Visiting Functions::.

`first-change-hook'
     *Note Change Hooks::.

`font-lock-beginning-of-syntax-function'
     *Note Syntactic Font Lock::.

`font-lock-fontify-buffer-function'
     *Note Other Font Lock Variables::.

`font-lock-fontify-region-function'
     *Note Other Font Lock Variables::.

`font-lock-mark-block-function'
     *Note Other Font Lock Variables::.

`font-lock-syntactic-face-function'
     *Note Syntactic Font Lock::.

`font-lock-unfontify-buffer-function'
     *Note Other Font Lock Variables::.

`font-lock-unfontify-region-function'
     *Note Other Font Lock Variables::.

`initial-calendar-window-hook'
     *Note Calendar Customizing: (emacs)Calendar Customizing.

`kbd-macro-termination-hook'
     *Note Keyboard Macros::.

`kill-buffer-hook'
     *Note Killing Buffers::.

`kill-buffer-query-functions'
     *Note Killing Buffers::.

`kill-emacs-hook'
     *Note Killing Emacs::.

`kill-emacs-query-functions'
     *Note Killing Emacs::.

`lisp-indent-function'

`list-diary-entries-hook'
     *Note Fancy Diary Display: (emacs)Fancy Diary Display.

`mail-setup-hook'
     *Note Mail Mode Miscellany: (emacs)Mail Mode Misc.

`mark-diary-entries-hook'
     *Note Fancy Diary Display: (emacs)Fancy Diary Display.

`menu-bar-update-hook'
     *Note Menu Bar::.

`minibuffer-setup-hook'
     *Note Minibuffer Misc::.

`minibuffer-exit-hook'
     *Note Minibuffer Misc::.

`mouse-position-function'
     *Note Mouse Position::.

`nongregorian-diary-listing-hook'
     *Note Hebrew/Islamic Entries: (emacs)Hebrew/Islamic Entries.

`nongregorian-diary-marking-hook'
     *Note Hebrew/Islamic Entries: (emacs)Hebrew/Islamic Entries.

`occur-hook'

`post-command-hook'
     *Note Command Overview::.

`pre-abbrev-expand-hook'
     *Note Abbrev Expansion::.

`pre-command-hook'
     *Note Command Overview::.

`print-diary-entries-hook'
     *Note Diary Customizing: (emacs)Diary Customizing.

`redisplay-end-trigger-functions'
     *Note Window Hooks::.

`scheme-indent-function'

`suspend-hook'
     *Note Suspending Emacs::.

`suspend-resume-hook'
     *Note Suspending Emacs::.

`temp-buffer-setup-hook'
     *Note Temporary Displays::.

`temp-buffer-show-function'
     *Note Temporary Displays::.

`temp-buffer-show-hook'
     *Note Temporary Displays::.

`term-setup-hook'
     *Note Terminal-Specific::.

`today-visible-calendar-hook'
     *Note Calendar Customizing: (emacs)Calendar Customizing.

`today-invisible-calendar-hook'
     *Note Calendar Customizing: (emacs)Calendar Customizing.

`window-configuration-change-hook'
     *Note Window Hooks::.

`window-scroll-functions'
     *Note Window Hooks::.

`window-setup-hook'
     *Note Window Systems::.

`window-size-change-functions'
     *Note Window Hooks::.

`write-contents-functions'
     *Note Saving Buffers::.

`write-file-functions'
     *Note Saving Buffers::.

`write-region-annotate-functions'
     *Note Saving Properties::.


File: elisp,  Node: Index,  Prev: Standard Hooks,  Up: Top

Index
*****

[index]
* Menu:

* " in printing:                         Output Functions.    (line   9)
* " in strings:                          Syntax for Strings.  (line   6)
* #$:                                    Docs and Compilation.
                                                              (line  48)
* #' syntax:                             Anonymous Functions. (line  83)
* #@COUNT:                               Docs and Compilation.
                                                              (line  48)
* #COLON read syntax:                    Symbol Type.         (line  59)
* #N# read syntax:                       Circular Objects.    (line   6)
* #N= read syntax:                       Circular Objects.    (line   6)
* $ in display:                          Truncation.          (line   6)
* $ in regexp:                           Regexp Special.      (line 160)
* %:                                     Arithmetic Operations.
                                                              (line 114)
* % in format:                           Formatting Strings.  (line  26)
* & in replacement:                      Replacing Match.     (line  43)
* &optional:                             Argument List.       (line  18)
* &rest:                                 Argument List.       (line  18)
* ' for quoting:                         Quoting.             (line  15)
* ( in regexp:                           Regexp Backslash.    (line  45)
* (...) in lists:                        Cons Cell Type.      (line  25)
* ) in regexp:                           Regexp Backslash.    (line  45)
* *:                                     Arithmetic Operations.
                                                              (line  69)
* * in interactive:                      Using Interactive.   (line  59)
* * in regexp:                           Regexp Special.      (line  16)
* *scratch*:                             Auto Major Mode.     (line  90)
* +:                                     Arithmetic Operations.
                                                              (line  44)
* + in regexp:                           Regexp Special.      (line  48)
* , (with backquote):                    Backquote.           (line  20)
* ,@ (with backquote):                   Backquote.           (line  39)
* -:                                     Arithmetic Operations.
                                                              (line  55)
* . in lists:                            Dotted Pair Notation.
                                                              (line   6)
* . in regexp:                           Regexp Special.      (line  10)
* .emacs:                                Init File.           (line   6)
* /:                                     Arithmetic Operations.
                                                              (line  80)
* /=:                                    Comparison of Numbers.
                                                              (line  57)
* 1+:                                    Arithmetic Operations.
                                                              (line  20)
* 1-:                                    Arithmetic Operations.
                                                              (line  41)
* 1value:                                Test Coverage.       (line  26)
* 2C-mode-map:                           Prefix Keys.         (line  38)
* ; in comment:                          Comments.            (line   6)
* <:                                     Comparison of Numbers.
                                                              (line  61)
* <=:                                    Comparison of Numbers.
                                                              (line  65)
* <ESC>:                                 Functions for Key Lookup.
                                                              (line  84)
* <SPC> in minibuffer:                   Text from Minibuffer.
                                                              (line 164)
* <TAB> in minibuffer:                   Text from Minibuffer.
                                                              (line 167)
* =:                                     Comparison of Numbers.
                                                              (line  47)
* >:                                     Comparison of Numbers.
                                                              (line  70)
* >=:                                    Comparison of Numbers.
                                                              (line  74)
* ? in character constant:               Basic Char Syntax.   (line   6)
* ? in minibuffer:                       Text from Minibuffer.
                                                              (line 170)
* ? in regexp:                           Regexp Special.      (line  54)
* @ in interactive:                      Using Interactive.   (line  62)
* [ in regexp:                           Regexp Special.      (line  72)
* [...] (Edebug):                        Specification List.  (line 127)
* \ in character constant:               General Escape Syntax.
                                                              (line  22)
* \ in display:                          Truncation.          (line   6)
* \ in printing:                         Output Functions.    (line   9)
* \ in regexp:                           Regexp Special.      (line 171)
* \ in replacement:                      Replacing Match.     (line  52)
* \ in strings:                          Syntax for Strings.  (line   6)
* \ in symbols:                          Symbol Type.         (line  23)
* \' in regexp:                          Regexp Backslash.    (line 148)
* \< in regexp:                          Regexp Backslash.    (line 169)
* \= in regexp:                          Regexp Backslash.    (line 152)
* \> in regexp:                          Regexp Backslash.    (line 174)
* \_< in regexp:                         Regexp Backslash.    (line 179)
* \_> in regexp:                         Regexp Backslash.    (line 185)
* \` in regexp:                          Regexp Backslash.    (line 144)
* \a:                                    Basic Char Syntax.   (line  27)
* \b:                                    Basic Char Syntax.   (line  27)
* \B in regexp:                          Regexp Backslash.    (line 165)
* \b in regexp:                          Regexp Backslash.    (line 156)
* \e:                                    Basic Char Syntax.   (line  27)
* \f:                                    Basic Char Syntax.   (line  27)
* \n:                                    Basic Char Syntax.   (line  27)
* \n in print:                           Output Variables.    (line  18)
* \N in replacement:                     Replacing Match.     (line  46)
* \r:                                    Basic Char Syntax.   (line  27)
* \s:                                    Basic Char Syntax.   (line  27)
* \s in regexp:                          Regexp Backslash.    (line 119)
* \S in regexp:                          Regexp Backslash.    (line 127)
* \t:                                    Basic Char Syntax.   (line  27)
* \v:                                    Basic Char Syntax.   (line  27)
* \W in regexp:                          Regexp Backslash.    (line 116)
* \w in regexp:                          Regexp Backslash.    (line 112)
* ] in regexp:                           Regexp Special.      (line  72)
* ^ in regexp:                           Regexp Special.      (line 133)
* `:                                     Backquote.           (line   6)
* ` (list substitution):                 Backquote.           (line   6)
* abbrev:                                Abbrevs.             (line   6)
* abbrev tables in modes:                Major Mode Conventions.
                                                              (line 118)
* abbrev-all-caps:                       Abbrev Expansion.    (line  48)
* abbrev-expansion:                      Abbrev Expansion.    (line  20)
* abbrev-file-name:                      Abbrev Files.        (line  16)
* abbrev-mode:                           Abbrev Mode.         (line  10)
* abbrev-prefix-mark:                    Abbrev Expansion.    (line  37)
* abbrev-start-location:                 Abbrev Expansion.    (line  54)
* abbrev-start-location-buffer:          Abbrev Expansion.    (line  62)
* abbrev-symbol:                         Abbrev Expansion.    (line  12)
* abbrev-table-name-list:                Abbrev Tables.       (line  38)
* abbreviate-file-name:                  Directory Names.     (line  98)
* abbrevs-changed:                       Abbrev Files.        (line  33)
* abnormal hook:                         Hooks.               (line  34)
* abort-recursive-edit:                  Recursive Editing.   (line  93)
* aborting:                              Recursive Editing.   (line  32)
* abs:                                   Comparison of Numbers.
                                                              (line  99)
* absolute file name:                    Relative File Names. (line   6)
* accept input from processes:           Accepting Output.    (line   6)
* accept-change-group:                   Atomic Changes.      (line  49)
* accept-process-output:                 Accepting Output.    (line  14)
* access-file:                           Testing Accessibility.
                                                              (line  81)
* accessibility of a file:               Testing Accessibility.
                                                              (line   6)
* accessible portion (of a buffer):      Narrowing.           (line   6)
* accessible-keymaps:                    Scanning Keymaps.    (line  10)
* acos:                                  Math Functions.      (line  21)
* action (button property):              Button Properties.   (line  12)
* action, customization keyword:         Type Keywords.       (line  61)
* activate-change-group:                 Atomic Changes.      (line  40)
* activate-mark-hook:                    The Mark.            (line 162)
* activating advice:                     Activation of Advice.
                                                              (line   6)
* active display table:                  Active Display Table.
                                                              (line   6)
* active keymap:                         Active Keymaps.      (line   6)
* active-minibuffer-window:              Minibuffer Windows.  (line  10)
* ad-activate:                           Activation of Advice.
                                                              (line  35)
* ad-activate-all:                       Activation of Advice.
                                                              (line  49)
* ad-activate-regexp:                    Activation of Advice.
                                                              (line  60)
* ad-add-advice:                         Computed Advice.     (line  12)
* ad-deactivate:                         Activation of Advice.
                                                              (line  42)
* ad-deactivate-all:                     Activation of Advice.
                                                              (line  52)
* ad-deactivate-regexp:                  Activation of Advice.
                                                              (line  65)
* ad-default-compilation-action:         Activation of Advice.
                                                              (line  88)
* ad-define-subr-args:                   Advising Primitives. (line  22)
* ad-disable-advice:                     Enabling Advice.     (line  21)
* ad-disable-regexp:                     Enabling Advice.     (line  34)
* ad-do-it:                              Around-Advice.       (line  22)
* ad-enable-advice:                      Enabling Advice.     (line  25)
* ad-enable-regexp:                      Enabling Advice.     (line  38)
* ad-get-arg:                            Argument Access in Advice.
                                                              (line  32)
* ad-get-args:                           Argument Access in Advice.
                                                              (line  35)
* ad-return-value:                       Defining Advice.     (line  33)
* ad-set-arg:                            Argument Access in Advice.
                                                              (line  39)
* ad-set-args:                           Argument Access in Advice.
                                                              (line  42)
* ad-start-advice:                       Activation of Advice.
                                                              (line  80)
* ad-stop-advice:                        Activation of Advice.
                                                              (line  84)
* ad-unadvise:                           Defining Advice.     (line 131)
* ad-unadvise-all:                       Defining Advice.     (line 134)
* ad-update:                             Activation of Advice.
                                                              (line  45)
* ad-update-all:                         Activation of Advice.
                                                              (line  55)
* ad-update-regexp:                      Activation of Advice.
                                                              (line  71)
* adaptive-fill-first-line-regexp:       Adaptive Fill.       (line  66)
* adaptive-fill-function:                Adaptive Fill.       (line  79)
* adaptive-fill-mode:                    Adaptive Fill.       (line  13)
* adaptive-fill-regexp:                  Adaptive Fill.       (line  57)
* add-hook:                              Hooks.               (line  88)
* add-name-to-file:                      Changing Files.      (line  28)
* add-text-properties:                   Changing Properties. (line  25)
* add-to-history:                        Minibuffer History.  (line  59)
* add-to-invisibility-spec:              Invisible Text.      (line  63)
* add-to-list:                           List Variables.      (line  23)
* add-to-ordered-list:                   List Variables.      (line  58)
* address field of register:             Cons Cell Type.      (line   6)
* adjust-window-trailing-edge:           Resizing Windows.    (line  67)
* adjusting point:                       Adjusting Point.     (line   6)
* advice, activating:                    Activation of Advice.
                                                              (line   6)
* advice, defining:                      Defining Advice.     (line   6)
* advice, enabling and disabling:        Enabling Advice.     (line   6)
* advice, preactivating:                 Preactivation.       (line   6)
* advising functions:                    Advising Functions.  (line   6)
* advising primitives:                   Advising Primitives. (line   6)
* after-advice:                          Defining Advice.     (line  25)
* after-change-functions:                Change Hooks.        (line  24)
* after-change-major-mode-hook:          Mode Hooks.          (line  47)
* after-find-file:                       Subroutines of Visiting.
                                                              (line  32)
* after-init-hook:                       Init File.           (line  60)
* after-insert-file-functions:           Saving Properties.   (line  36)
* after-load-alist:                      Hooks for Loading.   (line  48)
* after-make-frame-functions:            Creating Frames.     (line  36)
* after-revert-hook:                     Reverting.           (line  84)
* after-save-hook:                       Saving Buffers.      (line 133)
* after-string (overlay property):       Overlay Properties.  (line 173)
* alist:                                 Association Lists.   (line   6)
* alist vs. plist:                       Plists and Alists.   (line   6)
* all-completions:                       Basic Completion.    (line 111)
* alt characters:                        Other Char Bits.     (line  16)
* and:                                   Combining Conditions.
                                                              (line  18)
* anonymous function:                    Anonymous Functions. (line   6)
* apostrophe for quoting:                Quoting.             (line  15)
* append:                                Building Lists.      (line  62)
* append-to-file:                        Writing to Files.    (line  12)
* apply:                                 Calling Functions.   (line  53)
* apply, and debugging:                  Internals of Debugger.
                                                              (line  62)
* apropos:                               Help Functions.      (line  12)
* apropos-mode-map:                      Standard Keymaps.    (line  18)
* aref:                                  Array Functions.     (line  21)
* args, customization keyword:           Composite Types.     (line 207)
* argument binding:                      Argument List.       (line   6)
* argument lists, features:              Argument List.       (line   6)
* arguments for shell commands:          Shell Arguments.     (line   6)
* arguments, interactive entry:          Using Interactive.   (line   6)
* arguments, reading:                    Minibuffers.         (line   6)
* arith-error example:                   Handling Errors.     (line 126)
* arith-error in division:               Arithmetic Operations.
                                                              (line  93)
* arithmetic operations:                 Arithmetic Operations.
                                                              (line   6)
* arithmetic shift:                      Bitwise Operations.  (line  83)
* around-advice:                         Defining Advice.     (line  25)
* array:                                 Arrays.              (line   6)
* array elements:                        Array Functions.     (line  21)
* arrayp:                                Array Functions.     (line  10)
* ASCII character codes:                 Character Type.      (line   6)
* ascii-case-table:                      Case Tables.         (line  93)
* aset:                                  Array Functions.     (line  34)
* ash:                                   Bitwise Operations.  (line  83)
* asin:                                  Math Functions.      (line  16)
* ask-user-about-lock:                   File Locks.          (line  51)
* ask-user-about-supersession-threat:    Modification Time.   (line  77)
* asking the user questions:             Yes-or-No Queries.   (line   6)
* assoc:                                 Association Lists.   (line  60)
* assoc-default:                         Association Lists.   (line 157)
* assoc-string:                          Text Comparison.     (line 122)
* association list:                      Association Lists.   (line   6)
* assq:                                  Association Lists.   (line 100)
* assq-delete-all:                       Association Lists.   (line 213)
* asynchronous subprocess:               Asynchronous Processes.
                                                              (line   6)
* atan:                                  Math Functions.      (line  26)
* atom:                                  List-related Predicates.
                                                              (line  16)
* atomic changes:                        Atomic Changes.      (line   6)
* atoms:                                 Cons Cell Type.      (line  22)
* attributes of text:                    Text Properties.     (line   6)
* Auto Fill mode:                        Auto Filling.        (line   6)
* auto-coding-functions:                 Default Coding Systems.
                                                              (line  89)
* auto-coding-regexp-alist:              Default Coding Systems.
                                                              (line  18)
* auto-fill-chars:                       Auto Filling.        (line  36)
* auto-fill-function:                    Auto Filling.        (line  15)
* auto-hscroll-mode:                     Horizontal Scrolling.
                                                              (line  40)
* auto-mode-alist:                       Auto Major Mode.     (line 115)
* auto-raise-tool-bar-buttons:           Tool Bar.            (line 141)
* auto-resize-tool-bar:                  Tool Bar.            (line 132)
* auto-save-default:                     Auto-Saving.         (line 128)
* auto-save-file-name-p:                 Auto-Saving.         (line  30)
* auto-save-hook:                        Auto-Saving.         (line 125)
* auto-save-interval:                    Auto-Saving.         (line 106)
* auto-save-list-file-name:              Auto-Saving.         (line 179)
* auto-save-list-file-prefix:            Auto-Saving.         (line 196)
* auto-save-mode:                        Auto-Saving.         (line  23)
* auto-save-timeout:                     Auto-Saving.         (line 113)
* auto-save-visited-file-name:           Auto-Saving.         (line  84)
* auto-window-vscroll:                   Vertical Scrolling.  (line  54)
* autoload:                              Autoload.            (line   6)
* autoload cookie:                       Autoload.            (line  93)
* autoload errors:                       Autoload.            (line  79)
* automatic face assignment:             Auto Faces.          (line   6)
* automatically buffer-local:            Intro to Buffer-Local.
                                                              (line  39)
* back-to-indentation:                   Motion by Indent.    (line  10)
* backquote (list substitution):         Backquote.           (line   6)
* backslash in character constant:       General Escape Syntax.
                                                              (line  22)
* backslash in strings:                  Syntax for Strings.  (line   6)
* backslash in symbols:                  Symbol Type.         (line  23)
* backspace:                             Basic Char Syntax.   (line  27)
* backtrace:                             Internals of Debugger.
                                                              (line  21)
* backtrace-debug:                       Internals of Debugger.
                                                              (line  69)
* backtrace-frame:                       Internals of Debugger.
                                                              (line  89)
* backtracking:                          Backtracking.        (line   6)
* backup file:                           Backup Files.        (line   6)
* backup files, rename or copy:          Rename or Copy.      (line   6)
* backup-buffer:                         Making Backups.      (line   7)
* backup-by-copying:                     Rename or Copy.      (line  30)
* backup-by-copying-when-linked:         Rename or Copy.      (line  38)
* backup-by-copying-when-mismatch:       Rename or Copy.      (line  45)
* backup-by-copying-when-privileged-mismatch: Rename or Copy. (line  58)
* backup-directory-alist:                Making Backups.      (line  68)
* backup-enable-predicate:               Making Backups.      (line  44)
* backup-file-name-p:                    Backup Names.        (line  11)
* backup-inhibited:                      Making Backups.      (line  56)
* backups and auto-saving:               Backups and Auto-Saving.
                                                              (line   6)
* backward-button:                       Button Buffer Commands.
                                                              (line  43)
* backward-char:                         Character Motion.    (line  40)
* backward-delete-char-untabify:         Deletion.            (line  70)
* backward-delete-char-untabify-method:  Deletion.            (line  90)
* backward-list:                         List Motion.         (line  20)
* backward-prefix-chars:                 Motion and Syntax.   (line  35)
* backward-sexp:                         List Motion.         (line  52)
* backward-to-indentation:               Motion by Indent.    (line  15)
* backward-word:                         Word Motion.         (line  32)
* balanced parenthesis motion:           List Motion.         (line   6)
* balancing parentheses:                 Blinking.            (line   6)
* barf-if-buffer-read-only:              Read Only Buffers.   (line  58)
* base 64 encoding:                      Base 64.             (line   6)
* base buffer:                           Indirect Buffers.    (line   6)
* base coding system:                    Coding System Basics.
                                                              (line  44)
* base for reading an integer:           Integer Basics.      (line  22)
* base64-decode-region:                  Base 64.             (line  35)
* base64-decode-string:                  Base 64.             (line  43)
* base64-encode-region:                  Base 64.             (line  12)
* base64-encode-string:                  Base 64.             (line  24)
* basic code (of input character):       Keyboard Events.     (line  12)
* batch mode:                            Batch Mode.          (line   6)
* batch-byte-compile:                    Compilation Functions.
                                                              (line 132)
* baud-rate:                             Terminal Output.     (line  11)
* beep:                                  Beeping.             (line  18)
* before point, insertion:               Insertion.           (line   6)
* before-advice:                         Defining Advice.     (line  25)
* before-change-functions:               Change Hooks.        (line  17)
* before-init-hook:                      Init File.           (line  54)
* before-make-frame-hook:                Creating Frames.     (line  32)
* before-revert-hook:                    Reverting.           (line  80)
* before-save-hook:                      Saving Buffers.      (line 126)
* before-string (overlay property):      Overlay Properties.  (line 168)
* beginning of line:                     Text Lines.          (line  80)
* beginning of line in regexp:           Regexp Special.      (line 147)
* beginning-of-buffer:                   Buffer End Motion.   (line  19)
* beginning-of-defun:                    List Motion.         (line  56)
* beginning-of-defun-function:           List Motion.         (line  81)
* beginning-of-line:                     Text Lines.          (line  41)
* bell:                                  Beeping.             (line   6)
* bell character:                        Basic Char Syntax.   (line  27)
* benchmark.el:                          Compilation Tips.    (line  12)
* benchmarking:                          Compilation Tips.    (line  12)
* big endian:                            Bindat Spec.         (line  13)
* binary files and text files:           MS-DOS File Types.   (line   6)
* bindat-get-field:                      Bindat Functions.    (line  20)
* bindat-ip-to-string:                   Bindat Functions.    (line  54)
* bindat-length:                         Bindat Functions.    (line  39)
* bindat-pack:                           Bindat Functions.    (line  43)
* bindat-unpack:                         Bindat Functions.    (line  11)
* binding arguments:                     Argument List.       (line   6)
* binding local variables:               Local Variables.     (line   6)
* binding of a key:                      Keymap Basics.       (line   6)
* bitmap-spec-p:                         Face Attributes.     (line 182)
* bitmaps, fringe:                       Fringe Bitmaps.      (line   6)
* bitwise arithmetic:                    Bitwise Operations.  (line   6)
* blink-cursor-alist:                    Cursor Parameters.   (line  37)
* blink-matching-delay:                  Blinking.            (line  23)
* blink-matching-open:                   Blinking.            (line  29)
* blink-matching-paren:                  Blinking.            (line  16)
* blink-matching-paren-distance:         Blinking.            (line  19)
* blink-paren-function:                  Blinking.            (line  10)
* blinking parentheses:                  Blinking.            (line   6)
* bobp:                                  Near Point.          (line  62)
* body of function:                      Lambda Components.   (line  37)
* bolp:                                  Near Point.          (line  73)
* bool-vector-p:                         Bool-Vectors.        (line  22)
* Bool-vectors:                          Bool-Vectors.        (line   6)
* boolean:                               nil and t.           (line   6)
* booleanp:                              nil and t.           (line  39)
* boundp:                                Void Variables.      (line  71)
* box diagrams, for lists:               Box Diagrams.        (line   6)
* break:                                 Debugger.            (line   6)
* breakpoints (Edebug):                  Breakpoints.         (line   6)
* bucket (in obarray):                   Creating Symbols.    (line  11)
* buffer:                                Buffers.             (line   6)
* buffer contents:                       Text.                (line  23)
* buffer file name:                      Buffer File Name.    (line   6)
* buffer input stream:                   Input Streams.       (line  12)
* buffer internals:                      Buffer Internals.    (line   6)
* buffer list:                           The Buffer List.     (line   6)
* buffer modification:                   Buffer Modification. (line   6)
* buffer names:                          Buffer Names.        (line   6)
* buffer output stream:                  Output Streams.      (line  11)
* buffer text notation:                  Buffer Text Notation.
                                                              (line   6)
* buffer, read-only:                     Read Only Buffers.   (line   6)
* buffer-access-fontified-property:      Lazy Properties.     (line  30)
* buffer-access-fontify-functions:       Lazy Properties.     (line  15)
* buffer-auto-save-file-format:          Format Conversion.   (line 141)
* buffer-auto-save-file-name:            Auto-Saving.         (line  15)
* buffer-backed-up:                      Making Backups.      (line  20)
* buffer-base-buffer:                    Indirect Buffers.    (line  60)
* buffer-chars-modified-tick:            Buffer Modification. (line  58)
* buffer-disable-undo:                   Maintaining Undo.    (line  27)
* buffer-display-count:                  Buffers and Windows. (line  31)
* buffer-display-table:                  Active Display Table.
                                                              (line  22)
* buffer-display-time:                   Buffers and Windows. (line  75)
* buffer-enable-undo:                    Maintaining Undo.    (line  17)
* buffer-end:                            Point.               (line  51)
* buffer-file-coding-system:             Encoding and I/O.    (line  21)
* buffer-file-format:                    Format Conversion.   (line  99)
* buffer-file-name:                      Buffer File Name.    (line  14)
* buffer-file-number:                    Buffer File Name.    (line  44)
* buffer-file-truename:                  Buffer File Name.    (line  38)
* buffer-file-type:                      MS-DOS File Types.   (line  17)
* buffer-has-markers-at:                 Information from Markers.
                                                              (line  32)
* buffer-invisibility-spec:              Invisible Text.      (line  35)
* buffer-list:                           The Buffer List.     (line  28)
* buffer-live-p:                         Killing Buffers.     (line  95)
* buffer-local variables:                Buffer-Local Variables.
                                                              (line   6)
* buffer-local variables in modes:       Major Mode Conventions.
                                                              (line 144)
* buffer-local variables, general-purpose: Standard Buffer-Local Variables.
                                                              (line   6)
* buffer-local-value:                    Creating Buffer-Local.
                                                              (line  86)
* buffer-local-variables:                Creating Buffer-Local.
                                                              (line  92)
* Buffer-menu-mode-map:                  Standard Keymaps.    (line  21)
* buffer-modified-p:                     Buffer Modification. (line  23)
* buffer-modified-tick:                  Buffer Modification. (line  52)
* buffer-name:                           Buffer Names.        (line  19)
* buffer-name-history:                   Minibuffer History.  (line 103)
* buffer-offer-save:                     Killing Buffers.     (line  80)
* buffer-read-only:                      Read Only Buffers.   (line  28)
* buffer-save-without-query:             Killing Buffers.     (line  89)
* buffer-saved-size:                     Auto-Saving.         (line 166)
* buffer-size:                           Point.               (line  55)
* buffer-string:                         Buffer Contents.     (line  85)
* buffer-substring:                      Buffer Contents.     (line  10)
* buffer-substring-filters:              Buffer Contents.     (line  71)
* buffer-substring-no-properties:        Buffer Contents.     (line  44)
* buffer-undo-list:                      Undo.                (line  16)
* bufferp:                               Buffer Basics.       (line  41)
* buffers without undo information:      Buffer Names.        (line  12)
* buffers, controlled in windows:        Buffers and Windows. (line   6)
* buffers, creating:                     Creating Buffers.    (line   6)
* buffers, killing:                      Killing Buffers.     (line   6)
* bugs:                                  Caveats.             (line  27)
* bugs in this manual:                   Caveats.             (line   6)
* building Emacs:                        Building Emacs.      (line   6)
* building lists:                        Building Lists.      (line   6)
* built-in function:                     What Is a Function.  (line  22)
* bury-buffer:                           The Buffer List.     (line  93)
* butlast:                               List Elements.       (line 142)
* button (button property):              Button Properties.   (line  51)
* button buffer commands:                Button Buffer Commands.
                                                              (line   6)
* button properties:                     Button Properties.   (line   6)
* button types:                          Button Types.        (line   6)
* button-activate:                       Manipulating Buttons.
                                                              (line  29)
* button-at:                             Manipulating Buttons.
                                                              (line  45)
* button-down event:                     Button-Down Events.  (line   6)
* button-end:                            Manipulating Buttons.
                                                              (line  20)
* button-face, customization keyword:    Type Keywords.       (line  64)
* button-get:                            Manipulating Buttons.
                                                              (line  23)
* button-has-type-p:                     Manipulating Buttons.
                                                              (line  41)
* button-label:                          Manipulating Buttons.
                                                              (line  35)
* button-prefix, customization keyword:  Type Keywords.       (line  69)
* button-put:                            Manipulating Buttons.
                                                              (line  26)
* button-start:                          Manipulating Buttons.
                                                              (line  17)
* button-suffix, customization keyword:  Type Keywords.       (line  69)
* button-type:                           Manipulating Buttons.
                                                              (line  38)
* button-type-get:                       Manipulating Buttons.
                                                              (line  51)
* button-type-put:                       Manipulating Buttons.
                                                              (line  48)
* button-type-subtype-p:                 Manipulating Buttons.
                                                              (line  54)
* buttons in buffers:                    Buttons.             (line   6)
* byte compilation:                      Byte Compilation.    (line   6)
* byte compiler warnings, how to avoid:  Warning Tips.        (line   6)
* byte packing and unpacking:            Byte Packing.        (line   6)
* byte-boolean-vars <1>:                 Writing Emacs Primitives.
                                                              (line 180)
* byte-boolean-vars:                     Variables with Restricted Values.
                                                              (line  23)
* byte-code <1>:                         Compilation Functions.
                                                              (line 145)
* byte-code:                             Byte Compilation.    (line   6)
* byte-code function:                    Byte-Code Objects.   (line   6)
* byte-code interpreter:                 Compilation Functions.
                                                              (line 145)
* byte-code-function-p:                  What Is a Function.  (line  97)
* byte-compile:                          Compilation Functions.
                                                              (line  34)
* byte-compile-dynamic:                  Dynamic Loading.     (line  46)
* byte-compile-dynamic-docstrings:       Docs and Compilation.
                                                              (line  45)
* byte-compile-file:                     Compilation Functions.
                                                              (line  82)
* byte-compiling macros:                 Compiling Macros.    (line   6)
* byte-compiling require:                Named Features.      (line  46)
* byte-recompile-directory:              Compilation Functions.
                                                              (line 112)
* byte-to-position:                      Text Representations.
                                                              (line  66)
* bytes:                                 Strings and Characters.
                                                              (line   6)
* bytes and characters:                  Chars and Bytes.     (line   6)
* C-c:                                   Prefix Keys.         (line  21)
* C-g:                                   Quitting.            (line   6)
* C-h:                                   Prefix Keys.         (line  19)
* C-M-x:                                 Instrumenting.       (line  10)
* c-mode-map:                            Standard Keymaps.    (line  24)
* c-mode-syntax-table:                   Standard Syntax Tables.
                                                              (line  17)
* C-x:                                   Prefix Keys.         (line  27)
* C-x 4:                                 Prefix Keys.         (line  34)
* C-x 5:                                 Prefix Keys.         (line  36)
* C-x 6:                                 Prefix Keys.         (line  38)
* C-x <RET>:                             Prefix Keys.         (line  31)
* C-x v:                                 Prefix Keys.         (line  40)
* C-x X =:                               Coverage Testing.    (line  24)
* caar:                                  List Elements.       (line 129)
* cache-long-line-scans:                 Truncation.          (line  51)
* cadr:                                  List Elements.       (line 132)
* call stack:                            Internals of Debugger.
                                                              (line  21)
* call-interactively:                    Interactive Call.    (line  35)
* call-process:                          Synchronous Processes.
                                                              (line  31)
* call-process-region:                   Synchronous Processes.
                                                              (line 168)
* call-process-shell-command:            Synchronous Processes.
                                                              (line 219)
* called-interactively-p:                Distinguish Interactive.
                                                              (line  28)
* calling a function:                    Calling Functions.   (line   6)
* cancel-change-group:                   Atomic Changes.      (line  53)
* cancel-debug-on-entry:                 Function Debugging.  (line  63)
* cancel-timer:                          Timers.              (line 129)
* capitalization:                        Case Conversion.     (line  55)
* capitalize:                            Case Conversion.     (line  55)
* capitalize-region:                     Case Changes.        (line  13)
* capitalize-word:                       Case Changes.        (line  50)
* car:                                   List Elements.       (line   7)
* car-safe:                              List Elements.       (line  35)
* case conversion in buffers:            Case Changes.        (line   6)
* case conversion in Lisp:               Case Conversion.     (line   6)
* case in replacements:                  Replacing Match.     (line   9)
* case-fold-search:                      Searching and Case.  (line  35)
* case-replace:                          Searching and Case.  (line  25)
* case-table-p:                          Case Tables.         (line  62)
* catch:                                 Catch and Throw.     (line  61)
* categories of characters:              Categories.          (line   6)
* category (overlay property):           Overlay Properties.  (line  62)
* category (text property):              Special Properties.  (line  15)
* category table:                        Categories.          (line  12)
* category-docstring:                    Categories.          (line  37)
* category-set-mnemonics:                Categories.          (line  96)
* category-table:                        Categories.          (line  51)
* category-table-p:                      Categories.          (line  54)
* cdar:                                  List Elements.       (line 135)
* cddr:                                  List Elements.       (line 138)
* cdr:                                   List Elements.       (line  21)
* cdr-safe:                              List Elements.       (line  48)
* ceiling:                               Numeric Conversions. (line  53)
* centering point:                       Textual Scrolling.   (line 157)
* change hooks:                          Change Hooks.        (line   6)
* change hooks for a character:          Special Properties.  (line 197)
* change-major-mode-hook:                Creating Buffer-Local.
                                                              (line 161)
* changing key bindings:                 Changing Key Bindings.
                                                              (line   6)
* changing to another buffer:            Current Buffer.      (line   6)
* changing window size:                  Resizing Windows.    (line   6)
* char-after:                            Near Point.          (line  14)
* char-before:                           Near Point.          (line  27)
* char-category-set:                     Categories.          (line  86)
* char-charset:                          Character Sets.      (line  35)
* char-displayable-p:                    Fontsets.            (line 109)
* char-equal:                            Text Comparison.     (line   7)
* char-or-string-p:                      Predicates for Strings.
                                                              (line  17)
* char-property-alias-alist:             Examining Properties.
                                                              (line  51)
* char-syntax:                           Syntax Table Functions.
                                                              (line  66)
* char-table length:                     Sequence Functions.  (line  16)
* char-table-extra-slot:                 Char-Tables.         (line  65)
* char-table-p:                          Char-Tables.         (line  44)
* char-table-parent:                     Char-Tables.         (line  58)
* char-table-range:                      Char-Tables.         (line  76)
* char-table-subtype:                    Char-Tables.         (line  48)
* char-tables:                           Char-Tables.         (line   6)
* char-to-string:                        String Conversion.   (line  20)
* char-valid-p:                          Character Codes.     (line  17)
* char-width:                            Width.               (line  11)
* character alternative (in regexp):     Regexp Special.      (line  72)
* character arrays:                      Strings and Characters.
                                                              (line   6)
* character as bytes:                    Splitting Characters.
                                                              (line   6)
* character case:                        Case Conversion.     (line   6)
* character categories:                  Categories.          (line   6)
* character classes in regexp:           Char Classes.        (line   6)
* character code conversion:             Coding System Basics.
                                                              (line   6)
* character codes:                       Character Codes.     (line   6)
* character insertion:                   Commands for Insertion.
                                                              (line  17)
* character printing:                    Describing Characters.
                                                              (line  29)
* character sets:                        Character Sets.      (line   6)
* character to string:                   String Conversion.   (line  20)
* character translation tables:          Translation of Characters.
                                                              (line   6)
* characters:                            Strings and Characters.
                                                              (line   6)
* characters for interactive codes:      Interactive Codes.   (line   6)
* characters, multi-byte:                Non-ASCII Characters.
                                                              (line   6)
* character quote:                       Syntax Class Table.  (line  92)
* charset-after:                         Scanning Charsets.   (line  12)
* charset-bytes:                         Chars and Bytes.     (line  22)
* charset-dimension:                     Chars and Bytes.     (line  18)
* charset-list:                          Character Sets.      (line  28)
* charset-plist:                         Character Sets.      (line  40)
* charsetp:                              Character Sets.      (line  24)
* check-coding-system:                   Lisp and Coding Systems.
                                                              (line  19)
* checkdoc-minor-mode:                   Documentation Tips.  (line   6)
* child process:                         Processes.           (line   6)
* circular list:                         Cons Cells.          (line  33)
* circular structure, read syntax:       Circular Objects.    (line   6)
* cl:                                    Lisp History.        (line  28)
* CL note--allocate more storage:        Garbage Collection.  (line  41)
* CL note--case of letters:              Symbol Type.         (line  39)
* CL note--default optional arg:         Argument List.       (line  46)
* CL note--integers vrs eq:              Comparison of Numbers.
                                                              (line  40)
* CL note--interning existing symbol:    Creating Symbols.    (line 111)
* CL note--lack union, intersection:     Sets And Lists.      (line  14)
* CL note--no continuable errors:        Signaling Errors.    (line  87)
* CL note--only throw in Emacs:          Catch and Throw.     (line  55)
* CL note--rplaca vs setcar:             Modifying Lists.     (line  10)
* CL note--set local:                    Setting Variables.   (line  81)
* CL note--special forms compared:       Special Forms.       (line  96)
* CL note--special variables:            Variable Scoping.    (line  24)
* CL note--symbol in obarrays:           Creating Symbols.    (line  65)
* class of advice:                       Defining Advice.     (line  25)
* cleanup forms:                         Cleanups.            (line  13)
* clear-abbrev-table:                    Abbrev Tables.       (line  13)
* clear-image-cache:                     Image Cache.         (line  34)
* clear-string:                          Modifying Strings.   (line  27)
* clear-this-command-keys:               Command Loop Info.   (line  95)
* clear-visited-file-modtime:            Modification Time.   (line  35)
* click event:                           Click Events.        (line   6)
* clickable buttons in buffers:          Buttons.             (line   6)
* clickable text:                        Clickable Text.      (line   6)
* clipboard support (for MS-Windows):    Window System Selections.
                                                              (line  70)
* clone-indirect-buffer:                 Indirect Buffers.    (line  50)
* close parenthesis character:           Syntax Class Table.  (line  45)
* closures not available:                Extent.              (line  32)
* clrhash:                               Hash Access.         (line  29)
* codes, interactive, description of:    Interactive Codes.   (line   6)
* coding conventions in Emacs Lisp:      Coding Conventions.  (line   6)
* coding standards:                      Tips.                (line   6)
* coding system:                         Coding Systems.      (line   6)
* coding-system-change-eol-conversion:   Lisp and Coding Systems.
                                                              (line  46)
* coding-system-change-text-conversion:  Lisp and Coding Systems.
                                                              (line  57)
* coding-system-eol-type:                Lisp and Coding Systems.
                                                              (line  24)
* coding-system-for-read:                Specifying Coding Systems.
                                                              (line  10)
* coding-system-for-write:               Specifying Coding Systems.
                                                              (line  36)
* coding-system-get:                     Coding System Basics.
                                                              (line  65)
* coding-system-list:                    Lisp and Coding Systems.
                                                              (line   9)
* coding-system-p:                       Lisp and Coding Systems.
                                                              (line  15)
* color names:                           Color Names.         (line   6)
* color-defined-p:                       Color Names.         (line  23)
* color-gray-p:                          Color Names.         (line  59)
* color-supported-p:                     Color Names.         (line  47)
* color-values:                          Color Names.         (line  65)
* colors on text-only terminals:         Text Terminal Colors.
                                                              (line   6)
* columns:                               Columns.             (line   6)
* combine-after-change-calls:            Change Hooks.        (line  40)
* command:                               What Is a Function.  (line  54)
* command descriptions:                  A Sample Function Description.
                                                              (line   6)
* command history:                       Command History.     (line   6)
* command in keymap:                     Key Lookup.          (line  42)
* command loop:                          Command Loop.        (line   6)
* command loop, recursive:               Recursive Editing.   (line   6)
* command-debug-status:                  Internals of Debugger.
                                                              (line  78)
* command-error-function:                Processing of Errors.
                                                              (line  23)
* command-execute:                       Interactive Call.    (line  57)
* command-history:                       Command History.     (line  15)
* command-history-map:                   Standard Keymaps.    (line  27)
* command-line:                          Command-Line Arguments.
                                                              (line  20)
* command-line arguments:                Command-Line Arguments.
                                                              (line   6)
* command-line options:                  Command-Line Arguments.
                                                              (line  33)
* command-line-args:                     Command-Line Arguments.
                                                              (line  62)
* command-line-functions:                Command-Line Arguments.
                                                              (line  66)
* command-line-processed:                Command-Line Arguments.
                                                              (line  25)
* command-remapping:                     Remapping Commands.  (line  40)
* command-switch-alist:                  Command-Line Arguments.
                                                              (line  33)
* commandp:                              Interactive Call.    (line  13)
* commandp example:                      High-Level Completion.
                                                              (line  88)
* commands, defining:                    Defining Commands.   (line   6)
* comment syntax:                        Syntax Class Table.  (line 119)
* comments:                              Comments.            (line   6)
* comments, Lisp convention for:         Comment Tips.        (line   6)
* comment ender:                         Syntax Class Table.  (line 119)
* comment starter:                       Syntax Class Table.  (line 118)
* Common Lisp:                           Lisp History.        (line  11)
* compare-buffer-substrings:             Comparing Text.      (line  11)
* compare-strings:                       Text Comparison.     (line 102)
* compare-window-configurations:         Window Configurations.
                                                              (line  86)
* comparing buffer text:                 Comparing Text.      (line   6)
* comparing file modification time:      Modification Time.   (line   6)
* comparing numbers:                     Comparison of Numbers.
                                                              (line   6)
* compilation (Emacs Lisp):              Byte Compilation.    (line   6)
* compilation functions:                 Compilation Functions.
                                                              (line   6)
* compile-defun:                         Compilation Functions.
                                                              (line  72)
* compile-time constant:                 Eval During Compile. (line  42)
* compiled function:                     Byte-Code Objects.   (line   6)
* compiler errors:                       Compiler Errors.     (line   6)
* complete key:                          Keymap Basics.       (line   6)
* completing-read:                       Minibuffer Completion.
                                                              (line  11)
* completion:                            Completion.          (line   6)
* completion, file name:                 File Name Completion.
                                                              (line   6)
* completion-auto-help:                  Completion Commands. (line  87)
* completion-ignore-case:                Basic Completion.    (line 157)
* completion-ignored-extensions:         File Name Completion.
                                                              (line  62)
* completion-regexp-list:                Basic Completion.    (line 161)
* complex arguments:                     Minibuffers.         (line   6)
* complex command:                       Command History.     (line   6)
* Composite Types (customization):       Composite Types.     (line   6)
* composition (text property):           Special Properties.  (line 267)
* composition property, and point display: Adjusting Point.   (line   6)
* compute-motion:                        Screen Lines.        (line  85)
* concat:                                Creating Strings.    (line  98)
* concatenating lists:                   Rearrangement.       (line  16)
* concatenating strings:                 Creating Strings.    (line  98)
* cond:                                  Conditionals.        (line  52)
* condition name:                        Error Symbols.       (line   6)
* condition-case:                        Handling Errors.     (line  75)
* conditional evaluation:                Conditionals.        (line   6)
* conditional selection of windows:      Selecting Windows.   (line  93)
* cons:                                  Building Lists.      (line  12)
* cons cells:                            Building Lists.      (line   6)
* cons-cells-consed:                     Memory Usage.        (line  14)
* consing:                               Building Lists.      (line  25)
* consp:                                 List-related Predicates.
                                                              (line  12)
* constant variables:                    Constant Variables.  (line   6)
* constrain-to-field:                    Fields.              (line  71)
* continuation lines:                    Truncation.          (line   6)
* continue-process:                      Signals to Processes.
                                                              (line  76)
* control character key constants:       Changing Key Bindings.
                                                              (line  20)
* control character printing:            Describing Characters.
                                                              (line  29)
* control characters:                    Ctl-Char Syntax.     (line   6)
* control characters in display:         Usual Display.       (line  58)
* control characters, reading:           Quoted Character Input.
                                                              (line  12)
* control structures:                    Control Structures.  (line   6)
* Control-X-prefix:                      Prefix Keys.         (line  27)
* controller part, model/view/controller: Abstract Display Example.
                                                              (line  61)
* conventions for writing major modes:   Major Mode Conventions.
                                                              (line   6)
* conventions for writing minor modes:   Minor Mode Conventions.
                                                              (line   6)
* conversion of strings:                 String Conversion.   (line   6)
* convert-standard-filename:             Standard File Names. (line  21)
* converting numbers:                    Numeric Conversions. (line   6)
* coordinates-in-window-p:               Coordinates and Windows.
                                                              (line  17)
* copy-abbrev-table:                     Abbrev Tables.       (line  17)
* copy-alist:                            Association Lists.   (line 174)
* copy-category-table:                   Categories.          (line  61)
* copy-face:                             Face Functions.      (line  17)
* copy-file:                             Changing Files.      (line  82)
* copy-hash-table:                       Other Hash.          (line  12)
* copy-keymap:                           Creating Keymaps.    (line  40)
* copy-marker:                           Creating Markers.    (line  53)
* copy-region-as-kill:                   Kill Functions.      (line  39)
* copy-sequence:                         Sequence Functions.  (line  62)
* copy-syntax-table:                     Syntax Table Functions.
                                                              (line  21)
* copy-tree:                             Building Lists.      (line 171)
* copying alists:                        Association Lists.   (line 174)
* copying files:                         Changing Files.      (line   6)
* copying lists:                         Building Lists.      (line  62)
* copying sequences:                     Sequence Functions.  (line  62)
* copying strings:                       Creating Strings.    (line  98)
* copying vectors:                       Vector Functions.    (line  33)
* cos:                                   Math Functions.      (line  11)
* count-lines:                           Text Lines.          (line  98)
* count-loop:                            A Sample Function Description.
                                                              (line  67)
* count-screen-lines:                    Screen Lines.        (line  46)
* counting columns:                      Columns.             (line   6)
* coverage testing:                      Test Coverage.       (line   6)
* coverage testing (Edebug):             Coverage Testing.    (line   6)
* create-file-buffer:                    Subroutines of Visiting.
                                                              (line  11)
* create-fontset-from-fontset-spec:      Fontsets.            (line  15)
* create-glyph:                          Glyphs.              (line  57)
* create-image:                          Defining Images.     (line  11)
* creating and deleting directories:     Create/Delete Dirs.  (line   6)
* creating buffers:                      Creating Buffers.    (line   6)
* creating hash tables:                  Creating Hash.       (line   6)
* creating keymaps:                      Creating Keymaps.    (line   6)
* ctl-arrow:                             Usual Display.       (line  58)
* ctl-x-4-map:                           Prefix Keys.         (line  34)
* ctl-x-5-map:                           Prefix Keys.         (line  36)
* ctl-x-map:                             Prefix Keys.         (line  27)
* current binding:                       Local Variables.     (line  39)
* current buffer:                        Current Buffer.      (line   6)
* current buffer mark:                   The Mark.            (line  51)
* current buffer point and mark (Edebug): Edebug Display Update.
                                                              (line  22)
* current buffer position:               Point.               (line  32)
* current command:                       Command Loop Info.   (line  34)
* current stack frame:                   Using Debugger.      (line  24)
* current-active-maps:                   Active Keymaps.      (line  71)
* current-buffer:                        Current Buffer.      (line  91)
* current-case-table:                    Case Tables.         (line  72)
* current-column:                        Columns.             (line  23)
* current-fill-column:                   Margins.             (line  56)
* current-frame-configuration:           Frame Configurations.
                                                              (line  11)
* current-global-map:                    Controlling Active Maps.
                                                              (line  17)
* current-idle-time:                     Idle Timers.         (line  45)
* current-indentation:                   Primitive Indent.    (line  11)
* current-input-method:                  Input Methods.       (line  18)
* current-input-mode:                    Input Modes.         (line  35)
* current-justification:                 Filling.             (line 118)
* current-kill:                          Low-Level Kill Ring. (line  12)
* current-left-margin:                   Margins.             (line  49)
* current-local-map:                     Controlling Active Maps.
                                                              (line  25)
* current-message:                       Displaying Messages. (line  88)
* current-minor-mode-maps:               Controlling Active Maps.
                                                              (line  41)
* current-prefix-arg:                    Prefix Command Arguments.
                                                              (line  87)
* current-time:                          Time of Day.         (line  29)
* current-time-string:                   Time of Day.         (line  10)
* current-time-zone:                     Time of Day.         (line  43)
* current-window-configuration:          Window Configurations.
                                                              (line  20)
* current-word:                          Buffer Contents.     (line  99)
* cursor:                                Window Point.        (line  27)
* cursor (text property):                Special Properties.  (line 175)
* cursor, fringe:                        Fringe Cursors.      (line   6)
* cursor-in-echo-area:                   Echo Area Customization.
                                                              (line   9)
* cursor-in-non-selected-windows:        Cursor Parameters.   (line  50)
* cursor-type:                           Cursor Parameters.   (line  32)
* cust-print:                            Printing in Edebug.  (line   6)
* custom-add-frequent-value:             Variable Definitions.
                                                              (line 162)
* customization definitions:             Customization.       (line   6)
* customization groups, defining:        Group Definitions.   (line   6)
* customization keywords:                Common Keywords.     (line   6)
* customization types:                   Customization Types. (line   6)
* customization variables, how to define: Variable Definitions.
                                                              (line   6)
* customize-package-emacs-version-alist: Common Keywords.     (line 130)
* cut buffer:                            Window System Selections.
                                                              (line  46)
* cyclic ordering of windows:            Cyclic Window Ordering.
                                                              (line   6)
* data type:                             Lisp Data Types.     (line   6)
* data-directory:                        Help Functions.      (line 134)
* datagrams:                             Datagrams.           (line   6)
* date-leap-year-p:                      Time Calculations.   (line  31)
* date-to-time:                          Time Parsing.        (line  10)
* deactivate-mark:                       The Mark.            (line 154)
* deactivate-mark-hook:                  The Mark.            (line 163)
* deactivating advice:                   Activation of Advice.
                                                              (line  42)
* debug:                                 Invoking the Debugger.
                                                              (line  10)
* debug-ignored-errors:                  Error Debugging.     (line  35)
* debug-on-entry:                        Function Debugging.  (line  14)
* debug-on-error:                        Error Debugging.     (line  19)
* debug-on-error use:                    Processing of Errors.
                                                              (line  31)
* debug-on-next-call:                    Internals of Debugger.
                                                              (line  62)
* debug-on-quit:                         Infinite Loops.      (line  22)
* debug-on-signal:                       Error Debugging.     (line  57)
* debugger:                              Internals of Debugger.
                                                              (line  10)
* debugger command list:                 Debugger Commands.   (line   6)
* debugger for Emacs Lisp:               Debugger.            (line   6)
* debugger-mode-map:                     Standard Keymaps.    (line  42)
* debugging byte compilation problems:   Compilation Errors.  (line   6)
* debugging errors:                      Error Debugging.     (line   6)
* debugging invalid Lisp syntax:         Syntax Errors.       (line   6)
* debugging specific functions:          Function Debugging.  (line   6)
* declare:                               Defining Macros.     (line  38)
* decode process output:                 Decoding Output.     (line   6)
* decode-coding-inserted-region:         Explicit Encoding.   (line  71)
* decode-coding-region:                  Explicit Encoding.   (line  52)
* decode-coding-string:                  Explicit Encoding.   (line  61)
* decode-time:                           Time Conversion.     (line  24)
* decoding file formats:                 Format Conversion.   (line   6)
* decoding in coding systems:            Explicit Encoding.   (line   6)
* decrement field of register:           Cons Cell Type.      (line   6)
* dedicated window:                      Choosing Window.     (line 219)
* deep binding:                          Impl of Scope.       (line   6)
* def-edebug-spec:                       Instrumenting Macro Calls.
                                                              (line  38)
* defadvice:                             Defining Advice.     (line  10)
* defalias:                              Defining Functions.  (line  62)
* default argument string:               Interactive Codes.   (line  20)
* default init file:                     Init File.           (line  24)
* default key binding:                   Format of Keymaps.   (line  34)
* default value:                         Default Value.       (line   6)
* default value of char-table:           Char-Tables.         (line  29)
* default-abbrev-mode:                   Abbrev Mode.         (line  19)
* default-boundp:                        Default Value.       (line  28)
* default-buffer-file-type:              MS-DOS File Types.   (line  45)
* default-case-fold-search:              Searching and Case.  (line  40)
* default-ctl-arrow:                     Usual Display.       (line  64)
* default-directory:                     File Name Expansion. (line  69)
* default-enable-multibyte-characters:   Text Representations.
                                                              (line  49)
* default-file-modes:                    Changing Files.      (line 153)
* default-fill-column:                   Margins.             (line  32)
* default-frame-alist:                   Initial Parameters.  (line  48)
* default-fringe-indicator-alist:        Fringe Indicators.   (line 104)
* default-fringes-cursor-alist:          Fringe Cursors.      (line  37)
* default-header-line-format:            Header Lines.        (line  17)
* default-indicate-buffer-boundaries:    Fringe Indicators.   (line  55)
* default-input-method:                  Input Methods.       (line  24)
* default-justification:                 Filling.             (line 112)
* default-line-spacing:                  Line Height.         (line  69)
* default-major-mode:                    Auto Major Mode.     (line  67)
* default-minibuffer-frame:              Minibuffers and Frames.
                                                              (line  24)
* default-mode-line-format:              Mode Line Variables. (line 129)
* default-process-coding-system:         Default Coding Systems.
                                                              (line  80)
* default-text-properties:               Examining Properties.
                                                              (line  64)
* default-truncate-lines:                Truncation.          (line  32)
* default-value:                         Default Value.       (line  22)
* default.el:                            Startup Summary.     (line  41)
* defconst:                              Defining Variables.  (line 104)
* defcustom:                             Variable Definitions.
                                                              (line   9)
* defface:                               Defining Faces.      (line  12)
* defgroup:                              Group Definitions.   (line  23)
* defimage:                              Defining Images.     (line  30)
* define customization group:            Group Definitions.   (line   6)
* define customization options:          Variable Definitions.
                                                              (line   6)
* define hash comparisons:               Defining Hash.       (line   6)
* define-abbrev:                         Defining Abbrevs.    (line  16)
* define-abbrev-table:                   Abbrev Tables.       (line  23)
* define-button-type:                    Button Types.        (line  12)
* define-category:                       Categories.          (line  33)
* define-derived-mode:                   Derived Modes.       (line  11)
* define-fringe-bitmap:                  Customizing Bitmaps. (line   8)
* define-generic-mode:                   Generic Modes.       (line  14)
* define-globalized-minor-mode:          Defining Minor Modes.
                                                              (line 132)
* define-hash-table-test:                Defining Hash.       (line  22)
* define-key:                            Changing Key Bindings.
                                                              (line  46)
* define-key-after:                      Modifying Menus.     (line  12)
* define-logical-name:                   Changing Files.      (line 125)
* define-minor-mode:                     Defining Minor Modes.
                                                              (line  11)
* define-obsolete-function-alias:        Obsolete Functions.  (line  25)
* define-obsolete-variable-alias:        Variable Aliases.    (line  51)
* define-prefix-command:                 Prefix Keys.         (line  85)
* defined-colors:                        Color Names.         (line  39)
* defining a function:                   Defining Functions.  (line   6)
* defining advice:                       Defining Advice.     (line   6)
* defining commands:                     Defining Commands.   (line   6)
* defining Lisp variables in C:          Writing Emacs Primitives.
                                                              (line 180)
* defining menus:                        Defining Menus.      (line   6)
* defining-kbd-macro:                    Keyboard Macros.     (line  45)
* definitions of symbols:                Definitions.         (line   6)
* defmacro:                              Defining Macros.     (line  18)
* defsubr, Lisp symbol for a primitive:  Writing Emacs Primitives.
                                                              (line 162)
* defsubst:                              Inline Functions.    (line   6)
* defun:                                 Defining Functions.  (line  11)
* DEFUN, C macro to define Lisp primitives: Writing Emacs Primitives.
                                                              (line  40)
* defun-prompt-regexp:                   List Motion.         (line  68)
* defvar:                                Defining Variables.  (line  26)
* DEFVAR_INT, DEFVAR_LISP, DEFVAR_BOOL:  Writing Emacs Primitives.
                                                              (line 180)
* defvaralias:                           Variable Aliases.    (line  15)
* delay-mode-hooks:                      Mode Hooks.          (line  38)
* delete:                                Sets And Lists.      (line 123)
* delete-and-extract-region:             Deletion.            (line  35)
* delete-auto-save-file-if-necessary:    Auto-Saving.         (line 145)
* delete-auto-save-files:                Auto-Saving.         (line 154)
* delete-backward-char:                  Deletion.            (line  57)
* delete-blank-lines:                    User-Level Deletion. (line 103)
* delete-char:                           Deletion.            (line  44)
* delete-directory:                      Create/Delete Dirs.  (line  18)
* delete-dups:                           Sets And Lists.      (line 173)
* delete-exited-processes:               Deleting Processes.  (line  22)
* delete-field:                          Fields.              (line  67)
* delete-file:                           Changing Files.      (line 110)
* delete-frame:                          Deleting Frames.     (line  11)
* delete-frame event:                    Misc Events.         (line   8)
* delete-frame-functions:                Deleting Frames.     (line  11)
* delete-horizontal-space:               User-Level Deletion. (line  11)
* delete-indentation:                    User-Level Deletion. (line  39)
* delete-minibuffer-contents:            Minibuffer Contents. (line  38)
* delete-old-versions:                   Numbered Backups.    (line  45)
* delete-other-windows:                  Deleting Windows.    (line  31)
* delete-overlay:                        Managing Overlays.   (line  44)
* delete-process:                        Deleting Processes.  (line  29)
* delete-region:                         Deletion.            (line  29)
* delete-to-left-margin:                 Margins.             (line  71)
* delete-window:                         Deleting Windows.    (line  25)
* delete-windows-on:                     Deleting Windows.    (line  38)
* deleting files:                        Changing Files.      (line   6)
* deleting frames:                       Deleting Frames.     (line   6)
* deleting list elements:                Sets And Lists.      (line  32)
* deleting previous char:                Deletion.            (line  57)
* deleting processes:                    Deleting Processes.  (line   6)
* deleting text vs killing:              Deletion.            (line   6)
* deleting whitespace:                   User-Level Deletion. (line  11)
* deleting windows:                      Deleting Windows.    (line   6)
* delq:                                  Sets And Lists.      (line  32)
* derived mode:                          Derived Modes.       (line   6)
* describe characters and events:        Describing Characters.
                                                              (line   6)
* describe-bindings:                     Scanning Keymaps.    (line 120)
* describe-buffer-case-table:            Case Tables.         (line 114)
* describe-categories:                   Categories.          (line 113)
* describe-current-display-table:        Display Table Format.
                                                              (line  85)
* describe-display-table:                Display Table Format.
                                                              (line  81)
* describe-mode:                         Mode Help.           (line  12)
* describe-prefix-bindings:              Help Functions.      (line 110)
* description for interactive codes:     Interactive Codes.   (line   6)
* description format:                    Format of Descriptions.
                                                              (line   6)
* deserializing:                         Byte Packing.        (line  12)
* desktop save mode:                     Desktop Save Mode.   (line   6)
* desktop-buffer-mode-handlers:          Desktop Save Mode.   (line  33)
* desktop-save-buffer:                   Desktop Save Mode.   (line  17)
* destroy-fringe-bitmap:                 Customizing Bitmaps. (line  33)
* destructive list operations:           Modifying Lists.     (line   6)
* detect-coding-region:                  Lisp and Coding Systems.
                                                              (line  83)
* detect-coding-string:                  Lisp and Coding Systems.
                                                              (line  99)
* diagrams, boxed, for lists:            Box Diagrams.        (line   6)
* dialog boxes:                          Dialog Boxes.        (line   6)
* digit-argument:                        Prefix Command Arguments.
                                                              (line 109)
* dimension (of character set):          Chars and Bytes.     (line   6)
* ding:                                  Beeping.             (line  13)
* directory name:                        Directory Names.     (line   6)
* directory name abbreviation:           Directory Names.     (line  67)
* directory part (of file name):         File Name Components.
                                                              (line   6)
* directory-abbrev-alist:                Directory Names.     (line  75)
* directory-file-name:                   Directory Names.     (line  36)
* directory-files:                       Contents of Directories.
                                                              (line  16)
* directory-files-and-attributes:        Contents of Directories.
                                                              (line  46)
* directory-oriented functions:          Contents of Directories.
                                                              (line   6)
* dired-kept-versions:                   Numbered Backups.    (line  51)
* dired-mode-map:                        Standard Keymaps.    (line  45)
* disable-command:                       Disabling Commands.  (line  37)
* disable-point-adjustment:              Adjusting Point.     (line  16)
* disabled:                              Disabling Commands.  (line  11)
* disabled command:                      Disabling Commands.  (line   6)
* disabled-command-function:             Disabling Commands.  (line  42)
* disabling advice:                      Enabling Advice.     (line   6)
* disabling undo:                        Maintaining Undo.    (line  27)
* disassemble:                           Disassembly.         (line  21)
* disassembled byte-code:                Disassembly.         (line   6)
* discard-input:                         Event Input Misc.    (line  99)
* discarding input:                      Event Input Misc.    (line  99)
* display (overlay property):            Overlay Properties.  (line  95)
* display (text property):               Display Property.    (line   6)
* display feature testing:               Display Feature Testing.
                                                              (line   6)
* display margins:                       Display Margins.     (line   6)
* display message in echo area:          Displaying Messages. (line   6)
* display property, and point display:   Adjusting Point.     (line   6)
* display specification:                 Display Property.    (line   6)
* display table:                         Display Tables.      (line   6)
* display, abstract:                     Abstract Display.    (line   6)
* display, arbitrary objects:            Abstract Display.    (line   6)
* display-backing-store:                 Display Feature Testing.
                                                              (line 109)
* display-buffer:                        Choosing Window.     (line  13)
* display-buffer-function:               Choosing Window.     (line 209)
* display-buffer-reuse-frames:           Choosing Window.     (line  51)
* display-color-cells:                   Display Feature Testing.
                                                              (line 134)
* display-color-p:                       Display Feature Testing.
                                                              (line  35)
* display-completion-list:               Completion Commands. (line  60)
* display-graphic-p:                     Display Feature Testing.
                                                              (line  25)
* display-grayscale-p:                   Display Feature Testing.
                                                              (line  40)
* display-images-p:                      Display Feature Testing.
                                                              (line  70)
* display-message-or-buffer:             Displaying Messages. (line  69)
* display-mm-dimensions-alist:           Display Feature Testing.
                                                              (line 104)
* display-mm-height:                     Display Feature Testing.
                                                              (line  96)
* display-mm-width:                      Display Feature Testing.
                                                              (line 100)
* display-mouse-p:                       Display Feature Testing.
                                                              (line  31)
* display-pixel-height:                  Display Feature Testing.
                                                              (line  80)
* display-pixel-width:                   Display Feature Testing.
                                                              (line  88)
* display-planes:                        Display Feature Testing.
                                                              (line 124)
* display-popup-menus-p:                 Display Feature Testing.
                                                              (line  20)
* display-save-under:                    Display Feature Testing.
                                                              (line 119)
* display-screens:                       Display Feature Testing.
                                                              (line  76)
* display-selections-p:                  Display Feature Testing.
                                                              (line  65)
* display-supports-face-attributes-p:    Display Feature Testing.
                                                              (line  45)
* display-table-slot:                    Display Table Format.
                                                              (line  67)
* display-visual-class:                  Display Feature Testing.
                                                              (line 129)
* display-warning:                       Warning Basics.      (line  43)
* displaying a buffer:                   Displaying Buffers.  (line   6)
* displays, multiple:                    Multiple Displays.   (line   6)
* dnd-protocol-alist:                    Drag and Drop.       (line  20)
* do-auto-save:                          Auto-Saving.         (line 132)
* doc, customization keyword:            Type Keywords.       (line  86)
* doc-directory:                         Accessing Documentation.
                                                              (line 140)
* DOC-VERSION (documentation) file:      Documentation Basics.
                                                              (line  46)
* documentation:                         Accessing Documentation.
                                                              (line  26)
* documentation conventions:             Documentation Basics.
                                                              (line   6)
* documentation for major mode:          Mode Help.           (line   6)
* documentation notation:                Evaluation Notation. (line   6)
* documentation of function:             Function Documentation.
                                                              (line   6)
* documentation strings:                 Documentation.       (line   6)
* documentation strings, conventions and tips: Documentation Tips.
                                                              (line   6)
* documentation, keys in:                Keys in Documentation.
                                                              (line   6)
* documentation-property:                Accessing Documentation.
                                                              (line   7)
* dolist:                                Iteration.           (line  52)
* DOS file types:                        MS-DOS File Types.   (line   6)
* dotimes:                               Iteration.           (line  64)
* dotimes-with-progress-reporter:        Progress.            (line  98)
* dotted list:                           Cons Cells.          (line  33)
* dotted lists (Edebug):                 Specification List.  (line 143)
* dotted pair notation:                  Dotted Pair Notation.
                                                              (line   6)
* double-click events:                   Repeat Events.       (line   6)
* double-click-fuzz:                     Repeat Events.       (line  73)
* double-click-time:                     Repeat Events.       (line  83)
* double-quote in strings:               Syntax for Strings.  (line   6)
* down-list:                             List Motion.         (line  30)
* downcase:                              Case Conversion.     (line  20)
* downcase-region:                       Case Changes.        (line  36)
* downcase-word:                         Case Changes.        (line  64)
* downcasing in lookup-key:              Key Sequence Input.  (line  73)
* drag event:                            Drag Events.         (line   6)
* drag-n-drop event:                     Misc Events.         (line  43)
* dribble file:                          Recording Input.     (line  20)
* dump-emacs:                            Building Emacs.      (line  95)
* dumping Emacs:                         Building Emacs.      (line  22)
* dynamic loading of documentation:      Docs and Compilation.
                                                              (line   6)
* dynamic loading of functions:          Dynamic Loading.     (line   6)
* dynamic scoping:                       Variable Scoping.    (line  11)
* dynamic-completion-table:              Programmed Completion.
                                                              (line  58)
* easy-mmode-define-minor-mode:          Defining Minor Modes.
                                                              (line  77)
* echo area:                             The Echo Area.       (line   6)
* echo-area-clear-hook:                  Echo Area Customization.
                                                              (line  18)
* echo-keystrokes:                       Echo Area Customization.
                                                              (line  22)
* edebug:                                Source Breakpoints.  (line   6)
* Edebug debugging facility:             Edebug.              (line   6)
* Edebug execution modes:                Edebug Execution Modes.
                                                              (line   6)
* Edebug specification list:             Specification List.  (line   6)
* edebug-all-defs:                       Edebug Options.      (line  16)
* edebug-all-forms:                      Edebug Options.      (line  25)
* edebug-continue-kbd-macro:             Edebug Options.      (line  79)
* edebug-display-freq-count:             Coverage Testing.    (line  30)
* edebug-eval-macro-args:                Instrumenting Macro Calls.
                                                              (line  65)
* edebug-eval-top-level-form:            Instrumenting.       (line  26)
* edebug-global-break-condition:         Edebug Options.      (line  96)
* edebug-initial-mode:                   Edebug Options.      (line  60)
* edebug-on-error:                       Edebug Options.      (line  84)
* edebug-on-quit:                        Edebug Options.      (line  88)
* edebug-print-circle:                   Printing in Edebug.  (line  38)
* edebug-print-length:                   Printing in Edebug.  (line  16)
* edebug-print-level:                    Printing in Edebug.  (line  20)
* edebug-print-trace-after:              Trace Buffer.        (line  24)
* edebug-print-trace-before:             Trace Buffer.        (line  24)
* edebug-save-displayed-buffer-points:   Edebug Options.      (line  46)
* edebug-save-windows:                   Edebug Options.      (line  34)
* edebug-set-global-break-condition:     Global Break Condition.
                                                              (line  13)
* edebug-setup-hook:                     Edebug Options.      (line   9)
* edebug-sit-for-seconds:                Edebug Execution Modes.
                                                              (line  83)
* edebug-temp-display-freq-count:        Coverage Testing.    (line  24)
* edebug-test-coverage:                  Edebug Options.      (line  75)
* edebug-trace <1>:                      Trace Buffer.        (line  36)
* edebug-trace:                          Edebug Options.      (line  68)
* edebug-tracing:                        Trace Buffer.        (line  29)
* edebug-unwrap:                         Specification List.  (line  39)
* edit-abbrevs-map:                      Standard Keymaps.    (line  48)
* edit-and-eval-command:                 Object from Minibuffer.
                                                              (line  50)
* edit-tab-stops-map:                    Standard Keymaps.    (line  51)
* editing types:                         Editing Types.       (line   6)
* editor command loop:                   Command Loop.        (line   6)
* electric-buffer-menu-mode-map:         Standard Keymaps.    (line  54)
* electric-future-map:                   A Sample Variable Description.
                                                              (line  16)
* electric-history-map:                  Standard Keymaps.    (line  57)
* element (of list):                     Lists.               (line   6)
* elements of sequences:                 Sequence Functions.  (line  39)
* elp.el:                                Compilation Tips.    (line   9)
* elt:                                   Sequence Functions.  (line  39)
* Emacs event standard notation:         Describing Characters.
                                                              (line  14)
* emacs-build-time:                      Version Info.        (line  24)
* emacs-lisp-docstring-fill-column:      Documentation Basics.
                                                              (line  29)
* emacs-lisp-mode-map:                   Standard Keymaps.    (line  60)
* emacs-lisp-mode-syntax-table:          Standard Syntax Tables.
                                                              (line  20)
* emacs-major-version:                   Version Info.        (line  42)
* emacs-minor-version:                   Version Info.        (line  46)
* emacs-pid:                             System Environment.  (line 217)
* emacs-save-session-functions:          Session Management.  (line  19)
* emacs-startup-hook:                    Init File.           (line  66)
* emacs-version:                         Version Info.        (line  10)
* EMACSLOADPATH environment variable:    Library Search.      (line  10)
* empty list:                            Box Diagrams.        (line  41)
* emulation-mode-map-alists:             Controlling Active Maps.
                                                              (line 132)
* enable-command:                        Disabling Commands.  (line  32)
* enable-local-eval:                     File Local Variables.
                                                              (line 103)
* enable-local-variables:                File Local Variables.
                                                              (line  13)
* enable-multibyte-characters:           Text Representations.
                                                              (line  41)
* enable-recursive-minibuffers:          Recursive Mini.      (line  15)
* enabling advice:                       Enabling Advice.     (line   6)
* encode-coding-region:                  Explicit Encoding.   (line  36)
* encode-coding-string:                  Explicit Encoding.   (line  45)
* encode-time:                           Time Conversion.     (line  69)
* encoding file formats:                 Format Conversion.   (line   6)
* encoding in coding systems:            Explicit Encoding.   (line   6)
* end of line in regexp:                 Regexp Special.      (line 160)
* end-of-buffer:                         Buffer End Motion.   (line  33)
* end-of-defun:                          List Motion.         (line  62)
* end-of-defun-function:                 List Motion.         (line  86)
* end-of-file:                           Input Functions.     (line  13)
* end-of-line:                           Text Lines.          (line  62)
* end-of-line conversion:                Coding System Basics.
                                                              (line  38)
* endianness:                            Bindat Spec.         (line  13)
* enlarge-window:                        Resizing Windows.    (line  12)
* enlarge-window-horizontally:           Resizing Windows.    (line  42)
* environment:                           Intro Eval.          (line  52)
* environment variable access:           System Environment.  (line 105)
* environment variables, subprocesses:   Subprocess Creation. (line  59)
* eobp:                                  Near Point.          (line  68)
* EOL conversion:                        Coding System Basics.
                                                              (line  38)
* eolp:                                  Near Point.          (line  78)
* eq:                                    Equality Predicates. (line  12)
* eql:                                   Comparison of Numbers.
                                                              (line  51)
* equal:                                 Equality Predicates. (line  58)
* equal-including-properties:            Equality Predicates. (line 118)
* equality:                              Equality Predicates. (line   6)
* erase-buffer:                          Deletion.            (line  15)
* error:                                 Signaling Errors.    (line  27)
* error cleanup:                         Cleanups.            (line  13)
* error debugging:                       Error Debugging.     (line   6)
* error description:                     Handling Errors.     (line 108)
* error display:                         The Echo Area.       (line   6)
* error handler:                         Handling Errors.     (line   6)
* error in debug:                        Invoking the Debugger.
                                                              (line  62)
* error message notation:                Error Messages.      (line   6)
* error name:                            Error Symbols.       (line   6)
* error symbol:                          Error Symbols.       (line   6)
* error-conditions:                      Error Symbols.       (line   6)
* error-message-string:                  Handling Errors.     (line 121)
* errors:                                Errors.              (line   6)
* esc-map:                               Prefix Keys.         (line  15)
* ESC-prefix:                            Prefix Keys.         (line  15)
* escape (ASCII character):              Basic Char Syntax.   (line  27)
* escape characters:                     Output Variables.    (line  18)
* escape characters in printing:         Output Functions.    (line   9)
* escape sequence:                       Basic Char Syntax.   (line  45)
* escape-syntax character:               Syntax Class Table.  (line  82)
* eval:                                  Eval.                (line  22)
* eval, and debugging:                   Internals of Debugger.
                                                              (line  62)
* eval-after-load:                       Hooks for Loading.   (line  10)
* eval-and-compile:                      Eval During Compile. (line  10)
* eval-at-startup:                       Building Emacs.      (line  88)
* eval-buffer:                           Eval.                (line  70)
* eval-buffer (Edebug):                  Instrumenting.       (line  19)
* eval-current-buffer:                   Eval.                (line  83)
* eval-current-buffer (Edebug):          Instrumenting.       (line  19)
* eval-defun (Edebug):                   Instrumenting.       (line  10)
* eval-expression (Edebug):              Instrumenting.       (line  51)
* eval-expression-debug-on-error:        Error Debugging.     (line  50)
* eval-expression-print-length:          Output Variables.    (line  82)
* eval-expression-print-level:           Output Variables.    (line  83)
* eval-minibuffer:                       Object from Minibuffer.
                                                              (line  38)
* eval-region:                           Eval.                (line  47)
* eval-region (Edebug):                  Instrumenting.       (line  19)
* eval-when-compile:                     Eval During Compile. (line  36)
* evaluated expression argument:         Interactive Codes.   (line 189)
* evaluation:                            Evaluation.          (line   6)
* evaluation error:                      Local Variables.     (line 104)
* evaluation list group:                 Eval List.           (line  47)
* evaluation notation:                   Evaluation Notation. (line   6)
* evaluation of buffer contents:         Eval.                (line  68)
* evaporate (overlay property):          Overlay Properties.  (line 178)
* even-window-heights:                   Choosing Window.     (line  73)
* event printing:                        Describing Characters.
                                                              (line  29)
* event type:                            Classifying Events.  (line   6)
* event, reading only one:               Reading One Event.   (line   6)
* event-basic-type:                      Classifying Events.  (line  67)
* event-click-count:                     Repeat Events.       (line  66)
* event-convert-list:                    Classifying Events.  (line  93)
* event-end:                             Accessing Mouse.     (line  24)
* event-modifiers:                       Classifying Events.  (line  27)
* event-start:                           Accessing Mouse.     (line  17)
* eventp:                                Input Events.        (line  12)
* events:                                Input Events.        (line   6)
* ewoc:                                  Abstract Display.    (line   6)
* ewoc-buffer:                           Abstract Display Functions.
                                                              (line  30)
* ewoc-collect:                          Abstract Display Functions.
                                                              (line 108)
* ewoc-create:                           Abstract Display Functions.
                                                              (line  11)
* ewoc-data:                             Abstract Display Functions.
                                                              (line  61)
* ewoc-delete:                           Abstract Display Functions.
                                                              (line 100)
* ewoc-enter-after:                      Abstract Display Functions.
                                                              (line  47)
* ewoc-enter-before:                     Abstract Display Functions.
                                                              (line  46)
* ewoc-enter-first:                      Abstract Display Functions.
                                                              (line  41)
* ewoc-enter-last:                       Abstract Display Functions.
                                                              (line  42)
* ewoc-filter:                           Abstract Display Functions.
                                                              (line 103)
* ewoc-get-hf:                           Abstract Display Functions.
                                                              (line  33)
* ewoc-goto-next:                        Abstract Display Functions.
                                                              (line  80)
* ewoc-goto-node:                        Abstract Display Functions.
                                                              (line  87)
* ewoc-goto-prev:                        Abstract Display Functions.
                                                              (line  79)
* ewoc-invalidate:                       Abstract Display Functions.
                                                              (line  96)
* ewoc-locate:                           Abstract Display Functions.
                                                              (line  67)
* ewoc-location:                         Abstract Display Functions.
                                                              (line  76)
* ewoc-map:                              Abstract Display Functions.
                                                              (line 114)
* ewoc-next:                             Abstract Display Functions.
                                                              (line  52)
* ewoc-nth:                              Abstract Display Functions.
                                                              (line  56)
* ewoc-prev:                             Abstract Display Functions.
                                                              (line  51)
* ewoc-refresh:                          Abstract Display Functions.
                                                              (line  90)
* ewoc-set-data:                         Abstract Display Functions.
                                                              (line  64)
* ewoc-set-hf:                           Abstract Display Functions.
                                                              (line  37)
* examining the interactive form:        Using Interactive.   (line 112)
* examining windows:                     Buffers and Windows. (line   6)
* examples of using interactive:         Interactive Examples.
                                                              (line   6)
* excursion:                             Excursions.          (line   6)
* exec-directory:                        Subprocess Creation. (line  64)
* exec-path:                             Subprocess Creation. (line  70)
* exec-suffixes:                         Subprocess Creation. (line  32)
* executable-find:                       Locating Files.      (line  50)
* execute program:                       Subprocess Creation. (line  17)
* execute with prefix argument:          Interactive Call.    (line  81)
* execute-extended-command:              Interactive Call.    (line  76)
* execute-kbd-macro:                     Keyboard Macros.     (line  13)
* executing-kbd-macro:                   Keyboard Macros.     (line  38)
* execution speed:                       Compilation Tips.    (line   6)
* exit:                                  Recursive Editing.   (line  32)
* exit recursive editing:                Recursive Editing.   (line  32)
* exit-minibuffer:                       Minibuffer Commands. (line   9)
* exit-recursive-edit:                   Recursive Editing.   (line  88)
* exiting Emacs:                         Getting Out.         (line   6)
* exp:                                   Math Functions.      (line  32)
* expand-abbrev:                         Abbrev Expansion.    (line  27)
* expand-file-name:                      File Name Expansion. (line  13)
* expansion of file names:               File Name Expansion. (line   6)
* expansion of macros:                   Expansion.           (line   6)
* expression:                            Intro Eval.          (line  15)
* expression prefix:                     Syntax Class Table.  (line 110)
* expt:                                  Math Functions.      (line  47)
* extended-command-history:              Minibuffer History.  (line 109)
* extent:                                Variable Scoping.    (line  11)
* extra slots of char-table:             Char-Tables.         (line   6)
* extra-keyboard-modifiers:              Event Mod.           (line  12)
* face (button property):                Button Properties.   (line  23)
* face (overlay property):               Overlay Properties.  (line  67)
* face (text property):                  Special Properties.  (line  22)
* face alias:                            Face Functions.      (line  45)
* face attributes:                       Face Attributes.     (line   6)
* face codes of text:                    Special Properties.  (line  22)
* face id:                               Faces.               (line  12)
* face-attribute:                        Attribute Functions. (line  35)
* face-attribute-relative-p:             Attribute Functions. (line  64)
* face-background:                       Attribute Functions. (line 144)
* face-bold-p:                           Attribute Functions. (line 169)
* face-differs-from-default-p:           Face Functions.      (line  42)
* face-documentation <1>:                Face Functions.      (line  34)
* face-documentation:                    Accessing Documentation.
                                                              (line  48)
* face-equal:                            Face Functions.      (line  38)
* face-font:                             Attribute Functions. (line 166)
* face-font-family-alternatives:         Font Selection.      (line  55)
* face-font-registry-alternatives:       Font Selection.      (line  66)
* face-font-rescale-alist:               Font Selection.      (line  94)
* face-font-selection-order:             Font Selection.      (line  26)
* face-foreground:                       Attribute Functions. (line 143)
* face-id:                               Face Functions.      (line  31)
* face-inverse-video-p:                  Attribute Functions. (line 180)
* face-italic-p:                         Attribute Functions. (line 173)
* face-list:                             Face Functions.      (line  14)
* face-stipple:                          Attribute Functions. (line 155)
* face-underline-p:                      Attribute Functions. (line 177)
* facemenu-background-menu:              Standard Keymaps.    (line  69)
* facemenu-face-menu:                    Standard Keymaps.    (line  73)
* facemenu-foreground-menu:              Standard Keymaps.    (line  77)
* facemenu-indentation-menu:             Standard Keymaps.    (line  81)
* facemenu-justification-menu:           Standard Keymaps.    (line  85)
* facemenu-keymap:                       Prefix Keys.         (line  43)
* facemenu-menu:                         Standard Keymaps.    (line  66)
* facemenu-special-menu:                 Standard Keymaps.    (line  89)
* facep:                                 Faces.               (line  17)
* faces:                                 Faces.               (line   6)
* faces for font lock:                   Faces for Font Lock. (line   6)
* faces, automatic choice:               Auto Faces.          (line   6)
* false:                                 nil and t.           (line   6)
* fboundp:                               Function Cells.      (line  46)
* fceiling:                              Rounding Operations. (line  17)
* FEATURE-unload-function:               Unloading.           (line  31)
* featurep:                              Named Features.      (line 122)
* features:                              Named Features.      (line   6)
* fetch-bytecode:                        Dynamic Loading.     (line  50)
* ffloor:                                Rounding Operations. (line  13)
* field (text property):                 Special Properties.  (line 169)
* field width:                           Formatting Strings.  (line 124)
* field-beginning:                       Fields.              (line  37)
* field-end:                             Fields.              (line  48)
* field-string:                          Fields.              (line  59)
* field-string-no-properties:            Fields.              (line  63)
* fields:                                Fields.              (line   6)
* fifo data structure:                   Rings.               (line  64)
* file accessibility:                    Testing Accessibility.
                                                              (line   6)
* file age:                              Testing Accessibility.
                                                              (line  96)
* file attributes:                       File Attributes.     (line  13)
* file format conversion:                Format Conversion.   (line   6)
* file hard link:                        Changing Files.      (line  28)
* file local variables:                  File Local Variables.
                                                              (line   6)
* file locks:                            File Locks.          (line   6)
* file mode specification error:         Auto Major Mode.     (line  44)
* file modes and MS-DOS:                 Changing Files.      (line 162)
* file modification time:                Testing Accessibility.
                                                              (line  96)
* file name completion subroutines:      File Name Completion.
                                                              (line   6)
* file name of buffer:                   Buffer File Name.    (line   6)
* file name of directory:                Directory Names.     (line   6)
* file names:                            File Names.          (line   6)
* file names in directory:               Contents of Directories.
                                                              (line   6)
* file open error:                       Subroutines of Visiting.
                                                              (line  37)
* file symbolic links:                   Kinds of Files.      (line  10)
* file types on MS-DOS and Windows:      MS-DOS File Types.   (line   6)
* file with multiple names:              Changing Files.      (line  28)
* file, information about:               Information about Files.
                                                              (line   6)
* file-accessible-directory-p:           Testing Accessibility.
                                                              (line  65)
* file-already-exists:                   Changing Files.      (line 103)
* file-attributes:                       File Attributes.     (line  64)
* file-chase-links:                      Truenames.           (line  33)
* file-coding-system-alist:              Default Coding Systems.
                                                              (line  28)
* file-directory-p:                      Kinds of Files.      (line  33)
* file-error:                            How Programs Do Loading.
                                                              (line  76)
* file-executable-p:                     Testing Accessibility.
                                                              (line  40)
* file-exists-p:                         Testing Accessibility.
                                                              (line  12)
* file-expand-wildcards:                 Contents of Directories.
                                                              (line  60)
* file-local-copy:                       Magic File Names.    (line 156)
* file-locked:                           File Locks.          (line  62)
* file-locked-p:                         File Locks.          (line  24)
* file-modes:                            File Attributes.     (line  13)
* file-name-absolute-p:                  Relative File Names. (line  18)
* file-name-all-completions:             File Name Completion.
                                                              (line  10)
* file-name-all-versions:                Contents of Directories.
                                                              (line  56)
* file-name-as-directory:                Directory Names.     (line  26)
* file-name-buffer-file-type-alist:      MS-DOS File Types.   (line  29)
* file-name-coding-system:               Encoding and I/O.    (line  62)
* file-name-completion:                  File Name Completion.
                                                              (line  34)
* file-name-directory:                   File Name Components.
                                                              (line  26)
* file-name-extension:                   File Name Components.
                                                              (line  75)
* file-name-history:                     Minibuffer History.  (line 100)
* file-name-nondirectory:                File Name Components.
                                                              (line  43)
* file-name-sans-extension:              File Name Components.
                                                              (line  92)
* file-name-sans-versions:               File Name Components.
                                                              (line  57)
* file-newer-than-file-p:                Testing Accessibility.
                                                              (line  96)
* file-newest-backup:                    Backup Names.        (line  85)
* file-nlinks:                           File Attributes.     (line  48)
* file-ownership-preserved-p:            Testing Accessibility.
                                                              (line  86)
* file-precious-flag:                    Saving Buffers.      (line 138)
* file-readable-p:                       Testing Accessibility.
                                                              (line  29)
* file-regular-p:                        Kinds of Files.      (line  49)
* file-relative-name:                    Relative File Names. (line  34)
* file-remote-p:                         Magic File Names.    (line 168)
* file-supersession:                     Modification Time.   (line  84)
* file-symlink-p:                        Kinds of Files.      (line  10)
* file-truename:                         Truenames.           (line  15)
* file-writable-p:                       Testing Accessibility.
                                                              (line  47)
* fill-column:                           Margins.             (line  20)
* fill-context-prefix:                   Adaptive Fill.       (line  17)
* fill-individual-paragraphs:            Filling.             (line  53)
* fill-individual-varying-indent:        Filling.             (line  75)
* fill-nobreak-predicate:                Margins.             (line  90)
* fill-paragraph:                        Filling.             (line  34)
* fill-paragraph-function:               Filling.             (line 141)
* fill-prefix:                           Margins.             (line   7)
* fill-region:                           Filling.             (line  40)
* fill-region-as-paragraph:              Filling.             (line  80)
* fillarray:                             Array Functions.     (line  56)
* filling text:                          Filling.             (line   6)
* filling, automatic:                    Auto Filling.        (line   6)
* filter function:                       Filter Functions.    (line   6)
* filter multibyte flag, of process:     Decoding Output.     (line  27)
* filter-buffer-substring:               Buffer Contents.     (line  49)
* find file in path:                     Locating Files.      (line   6)
* find library:                          Library Search.      (line   6)
* find-backup-file-name:                 Backup Names.        (line  65)
* find-buffer-visiting:                  Buffer File Name.    (line  74)
* find-charset-region:                   Scanning Charsets.   (line  18)
* find-charset-string:                   Scanning Charsets.   (line  28)
* find-coding-systems-for-charsets:      Lisp and Coding Systems.
                                                              (line  79)
* find-coding-systems-region:            Lisp and Coding Systems.
                                                              (line  63)
* find-coding-systems-string:            Lisp and Coding Systems.
                                                              (line  72)
* find-file:                             Visiting Functions.  (line  18)
* find-file-hook:                        Visiting Functions.  (line 116)
* find-file-name-handler:                Magic File Names.    (line 148)
* find-file-noselect:                    Visiting Functions.  (line  38)
* find-file-not-found-functions:         Visiting Functions.  (line 125)
* find-file-other-window:                Visiting Functions.  (line  85)
* find-file-read-only:                   Visiting Functions.  (line  92)
* find-file-wildcards:                   Visiting Functions.  (line 108)
* find-image:                            Defining Images.     (line  54)
* find-operation-coding-system:          Default Coding Systems.
                                                              (line 104)
* finding files:                         Visiting Files.      (line   6)
* finding windows:                       Selecting Windows.   (line  49)
* first-change-hook:                     Change Hooks.        (line  62)
* fit-window-to-buffer:                  Resizing Windows.    (line  75)
* fixup-whitespace:                      User-Level Deletion. (line  69)
* flags in format specifications:        Formatting Strings.  (line 149)
* float:                                 Numeric Conversions. (line   9)
* float-output-format:                   Output Variables.    (line 116)
* float-time:                            Time of Day.         (line  71)
* floating-point functions:              Math Functions.      (line   6)
* floatp:                                Predicates on Numbers.
                                                              (line  14)
* floats-consed:                         Memory Usage.        (line  18)
* floor:                                 Numeric Conversions. (line  35)
* flushing input:                        Event Input Misc.    (line  99)
* fmakunbound:                           Function Cells.      (line  51)
* fn in function's documentation string: Autoload.            (line 134)
* focus event:                           Focus Events.        (line   6)
* focus-follows-mouse:                   Input Focus.         (line 110)
* follow links:                          Links and Mouse-1.   (line   6)
* follow-link (button property):         Button Properties.   (line  47)
* following-char:                        Near Point.          (line  34)
* font lock faces:                       Faces for Font Lock. (line   6)
* Font Lock mode:                        Font Lock Mode.      (line   6)
* font-list-limit:                       Font Lookup.         (line  66)
* font-lock-add-keywords:                Customizing Keywords.
                                                              (line  11)
* font-lock-beginning-of-syntax-function: Syntactic Font Lock.
                                                              (line  27)
* font-lock-builtin-face:                Faces for Font Lock. (line  31)
* font-lock-comment-delimiter-face:      Faces for Font Lock. (line  18)
* font-lock-comment-face:                Faces for Font Lock. (line  15)
* font-lock-constant-face:               Faces for Font Lock. (line  46)
* font-lock-defaults:                    Font Lock Basics.    (line  13)
* font-lock-doc-face:                    Faces for Font Lock. (line  21)
* font-lock-extend-after-change-region-function: Region to Fontify.
                                                              (line  16)
* font-lock-extra-managed-props:         Other Font Lock Variables.
                                                              (line  23)
* font-lock-face (text property):        Special Properties.  (line  51)
* font-lock-fontify-buffer-function:     Other Font Lock Variables.
                                                              (line  32)
* font-lock-fontify-region-function:     Other Font Lock Variables.
                                                              (line  41)
* font-lock-function-name-face:          Faces for Font Lock. (line  34)
* font-lock-keyword-face:                Faces for Font Lock. (line  27)
* font-lock-keywords:                    Search-based Fontification.
                                                              (line  12)
* font-lock-keywords-case-fold-search:   Search-based Fontification.
                                                              (line 203)
* font-lock-keywords-only:               Syntactic Font Lock. (line  15)
* font-lock-mark-block-function:         Other Font Lock Variables.
                                                              (line  11)
* font-lock-multiline:                   Font Lock Multiline. (line  23)
* font-lock-negation-char-face:          Faces for Font Lock. (line  52)
* font-lock-preprocessor-face:           Faces for Font Lock. (line  49)
* font-lock-remove-keywords:             Customizing Keywords.
                                                              (line  43)
* font-lock-string-face:                 Faces for Font Lock. (line  24)
* font-lock-syntactic-face-function:     Syntactic Font Lock. (line  46)
* font-lock-syntactic-keywords:          Setting Syntax Properties.
                                                              (line  11)
* font-lock-syntax-table:                Syntactic Font Lock. (line  21)
* font-lock-type-face:                   Faces for Font Lock. (line  42)
* font-lock-unfontify-buffer-function:   Other Font Lock Variables.
                                                              (line  36)
* font-lock-unfontify-region-function:   Other Font Lock Variables.
                                                              (line  48)
* font-lock-variable-name-face:          Faces for Font Lock. (line  38)
* font-lock-warning-face:                Faces for Font Lock. (line  55)
* fontification-functions:               Auto Faces.          (line  11)
* fontified (text property):             Special Properties.  (line  68)
* fonts in this manual:                  Some Terms.          (line  14)
* foo:                                   A Sample Function Description.
                                                              (line  25)
* for:                                   Argument Evaluation. (line  12)
* force-mode-line-update:                Mode Line Basics.    (line  24)
* force-window-update:                   Forcing Redisplay.   (line  30)
* forcing redisplay:                     Forcing Redisplay.   (line   6)
* format:                                Formatting Strings.  (line  17)
* format definition:                     Format Conversion.   (line  16)
* format of keymaps:                     Format of Keymaps.   (line   6)
* format specification:                  Formatting Strings.  (line  26)
* format, customization keyword:         Type Keywords.       (line  23)
* format-alist:                          Format Conversion.   (line  13)
* format-find-file:                      Format Conversion.   (line 118)
* format-insert-file:                    Format Conversion.   (line 127)
* format-mode-line:                      Emulating Mode Line. (line  11)
* format-network-address:                Misc Network.        (line  37)
* format-time-string:                    Time Parsing.        (line  14)
* format-write-file:                     Format Conversion.   (line 109)
* formatting strings:                    Formatting Strings.  (line   6)
* formfeed:                              Basic Char Syntax.   (line  27)
* forms:                                 Intro Eval.          (line  15)
* forward advice:                        Defining Advice.     (line  80)
* forward-button:                        Button Buffer Commands.
                                                              (line  34)
* forward-char:                          Character Motion.    (line  27)
* forward-comment:                       Motion via Parsing.  (line  42)
* forward-line:                          Text Lines.          (line  80)
* forward-list:                          List Motion.         (line  15)
* forward-sexp:                          List Motion.         (line  35)
* forward-to-indentation:                Motion by Indent.    (line  20)
* forward-word:                          Word Motion.         (line  10)
* frame:                                 Frames.              (line   6)
* frame configuration:                   Frame Configurations.
                                                              (line   6)
* frame parameters:                      Frame Parameters.    (line   6)
* frame size:                            Size and Position.   (line   6)
* frame title:                           Frame Titles.        (line   6)
* frame visibility:                      Visibility of Frames.
                                                              (line   6)
* frame-background-mode:                 Defining Faces.      (line 125)
* frame-char-height:                     Size and Position.   (line  53)
* frame-char-width:                      Size and Position.   (line  54)
* frame-current-scroll-bars:             Scroll Bars.         (line  13)
* frame-first-window:                    Frames and Windows.  (line  20)
* frame-height:                          Size and Position.   (line  29)
* frame-list:                            Finding All Frames.  (line   7)
* frame-live-p:                          Deleting Frames.     (line  22)
* frame-parameter:                       Parameter Access.    (line   9)
* frame-parameters:                      Parameter Access.    (line  15)
* frame-pixel-height:                    Size and Position.   (line  42)
* frame-pixel-width:                     Size and Position.   (line  43)
* frame-selected-window:                 Frames and Windows.  (line  29)
* frame-title-format:                    Frame Titles.        (line  17)
* frame-visible-p:                       Visibility of Frames.
                                                              (line  33)
* frame-width:                           Size and Position.   (line  30)
* framep:                                Frames.              (line  26)
* frames, scanning all:                  Finding All Frames.  (line   6)
* free list:                             Garbage Collection.  (line  35)
* frequency counts:                      Coverage Testing.    (line   6)
* fringe bitmaps:                        Fringe Bitmaps.      (line   6)
* fringe cursors:                        Fringe Cursors.      (line   6)
* fringe indicators:                     Fringe Indicators.   (line   6)
* fringe-bitmaps-at-pos:                 Fringe Bitmaps.      (line  24)
* fringe-cursor-alist:                   Fringe Cursors.      (line  24)
* fringe-indicator-alist:                Fringe Indicators.   (line  59)
* fringes:                               Fringes.             (line   6)
* fringes, and empty line indication:    Fringe Indicators.   (line  11)
* fringes-outside-margins:               Fringe Size/Pos.     (line  10)
* fround:                                Rounding Operations. (line  25)
* fset:                                  Function Cells.      (line  66)
* ftp-login:                             Cleanups.            (line  58)
* ftruncate:                             Rounding Operations. (line  21)
* full keymap:                           Format of Keymaps.   (line   6)
* funcall:                               Calling Functions.   (line  23)
* funcall, and debugging:                Internals of Debugger.
                                                              (line  62)
* function <1>:                          Anonymous Functions. (line  93)
* function:                              What Is a Function.  (line  16)
* function aliases:                      Defining Functions.  (line  61)
* function call:                         Function Forms.      (line   6)
* function call debugging:               Function Debugging.  (line   6)
* function cell:                         Symbol Components.   (line  21)
* function cell in autoload:             Autoload.            (line  62)
* function definition:                   Function Names.      (line   6)
* function descriptions:                 A Sample Function Description.
                                                              (line   6)
* function form evaluation:              Function Forms.      (line   6)
* function input stream:                 Input Streams.       (line  27)
* function invocation:                   Calling Functions.   (line   6)
* function keys:                         Function Keys.       (line   6)
* function name:                         Function Names.      (line   6)
* function output stream:                Output Streams.      (line  24)
* function quoting:                      Anonymous Functions. (line  93)
* function safety:                       Function Safety.     (line   6)
* function-documentation:                Documentation Basics.
                                                              (line  35)
* function-key-map:                      Translation Keymaps. (line  13)
* functionals:                           Calling Functions.   (line  78)
* functionp:                             What Is a Function.  (line  80)
* functions in modes:                    Major Mode Conventions.
                                                              (line  48)
* functions, making them interactive:    Defining Commands.   (line   6)
* Fundamental mode:                      Major Mode Basics.   (line   6)
* fundamental-mode:                      Auto Major Mode.     (line  11)
* fundamental-mode-abbrev-table:         Standard Abbrev Tables.
                                                              (line  20)
* fundamental-mode-map:                  Standard Keymaps.    (line  98)
* gamma correction:                      Color Parameters.    (line  27)
* gap-position:                          Buffer Gap.          (line  20)
* gap-size:                              Buffer Gap.          (line  24)
* garbage collection:                    Garbage Collection.  (line   6)
* garbage collection protection:         Writing Emacs Primitives.
                                                              (line  15)
* garbage-collect:                       Garbage Collection.  (line  54)
* garbage-collection-messages:           Garbage Collection.  (line 143)
* gc-cons-percentage:                    Garbage Collection.  (line 174)
* gc-cons-threshold:                     Garbage Collection.  (line 153)
* gc-elapsed:                            Garbage Collection.  (line 211)
* GCPRO and UNGCPRO:                     Writing Emacs Primitives.
                                                              (line 115)
* gcs-done:                              Garbage Collection.  (line 207)
* generate characters in charsets:       Splitting Characters.
                                                              (line  27)
* generate-new-buffer:                   Creating Buffers.    (line  36)
* generate-new-buffer-name:              Buffer Names.        (line  67)
* generic characters:                    Splitting Characters.
                                                              (line  42)
* generic mode:                          Generic Modes.       (line   6)
* generic comment delimiter:             Syntax Class Table.  (line 132)
* generic string delimiter:              Syntax Class Table.  (line 145)
* geometry specification:                Geometry.            (line  10)
* get:                                   Symbol Plists.       (line  25)
* get, defcustom keyword:                Variable Definitions.
                                                              (line  69)
* get-buffer:                            Buffer Names.        (line  50)
* get-buffer-create:                     Creating Buffers.    (line  17)
* get-buffer-process:                    Process Buffers.     (line  52)
* get-buffer-window:                     Buffers and Windows. (line  44)
* get-buffer-window-list:                Buffers and Windows. (line  65)
* get-char-property:                     Examining Properties.
                                                              (line  26)
* get-char-property-and-overlay:         Examining Properties.
                                                              (line  39)
* get-file-buffer:                       Buffer File Name.    (line  58)
* get-file-char:                         Input Streams.       (line 139)
* get-internal-run-time:                 Processor Run Time.  (line   7)
* get-largest-window:                    Selecting Windows.   (line  79)
* get-load-suffixes:                     Load Suffixes.       (line  33)
* get-lru-window:                        Selecting Windows.   (line  53)
* get-process:                           Process Information. (line  25)
* get-register:                          Registers.           (line  58)
* get-text-property:                     Examining Properties.
                                                              (line  17)
* get-unused-category:                   Categories.          (line  46)
* get-window-with-predicate:             Selecting Windows.   (line  95)
* getenv:                                System Environment.  (line 105)
* gethash:                               Hash Access.         (line  12)
* GIF:                                   GIF Images.          (line   6)
* global binding:                        Local Variables.     (line   6)
* global break condition:                Global Break Condition.
                                                              (line   6)
* global keymap:                         Active Keymaps.      (line   6)
* global variable:                       Global Variables.    (line   6)
* global-abbrev-table:                   Standard Abbrev Tables.
                                                              (line  10)
* global-disable-point-adjustment:       Adjusting Point.     (line  25)
* global-key-binding:                    Functions for Key Lookup.
                                                              (line  61)
* global-map:                            Controlling Active Maps.
                                                              (line   7)
* global-mode-string:                    Mode Line Variables. (line 114)
* global-set-key:                        Key Binding Commands.
                                                              (line  52)
* global-unset-key:                      Key Binding Commands.
                                                              (line  60)
* glyph:                                 Glyphs.              (line   6)
* glyph-char:                            Glyphs.              (line  22)
* glyph-face:                            Glyphs.              (line  25)
* glyph-table:                           Glyphs.              (line  32)
* goto-char:                             Character Motion.    (line  10)
* goto-line:                             Text Lines.          (line  15)
* grep-mode-map:                         Standard Keymaps.    (line 106)
* group, customization keyword:          Common Keywords.     (line  26)
* hack-local-variables:                  File Local Variables.
                                                              (line  33)
* handle-switch-frame:                   Input Focus.         (line  73)
* handling errors:                       Handling Errors.     (line   6)
* hash code:                             Defining Hash.       (line   6)
* hash notation:                         Printed Representation.
                                                              (line  13)
* hash tables:                           Hash Tables.         (line   6)
* hash-table-count:                      Other Hash.          (line  16)
* hash-table-p:                          Other Hash.          (line   9)
* hash-table-rehash-size:                Other Hash.          (line  28)
* hash-table-rehash-threshold:           Other Hash.          (line  31)
* hash-table-size:                       Other Hash.          (line  34)
* hash-table-test:                       Other Hash.          (line  19)
* hash-table-weakness:                   Other Hash.          (line  24)
* hashing:                               Creating Symbols.    (line  11)
* header comments:                       Library Headers.     (line   6)
* header line (of a window):             Header Lines.        (line   6)
* header-line prefix key:                Key Sequence Input.  (line  84)
* header-line-format:                    Header Lines.        (line  11)
* help for major mode:                   Mode Help.           (line   6)
* help-char:                             Help Functions.      (line  65)
* help-command:                          Help Functions.      (line  44)
* help-echo (overlay property):          Overlay Properties.  (line 101)
* help-echo (text property):             Special Properties.  (line  81)
* help-echo event:                       Misc Events.         (line  56)
* help-echo, customization keyword:      Type Keywords.       (line  96)
* help-event-list:                       Help Functions.      (line  83)
* help-form:                             Help Functions.      (line  88)
* help-index (button property):          Button Properties.   (line  43)
* help-map:                              Help Functions.      (line  40)
* help-mode-map:                         Standard Keymaps.    (line 113)
* Helper-describe-bindings:              Help Functions.      (line 121)
* Helper-help:                           Help Functions.      (line 126)
* Helper-help-map:                       Standard Keymaps.    (line 116)
* hex numbers:                           Integer Basics.      (line  22)
* hidden buffers:                        Buffer Names.        (line  12)
* history list:                          Minibuffer History.  (line   6)
* history of commands:                   Command History.     (line   6)
* history-add-new-input:                 Minibuffer History.  (line  72)
* history-delete-duplicates:             Minibuffer History.  (line  87)
* history-length:                        Minibuffer History.  (line  79)
* HOME environment variable:             Subprocess Creation. (line  17)
* hook variables, list of:               Standard Hooks.      (line   6)
* hooks:                                 Hooks.               (line   6)
* hooks for changing a character:        Special Properties.  (line 197)
* hooks for loading:                     Hooks for Loading.   (line   6)
* hooks for motion of point:             Special Properties.  (line 227)
* hooks for text changes:                Change Hooks.        (line   6)
* hooks for window operations:           Window Hooks.        (line   6)
* horizontal position:                   Columns.             (line   6)
* horizontal scrolling:                  Horizontal Scrolling.
                                                              (line   6)
* horizontal-scroll-bar prefix key:      Key Sequence Input.  (line  84)
* hyper characters:                      Other Char Bits.     (line  16)
* hyperlinks in documentation strings:   Documentation Tips.  (line 103)
* icon-title-format:                     Frame Titles.        (line  24)
* iconified frame:                       Visibility of Frames.
                                                              (line   6)
* iconify-frame:                         Visibility of Frames.
                                                              (line  29)
* iconify-frame event:                   Misc Events.         (line  16)
* identity:                              Calling Functions.   (line  88)
* idleness:                              Idle Timers.         (line  24)
* IEEE floating point:                   Float Basics.        (line  18)
* if:                                    Conditionals.        (line  12)
* ignore:                                Calling Functions.   (line  91)
* ignored-local-variables:               File Local Variables.
                                                              (line  95)
* image cache:                           Image Cache.         (line   6)
* image descriptor:                      Image Descriptors.   (line   6)
* image-cache-eviction-delay:            Image Cache.         (line  43)
* image-library-alist:                   Images.              (line  45)
* image-load-path:                       Defining Images.     (line  70)
* image-load-path-for-library:           Defining Images.     (line  90)
* image-mask-p:                          Image Descriptors.   (line 160)
* image-refresh:                         Image Cache.         (line  24)
* image-size:                            Showing Images.      (line  68)
* image-type-available-p:                Images.              (line  62)
* image-types:                           Images.              (line  35)
* images in buffers:                     Images.              (line   6)
* Imenu:                                 Imenu.               (line   6)
* imenu-add-to-menubar:                  Imenu.               (line  15)
* imenu-case-fold-search:                Imenu.               (line  70)
* imenu-create-index-function:           Imenu.               (line 130)
* imenu-extract-index-name-function:     Imenu.               (line 119)
* imenu-generic-expression:              Imenu.               (line  27)
* imenu-prev-index-position-function:    Imenu.               (line 109)
* imenu-syntax-alist:                    Imenu.               (line  78)
* implicit progn:                        Sequencing.          (line  21)
* inc:                                   Simple Macro.        (line  11)
* indent-according-to-mode:              Mode-Specific Indent.
                                                              (line  21)
* indent-code-rigidly:                   Region Indent.       (line  61)
* indent-for-tab-command:                Mode-Specific Indent.
                                                              (line  26)
* indent-line-function:                  Mode-Specific Indent.
                                                              (line  12)
* indent-region:                         Region Indent.       (line  10)
* indent-region-function:                Region Indent.       (line  24)
* indent-relative:                       Relative Indent.     (line  10)
* indent-relative-maybe:                 Relative Indent.     (line  51)
* indent-rigidly:                        Region Indent.       (line  45)
* indent-tabs-mode:                      Primitive Indent.    (line  29)
* indent-to:                             Primitive Indent.    (line  17)
* indent-to-left-margin:                 Margins.             (line  78)
* indentation:                           Indentation.         (line   6)
* indicate-buffer-boundaries:            Fringe Indicators.   (line  17)
* indicate-empty-lines:                  Fringe Indicators.   (line  11)
* indicators, fringe:                    Fringe Indicators.   (line   6)
* indirect buffers:                      Indirect Buffers.    (line   6)
* indirect specifications:               Specification List.  (line 109)
* indirect-function:                     Function Indirection.
                                                              (line  62)
* indirect-variable:                     Variable Aliases.    (line  59)
* indirection for functions:             Function Indirection.
                                                              (line   6)
* infinite loops:                        Infinite Loops.      (line   6)
* infinite recursion:                    Local Variables.     (line 104)
* infinity:                              Float Basics.        (line  18)
* Info-edit-map:                         Standard Keymaps.    (line 120)
* Info-mode-map:                         Standard Keymaps.    (line 123)
* inheritance of text properties:        Sticky Properties.   (line   6)
* inheriting a keymap's bindings:        Inheritance and Keymaps.
                                                              (line   6)
* inherit standard syntax:               Syntax Class Table.  (line 127)
* inhibit-default-init:                  Init File.           (line  48)
* inhibit-eol-conversion:                Specifying Coding Systems.
                                                              (line  45)
* inhibit-field-text-motion:             Word Motion.         (line  43)
* inhibit-file-name-handlers:            Magic File Names.    (line 141)
* inhibit-file-name-operation:           Magic File Names.    (line 145)
* inhibit-modification-hooks:            Change Hooks.        (line  66)
* inhibit-point-motion-hooks:            Special Properties.  (line 252)
* inhibit-quit:                          Quitting.            (line  80)
* inhibit-read-only:                     Read Only Buffers.   (line  32)
* inhibit-startup-echo-area-message:     Startup Summary.     (line  81)
* inhibit-startup-message:               Startup Summary.     (line  70)
* init file:                             Init File.           (line   6)
* init-file-user:                        User Identification. (line   7)
* initial-frame-alist:                   Initial Parameters.  (line  10)
* initial-major-mode:                    Auto Major Mode.     (line  90)
* initialization of Emacs:               Startup Summary.     (line   6)
* initialize, defcustom keyword:         Variable Definitions.
                                                              (line  82)
* inline functions:                      Inline Functions.    (line   6)
* innermost containing parentheses:      Parser State.        (line  17)
* input events:                          Input Events.        (line   6)
* input focus:                           Input Focus.         (line   6)
* input methods:                         Input Methods.       (line   6)
* input modes:                           Input Modes.         (line   6)
* input stream:                          Input Streams.       (line   6)
* input-method-alist:                    Input Methods.       (line  44)
* input-method-function:                 Invoking the Input Method.
                                                              (line  13)
* input-pending-p:                       Event Input Misc.    (line  53)
* insert:                                Insertion.           (line  37)
* insert-abbrev-table-description:       Abbrev Tables.       (line  42)
* insert-and-inherit:                    Sticky Properties.   (line  72)
* insert-before-markers:                 Insertion.           (line  43)
* insert-before-markers-and-inherit:     Sticky Properties.   (line  76)
* insert-behind-hooks (overlay property): Overlay Properties. (line 142)
* insert-behind-hooks (text property):   Special Properties.  (line 215)
* insert-buffer:                         Commands for Insertion.
                                                              (line  11)
* insert-buffer-substring:               Insertion.           (line  70)
* insert-buffer-substring-as-yank:       Yanking.             (line  19)
* insert-buffer-substring-no-properties: Insertion.           (line  92)
* insert-button:                         Making Buttons.      (line  36)
* insert-char:                           Insertion.           (line  56)
* insert-default-directory:              Reading File Names.  (line 121)
* insert-directory:                      Contents of Directories.
                                                              (line  73)
* insert-directory-program:              Contents of Directories.
                                                              (line 104)
* insert-file-contents:                  Reading from Files.  (line  12)
* insert-file-contents-literally:        Reading from Files.  (line  53)
* insert-for-yank:                       Yanking.             (line  12)
* insert-image:                          Showing Images.      (line  10)
* insert-in-front-hooks (overlay property): Overlay Properties.
                                                              (line 136)
* insert-in-front-hooks (text property): Special Properties.  (line 215)
* insert-register:                       Registers.           (line  70)
* insert-sliced-image:                   Showing Images.      (line  35)
* insert-text-button:                    Making Buttons.      (line  51)
* inserting killed text:                 Yank Commands.       (line  12)
* insertion before point:                Insertion.           (line   6)
* insertion of text:                     Insertion.           (line   6)
* insertion type of a marker:            Marker Insertion Types.
                                                              (line   6)
* inside comment:                        Parser State.        (line  27)
* inside string:                         Parser State.        (line  23)
* installation-directory:                System Environment.  (line 183)
* int-to-string:                         String Conversion.   (line  55)
* intangible (overlay property):         Overlay Properties.  (line 153)
* intangible (text property):            Special Properties.  (line 155)
* integer to decimal:                    String Conversion.   (line  43)
* integer to hexadecimal:                Formatting Strings.  (line  83)
* integer to octal:                      Formatting Strings.  (line  74)
* integer to string:                     String Conversion.   (line  43)
* integer-or-marker-p:                   Predicates on Markers.
                                                              (line  16)
* integerp:                              Predicates on Numbers.
                                                              (line  20)
* integers:                              Numbers.             (line   6)
* integers in specific radix:            Integer Basics.      (line  22)
* interactive:                           Using Interactive.   (line  11)
* interactive call:                      Interactive Call.    (line   6)
* interactive code description:          Interactive Codes.   (line   6)
* interactive completion:                Interactive Codes.   (line  10)
* interactive function:                  Defining Commands.   (line   6)
* interactive, examples of using:        Interactive Examples.
                                                              (line   6)
* interactive-form:                      Using Interactive.   (line 113)
* interactive-p:                         Distinguish Interactive.
                                                              (line  68)
* intern:                                Creating Symbols.    (line  96)
* intern-soft:                           Creating Symbols.    (line 116)
* internals, of buffer:                  Buffer Internals.    (line   6)
* internals, of process:                 Process Internals.   (line   6)
* internals, of window:                  Window Internals.    (line   6)
* interning:                             Creating Symbols.    (line  23)
* interpreter:                           Evaluation.          (line   6)
* interpreter-mode-alist:                Auto Major Mode.     (line  95)
* interprogram-cut-function:             Low-Level Kill Ring. (line  74)
* interprogram-paste-function:           Low-Level Kill Ring. (line  60)
* interrupt Lisp functions:              Quitting.            (line   6)
* interrupt-process:                     Signals to Processes.
                                                              (line  49)
* intervals:                             Not Intervals.       (line   6)
* intervals-consed:                      Memory Usage.        (line  39)
* introduction sequence (of character):  Chars and Bytes.     (line   6)
* invalid prefix key error:              Changing Key Bindings.
                                                              (line  57)
* invalid-function:                      Function Indirection.
                                                              (line  21)
* invalid-read-syntax:                   Printed Representation.
                                                              (line  25)
* invalid-regexp:                        Regexp Backslash.    (line 189)
* invert-face:                           Attribute Functions. (line 134)
* invisible (overlay property):          Overlay Properties.  (line 148)
* invisible (text property):             Special Properties.  (line 151)
* invisible frame:                       Visibility of Frames.
                                                              (line   6)
* invisible text:                        Invisible Text.      (line   6)
* invisible/intangible text, and point:  Adjusting Point.     (line   6)
* invocation-directory:                  System Environment.  (line 178)
* invocation-name:                       System Environment.  (line 173)
* isearch-mode-map:                      Standard Keymaps.    (line 126)
* iteration:                             Iteration.           (line   6)
* joining lists:                         Rearrangement.       (line  16)
* just-one-space:                        User-Level Deletion. (line  99)
* justify-current-line:                  Filling.             (line  94)
* kbd:                                   Key Sequences.       (line  35)
* kbd-macro-termination-hook:            Keyboard Macros.     (line  63)
* kept-new-versions:                     Numbered Backups.    (line  29)
* kept-old-versions:                     Numbered Backups.    (line  34)
* key:                                   Key Sequences.       (line   6)
* key binding:                           Keymap Basics.       (line   6)
* key binding, conventions for:          Key Binding Conventions.
                                                              (line   6)
* key lookup:                            Key Lookup.          (line   6)
* key sequence:                          Key Sequences.       (line   6)
* key sequence error:                    Changing Key Bindings.
                                                              (line  57)
* key sequence input:                    Key Sequence Input.  (line   6)
* key translation function:              Translation Keymaps. (line  72)
* key-binding:                           Active Keymaps.      (line  79)
* key-description:                       Describing Characters.
                                                              (line  14)
* key-translation-map:                   Translation Keymaps. (line  48)
* keyboard events:                       Keyboard Events.     (line   6)
* keyboard events in strings:            Strings of Events.   (line   6)
* keyboard input:                        Reading Input.       (line   6)
* keyboard input decoding on X:          Locales.             (line  11)
* keyboard macro execution:              Interactive Call.    (line  57)
* keyboard macro termination:            Beeping.             (line  13)
* keyboard macro, terminating:           Event Input Misc.    (line  99)
* keyboard macros:                       Keyboard Macros.     (line   6)
* keyboard macros (Edebug):              Edebug Execution Modes.
                                                              (line  69)
* keyboard-coding-system:                Terminal I/O Encoding.
                                                              (line  12)
* keyboard-quit:                         Quitting.            (line 106)
* keyboard-translate:                    Event Mod.           (line  55)
* keyboard-translate-table:              Event Mod.           (line  33)
* keymap:                                Keymaps.             (line   6)
* keymap (button property):              Button Properties.   (line  32)
* keymap (overlay property):             Overlay Properties.  (line 190)
* keymap (text property):                Special Properties.  (line 111)
* keymap entry:                          Key Lookup.          (line   6)
* keymap format:                         Format of Keymaps.   (line   6)
* keymap in keymap:                      Key Lookup.          (line  52)
* keymap inheritance:                    Inheritance and Keymaps.
                                                              (line   6)
* keymap of character:                   Special Properties.  (line 111)
* keymap of character (and overlays):    Overlay Properties.  (line 184)
* keymap prompt string:                  Format of Keymaps.   (line  50)
* keymap-parent:                         Inheritance and Keymaps.
                                                              (line  28)
* keymap-prompt:                         Defining Menus.      (line  21)
* keymapp:                               Format of Keymaps.   (line  98)
* keymaps for translating events:        Translation Keymaps. (line   6)
* keymaps in modes:                      Major Mode Conventions.
                                                              (line  60)
* keys in documentation strings:         Keys in Documentation.
                                                              (line   6)
* keys, reserved:                        Key Binding Conventions.
                                                              (line  14)
* keystroke:                             Key Sequences.       (line   6)
* keystroke command:                     What Is a Function.  (line  69)
* keyword symbol:                        Constant Variables.  (line   6)
* keywordp:                              Constant Variables.  (line  20)
* kill command repetition:               Command Loop Info.   (line  43)
* kill ring:                             The Kill Ring.       (line   6)
* kill-all-local-variables:              Creating Buffer-Local.
                                                              (line 139)
* kill-append:                           Low-Level Kill Ring. (line  48)
* kill-buffer:                           Killing Buffers.     (line  33)
* kill-buffer-hook:                      Killing Buffers.     (line  73)
* kill-buffer-query-functions:           Killing Buffers.     (line  65)
* kill-emacs:                            Killing Emacs.       (line  11)
* kill-emacs-hook:                       Killing Emacs.       (line  39)
* kill-emacs-query-functions:            Killing Emacs.       (line  30)
* kill-local-variable:                   Creating Buffer-Local.
                                                              (line 119)
* kill-new:                              Low-Level Kill Ring. (line  32)
* kill-process:                          Signals to Processes.
                                                              (line  57)
* kill-read-only-ok:                     Kill Functions.      (line  34)
* kill-region:                           Kill Functions.      (line  15)
* kill-ring:                             Internals of Kill Ring.
                                                              (line  52)
* kill-ring-max:                         Internals of Kill Ring.
                                                              (line  62)
* kill-ring-yank-pointer:                Internals of Kill Ring.
                                                              (line  56)
* killing buffers:                       Killing Buffers.     (line   6)
* killing Emacs:                         Killing Emacs.       (line   6)
* kmacro-map:                            Standard Keymaps.    (line 134)
* lambda expression:                     Lambda Expressions.  (line   6)
* lambda in debug:                       Invoking the Debugger.
                                                              (line  33)
* lambda in keymap:                      Key Lookup.          (line  61)
* lambda list:                           Lambda Components.   (line  14)
* lambda-list (Edebug):                  Specification List.  (line 178)
* last:                                  List Elements.       (line 111)
* last-abbrev:                           Abbrev Expansion.    (line  68)
* last-abbrev-location:                  Abbrev Expansion.    (line  74)
* last-abbrev-text:                      Abbrev Expansion.    (line  79)
* last-coding-system-used:               Encoding and I/O.    (line  49)
* last-command:                          Command Loop Info.   (line  12)
* last-command-char:                     Command Loop Info.   (line 112)
* last-command-event:                    Command Loop Info.   (line 111)
* last-event-frame:                      Command Loop Info.   (line 127)
* last-input-char:                       Event Input Misc.    (line  60)
* last-input-event:                      Event Input Misc.    (line  59)
* last-kbd-macro:                        Keyboard Macros.     (line  56)
* last-nonmenu-event:                    Command Loop Info.   (line 103)
* last-prefix-arg:                       Prefix Command Arguments.
                                                              (line  98)
* last-repeatable-command:               Command Loop Info.   (line  29)
* lax-plist-get:                         Other Plists.        (line  47)
* lax-plist-put:                         Other Plists.        (line  51)
* lazy loading:                          Dynamic Loading.     (line   6)
* lazy-completion-table:                 Basic Completion.    (line 167)
* leading code:                          Text Representations.
                                                              (line  19)
* left-fringe-width:                     Fringe Size/Pos.     (line  15)
* left-margin:                           Margins.             (line  85)
* left-margin-width:                     Display Margins.     (line  32)
* length:                                Sequence Functions.  (line  16)
* let:                                   Local Variables.     (line  52)
* let*:                                  Local Variables.     (line  74)
* lexical binding (Edebug):              Edebug Eval.         (line  25)
* lexical comparison:                    Text Comparison.     (line  52)
* lexical scoping:                       Variable Scoping.    (line  11)
* library:                               Loading.             (line   6)
* library compilation:                   Compilation Functions.
                                                              (line 112)
* library header comments:               Library Headers.     (line   6)
* library search:                        Library Search.      (line   6)
* line end conversion:                   Coding System Basics.
                                                              (line  38)
* line height:                           Line Height.         (line   6)
* line number:                           Text Lines.          (line 113)
* line truncation:                       Truncation.          (line   6)
* line wrapping:                         Truncation.          (line   6)
* line-beginning-position:               Text Lines.          (line  59)
* line-end-position:                     Text Lines.          (line  77)
* line-height (text property) <1>:       Special Properties.  (line 192)
* line-height (text property):           Line Height.         (line  22)
* line-move-ignore-invisible:            Invisible Text.      (line  89)
* line-number-at-pos:                    Text Lines.          (line 113)
* line-spacing:                          Line Height.         (line  77)
* line-spacing (text property) <1>:      Special Properties.  (line 186)
* line-spacing (text property):          Line Height.         (line  83)
* lines:                                 Text Lines.          (line   6)
* lines in region:                       Text Lines.          (line  98)
* link, customization keyword:           Common Keywords.     (line  36)
* linking files:                         Changing Files.      (line   6)
* Lisp debugger:                         Debugger.            (line   6)
* Lisp expression motion:                List Motion.         (line   6)
* Lisp history:                          Lisp History.        (line   6)
* Lisp library:                          Loading.             (line   6)
* Lisp nesting error:                    Eval.                (line  93)
* Lisp object:                           Lisp Data Types.     (line   6)
* Lisp printer:                          Output Functions.    (line  40)
* Lisp reader:                           Streams Intro.       (line   6)
* lisp-interaction-mode-map:             Standard Keymaps.    (line 137)
* lisp-mode-abbrev-table:                Standard Abbrev Tables.
                                                              (line  28)
* lisp-mode-map:                         Standard Keymaps.    (line 140)
* lisp-mode.el:                          Example Major Modes. (line  82)
* list:                                  Building Lists.      (line  36)
* list elements:                         List Elements.       (line   6)
* list form evaluation:                  Classifying Lists.   (line   6)
* list in keymap:                        Key Lookup.          (line  56)
* list length:                           Sequence Functions.  (line  16)
* list motion:                           List Motion.         (line   6)
* list structure:                        Cons Cells.          (line  46)
* list-buffers-directory:                Buffer File Name.    (line 122)
* list-charset-chars:                    Character Sets.      (line  46)
* list-processes:                        Process Information. (line  10)
* listify-key-sequence:                  Event Input Misc.    (line  41)
* listp:                                 List-related Predicates.
                                                              (line  23)
* lists:                                 Lists.               (line   6)
* lists and cons cells:                  Cons Cells.          (line   6)
* lists as sets:                         Sets And Lists.      (line   6)
* literal evaluation:                    Self-Evaluating Forms.
                                                              (line   6)
* little endian:                         Bindat Spec.         (line  13)
* ln:                                    Changing Files.      (line 103)
* load:                                  How Programs Do Loading.
                                                              (line  15)
* load error with require:               Named Features.      (line  22)
* load errors:                           How Programs Do Loading.
                                                              (line  72)
* load, customization keyword:           Common Keywords.     (line  94)
* load-average:                          System Environment.  (line 190)
* load-file:                             How Programs Do Loading.
                                                              (line  87)
* load-file-rep-suffixes:                Load Suffixes.       (line  17)
* load-history:                          Where Defined.       (line  19)
* load-in-progress:                      How Programs Do Loading.
                                                              (line  99)
* load-library:                          How Programs Do Loading.
                                                              (line  95)
* load-path:                             Library Search.      (line  10)
* load-read-function:                    How Programs Do Loading.
                                                              (line 103)
* load-suffixes:                         Load Suffixes.       (line  10)
* loading:                               Loading.             (line   6)
* loading hooks:                         Hooks for Loading.   (line   6)
* loadup.el:                             Building Emacs.      (line  16)
* local binding:                         Local Variables.     (line   6)
* local keymap:                          Active Keymaps.      (line   6)
* local variables:                       Local Variables.     (line   6)
* local-abbrev-table:                    Standard Abbrev Tables.
                                                              (line  16)
* local-key-binding:                     Functions for Key Lookup.
                                                              (line  54)
* local-map (overlay property):          Overlay Properties.  (line 184)
* local-map (text property):             Special Properties.  (line 124)
* local-set-key:                         Key Binding Commands.
                                                              (line  79)
* local-unset-key:                       Key Binding Commands.
                                                              (line  87)
* local-variable-if-set-p:               Creating Buffer-Local.
                                                              (line  82)
* local-variable-p:                      Creating Buffer-Local.
                                                              (line  78)
* locale:                                Locales.             (line   6)
* locale-coding-system:                  Locales.             (line  11)
* locale-info:                           Locales.             (line  31)
* locate file in path:                   Locating Files.      (line   6)
* locate-file:                           Locating Files.      (line  16)
* locate-library:                        Library Search.      (line  99)
* lock file:                             File Locks.          (line   6)
* lock-buffer:                           File Locks.          (line  33)
* log:                                   Math Functions.      (line  37)
* log10:                                 Math Functions.      (line  42)
* logand:                                Bitwise Operations.  (line 131)
* logb:                                  Float Basics.        (line  51)
* logging echo-area messages:            Logging Messages.    (line   6)
* logical arithmetic:                    Bitwise Operations.  (line   6)
* logical shift:                         Bitwise Operations.  (line  15)
* logior:                                Bitwise Operations.  (line 169)
* lognot:                                Bitwise Operations.  (line 205)
* logxor:                                Bitwise Operations.  (line 187)
* looking-at:                            Regexp Search.       (line 110)
* looking-back:                          Regexp Search.       (line 133)
* lookup tables:                         Hash Tables.         (line   6)
* lookup-key:                            Functions for Key Lookup.
                                                              (line   9)
* loops, infinite:                       Infinite Loops.      (line   6)
* lower case:                            Case Conversion.     (line   6)
* lower-frame:                           Raising and Lowering.
                                                              (line  27)
* lowering a frame:                      Raising and Lowering.
                                                              (line  13)
* lsh:                                   Bitwise Operations.  (line  15)
* lwarn:                                 Warning Basics.      (line  51)
* M-o:                                   Prefix Keys.         (line  43)
* M-x:                                   Interactive Call.    (line  86)
* Maclisp:                               Lisp History.        (line  11)
* macro:                                 What Is a Function.  (line  46)
* macro argument evaluation:             Argument Evaluation. (line  57)
* macro call:                            Expansion.           (line   6)
* macro call evaluation:                 Macro Forms.         (line   6)
* macro compilation:                     Compilation Functions.
                                                              (line  15)
* macro descriptions:                    A Sample Function Description.
                                                              (line   6)
* macro expansion:                       Expansion.           (line  37)
* macroexpand:                           Expansion.           (line  37)
* macroexpand-all:                       Expansion.           (line  71)
* macros:                                Macros.              (line   6)
* macros, at compile time:               Eval During Compile. (line  48)
* magic autoload comment:                Autoload.            (line  93)
* magic file names:                      Magic File Names.    (line   6)
* magic-fallback-mode-alist:             Auto Major Mode.     (line 111)
* magic-mode-alist:                      Auto Major Mode.     (line 103)
* mail-host-address:                     System Environment.  (line  97)
* major mode:                            Major Modes.         (line   6)
* major mode conventions:                Major Mode Conventions.
                                                              (line   6)
* major mode hook:                       Major Mode Conventions.
                                                              (line 157)
* major mode keymap:                     Active Keymaps.      (line  51)
* major mode, automatic selection:       Auto Major Mode.     (line   6)
* major-mode:                            Mode Help.           (line  20)
* make-abbrev-table:                     Abbrev Tables.       (line   9)
* make-auto-save-file-name:              Auto-Saving.         (line  55)
* make-backup-file-name:                 Backup Names.        (line  36)
* make-backup-file-name-function:        Making Backups.      (line  91)
* make-backup-files:                     Making Backups.      (line  27)
* make-bool-vector:                      Bool-Vectors.        (line  18)
* make-button:                           Making Buttons.      (line  32)
* make-byte-code:                        Byte-Code Objects.   (line  56)
* make-category-set:                     Categories.          (line  76)
* make-category-table:                   Categories.          (line  71)
* make-char:                             Splitting Characters.
                                                              (line  28)
* make-char-table:                       Char-Tables.         (line  34)
* make-directory:                        Create/Delete Dirs.  (line  12)
* make-display-table:                    Display Table Format.
                                                              (line  10)
* make-face:                             Face Functions.      (line   9)
* make-frame:                            Creating Frames.     (line   9)
* make-frame-invisible:                  Visibility of Frames.
                                                              (line  22)
* make-frame-on-display:                 Multiple Displays.   (line  40)
* make-frame-visible:                    Visibility of Frames.
                                                              (line  16)
* make-frame-visible event:              Misc Events.         (line  23)
* make-glyph-code:                       Glyphs.              (line  18)
* make-hash-table:                       Creating Hash.       (line   9)
* make-help-screen:                      Help Functions.      (line 139)
* make-indirect-buffer:                  Indirect Buffers.    (line  32)
* make-keymap:                           Creating Keymaps.    (line  26)
* make-list:                             Building Lists.      (line  48)
* make-local-variable:                   Creating Buffer-Local.
                                                              (line   7)
* make-marker:                           Creating Markers.    (line  15)
* make-network-process:                  Network Processes.   (line  11)
* make-obsolete:                         Obsolete Functions.  (line  10)
* make-obsolete-variable:                Variable Aliases.    (line  37)
* make-overlay:                          Managing Overlays.   (line  16)
* make-progress-reporter:                Progress.            (line  24)
* make-ring:                             Rings.               (line  11)
* make-sparse-keymap:                    Creating Keymaps.    (line   9)
* make-string:                           Creating Strings.    (line  10)
* make-symbol:                           Creating Symbols.    (line  84)
* make-symbolic-link:                    Changing Files.      (line 103)
* make-syntax-table:                     Syntax Table Functions.
                                                              (line  10)
* make-temp-file:                        Unique File Names.   (line  15)
* make-temp-name:                        Unique File Names.   (line  59)
* make-text-button:                      Making Buttons.      (line  47)
* make-translation-table:                Translation of Characters.
                                                              (line  20)
* make-variable-buffer-local:            Creating Buffer-Local.
                                                              (line  47)
* make-vector:                           Vector Functions.    (line  26)
* makehash:                              Creating Hash.       (line 104)
* making buttons:                        Making Buttons.      (line   6)
* makunbound:                            Void Variables.      (line  21)
* manipulating buttons:                  Manipulating Buttons.
                                                              (line   6)
* map-char-table:                        Char-Tables.         (line 122)
* map-keymap:                            Scanning Keymaps.    (line  65)
* map-y-or-n-p:                          Multiple Queries.    (line  14)
* mapatoms:                              Creating Symbols.    (line 144)
* mapc:                                  Mapping Functions.   (line  53)
* mapcar:                                Mapping Functions.   (line  20)
* mapconcat:                             Mapping Functions.   (line  58)
* maphash:                               Hash Access.         (line  37)
* mapping functions:                     Mapping Functions.   (line   6)
* margins, display:                      Display Margins.     (line   6)
* mark:                                  The Mark.            (line  51)
* mark excursion:                        Excursions.          (line  18)
* mark ring:                             The Mark.            (line   6)
* mark, the:                             The Mark.            (line   6)
* mark-active:                           The Mark.            (line 158)
* mark-even-if-inactive:                 The Mark.            (line 132)
* mark-marker:                           The Mark.            (line  60)
* mark-ring:                             The Mark.            (line 169)
* mark-ring-max:                         The Mark.            (line 178)
* marker argument:                       Interactive Codes.   (line 128)
* marker garbage collection:             Overview of Markers. (line  31)
* marker input stream:                   Input Streams.       (line  17)
* marker output stream:                  Output Streams.      (line  15)
* marker relocation:                     Overview of Markers. (line  24)
* marker-buffer:                         Information from Markers.
                                                              (line  14)
* marker-insertion-type:                 Marker Insertion Types.
                                                              (line  20)
* marker-position:                       Information from Markers.
                                                              (line  10)
* markerp:                               Predicates on Markers.
                                                              (line  11)
* markers:                               Markers.             (line   6)
* markers as numbers:                    Overview of Markers. (line  38)
* match data:                            Match Data.          (line   6)
* match, customization keyword:          Type Keywords.       (line 104)
* match-alternatives, customization keyword: Composite Types. (line 203)
* match-beginning:                       Simple Match Data.   (line  56)
* match-data:                            Entire Match Data.   (line  10)
* match-end:                             Simple Match Data.   (line  68)
* match-string:                          Simple Match Data.   (line  35)
* match-string-no-properties:            Simple Match Data.   (line  52)
* mathematical functions:                Math Functions.      (line   6)
* max:                                   Comparison of Numbers.
                                                              (line  79)
* max-image-size:                        Showing Images.      (line  77)
* max-lisp-eval-depth:                   Eval.                (line  86)
* max-mini-window-height:                Minibuffer Misc.     (line  33)
* max-specpdl-size:                      Local Variables.     (line 104)
* md5:                                   MD5 Checksum.        (line  14)
* MD5 checksum:                          MD5 Checksum.        (line   6)
* member:                                Sets And Lists.      (line 107)
* member-ignore-case:                    Sets And Lists.      (line 166)
* membership in a list:                  Sets And Lists.      (line  20)
* memory allocation:                     Garbage Collection.  (line   6)
* memory usage:                          Memory Usage.        (line   6)
* memory-full:                           Garbage Collection.  (line 197)
* memory-limit:                          Garbage Collection.  (line 189)
* memory-use-counts:                     Garbage Collection.  (line 201)
* memq:                                  Sets And Lists.      (line  20)
* memql:                                 Sets And Lists.      (line  89)
* menu bar:                              Menu Bar.            (line   6)
* menu definition example:               Menu Example.        (line   6)
* menu keymaps:                          Menu Keymaps.        (line   6)
* menu prompt string:                    Defining Menus.      (line   6)
* menu separators:                       Menu Separators.     (line   6)
* menu-bar prefix key:                   Key Sequence Input.  (line  84)
* menu-bar-edit-menu:                    Standard Keymaps.    (line 143)
* menu-bar-files-menu:                   Standard Keymaps.    (line 146)
* menu-bar-final-items:                  Menu Bar.            (line  64)
* menu-bar-help-menu:                    Standard Keymaps.    (line 149)
* menu-bar-mule-menu:                    Standard Keymaps.    (line 152)
* menu-bar-search-menu:                  Standard Keymaps.    (line 155)
* menu-bar-tools-menu:                   Standard Keymaps.    (line 158)
* menu-bar-update-hook:                  Menu Bar.            (line  74)
* menu-item:                             Extended Menu Items. (line   6)
* menu-prompt-more-char:                 Keyboard Menus.      (line  27)
* merge-face-attribute:                  Attribute Functions. (line  79)
* message:                               Displaying Messages. (line  10)
* message digest computation:            MD5 Checksum.        (line   6)
* message-box:                           Displaying Messages. (line  61)
* message-log-max:                       Logging Messages.    (line  11)
* message-or-box:                        Displaying Messages. (line  48)
* message-truncate-lines:                Echo Area Customization.
                                                              (line  34)
* meta character key constants:          Changing Key Bindings.
                                                              (line  20)
* meta character printing:               Describing Characters.
                                                              (line  29)
* meta characters:                       Meta-Char Syntax.    (line   6)
* meta characters lookup:                Format of Keymaps.   (line  61)
* meta-prefix-char:                      Functions for Key Lookup.
                                                              (line  84)
* min:                                   Comparison of Numbers.
                                                              (line  91)
* minibuffer:                            Minibuffers.         (line   6)
* minibuffer completion:                 Minibuffer Completion.
                                                              (line   6)
* minibuffer history:                    Minibuffer History.  (line   6)
* minibuffer input:                      Recursive Editing.   (line  25)
* minibuffer window, and next-window:    Cyclic Window Ordering.
                                                              (line  24)
* minibuffer windows:                    Minibuffer Windows.  (line   6)
* minibuffer-allow-text-properties:      Text from Minibuffer.
                                                              (line  98)
* minibuffer-auto-raise:                 Raising and Lowering.
                                                              (line  30)
* minibuffer-complete:                   Completion Commands. (line  39)
* minibuffer-complete-and-exit:          Completion Commands. (line  42)
* minibuffer-complete-word:              Completion Commands. (line  32)
* minibuffer-completion-confirm:         Completion Commands. (line  26)
* minibuffer-completion-contents:        Minibuffer Contents. (line  33)
* minibuffer-completion-help:            Completion Commands. (line  50)
* minibuffer-completion-predicate:       Completion Commands. (line  21)
* minibuffer-completion-table:           Completion Commands. (line  15)
* minibuffer-contents:                   Minibuffer Contents. (line  22)
* minibuffer-contents-no-properties:     Minibuffer Contents. (line  28)
* minibuffer-depth:                      Recursive Mini.      (line  10)
* minibuffer-exit-hook:                  Minibuffer Misc.     (line  15)
* minibuffer-frame-alist:                Initial Parameters.  (line  43)
* minibuffer-help-form:                  Minibuffer Misc.     (line  19)
* minibuffer-history:                    Minibuffer History.  (line  93)
* minibuffer-local-completion-map:       Completion Commands. (line  93)
* minibuffer-local-filename-completion-map: Completion Commands.
                                                              (line 134)
* minibuffer-local-map:                  Text from Minibuffer.
                                                              (line 108)
* minibuffer-local-must-match-filename-map: Completion Commands.
                                                              (line 139)
* minibuffer-local-must-match-map:       Completion Commands. (line 110)
* minibuffer-local-ns-map:               Text from Minibuffer.
                                                              (line 158)
* minibuffer-message:                    Minibuffer Misc.     (line  38)
* minibuffer-prompt:                     Minibuffer Contents. (line   9)
* minibuffer-prompt-end:                 Minibuffer Contents. (line  13)
* minibuffer-prompt-width:               Minibuffer Contents. (line  18)
* minibuffer-scroll-window:              Minibuffer Misc.     (line  23)
* minibuffer-selected-window:            Minibuffer Misc.     (line  28)
* minibuffer-setup-hook:                 Minibuffer Misc.     (line  11)
* minibuffer-window:                     Minibuffer Windows.  (line  14)
* minibuffer-window-active-p:            Minibuffer Windows.  (line  38)
* minibufferp:                           Minibuffer Misc.     (line   7)
* minimum window size:                   Resizing Windows.    (line 122)
* minor mode:                            Minor Modes.         (line   6)
* minor mode conventions:                Minor Mode Conventions.
                                                              (line   6)
* minor-mode-alist:                      Mode Line Variables. (line  96)
* minor-mode-key-binding:                Functions for Key Lookup.
                                                              (line  68)
* minor-mode-list:                       Minor Modes.         (line  29)
* minor-mode-map-alist:                  Controlling Active Maps.
                                                              (line  57)
* minor-mode-overriding-map-alist:       Controlling Active Maps.
                                                              (line  83)
* misc-objects-consed:                   Memory Usage.        (line  34)
* mod:                                   Arithmetic Operations.
                                                              (line 140)
* mode:                                  Modes.               (line   6)
* mode help:                             Mode Help.           (line   6)
* mode hook:                             Major Mode Conventions.
                                                              (line 157)
* mode line:                             Mode Line Format.    (line   6)
* mode loading:                          Major Mode Conventions.
                                                              (line 202)
* mode variable:                         Minor Mode Conventions.
                                                              (line  16)
* mode-class (property):                 Major Mode Conventions.
                                                              (line 181)
* mode-line construct:                   Mode Line Data.      (line   6)
* mode-line prefix key:                  Key Sequence Input.  (line  84)
* mode-line-buffer-identification:       Mode Line Variables. (line  38)
* mode-line-format:                      Mode Line Top.       (line   9)
* mode-line-frame-identification:        Mode Line Variables. (line  32)
* mode-line-modes:                       Mode Line Variables. (line  67)
* mode-line-modified:                    Mode Line Variables. (line  21)
* mode-line-mule-info:                   Mode Line Variables. (line  16)
* mode-line-position:                    Mode Line Variables. (line  43)
* mode-line-process:                     Mode Line Variables. (line  87)
* mode-name:                             Mode Line Variables. (line  82)
* mode-specific-map:                     Prefix Keys.         (line  21)
* model/view/controller:                 Abstract Display.    (line   6)
* modification flag (of buffer):         Buffer Modification. (line   6)
* modification of lists:                 Rearrangement.       (line   6)
* modification time of buffer:           Modification Time.   (line   6)
* modification time of file:             File Attributes.     (line  93)
* modification-hooks (overlay property): Overlay Properties.  (line 107)
* modification-hooks (text property):    Special Properties.  (line 197)
* modifier bits (of input character):    Keyboard Events.     (line  12)
* modify-all-frames-parameters:          Parameter Access.    (line  27)
* modify-category-entry:                 Categories.          (line 105)
* modify-frame-parameters:               Parameter Access.    (line  20)
* modify-syntax-entry:                   Syntax Table Functions.
                                                              (line  27)
* modulus:                               Arithmetic Operations.
                                                              (line 140)
* momentary-string-display:              Temporary Displays.  (line  83)
* most-negative-fixnum:                  Integer Basics.      (line  81)
* most-positive-fixnum:                  Integer Basics.      (line  77)
* motion by chars, words, lines, lists:  Motion.              (line   6)
* motion event:                          Motion Events.       (line   6)
* mouse click event:                     Click Events.        (line   6)
* mouse drag event:                      Drag Events.         (line   6)
* mouse events, data in:                 Accessing Mouse.     (line   6)
* mouse events, in special parts of frame: Key Sequence Input.
                                                              (line  84)
* mouse events, repeated:                Repeat Events.       (line   6)
* mouse motion events:                   Motion Events.       (line   6)
* mouse pointer shape:                   Pointer Shape.       (line   6)
* mouse position:                        Mouse Position.      (line   6)
* mouse position list, accessing:        Accessing Mouse.     (line  31)
* mouse tracking:                        Mouse Tracking.      (line   6)
* mouse, availability:                   Display Feature Testing.
                                                              (line  31)
* mouse-1:                               Links and Mouse-1.   (line   6)
* mouse-2:                               Key Binding Conventions.
                                                              (line   6)
* mouse-action (button property):        Button Properties.   (line  17)
* mouse-face (button property):          Button Properties.   (line  27)
* mouse-face (overlay property):         Overlay Properties.  (line  91)
* mouse-face (text property):            Special Properties.  (line  62)
* mouse-movement-p:                      Classifying Events.  (line  89)
* mouse-on-link-p:                       Links and Mouse-1.   (line  98)
* mouse-pixel-position:                  Mouse Position.      (line  32)
* mouse-position:                        Mouse Position.      (line  10)
* mouse-position-function:               Mouse Position.      (line  16)
* move to beginning or end of buffer:    Buffer End Motion.   (line   6)
* move-marker:                           Moving Markers.      (line  34)
* move-overlay:                          Managing Overlays.   (line  53)
* move-to-column:                        Columns.             (line  32)
* move-to-left-margin:                   Margins.             (line  62)
* move-to-window-line:                   Screen Lines.        (line  65)
* movemail:                              Subprocess Creation. (line  64)
* MS-DOS and file modes:                 Changing Files.      (line 162)
* MS-DOS file types:                     MS-DOS File Types.   (line   6)
* mule-keymap:                           Prefix Keys.         (line  31)
* multibyte characters:                  Non-ASCII Characters.
                                                              (line   6)
* multibyte text:                        Text Representations.
                                                              (line  19)
* multibyte-char-to-unibyte:             Converting Representations.
                                                              (line  97)
* multibyte-string-p:                    Text Representations.
                                                              (line  71)
* multibyte-syntax-as-symbol:            Control Parsing.     (line   7)
* multiline font lock:                   Multiline Font Lock. (line   6)
* multiple windows:                      Basic Windows.       (line  60)
* multiple X displays:                   Multiple Displays.   (line   6)
* multiple-frames:                       Frame Titles.        (line  29)
* named function:                        Function Names.      (line   6)
* NaN:                                   Float Basics.        (line  18)
* narrow-to-page:                        Narrowing.           (line  33)
* narrow-to-region:                      Narrowing.           (line  25)
* narrowing:                             Narrowing.           (line   6)
* natnump:                               Predicates on Numbers.
                                                              (line  33)
* natural numbers:                       Predicates on Numbers.
                                                              (line  28)
* nbutlast:                              List Elements.       (line 149)
* nconc:                                 Rearrangement.       (line  16)
* negative infinity:                     Float Basics.        (line  18)
* negative-argument:                     Prefix Command Arguments.
                                                              (line 116)
* network byte ordering:                 Bindat Spec.         (line  13)
* network connection:                    Network.             (line   6)
* network servers:                       Network Servers.     (line   6)
* network-coding-system-alist:           Default Coding Systems.
                                                              (line  72)
* network-interface-info:                Misc Network.        (line  17)
* network-interface-list:                Misc Network.        (line  10)
* new file message:                      Subroutines of Visiting.
                                                              (line  37)
* newline <1>:                           Basic Char Syntax.   (line  27)
* newline:                               Commands for Insertion.
                                                              (line  43)
* newline and Auto Fill mode:            Commands for Insertion.
                                                              (line  47)
* newline in print:                      Output Functions.    (line  84)
* newline in strings:                    Syntax for Strings.  (line  13)
* newline-and-indent:                    Mode-Specific Indent.
                                                              (line  32)
* next input:                            Event Input Misc.    (line  11)
* next-button:                           Button Buffer Commands.
                                                              (line  52)
* next-char-property-change:             Property Search.     (line  84)
* next-frame:                            Finding All Frames.  (line  20)
* next-history-element:                  Minibuffer Commands. (line  22)
* next-matching-history-element:         Minibuffer Commands. (line  31)
* next-overlay-change:                   Finding Overlays.    (line  35)
* next-property-change:                  Property Search.     (line  26)
* next-screen-context-lines:             Textual Scrolling.   (line 150)
* next-single-char-property-change:      Property Search.     (line 100)
* next-single-property-change:           Property Search.     (line  60)
* next-window:                           Cyclic Window Ordering.
                                                              (line  24)
* nil:                                   nil and t.           (line   6)
* nil as a list:                         Box Diagrams.        (line  41)
* nil in keymap:                         Key Lookup.          (line  36)
* nil input stream:                      Input Streams.       (line  51)
* nil output stream:                     Output Streams.      (line  34)
* nlistp:                                List-related Predicates.
                                                              (line  32)
* no-byte-compile:                       Byte Compilation.    (line  27)
* no-catch:                              Catch and Throw.     (line  86)
* no-redraw-on-reenter:                  Refresh Screen.      (line  30)
* no-self-insert property:               Defining Abbrevs.    (line  33)
* non-ASCII characters:                  Non-ASCII Characters.
                                                              (line   6)
* non-ASCII text in keybindings:         Key Binding Commands.
                                                              (line  29)
* nonascii-insert-offset:                Converting Representations.
                                                              (line  47)
* nonascii-translation-table:            Converting Representations.
                                                              (line  59)
* nondirectory part (of file name):      File Name Components.
                                                              (line   6)
* noninteractive:                        Batch Mode.          (line  25)
* nonlocal exits:                        Nonlocal Exits.      (line   6)
* nonprinting characters, reading:       Quoted Character Input.
                                                              (line  12)
* noreturn:                              Test Coverage.       (line  30)
* normal hook:                           Hooks.               (line  12)
* normal-auto-fill-function:             Auto Filling.        (line  30)
* normal-backup-enable-predicate:        Making Backups.      (line  51)
* normal-mode:                           Auto Major Mode.     (line  20)
* not:                                   Combining Conditions.
                                                              (line  12)
* not-modified:                          Buffer Modification. (line  43)
* notation:                              Evaluation Notation. (line   6)
* nreverse:                              Rearrangement.       (line  64)
* nth:                                   List Elements.       (line  77)
* nthcdr:                                List Elements.       (line  97)
* null:                                  List-related Predicates.
                                                              (line  38)
* num-input-keys:                        Key Sequence Input.  (line 105)
* num-nonmacro-input-events:             Reading One Event.   (line  92)
* number comparison:                     Comparison of Numbers.
                                                              (line   6)
* number conversions:                    Numeric Conversions. (line   6)
* number-or-marker-p:                    Predicates on Markers.
                                                              (line  20)
* number-sequence:                       Building Lists.      (line 180)
* number-to-string:                      String Conversion.   (line  43)
* numberp:                               Predicates on Numbers.
                                                              (line  24)
* numbers:                               Numbers.             (line   6)
* numeric prefix argument:               Prefix Command Arguments.
                                                              (line   6)
* numeric prefix argument usage:         Interactive Codes.   (line 146)
* numerical RGB color specification:     Color Names.         (line   6)
* obarray:                               Creating Symbols.    (line 140)
* obarray in completion:                 Basic Completion.    (line  39)
* object:                                Lisp Data Types.     (line   6)
* object internals:                      Object Internals.    (line   6)
* object to string:                      Output Functions.    (line  91)
* occur-mode-map:                        Standard Keymaps.    (line 168)
* octal character code:                  General Escape Syntax.
                                                              (line  22)
* octal character input:                 Quoted Character Input.
                                                              (line  12)
* octal numbers:                         Integer Basics.      (line  22)
* one-window-p:                          Splitting Windows.   (line 141)
* only-global-abbrevs:                   Defining Abbrevs.    (line  53)
* open-dribble-file:                     Recording Input.     (line  20)
* open-network-stream:                   Network.             (line  52)
* open-paren-in-column-0-is-defun-start: List Motion.         (line  75)
* open-termscript:                       Terminal Output.     (line  49)
* open parenthesis character:            Syntax Class Table.  (line  44)
* operating system environment:          System Environment.  (line   6)
* operations (property):                 Magic File Names.    (line 126)
* option descriptions:                   A Sample Variable Description.
                                                              (line   6)
* optional arguments:                    Argument List.       (line  18)
* options on command line:               Command-Line Arguments.
                                                              (line  33)
* options, defcustom keyword:            Variable Definitions.
                                                              (line  52)
* or:                                    Combining Conditions.
                                                              (line  60)
* ordering of windows, cyclic:           Cyclic Window Ordering.
                                                              (line   6)
* other-buffer:                          The Buffer List.     (line  68)
* other-window:                          Cyclic Window Ordering.
                                                              (line  85)
* other-window-scroll-buffer:            Textual Scrolling.   (line  92)
* output from processes:                 Output from Processes.
                                                              (line   6)
* output stream:                         Output Streams.      (line   6)
* output-controlling variables:          Output Variables.    (line   6)
* overall prompt string:                 Format of Keymaps.   (line  50)
* overflow:                              Integer Basics.      (line   9)
* overflow-newline-into-fringe:          Fringe Cursors.      (line  18)
* overlay-arrow-position:                Overlay Arrow.       (line  20)
* overlay-arrow-string:                  Overlay Arrow.       (line  13)
* overlay-arrow-variable-list:           Overlay Arrow.       (line  41)
* overlay-buffer:                        Managing Overlays.   (line  40)
* overlay-end:                           Managing Overlays.   (line  36)
* overlay-get:                           Overlay Properties.  (line  23)
* overlay-properties:                    Overlay Properties.  (line  34)
* overlay-put:                           Overlay Properties.  (line  30)
* overlay-recenter:                      Managing Overlays.   (line 137)
* overlay-start:                         Managing Overlays.   (line  32)
* overlayp:                              Managing Overlays.   (line  12)
* overlays:                              Overlays.            (line   6)
* overlays-at:                           Finding Overlays.    (line   7)
* overlays-in:                           Finding Overlays.    (line  27)
* overriding-local-map:                  Controlling Active Maps.
                                                              (line  96)
* overriding-local-map-menu-flag:        Controlling Active Maps.
                                                              (line 112)
* overriding-terminal-local-map:         Controlling Active Maps.
                                                              (line 103)
* overwrite-mode:                        Commands for Insertion.
                                                              (line  62)
* package-version, customization keyword: Common Keywords.    (line 113)
* packing:                               Byte Packing.        (line  12)
* padding:                               Formatting Strings.  (line 124)
* page-delimiter:                        Standard Regexps.    (line  10)
* paired delimiter:                      Syntax Class Table.  (line 103)
* paragraph-separate:                    Standard Regexps.    (line  25)
* paragraph-start:                       Standard Regexps.    (line  32)
* parent of char-table:                  Char-Tables.         (line  23)
* parent process:                        Processes.           (line   6)
* parenthesis:                           Cons Cell Type.      (line  25)
* parenthesis depth:                     Low-Level Parsing.   (line  18)
* parenthesis matching:                  Blinking.            (line   6)
* parenthesis mismatch, debugging:       Syntax Errors.       (line  20)
* parenthesis syntax:                    Syntax Class Table.  (line  45)
* parse-colon-path:                      System Environment.  (line 162)
* parse-partial-sexp:                    Low-Level Parsing.   (line  12)
* parse-sexp-ignore-comments:            Control Parsing.     (line  13)
* parse-sexp-lookup-properties <1>:      Syntax Properties.   (line  28)
* parse-sexp-lookup-properties:          Control Parsing.     (line  17)
* parser state:                          Parser State.        (line   6)
* parsing buffer text:                   Syntax Tables.       (line   6)
* passwords, reading:                    Reading a Password.  (line   6)
* PATH environment variable:             Subprocess Creation. (line  17)
* path-separator:                        System Environment.  (line 156)
* PBM:                                   Other Image Types.   (line   6)
* peculiar error:                        Error Symbols.       (line  29)
* peeking at input:                      Event Input Misc.    (line  11)
* percent symbol in mode line:           Mode Line Data.      (line  20)
* perform-replace:                       Search and Replace.  (line  45)
* performance analysis:                  Coverage Testing.    (line   6)
* permanent local variable:              Creating Buffer-Local.
                                                              (line 171)
* permission:                            File Attributes.     (line  13)
* piece of advice:                       Advising Functions.  (line  11)
* pipes:                                 Asynchronous Processes.
                                                              (line  71)
* play-sound:                            Sound Output.        (line  15)
* play-sound-file:                       Sound Output.        (line  48)
* play-sound-functions:                  Sound Output.        (line  52)
* plist:                                 Property Lists.      (line   6)
* plist vs. alist:                       Plists and Alists.   (line   6)
* plist-get:                             Other Plists.        (line  10)
* plist-member:                          Other Plists.        (line  55)
* plist-put:                             Other Plists.        (line  27)
* point:                                 Point.               (line   6)
* point excursion:                       Excursions.          (line  18)
* point in window:                       Window Point.        (line   6)
* point with narrowing:                  Point.               (line  17)
* point-entered (text property):         Special Properties.  (line 227)
* point-left (text property):            Special Properties.  (line 227)
* point-marker:                          Creating Markers.    (line  22)
* point-max:                             Point.               (line  45)
* point-max-marker:                      Creating Markers.    (line  32)
* point-min:                             Point.               (line  39)
* point-min-marker:                      Creating Markers.    (line  27)
* pointer (text property):               Special Properties.  (line 181)
* pointer shape:                         Pointer Shape.       (line   6)
* pointers:                              Cons Cell Type.      (line   6)
* pop:                                   List Elements.       (line  61)
* pop-mark:                              The Mark.            (line 112)
* pop-to-buffer:                         Displaying Buffers.  (line  67)
* pop-up-frame-alist:                    Choosing Window.     (line 105)
* pop-up-frame-function:                 Choosing Window.     (line  95)
* pop-up-frames:                         Choosing Window.     (line  81)
* pop-up-windows:                        Choosing Window.     (line  60)
* pos-visible-in-window-p:               Window Start.        (line 121)
* position (in buffer):                  Positions.           (line   6)
* position argument:                     Interactive Codes.   (line  72)
* position in window:                    Window Point.        (line   6)
* position of mouse:                     Mouse Position.      (line   6)
* position-bytes:                        Text Representations.
                                                              (line  60)
* positive infinity:                     Float Basics.        (line  18)
* posix-looking-at:                      POSIX Regexps.       (line  34)
* posix-search-backward:                 POSIX Regexps.       (line  29)
* posix-search-forward:                  POSIX Regexps.       (line  23)
* posix-string-match:                    POSIX Regexps.       (line  39)
* posn-actual-col-row:                   Accessing Mouse.     (line  71)
* posn-area:                             Accessing Mouse.     (line  38)
* posn-at-point:                         Accessing Mouse.     (line 109)
* posn-at-x-y:                           Accessing Mouse.     (line 116)
* posn-col-row:                          Accessing Mouse.     (line  65)
* posn-image:                            Accessing Mouse.     (line  82)
* posn-object:                           Accessing Mouse.     (line  86)
* posn-object-width-height:              Accessing Mouse.     (line  96)
* posn-object-x-y:                       Accessing Mouse.     (line  90)
* posn-point:                            Accessing Mouse.     (line  43)
* posn-string:                           Accessing Mouse.     (line  78)
* posn-timestamp:                        Accessing Mouse.     (line 101)
* posn-window:                           Accessing Mouse.     (line  35)
* posn-x-y:                              Accessing Mouse.     (line  49)
* post-command-hook:                     Command Overview.    (line  45)
* post-gc-hook:                          Garbage Collection.  (line 148)
* postscript images:                     PostScript Images.   (line   6)
* pre-abbrev-expand-hook:                Abbrev Expansion.    (line  86)
* pre-command-hook:                      Command Overview.    (line  39)
* preactivating advice:                  Preactivation.       (line   6)
* preceding-char:                        Near Point.          (line  56)
* precision in format specifications:    Formatting Strings.  (line 184)
* predicates for numbers:                Predicates on Numbers.
                                                              (line   6)
* prefix argument:                       Prefix Command Arguments.
                                                              (line   6)
* prefix argument unreading:             Event Input Misc.    (line  20)
* prefix command:                        Prefix Keys.         (line  85)
* prefix key:                            Prefix Keys.         (line   6)
* prefix, defgroup keyword:              Group Definitions.   (line  46)
* prefix-arg:                            Prefix Command Arguments.
                                                              (line  92)
* prefix-help-command:                   Help Functions.      (line 103)
* prefix-numeric-value:                  Prefix Command Arguments.
                                                              (line  79)
* preloading additional functions and variables: Building Emacs.
                                                              (line  57)
* prepare-change-group:                  Atomic Changes.      (line  31)
* preventing backtracking:               Specification List.  (line 102)
* preventing prefix key:                 Key Lookup.          (line 102)
* preventing quitting:                   Quitting.            (line  45)
* previous complete subexpression:       Parser State.        (line  20)
* previous-button:                       Button Buffer Commands.
                                                              (line  53)
* previous-char-property-change:         Property Search.     (line  94)
* previous-frame:                        Finding All Frames.  (line  45)
* previous-history-element:              Minibuffer Commands. (line  18)
* previous-matching-history-element:     Minibuffer Commands. (line  26)
* previous-overlay-change:               Finding Overlays.    (line  40)
* previous-property-change:              Property Search.     (line  54)
* previous-single-char-property-change:  Property Search.     (line 110)
* previous-single-property-change:       Property Search.     (line  78)
* previous-window:                       Cyclic Window Ordering.
                                                              (line  80)
* primitive:                             What Is a Function.  (line  22)
* primitive function internals:          Writing Emacs Primitives.
                                                              (line   6)
* primitive type:                        Lisp Data Types.     (line  16)
* primitive-undo:                        Undo.                (line 108)
* prin1:                                 Output Functions.    (line  57)
* prin1-to-string:                       Output Functions.    (line  91)
* princ:                                 Output Functions.    (line  69)
* print:                                 Output Functions.    (line  40)
* print example:                         Output Streams.      (line  50)
* print name cell:                       Symbol Components.   (line  10)
* print-circle:                          Output Variables.    (line  92)
* print-continuous-numbering:            Output Variables.    (line 102)
* print-escape-multibyte:                Output Variables.    (line  52)
* print-escape-newlines:                 Output Variables.    (line  18)
* print-escape-nonascii:                 Output Variables.    (line  43)
* print-gensym:                          Output Variables.    (line  96)
* print-help-return-message:             Help Functions.      (line  52)
* print-length:                          Output Variables.    (line  62)
* print-level:                           Output Variables.    (line  76)
* print-number-table:                    Output Variables.    (line 111)
* print-quoted:                          Output Variables.    (line  12)
* printed representation:                Printed Representation.
                                                              (line   6)
* printed representation for characters: Basic Char Syntax.   (line   6)
* printing:                              Streams Intro.       (line   6)
* printing (Edebug):                     Printing in Edebug.  (line   6)
* printing circular structures:          Printing in Edebug.  (line   6)
* printing limits:                       Output Variables.    (line  62)
* printing notation:                     Printing Notation.   (line   6)
* priority (overlay property):           Overlay Properties.  (line  44)
* process:                               Processes.           (line   6)
* process filter:                        Filter Functions.    (line   6)
* process filter multibyte flag:         Decoding Output.     (line  27)
* process input:                         Input to Processes.  (line   6)
* process internals:                     Process Internals.   (line   6)
* process output:                        Output from Processes.
                                                              (line   6)
* process sentinel:                      Sentinels.           (line   6)
* process signals:                       Signals to Processes.
                                                              (line   6)
* process-adaptive-read-buffering:       Output from Processes.
                                                              (line  28)
* process-buffer:                        Process Buffers.     (line  21)
* process-coding-system:                 Process Information. (line 115)
* process-coding-system-alist:           Default Coding Systems.
                                                              (line  49)
* process-command:                       Process Information. (line  32)
* process-connection-type:               Asynchronous Processes.
                                                              (line  71)
* process-contact:                       Network.             (line  69)
* process-datagram-address:              Datagrams.           (line  21)
* process-environment:                   System Environment.  (line 139)
* process-exit-status:                   Process Information. (line 103)
* process-file:                          Synchronous Processes.
                                                              (line 127)
* process-filter:                        Filter Functions.    (line  89)
* process-filter-multibyte-p:            Decoding Output.     (line  44)
* process-get:                           Process Information. (line 132)
* process-id:                            Process Information. (line  41)
* process-kill-without-query:            Query Before Exit.   (line  25)
* process-list:                          Process Information. (line  18)
* process-mark:                          Process Buffers.     (line  27)
* process-name:                          Process Information. (line  48)
* process-plist:                         Process Information. (line 140)
* process-put:                           Process Information. (line 136)
* process-query-on-exit-flag:            Query Before Exit.   (line  14)
* process-running-child-p:               Input to Processes.  (line  71)
* process-send-eof:                      Input to Processes.  (line  62)
* process-send-region:                   Input to Processes.  (line  54)
* process-send-string:                   Input to Processes.  (line  36)
* process-sentinel:                      Sentinels.           (line  93)
* process-status:                        Process Information. (line  51)
* process-tty-name:                      Process Information. (line 109)
* processor run time:                    Processor Run Time.  (line   6)
* processp:                              Processes.           (line  24)
* profiling:                             Compilation Tips.    (line   9)
* prog1:                                 Sequencing.          (line  48)
* prog2:                                 Sequencing.          (line  65)
* progn:                                 Sequencing.          (line  33)
* program arguments:                     Subprocess Creation. (line  50)
* program directories:                   Subprocess Creation. (line  73)
* programmed completion:                 Programmed Completion.
                                                              (line   6)
* programming conventions:               Programming Tips.    (line   6)
* programming types:                     Programming Types.   (line   6)
* progress reporting:                    Progress.            (line   6)
* progress-reporter-done:                Progress.            (line  87)
* progress-reporter-force-update:        Progress.            (line  77)
* progress-reporter-update:              Progress.            (line  57)
* prompt for file name:                  Reading File Names.  (line   6)
* prompt string (of menu):               Defining Menus.      (line   6)
* prompt string of keymap:               Format of Keymaps.   (line  50)
* properties of text:                    Text Properties.     (line   6)
* propertize:                            Changing Properties. (line  94)
* property category of text character:   Special Properties.  (line  15)
* property list:                         Property Lists.      (line   6)
* property list cell:                    Symbol Components.   (line  30)
* property lists vs association lists:   Plists and Alists.   (line   6)
* protect C variables from garbage collection: Writing Emacs Primitives.
                                                              (line 115)
* protected forms:                       Cleanups.            (line  13)
* provide:                               Named Features.      (line  69)
* providing features:                    Named Features.      (line   6)
* PTYs:                                  Asynchronous Processes.
                                                              (line  71)
* punctuation character:                 Syntax Class Table.  (line  34)
* pure storage:                          Pure Storage.        (line   6)
* pure-bytes-used:                       Pure Storage.        (line  42)
* purecopy:                              Pure Storage.        (line  29)
* purify-flag:                           Pure Storage.        (line  48)
* push:                                  List Variables.      (line  10)
* push-button:                           Button Buffer Commands.
                                                              (line  22)
* push-mark:                             The Mark.            (line 101)
* put:                                   Symbol Plists.       (line  36)
* put-image:                             Showing Images.      (line  40)
* put-text-property:                     Changing Properties. (line  20)
* puthash:                               Hash Access.         (line  16)
* query-replace-history:                 Minibuffer History.  (line  96)
* query-replace-map:                     Search and Replace.  (line  81)
* querying the user:                     Yes-or-No Queries.   (line   6)
* question mark in character constant:   Basic Char Syntax.   (line   6)
* quietly-read-abbrev-file:              Abbrev Files.        (line  19)
* quit-flag:                             Quitting.            (line  75)
* quit-process:                          Signals to Processes.
                                                              (line  62)
* quitting:                              Quitting.            (line   6)
* quitting from infinite loop:           Infinite Loops.      (line   6)
* quote:                                 Quoting.             (line  13)
* quote character:                       Parser State.        (line  30)
* quoted character input:                Quoted Character Input.
                                                              (line   6)
* quoted-insert suppression:             Changing Key Bindings.
                                                              (line 159)
* quoting characters in printing:        Output Functions.    (line   9)
* quoting using apostrophe:              Quoting.             (line  15)
* radix for reading an integer:          Integer Basics.      (line  22)
* raise-frame:                           Raising and Lowering.
                                                              (line  23)
* random:                                Random Numbers.      (line  27)
* random numbers:                        Random Numbers.      (line   6)
* rassoc:                                Association Lists.   (line  91)
* rassq:                                 Association Lists.   (line 125)
* rassq-delete-all:                      Association Lists.   (line 228)
* raw prefix argument:                   Prefix Command Arguments.
                                                              (line   6)
* raw prefix argument usage:             Interactive Codes.   (line 150)
* re-builder:                            Regular Expressions. (line  11)
* re-search-backward:                    Regexp Search.       (line  62)
* re-search-forward:                     Regexp Search.       (line  17)
* reactivating advice:                   Activation of Advice.
                                                              (line  72)
* read:                                  Input Functions.     (line  17)
* read command name:                     Interactive Call.    (line  76)
* read file names:                       Reading File Names.  (line   6)
* read input:                            Reading Input.       (line   6)
* read syntax:                           Printed Representation.
                                                              (line   6)
* read syntax for characters:            Basic Char Syntax.   (line   6)
* read-buffer:                           High-Level Completion.
                                                              (line  15)
* read-buffer-function:                  High-Level Completion.
                                                              (line  52)
* read-char:                             Reading One Event.   (line  62)
* read-char-exclusive:                   Reading One Event.   (line  86)
* read-coding-system:                    User-Chosen Coding Systems.
                                                              (line  65)
* read-command:                          High-Level Completion.
                                                              (line  58)
* read-directory-name:                   Reading File Names.  (line 110)
* read-event:                            Reading One Event.   (line  12)
* read-expression-history:               Minibuffer History.  (line 115)
* read-file-name:                        Reading File Names.  (line  12)
* read-file-name-completion-ignore-case: Reading File Names.  (line 105)
* read-file-name-function:               Reading File Names.  (line  99)
* read-from-minibuffer:                  Text from Minibuffer.
                                                              (line  19)
* read-from-string:                      Input Functions.     (line  22)
* read-input-method-name:                Input Methods.       (line  36)
* read-kbd-macro:                        Describing Characters.
                                                              (line  76)
* read-key-sequence:                     Key Sequence Input.  (line  12)
* read-key-sequence-vector:              Key Sequence Input.  (line  69)
* read-minibuffer:                       Object from Minibuffer.
                                                              (line  10)
* read-no-blanks-input:                  Text from Minibuffer.
                                                              (line 138)
* read-non-nil-coding-system:            User-Chosen Coding Systems.
                                                              (line  71)
* read-only (text property):             Special Properties.  (line 134)
* read-only buffer:                      Read Only Buffers.   (line   6)
* read-only buffers in interactive:      Using Interactive.   (line  59)
* read-only character:                   Special Properties.  (line 134)
* read-passwd:                           Reading a Password.  (line  10)
* read-quoted-char:                      Quoted Character Input.
                                                              (line  12)
* read-quoted-char quitting:             Quitting.            (line  55)
* read-string:                           Text from Minibuffer.
                                                              (line  74)
* read-variable:                         High-Level Completion.
                                                              (line  94)
* reading:                               Streams Intro.       (line   6)
* reading a single event:                Reading One Event.   (line   6)
* reading from files:                    Reading from Files.  (line   6)
* reading from minibuffer with completion: Minibuffer Completion.
                                                              (line   6)
* reading interactive arguments:         Interactive Codes.   (line  41)
* reading numbers in hex, octal, and binary: Integer Basics.  (line  22)
* reading symbols:                       Creating Symbols.    (line   6)
* real-last-command:                     Command Loop Info.   (line  25)
* rearrangement of lists:                Rearrangement.       (line   6)
* rebinding:                             Changing Key Bindings.
                                                              (line   6)
* recent-auto-save-p:                    Auto-Saving.         (line  97)
* recent-keys:                           Recording Input.     (line   7)
* recenter:                              Textual Scrolling.   (line 157)
* record command history:                Interactive Call.    (line  45)
* recording input:                       Recording Input.     (line   6)
* recursion:                             Iteration.           (line   6)
* recursion-depth:                       Recursive Editing.   (line 104)
* recursive command loop:                Recursive Editing.   (line   6)
* recursive editing level:               Recursive Editing.   (line   6)
* recursive evaluation:                  Intro Eval.          (line  38)
* recursive minibuffers:                 Recursive Mini.      (line   6)
* recursive-edit:                        Recursive Editing.   (line  62)
* redirect-frame-focus:                  Input Focus.         (line  79)
* redisplay:                             Forcing Redisplay.   (line  12)
* redisplay-dont-pause:                  Forcing Redisplay.   (line  48)
* redisplay-end-trigger-functions:       Window Hooks.        (line  53)
* redisplay-preemption-period:           Forcing Redisplay.   (line  53)
* redo:                                  Undo.                (line   6)
* redraw-display:                        Refresh Screen.      (line  16)
* redraw-frame:                          Refresh Screen.      (line  11)
* references, following:                 Key Binding Conventions.
                                                              (line   6)
* regexp:                                Regular Expressions. (line   6)
* regexp alternative:                    Regexp Backslash.    (line  13)
* regexp grouping:                       Regexp Backslash.    (line  45)
* regexp searching:                      Regexp Search.       (line   6)
* regexp-history:                        Minibuffer History.  (line 106)
* regexp-opt:                            Regexp Functions.    (line  30)
* regexp-opt-depth:                      Regexp Functions.    (line  52)
* regexp-quote:                          Regexp Functions.    (line   9)
* regexps used standardly in editing:    Standard Regexps.    (line   6)
* region (between point and mark):       The Region.          (line   6)
* region argument:                       Interactive Codes.   (line 154)
* region-beginning:                      The Region.          (line  17)
* region-end:                            The Region.          (line  22)
* register-alist:                        Registers.           (line  14)
* registers:                             Registers.           (line   6)
* regular expression:                    Regular Expressions. (line   6)
* regular expression searching:          Regexp Search.       (line   6)
* regular expressions, developing:       Regular Expressions. (line  11)
* reindent-then-newline-and-indent:      Mode-Specific Indent.
                                                              (line  42)
* relative file name:                    Relative File Names. (line   6)
* remainder:                             Arithmetic Operations.
                                                              (line 114)
* remapping commands:                    Remapping Commands.  (line   6)
* remhash:                               Hash Access.         (line  21)
* remove:                                Sets And Lists.      (line 152)
* remove-from-invisibility-spec:         Invisible Text.      (line  69)
* remove-hook:                           Hooks.               (line 119)
* remove-images:                         Showing Images.      (line  59)
* remove-list-of-text-properties:        Changing Properties. (line  67)
* remove-overlays:                       Managing Overlays.   (line  69)
* remove-text-properties:                Changing Properties. (line  45)
* remq:                                  Sets And Lists.      (line  77)
* rename-auto-save-file:                 Auto-Saving.         (line 160)
* rename-buffer:                         Buffer Names.        (line  38)
* rename-file:                           Changing Files.      (line  73)
* repeat events:                         Repeat Events.       (line   6)
* repeated loading:                      Repeated Loading.    (line   6)
* replace bindings:                      Changing Key Bindings.
                                                              (line 112)
* replace characters:                    Substitution.        (line  11)
* replace matched text:                  Replacing Match.     (line   6)
* replace-buffer-in-windows:             Displaying Buffers.  (line 109)
* replace-match:                         Replacing Match.     (line  11)
* replace-regexp-in-string:              Search and Replace.  (line  22)
* replacement after search:              Search and Replace.  (line   6)
* require:                               Named Features.      (line 101)
* require, customization keyword:        Common Keywords.     (line  99)
* require-final-newline:                 Saving Buffers.      (line 154)
* requiring features:                    Named Features.      (line   6)
* reserved keys:                         Key Binding Conventions.
                                                              (line  14)
* resize frame:                          Size and Position.   (line   6)
* resize window:                         Resizing Windows.    (line   6)
* rest arguments:                        Argument List.       (line  18)
* restore-buffer-modified-p:             Buffer Modification. (line  39)
* restriction (in a buffer):             Narrowing.           (line   6)
* resume (cf. no-redraw-on-reenter):     Refresh Screen.      (line  30)
* return (ASCII character):              Basic Char Syntax.   (line  27)
* reverse:                               Building Lists.      (line 159)
* reversing a list:                      Rearrangement.       (line  64)
* revert-buffer:                         Reverting.           (line  13)
* revert-buffer-function:                Reverting.           (line  56)
* revert-buffer-insert-file-contents-function: Reverting.     (line  68)
* revert-without-query:                  Reverting.           (line  45)
* rgb value:                             Color Names.         (line  65)
* right-fringe-width:                    Fringe Size/Pos.     (line  20)
* right-margin-width:                    Display Margins.     (line  36)
* ring data structure:                   Rings.               (line   6)
* ring-bell-function:                    Beeping.             (line  28)
* ring-copy:                             Rings.               (line  28)
* ring-elements:                         Rings.               (line  25)
* ring-empty-p:                          Rings.               (line  32)
* ring-insert:                           Rings.               (line  45)
* ring-insert-at-beginning:              Rings.               (line  58)
* ring-length:                           Rings.               (line  21)
* ring-p:                                Rings.               (line  15)
* ring-ref:                              Rings.               (line  40)
* ring-remove:                           Rings.               (line  52)
* ring-size:                             Rings.               (line  18)
* risky-local-variable-p:                File Local Variables.
                                                              (line  85)
* rm:                                    Changing Files.      (line 110)
* round:                                 Numeric Conversions. (line  66)
* rounding in conversions:               Numeric Conversions. (line   6)
* rounding without conversion:           Rounding Operations. (line   6)
* rplaca:                                Modifying Lists.     (line  10)
* rplacd:                                Modifying Lists.     (line  10)
* run time stack:                        Internals of Debugger.
                                                              (line  21)
* run-at-time:                           Timers.              (line  44)
* run-hook-with-args:                    Hooks.               (line  68)
* run-hook-with-args-until-failure:      Hooks.               (line  73)
* run-hook-with-args-until-success:      Hooks.               (line  80)
* run-hooks:                             Hooks.               (line  54)
* run-mode-hooks:                        Mode Hooks.          (line  28)
* run-with-idle-timer:                   Idle Timers.         (line  11)
* safe local variable:                   File Local Variables.
                                                              (line  50)
* safe-length:                           List Elements.       (line 117)
* safe-local-eval-forms:                 File Local Variables.
                                                              (line 110)
* safe-local-variable-p:                 File Local Variables.
                                                              (line  72)
* safe-local-variable-values:            File Local Variables.
                                                              (line  61)
* safe-magic (property):                 Magic File Names.    (line 118)
* safety of functions:                   Function Safety.     (line   6)
* same-window-buffer-names:              Choosing Window.     (line 193)
* same-window-p:                         Choosing Window.     (line 205)
* same-window-regexps:                   Choosing Window.     (line 199)
* save-abbrevs:                          Abbrev Files.        (line  27)
* save-buffer:                           Saving Buffers.      (line  13)
* save-buffer-coding-system:             Encoding and I/O.    (line  36)
* save-current-buffer:                   Current Buffer.      (line 107)
* save-excursion:                        Excursions.          (line  18)
* save-match-data:                       Saving Match Data.   (line  21)
* save-restriction:                      Narrowing.           (line  51)
* save-selected-window:                  Selecting Windows.   (line  29)
* save-some-buffers:                     Saving Buffers.      (line  35)
* save-window-excursion:                 Window Configurations.
                                                              (line  53)
* saving buffers:                        Saving Buffers.      (line   6)
* saving text properties:                Saving Properties.   (line   6)
* saving window information:             Window Configurations.
                                                              (line   6)
* scalable-fonts-allowed:                Font Selection.      (line  81)
* scan-lists:                            Motion via Parsing.  (line  10)
* scan-sexps:                            Motion via Parsing.  (line  29)
* scope:                                 Variable Scoping.    (line  11)
* scrap support (for Mac OS):            Window System Selections.
                                                              (line  76)
* screen layout:                         Frame Configuration Type.
                                                              (line   6)
* screen of terminal:                    Basic Windows.       (line  73)
* screen size:                           Size and Position.   (line   6)
* screen-height:                         Size and Position.   (line  35)
* screen-width:                          Size and Position.   (line  36)
* scroll bar events, data in:            Accessing Scroll.    (line   6)
* scroll bars:                           Scroll Bars.         (line   6)
* scroll-bar-event-ratio:                Accessing Scroll.    (line   9)
* scroll-bar-mode:                       Scroll Bars.         (line  65)
* scroll-bar-scale:                      Accessing Scroll.    (line  15)
* scroll-bar-width:                      Scroll Bars.         (line  80)
* scroll-conservatively:                 Textual Scrolling.   (line 104)
* scroll-down:                           Textual Scrolling.   (line  55)
* scroll-down-aggressively:              Textual Scrolling.   (line 117)
* scroll-left:                           Horizontal Scrolling.
                                                              (line  48)
* scroll-margin:                         Textual Scrolling.   (line  96)
* scroll-other-window:                   Textual Scrolling.   (line  66)
* scroll-preserve-screen-position:       Textual Scrolling.   (line 141)
* scroll-right:                          Horizontal Scrolling.
                                                              (line  67)
* scroll-step:                           Textual Scrolling.   (line 135)
* scroll-up:                             Textual Scrolling.   (line  44)
* scroll-up-aggressively:                Textual Scrolling.   (line 130)
* scrolling textually:                   Textual Scrolling.   (line   6)
* search-backward:                       String Search.       (line  62)
* search-failed:                         String Search.       (line  41)
* search-forward:                        String Search.       (line  16)
* search-spaces-regexp:                  Regexp Search.       (line 154)
* searching:                             Searching and Matching.
                                                              (line   6)
* searching active keymaps for keys:     Searching Keymaps.   (line   6)
* searching and case:                    Searching and Case.  (line   6)
* searching and replacing:               Search and Replace.  (line   6)
* searching for regexp:                  Regexp Search.       (line   6)
* seconds-to-time:                       Time Parsing.        (line 160)
* select safe coding system:             User-Chosen Coding Systems.
                                                              (line   6)
* select-frame:                          Input Focus.         (line  51)
* select-frame-set-input-focus:          Input Focus.         (line  44)
* select-safe-coding-system:             User-Chosen Coding Systems.
                                                              (line   8)
* select-safe-coding-system-accept-default-p: User-Chosen Coding Systems.
                                                              (line  46)
* select-window:                         Selecting Windows.   (line  14)
* selected window:                       Basic Windows.       (line   6)
* selected-frame:                        Input Focus.         (line  21)
* selected-window:                       Selecting Windows.   (line  10)
* selecting a buffer:                    Current Buffer.      (line   6)
* selecting a window:                    Selecting Windows.   (line   6)
* selection (for window systems):        Window System Selections.
                                                              (line   6)
* selection-coding-system:               Window System Selections.
                                                              (line  65)
* selective-display:                     Selective Display.   (line  40)
* selective-display-ellipses:            Selective Display.   (line  86)
* self-evaluating form:                  Self-Evaluating Forms.
                                                              (line   6)
* self-insert-and-exit:                  Minibuffer Commands. (line  13)
* self-insert-command:                   Commands for Insertion.
                                                              (line  17)
* self-insert-command override:          Changing Key Bindings.
                                                              (line 149)
* self-insert-command, minor modes:      Keymaps and Minor Modes.
                                                              (line  11)
* self-insertion:                        Commands for Insertion.
                                                              (line  17)
* send-string-to-terminal:               Terminal Output.     (line  35)
* sending signals:                       Signals to Processes.
                                                              (line   6)
* sentence-end:                          Standard Regexps.    (line  38)
* sentence-end-double-space:             Filling.             (line 127)
* sentence-end-without-period:           Filling.             (line 132)
* sentence-end-without-space:            Filling.             (line 137)
* sentinel (of process):                 Sentinels.           (line   6)
* sequence:                              Sequences Arrays Vectors.
                                                              (line   6)
* sequence length:                       Sequence Functions.  (line  16)
* sequencep:                             Sequence Functions.  (line  12)
* serializing:                           Byte Packing.        (line  12)
* session manager:                       Session Management.  (line   6)
* set:                                   Setting Variables.   (line  42)
* set, defcustom keyword:                Variable Definitions.
                                                              (line  61)
* set-after, defcustom keyword:          Variable Definitions.
                                                              (line 130)
* set-auto-mode:                         Auto Major Mode.     (line  49)
* set-buffer:                            Current Buffer.      (line  97)
* set-buffer-auto-saved:                 Auto-Saving.         (line 101)
* set-buffer-major-mode:                 Auto Major Mode.     (line  79)
* set-buffer-modified-p:                 Buffer Modification. (line  29)
* set-buffer-multibyte:                  Selecting a Representation.
                                                              (line  10)
* set-case-syntax:                       Case Tables.         (line 111)
* set-case-syntax-delims:                Case Tables.         (line 107)
* set-case-syntax-pair:                  Case Tables.         (line 103)
* set-case-table:                        Case Tables.         (line  75)
* set-category-table:                    Categories.          (line  67)
* set-char-table-default:                Char-Tables.         (line  51)
* set-char-table-extra-slot:             Char-Tables.         (line  70)
* set-char-table-parent:                 Char-Tables.         (line  62)
* set-char-table-range:                  Char-Tables.         (line  98)
* set-default:                           Default Value.       (line  77)
* set-default-file-modes:                Changing Files.      (line 134)
* set-display-table-slot:                Display Table Format.
                                                              (line  74)
* set-face-attribute:                    Attribute Functions. (line  10)
* set-face-background:                   Attribute Functions. (line  92)
* set-face-bold-p:                       Attribute Functions. (line 115)
* set-face-font:                         Attribute Functions. (line 110)
* set-face-foreground:                   Attribute Functions. (line  91)
* set-face-inverse-video-p:              Attribute Functions. (line 131)
* set-face-italic-p:                     Attribute Functions. (line 120)
* set-face-stipple:                      Attribute Functions. (line 100)
* set-face-underline-p:                  Attribute Functions. (line 125)
* set-file-modes:                        Changing Files.      (line 129)
* set-file-times:                        Changing Files.      (line 156)
* set-fontset-font:                      Fontsets.            (line  84)
* set-frame-configuration:               Frame Configurations.
                                                              (line  15)
* set-frame-height:                      Size and Position.   (line  68)
* set-frame-position:                    Size and Position.   (line  16)
* set-frame-selected-window:             Frames and Windows.  (line  33)
* set-frame-size:                        Size and Position.   (line  60)
* set-frame-width:                       Size and Position.   (line  82)
* set-fringe-bitmap-face:                Customizing Bitmaps. (line  39)
* set-input-method:                      Input Methods.       (line  29)
* set-input-mode:                        Input Modes.         (line   7)
* set-keyboard-coding-system:            Terminal I/O Encoding.
                                                              (line  16)
* set-keymap-parent:                     Inheritance and Keymaps.
                                                              (line  32)
* set-left-margin:                       Margins.             (line  39)
* set-mark:                              The Mark.            (line  79)
* set-marker:                            Moving Markers.      (line  13)
* set-marker-insertion-type:             Marker Insertion Types.
                                                              (line  14)
* set-match-data:                        Entire Match Data.   (line  50)
* set-minibuffer-window:                 Minibuffer Windows.  (line  21)
* set-mouse-pixel-position:              Mouse Position.      (line  36)
* set-mouse-position:                    Mouse Position.      (line  25)
* set-network-process-option:            Network Options.     (line  67)
* set-process-buffer:                    Process Buffers.     (line  48)
* set-process-coding-system:             Process Information. (line 123)
* set-process-datagram-address:          Datagrams.           (line  25)
* set-process-filter:                    Filter Functions.    (line  85)
* set-process-filter-multibyte:          Decoding Output.     (line  40)
* set-process-plist:                     Process Information. (line 143)
* set-process-query-on-exit-flag:        Query Before Exit.   (line  17)
* set-process-sentinel:                  Sentinels.           (line  73)
* set-register:                          Registers.           (line  62)
* set-right-margin:                      Margins.             (line  44)
* set-screen-height:                     Size and Position.   (line  85)
* set-screen-width:                      Size and Position.   (line  85)
* set-standard-case-table:               Case Tables.         (line  65)
* set-syntax-table:                      Syntax Table Functions.
                                                              (line  93)
* set-terminal-coding-system:            Terminal I/O Encoding.
                                                              (line  25)
* set-text-properties:                   Changing Properties. (line  72)
* set-time-zone-rule:                    Time of Day.         (line  65)
* set-visited-file-modtime:              Modification Time.   (line  63)
* set-visited-file-name:                 Buffer File Name.    (line  86)
* set-window-buffer:                     Buffers and Windows. (line  15)
* set-window-configuration:              Window Configurations.
                                                              (line  25)
* set-window-dedicated-p:                Choosing Window.     (line 228)
* set-window-display-table:              Active Display Table.
                                                              (line  18)
* set-window-fringes:                    Fringe Size/Pos.     (line  31)
* set-window-hscroll:                    Horizontal Scrolling.
                                                              (line  90)
* set-window-margins:                    Display Margins.     (line  47)
* set-window-point:                      Window Point.        (line  46)
* set-window-redisplay-end-trigger:      Window Hooks.        (line  63)
* set-window-scroll-bars:                Scroll Bars.         (line  31)
* set-window-start:                      Window Start.        (line  67)
* set-window-vscroll:                    Vertical Scrolling.  (line  35)
* setcar:                                Setcar.              (line  10)
* setcdr:                                Setcdr.              (line   9)
* setenv:                                System Environment.  (line 122)
* setplist:                              Symbol Plists.       (line  10)
* setprv:                                System Environment.  (line 226)
* setq:                                  Setting Variables.   (line  11)
* setq-default:                          Default Value.       (line  36)
* sets:                                  Sets And Lists.      (line   6)
* setting modes of files:                Changing Files.      (line   6)
* setting-constant:                      Constant Variables.  (line   6)
* severity level:                        Warning Basics.      (line   6)
* sexp motion:                           List Motion.         (line   6)
* shadowing of variables:                Local Variables.     (line  17)
* shallow binding:                       Impl of Scope.       (line  26)
* shared structure, read syntax:         Circular Objects.    (line   6)
* shell command arguments:               Shell Arguments.     (line   6)
* shell-command-history:                 Minibuffer History.  (line 112)
* shell-command-to-string:               Synchronous Processes.
                                                              (line 225)
* shell-quote-argument:                  Shell Arguments.     (line  14)
* show-help-function:                    Special Properties.  (line 258)
* shrink-window:                         Resizing Windows.    (line  50)
* shrink-window-horizontally:            Resizing Windows.    (line  59)
* shrink-window-if-larger-than-buffer:   Resizing Windows.    (line  86)
* side effect:                           Intro Eval.          (line  58)
* signal:                                Signaling Errors.    (line  49)
* signal-process:                        Signals to Processes.
                                                              (line  81)
* signaling errors:                      Signaling Errors.    (line   6)
* signals:                               Signals to Processes.
                                                              (line   6)
* sigusr1 event:                         Misc Events.         (line  67)
* sigusr2 event:                         Misc Events.         (line  67)
* sin:                                   Math Functions.      (line  10)
* single-key-description:                Describing Characters.
                                                              (line  29)
* sit-for:                               Waiting.             (line  13)
* site-init.el:                          Building Emacs.      (line  57)
* site-load.el:                          Building Emacs.      (line  42)
* site-run-file:                         Init File.           (line  39)
* site-start.el:                         Startup Summary.     (line  31)
* size of frame:                         Size and Position.   (line   6)
* size of window:                        Size of Window.      (line   6)
* skip-chars-backward:                   Skipping Characters. (line  53)
* skip-chars-forward:                    Skipping Characters. (line  15)
* skip-syntax-backward:                  Motion and Syntax.   (line  23)
* skip-syntax-forward:                   Motion and Syntax.   (line  10)
* skipping characters:                   Skipping Characters. (line   6)
* skipping comments:                     Control Parsing.     (line  13)
* sleep-for:                             Waiting.             (line  42)
* small-temporary-file-directory:        Unique File Names.   (line  86)
* Snarf-documentation:                   Accessing Documentation.
                                                              (line 128)
* sort:                                  Rearrangement.       (line  99)
* sort-columns:                          Sorting.             (line 211)
* sort-fields:                           Sorting.             (line 189)
* sort-fold-case:                        Sorting.             (line 108)
* sort-lines:                            Sorting.             (line 174)
* sort-numeric-base:                     Sorting.             (line 207)
* sort-numeric-fields:                   Sorting.             (line 196)
* sort-pages:                            Sorting.             (line 184)
* sort-paragraphs:                       Sorting.             (line 179)
* sort-regexp-fields:                    Sorting.             (line 113)
* sort-subr:                             Sorting.             (line  13)
* sorting lists:                         Rearrangement.       (line  99)
* sorting text:                          Sorting.             (line   6)
* sound:                                 Sound Output.        (line   6)
* source breakpoints:                    Source Breakpoints.  (line   6)
* space (ASCII character):               Basic Char Syntax.   (line  27)
* spaces, pixel specification:           Pixel Specification. (line   6)
* spaces, specified height or width:     Specified Space.     (line   6)
* sparse keymap:                         Format of Keymaps.   (line   6)
* special:                               Major Mode Conventions.
                                                              (line 181)
* special events:                        Special Events.      (line   6)
* special form descriptions:             A Sample Function Description.
                                                              (line   6)
* special form evaluation:               Special Forms.       (line   6)
* special forms:                         Primitive Function Type.
                                                              (line   6)
* special forms for control structures:  Control Structures.  (line   6)
* special-display-buffer-names:          Choosing Window.     (line 110)
* special-display-frame-alist:           Choosing Window.     (line 189)
* special-display-function:              Choosing Window.     (line 161)
* special-display-p:                     Choosing Window.     (line 155)
* special-display-popup-frame:           Choosing Window.     (line 169)
* special-display-regexps:               Choosing Window.     (line 141)
* special-event-map:                     Controlling Active Maps.
                                                              (line 126)
* specify color:                         Color Names.         (line   6)
* speedups:                              Compilation Tips.    (line   6)
* splicing (with backquote):             Backquote.           (line  39)
* split-char:                            Splitting Characters.
                                                              (line  12)
* split-height-threshold:                Choosing Window.     (line  66)
* split-string:                          Creating Strings.    (line 133)
* split-string-default-separators:       Creating Strings.    (line 202)
* split-window:                          Splitting Windows.   (line  16)
* split-window-horizontally:             Splitting Windows.   (line 124)
* split-window-keep-point:               Splitting Windows.   (line 111)
* split-window-vertically:               Splitting Windows.   (line  98)
* splitting windows:                     Splitting Windows.   (line   6)
* sqrt:                                  Math Functions.      (line  52)
* stable sort:                           Rearrangement.       (line  99)
* standard buffer-local variables:       Standard Buffer-Local Variables.
                                                              (line   6)
* standard colors for character terminals: Color Parameters.  (line  13)
* standard errors:                       Standard Errors.     (line   6)
* standard hooks:                        Standard Hooks.      (line   6)
* standard keymaps:                      Standard Keymaps.    (line   6)
* standard regexps used in editing:      Standard Regexps.    (line   6)
* standard-case-table:                   Case Tables.         (line  69)
* standard-category-table:               Categories.          (line  58)
* standard-display-table:                Active Display Table.
                                                              (line  28)
* standard-input:                        Input Functions.     (line  52)
* standard-output:                       Output Variables.    (line   7)
* standard-syntax-table:                 Standard Syntax Tables.
                                                              (line  10)
* standard-translation-table-for-decode: Translation of Characters.
                                                              (line  57)
* standard-translation-table-for-encode: Translation of Characters.
                                                              (line  61)
* standards of coding style:             Tips.                (line   6)
* start-process:                         Asynchronous Processes.
                                                              (line  18)
* start-process-shell-command:           Asynchronous Processes.
                                                              (line  56)
* startup of Emacs:                      Startup Summary.     (line   6)
* startup.el:                            Startup Summary.     (line   6)
* staticpro, protection from GC:         Writing Emacs Primitives.
                                                              (line 189)
* sticky text properties:                Sticky Properties.   (line   6)
* stop points:                           Using Edebug.        (line  36)
* stop-process:                          Signals to Processes.
                                                              (line  67)
* stopping an infinite loop:             Infinite Loops.      (line   6)
* stopping on events:                    Global Break Condition.
                                                              (line   6)
* store-match-data:                      Entire Match Data.   (line  62)
* store-substring:                       Modifying Strings.   (line  15)
* stream (for printing):                 Output Streams.      (line   6)
* stream (for reading):                  Input Streams.       (line   6)
* string:                                Creating Strings.    (line  23)
* string equality:                       Text Comparison.     (line   6)
* string in keymap:                      Key Lookup.          (line  46)
* string input stream:                   Input Streams.       (line  23)
* string length:                         Sequence Functions.  (line  16)
* string search:                         String Search.       (line   6)
* string to character:                   String Conversion.   (line  25)
* string to number:                      String Conversion.   (line  60)
* string to object:                      Input Functions.     (line  22)
* string, number of bytes:               Text Representations.
                                                              (line  74)
* string, writing a doc string:          Documentation Basics.
                                                              (line   6)
* string-as-multibyte:                   Selecting a Representation.
                                                              (line  44)
* string-as-unibyte:                     Selecting a Representation.
                                                              (line  33)
* string-bytes:                          Text Representations.
                                                              (line  74)
* string-chars-consed:                   Memory Usage.        (line  30)
* string-equal:                          Text Comparison.     (line  50)
* string-lessp:                          Text Comparison.     (line  98)
* string-make-multibyte:                 Converting Representations.
                                                              (line  78)
* string-make-unibyte:                   Converting Representations.
                                                              (line  69)
* string-match:                          Regexp Search.       (line  81)
* string-or-null-p:                      Predicates for Strings.
                                                              (line  13)
* string-to-char:                        String Conversion.   (line  25)
* string-to-int:                         String Conversion.   (line  89)
* string-to-multibyte:                   Converting Representations.
                                                              (line  90)
* string-to-number:                      String Conversion.   (line  60)
* string-to-syntax:                      Syntax Table Internals.
                                                              (line  41)
* string-width:                          Width.               (line  15)
* string<:                               Text Comparison.     (line  53)
* string=:                               Text Comparison.     (line  18)
* stringp:                               Predicates for Strings.
                                                              (line  10)
* strings:                               Strings and Characters.
                                                              (line   6)
* strings with keyboard events:          Strings of Events.   (line   6)
* strings, formatting them:              Formatting Strings.  (line   6)
* strings-consed:                        Memory Usage.        (line  43)
* string quote:                          Syntax Class Table.  (line  61)
* subprocess:                            Processes.           (line   6)
* subr:                                  What Is a Function.  (line  22)
* subr-arity:                            What Is a Function.  (line 104)
* subrp:                                 What Is a Function.  (line  88)
* subst-char-in-region:                  Substitution.        (line  11)
* substitute-command-keys:               Keys in Documentation.
                                                              (line  36)
* substitute-in-file-name:               File Name Expansion. (line  83)
* substitute-key-definition:             Changing Key Bindings.
                                                              (line 112)
* substituting keys in documentation:    Keys in Documentation.
                                                              (line   6)
* substring:                             Creating Strings.    (line  29)
* substring-no-properties:               Creating Strings.    (line  92)
* subtype of char-table:                 Char-Tables.         (line  14)
* suggestions:                           Caveats.             (line  27)
* super characters:                      Other Char Bits.     (line  16)
* suppress-keymap:                       Changing Key Bindings.
                                                              (line 149)
* suspend (cf. no-redraw-on-reenter):    Refresh Screen.      (line  30)
* suspend evaluation:                    Recursive Editing.   (line  62)
* suspend-emacs:                         Suspending Emacs.    (line  24)
* suspend-hook:                          Suspending Emacs.    (line  74)
* suspend-resume-hook:                   Suspending Emacs.    (line  77)
* suspending Emacs:                      Suspending Emacs.    (line   6)
* switch-to-buffer:                      Displaying Buffers.  (line  23)
* switch-to-buffer-other-window:         Displaying Buffers.  (line  51)
* switches on command line:              Command-Line Arguments.
                                                              (line  33)
* switching to a buffer:                 Displaying Buffers.  (line   6)
* sxhash:                                Defining Hash.       (line  42)
* symbol:                                Symbols.             (line   6)
* symbol components:                     Symbol Components.   (line   6)
* symbol equality:                       Creating Symbols.    (line  39)
* symbol evaluation:                     Symbol Forms.        (line   6)
* symbol function indirection:           Function Indirection.
                                                              (line   6)
* symbol in keymap:                      Key Lookup.          (line  82)
* symbol name hashing:                   Creating Symbols.    (line  11)
* symbol that evaluates to itself:       Constant Variables.  (line   6)
* symbol with constant value:            Constant Variables.  (line   6)
* symbol-file:                           Where Defined.       (line   7)
* symbol-function:                       Function Cells.      (line  14)
* symbol-name:                           Creating Symbols.    (line  73)
* symbol-plist:                          Symbol Plists.       (line   7)
* symbol-value:                          Accessing Variables. (line  13)
* symbolp:                               Symbols.             (line  17)
* symbols-consed:                        Memory Usage.        (line  26)
* symbol constituent:                    Syntax Class Table.  (line  24)
* synchronous subprocess:                Synchronous Processes.
                                                              (line   6)
* syntactic font lock:                   Syntactic Font Lock. (line   6)
* syntax class:                          Syntax Descriptors.  (line   6)
* syntax descriptor:                     Syntax Descriptors.  (line  23)
* syntax error (Edebug):                 Backtracking.        (line   6)
* syntax flags:                          Syntax Flags.        (line   6)
* syntax for characters:                 Basic Char Syntax.   (line   6)
* syntax table:                          Syntax Tables.       (line   6)
* syntax table example:                  Example Major Modes. (line  87)
* syntax table internals:                Syntax Table Internals.
                                                              (line   6)
* syntax tables in modes:                Major Mode Conventions.
                                                              (line 109)
* syntax-after:                          Syntax Table Internals.
                                                              (line  45)
* syntax-begin-function:                 Position Parse.      (line  34)
* syntax-class:                          Syntax Table Internals.
                                                              (line  52)
* syntax-ppss:                           Position Parse.      (line  11)
* syntax-ppss-flush-cache:               Position Parse.      (line  27)
* syntax-ppss-toplevel-pos:              Parser State.        (line  57)
* syntax-table:                          Syntax Table Functions.
                                                              (line  97)
* syntax-table (text property):          Syntax Properties.   (line   6)
* syntax-table-p:                        Syntax Basics.       (line  42)
* system type and name:                  System Environment.  (line  15)
* system-configuration:                  System Environment.  (line  11)
* system-key-alist:                      X11 Keysyms.         (line  10)
* system-messages-locale:                Locales.             (line  17)
* system-name:                           System Environment.  (line  86)
* system-time-locale:                    Locales.             (line  24)
* system-type:                           System Environment.  (line  16)
* t:                                     nil and t.           (line  26)
* t input stream:                        Input Streams.       (line  41)
* t output stream:                       Output Streams.      (line  31)
* tab (ASCII character):                 Basic Char Syntax.   (line  27)
* tab deletion:                          Deletion.            (line  70)
* tab-stop-list:                         Indent Tabs.         (line  24)
* tab-to-tab-stop:                       Indent Tabs.         (line  17)
* tab-width:                             Usual Display.       (line  68)
* tabs stops for indentation:            Indent Tabs.         (line   6)
* tag on run time stack:                 Catch and Throw.     (line  61)
* tag, customization keyword:            Common Keywords.     (line  16)
* tan:                                   Math Functions.      (line  12)
* TCP:                                   Network.             (line   6)
* temacs:                                Building Emacs.      (line   6)
* TEMP environment variable:             Unique File Names.   (line  68)
* temp-buffer-setup-hook:                Temporary Displays.  (line  68)
* temp-buffer-show-function:             Temporary Displays.  (line  58)
* temp-buffer-show-hook:                 Temporary Displays.  (line  74)
* temporary-file-directory:              Unique File Names.   (line  68)
* TERM environment variable:             Terminal-Specific.   (line  46)
* term-file-prefix:                      Terminal-Specific.   (line  46)
* term-setup-hook:                       Terminal-Specific.   (line  60)
* Termcap:                               Terminal-Specific.   (line  15)
* terminal frame:                        Frames.              (line  16)
* terminal input:                        Terminal Input.      (line   6)
* terminal input modes:                  Input Modes.         (line   6)
* terminal output:                       Terminal Output.     (line   6)
* terminal screen:                       Basic Windows.       (line  73)
* terminal-coding-system:                Terminal I/O Encoding.
                                                              (line  21)
* terminal-specific initialization:      Terminal-Specific.   (line   6)
* termscript file:                       Terminal Output.     (line  49)
* terpri:                                Output Functions.    (line  84)
* test-completion:                       Basic Completion.    (line 137)
* testcover-mark-all:                    Test Coverage.       (line   6)
* testcover-next-mark:                   Test Coverage.       (line   6)
* testcover-start:                       Test Coverage.       (line   6)
* testing types:                         Type Predicates.     (line  21)
* text:                                  Text.                (line   6)
* text deletion:                         Deletion.            (line   6)
* text files and binary files:           MS-DOS File Types.   (line   6)
* text insertion:                        Insertion.           (line   6)
* text near point:                       Near Point.          (line   6)
* text parsing:                          Syntax Tables.       (line   6)
* text properties:                       Text Properties.     (line   6)
* text properties in files:              Saving Properties.   (line   6)
* text properties in the mode line:      Properties in Mode.  (line   6)
* text representations:                  Text Representations.
                                                              (line   6)
* text-char-description:                 Describing Characters.
                                                              (line  55)
* text-mode-abbrev-table:                Standard Abbrev Tables.
                                                              (line  25)
* text-mode-map:                         Standard Keymaps.    (line 177)
* text-mode-syntax-table:                Standard Syntax Tables.
                                                              (line  14)
* text-properties-at:                    Examining Properties.
                                                              (line  59)
* text-property-any:                     Property Search.     (line 115)
* text-property-default-nonsticky:       Sticky Properties.   (line  54)
* text-property-not-all:                 Property Search.     (line 126)
* textual scrolling:                     Textual Scrolling.   (line   6)
* thing-at-point:                        Buffer Contents.     (line 112)
* this-command:                          Command Loop Info.   (line  34)
* this-command-keys:                     Command Loop Info.   (line  74)
* this-command-keys-vector:              Command Loop Info.   (line  90)
* this-original-command:                 Command Loop Info.   (line  67)
* three-step-help:                       Help Functions.      (line 162)
* throw:                                 Catch and Throw.     (line  77)
* throw example:                         Recursive Editing.   (line  32)
* tiled windows:                         Basic Windows.       (line  73)
* time-add:                              Time Calculations.   (line  17)
* time-less-p:                           Time Calculations.   (line  10)
* time-subtract:                         Time Calculations.   (line  13)
* time-to-day-in-year:                   Time Calculations.   (line  28)
* time-to-days:                          Time Calculations.   (line  24)
* timer:                                 Timers.              (line   6)
* timer-max-repeats:                     Timers.              (line 101)
* timestamp of a mouse event:            Accessing Mouse.     (line 100)
* timing programs:                       Compilation Tips.    (line   9)
* tips for writing Lisp:                 Tips.                (line   6)
* TMP environment variable:              Unique File Names.   (line  68)
* TMPDIR environment variable:           Unique File Names.   (line  68)
* toggle-read-only:                      Read Only Buffers.   (line  46)
* tool bar:                              Tool Bar.            (line   6)
* tool-bar-add-item:                     Tool Bar.            (line  91)
* tool-bar-add-item-from-menu:           Tool Bar.            (line 112)
* tool-bar-border:                       Tool Bar.            (line 154)
* tool-bar-button-margin:                Tool Bar.            (line 145)
* tool-bar-button-relief:                Tool Bar.            (line 150)
* tool-bar-local-item-from-menu:         Tool Bar.            (line 126)
* tool-bar-map:                          Tool Bar.            (line  76)
* tooltip:                               Special Properties.  (line  81)
* top-level:                             Recursive Editing.   (line  99)
* top-level form:                        Loading.             (line  15)
* tq-close:                              Transaction Queues.  (line  40)
* tq-create:                             Transaction Queues.  (line  12)
* tq-enqueue:                            Transaction Queues.  (line  20)
* trace buffer:                          Trace Buffer.        (line   6)
* track-mouse:                           Mouse Tracking.      (line  19)
* trailing codes:                        Text Representations.
                                                              (line  19)
* transaction queue:                     Transaction Queues.  (line   6)
* transcendental functions:              Math Functions.      (line   6)
* transient-mark-mode:                   The Mark.            (line 120)
* translate-region:                      Substitution.        (line  34)
* translation tables:                    Translation of Characters.
                                                              (line   6)
* translation-table-for-input:           Translation of Characters.
                                                              (line  65)
* transpose-regions:                     Transposition.       (line  10)
* triple-click events:                   Repeat Events.       (line   6)
* true:                                  nil and t.           (line  26)
* true list:                             Cons Cells.          (line  25)
* truename (of file):                    Truenames.           (line   6)
* truncate:                              Numeric Conversions. (line  22)
* truncate-lines:                        Truncation.          (line  22)
* truncate-partial-width-windows:        Truncation.          (line  36)
* truncate-string-to-width:              Width.               (line  20)
* truth value:                           nil and t.           (line   6)
* try-completion:                        Basic Completion.    (line  15)
* tty-color-alist:                       Text Terminal Colors.
                                                              (line  41)
* tty-color-approximate:                 Text Terminal Colors.
                                                              (line  51)
* tty-color-clear:                       Text Terminal Colors.
                                                              (line  37)
* tty-color-define:                      Text Terminal Colors.
                                                              (line  27)
* tty-color-translate:                   Text Terminal Colors.
                                                              (line  57)
* tty-erase-char:                        System Environment.  (line 221)
* two's complement:                      Integer Basics.      (line  49)
* type:                                  Lisp Data Types.     (line   6)
* type (button property):                Button Properties.   (line  38)
* type checking:                         Type Predicates.     (line   6)
* type checking internals:               Object Internals.    (line  21)
* type predicates:                       Type Predicates.     (line  21)
* type, defcustom keyword:               Customization Types. (line  11)
* type-of:                               Type Predicates.     (line 179)
* UDP:                                   Network.             (line   6)
* umask:                                 Changing Files.      (line 134)
* unbalanced parentheses:                Syntax Errors.       (line  20)
* unbinding keys:                        Key Binding Commands.
                                                              (line  60)
* undefined:                             Functions for Key Lookup.
                                                              (line  50)
* undefined in keymap:                   Key Lookup.          (line  96)
* undefined key:                         Keymap Basics.       (line   6)
* undo avoidance:                        Substitution.        (line  15)
* undo-ask-before-discard:               Maintaining Undo.    (line  62)
* undo-boundary:                         Undo.                (line  79)
* undo-in-progress:                      Undo.                (line 103)
* undo-limit:                            Maintaining Undo.    (line  45)
* undo-outer-limit:                      Maintaining Undo.    (line  57)
* undo-strong-limit:                     Maintaining Undo.    (line  50)
* unexec:                                Building Emacs.      (line  95)
* unhandled-file-name-directory:         Magic File Names.    (line 186)
* unibyte text:                          Text Representations.
                                                              (line  13)
* unibyte-char-to-multibyte:             Converting Representations.
                                                              (line 101)
* unicode character escape:              General Escape Syntax.
                                                              (line  10)
* unintern:                              Creating Symbols.    (line 163)
* uninterned symbol:                     Creating Symbols.    (line  39)
* universal-argument:                    Prefix Command Arguments.
                                                              (line 104)
* unless:                                Conditionals.        (line  42)
* unload-feature:                        Unloading.           (line  11)
* unload-feature-special-hooks:          Unloading.           (line  50)
* unloading packages:                    Unloading.           (line   6)
* unloading packages, preparing for:     Coding Conventions.  (line 103)
* unlock-buffer:                         File Locks.          (line  40)
* unpacking:                             Byte Packing.        (line  12)
* unread-command-char:                   Event Input Misc.    (line  45)
* unread-command-events:                 Event Input Misc.    (line  11)
* unsafep:                               Function Safety.     (line  14)
* unwind-protect:                        Cleanups.            (line  13)
* unwinding:                             Cleanups.            (line  13)
* up-list:                               List Motion.         (line  25)
* upcase:                                Case Conversion.     (line  37)
* upcase-initials:                       Case Conversion.     (line  79)
* upcase-region:                         Case Changes.        (line  43)
* upcase-word:                           Case Changes.        (line  73)
* update-directory-autoloads:            Autoload.            (line  93)
* update-file-autoloads:                 Autoload.            (line  93)
* upper case:                            Case Conversion.     (line   6)
* upper case key sequence:               Key Sequence Input.  (line  73)
* use-global-map:                        Controlling Active Maps.
                                                              (line  45)
* use-hard-newlines:                     Filling.             (line 155)
* use-local-map:                         Controlling Active Maps.
                                                              (line  51)
* user identification:                   User Identification. (line   6)
* user option:                           Defining Variables.  (line 129)
* user signals:                          Misc Events.         (line  67)
* user-defined error:                    Error Symbols.       (line   6)
* user-full-name:                        User Identification. (line  46)
* user-init-file:                        Init File.           (line  70)
* user-login-name:                       User Identification. (line  27)
* user-mail-address:                     User Identification. (line  20)
* user-real-login-name:                  User Identification. (line  41)
* user-real-uid:                         User Identification. (line  68)
* user-uid:                              User Identification. (line  75)
* user-variable-p:                       Defining Variables.  (line 129)
* user-variable-p example:               High-Level Completion.
                                                              (line 119)
* value cell:                            Symbol Components.   (line  15)
* value of expression:                   Evaluation.          (line   6)
* values:                                Eval.                (line 110)
* variable:                              Variables.           (line   6)
* variable aliases:                      Variable Aliases.    (line   6)
* variable definition:                   Defining Variables.  (line   6)
* variable descriptions:                 A Sample Variable Description.
                                                              (line   6)
* variable limit error:                  Local Variables.     (line 104)
* variable with constant value:          Constant Variables.  (line   6)
* variable, buffer-local:                Buffer-Local Variables.
                                                              (line   6)
* variable-documentation:                Documentation Basics.
                                                              (line  42)
* variable-interactive:                  Defining Variables.  (line 142)
* variable-width spaces:                 Specified Space.     (line   6)
* variant coding system:                 Coding System Basics.
                                                              (line  44)
* vc-mode:                               Mode Line Variables. (line  61)
* vc-prefix-map:                         Prefix Keys.         (line  40)
* vconcat:                               Vector Functions.    (line  33)
* vector:                                Vector Functions.    (line  17)
* vector (type):                         Vectors.             (line   6)
* vector evaluation:                     Self-Evaluating Forms.
                                                              (line   6)
* vector length:                         Sequence Functions.  (line  16)
* vector-cells-consed:                   Memory Usage.        (line  22)
* vectorp:                               Vector Functions.    (line   9)
* verify-visited-file-modtime:           Modification Time.   (line  15)
* version number (in file name):         File Name Components.
                                                              (line   6)
* version, customization keyword:        Common Keywords.     (line 108)
* version-control:                       Numbered Backups.    (line  11)
* vertical fractional scrolling:         Vertical Scrolling.  (line   6)
* vertical tab:                          Basic Char Syntax.   (line  27)
* vertical-line prefix key:              Key Sequence Input.  (line  84)
* vertical-motion:                       Screen Lines.        (line  31)
* vertical-scroll-bar:                   Scroll Bars.         (line  20)
* vertical-scroll-bar prefix key:        Key Sequence Input.  (line  84)
* view part, model/view/controller:      Abstract Display.    (line   6)
* view-file:                             Visiting Functions.  (line  99)
* view-mode-map:                         Standard Keymaps.    (line 183)
* view-register:                         Registers.           (line  67)
* visible frame:                         Visibility of Frames.
                                                              (line   6)
* visible-bell:                          Beeping.             (line  21)
* visible-frame-list:                    Finding All Frames.  (line  14)
* visited file:                          Buffer File Name.    (line   6)
* visited file mode:                     Auto Major Mode.     (line  49)
* visited-file-modtime:                  Modification Time.   (line  45)
* visiting files:                        Visiting Files.      (line   6)
* void function:                         Function Indirection.
                                                              (line   6)
* void function cell:                    Function Cells.      (line  30)
* void variable:                         Void Variables.      (line   6)
* void-function:                         Function Cells.      (line  14)
* void-text-area-pointer:                Pointer Shape.       (line  19)
* void-variable:                         Void Variables.      (line   6)
* waiting:                               Waiting.             (line   6)
* waiting for command key input:         Event Input Misc.    (line  53)
* waiting-for-user-input-p:              Sentinels.           (line  97)
* walk-windows:                          Cyclic Window Ordering.
                                                              (line  96)
* warn:                                  Warning Basics.      (line  56)
* warning type:                          Warning Basics.      (line  36)
* warning-fill-prefix:                   Warning Variables.   (line  62)
* warning-levels:                        Warning Variables.   (line  10)
* warning-minimum-level:                 Warning Options.     (line  10)
* warning-minimum-log-level:             Warning Options.     (line  15)
* warning-prefix-function:               Warning Variables.   (line  26)
* warning-series:                        Warning Variables.   (line  42)
* warning-suppress-log-types:            Warning Options.     (line  26)
* warning-suppress-types:                Warning Options.     (line  20)
* warning-type-format:                   Warning Variables.   (line  66)
* warnings:                              Warnings.            (line   6)
* wheel-down event:                      Misc Events.         (line  28)
* wheel-up event:                        Misc Events.         (line  28)
* when:                                  Conditionals.        (line  32)
* where-is-internal:                     Scanning Keymaps.    (line  77)
* while:                                 Iteration.           (line  12)
* while-no-input:                        Event Input Misc.    (line  79)
* whitespace:                            Basic Char Syntax.   (line  27)
* whitespace character:                  Syntax Class Table.  (line  10)
* wholenump:                             Predicates on Numbers.
                                                              (line  28)
* widen:                                 Narrowing.           (line  44)
* widening:                              Narrowing.           (line  44)
* window:                                Basic Windows.       (line   6)
* window (overlay property):             Overlay Properties.  (line  58)
* window configuration (Edebug):         Edebug Display Update.
                                                              (line  25)
* window configurations:                 Window Configurations.
                                                              (line   6)
* window excursions:                     Excursions.          (line  33)
* window frame:                          Frames.              (line  20)
* window header line:                    Header Lines.        (line   6)
* window internals:                      Window Internals.    (line   6)
* window layout in a frame:              Window Configuration Type.
                                                              (line   6)
* window layout, all frames:             Frame Configuration Type.
                                                              (line   6)
* window manager, and frame parameters:  Management Parameters.
                                                              (line   6)
* window ordering, cyclic:               Cyclic Window Ordering.
                                                              (line   6)
* window point:                          Window Point.        (line   6)
* window point internals:                Window Internals.    (line  67)
* window position:                       Window Point.        (line   6)
* window resizing:                       Resizing Windows.    (line   6)
* window size:                           Size of Window.      (line   6)
* window size, changing:                 Resizing Windows.    (line   6)
* window splitting:                      Splitting Windows.   (line   6)
* window start position:                 Window Start.        (line   6)
* window that satisfies a predicate:     Selecting Windows.   (line  93)
* window top line:                       Window Start.        (line  22)
* window tree:                           Window Tree.         (line   6)
* window-at:                             Coordinates and Windows.
                                                              (line   9)
* window-body-height:                    Size of Window.      (line  30)
* window-buffer:                         Buffers and Windows. (line  36)
* window-configuration-change-hook:      Window Hooks.        (line  70)
* window-configuration-frame:            Window Configurations.
                                                              (line  96)
* window-configuration-p:                Window Configurations.
                                                              (line  83)
* window-current-scroll-bars:            Scroll Bars.         (line  72)
* window-dedicated-p:                    Choosing Window.     (line 224)
* window-display-table:                  Active Display Table.
                                                              (line  13)
* window-edges:                          Size of Window.      (line  51)
* window-end:                            Window Start.        (line  43)
* window-frame:                          Frames and Windows.  (line  10)
* window-fringes:                        Fringe Size/Pos.     (line  41)
* window-full-width-p:                   Size of Window.      (line  46)
* window-height:                         Size of Window.      (line  15)
* window-hscroll:                        Horizontal Scrolling.
                                                              (line  73)
* window-inside-edges:                   Size of Window.      (line  69)
* window-inside-pixel-edges:             Size of Window.      (line 122)
* window-line-height:                    Window Start.        (line 155)
* window-list:                           Cyclic Window Ordering.
                                                              (line 104)
* window-live-p:                         Deleting Windows.    (line  18)
* window-margins:                        Display Margins.     (line  52)
* window-min-height:                     Resizing Windows.    (line 126)
* window-min-width:                      Resizing Windows.    (line 135)
* window-minibuffer-p:                   Minibuffer Windows.  (line  29)
* window-pixel-edges:                    Size of Window.      (line 117)
* window-point:                          Window Point.        (line  32)
* window-redisplay-end-trigger:          Window Hooks.        (line  66)
* window-scroll-bars:                    Scroll Bars.         (line  46)
* window-scroll-functions:               Window Hooks.        (line  14)
* window-setup-hook:                     Window Systems.      (line  31)
* window-size-change-functions:          Window Hooks.        (line  31)
* window-size-fixed:                     Resizing Windows.    (line 101)
* window-start:                          Window Start.        (line  22)
* window-system:                         Window Systems.      (line  12)
* window-tree:                           Window Tree.         (line  10)
* window-vscroll:                        Vertical Scrolling.  (line  26)
* window-width:                          Size of Window.      (line  34)
* windowp:                               Basic Windows.       (line  84)
* Windows file types:                    MS-DOS File Types.   (line   6)
* windows, controlling precisely:        Buffers and Windows. (line   6)
* with-case-table:                       Case Tables.         (line  78)
* with-current-buffer:                   Current Buffer.      (line 119)
* with-local-quit:                       Quitting.            (line  85)
* with-no-warnings:                      Compiler Errors.     (line  38)
* with-output-to-string:                 Output Functions.    (line 112)
* with-output-to-temp-buffer:            Temporary Displays.  (line  11)
* with-selected-window:                  Selecting Windows.   (line  43)
* with-syntax-table:                     Syntax Table Functions.
                                                              (line 101)
* with-temp-buffer:                      Current Buffer.      (line 130)
* with-temp-file:                        Writing to Files.    (line  84)
* with-temp-message:                     Displaying Messages. (line  42)
* with-timeout:                          Timers.              (line 106)
* word-search-backward:                  String Search.       (line 108)
* word-search-forward:                   String Search.       (line  67)
* words-include-escapes:                 Word Motion.         (line  37)
* word constituent:                      Syntax Class Table.  (line  18)
* write-abbrev-file:                     Abbrev Files.        (line  38)
* write-char:                            Output Functions.    (line  88)
* write-contents-functions:              Saving Buffers.      (line 113)
* write-file:                            Saving Buffers.      (line  56)
* write-file-functions:                  Saving Buffers.      (line  77)
* write-region:                          Writing to Files.    (line  26)
* write-region-annotate-functions:       Saving Properties.   (line  11)
* writing a documentation string:        Documentation Basics.
                                                              (line   6)
* writing Emacs primitives:              Writing Emacs Primitives.
                                                              (line   6)
* writing to files:                      Writing to Files.    (line   6)
* wrong-number-of-arguments:             Argument List.       (line   6)
* wrong-type-argument:                   Type Predicates.     (line   6)
* X Window System:                       Window Systems.      (line  16)
* x-alt-keysym:                          X11 Keysyms.         (line  30)
* x-bitmap-file-path:                    Face Attributes.     (line 178)
* x-close-connection:                    Multiple Displays.   (line  71)
* x-color-defined-p:                     Color Names.         (line  35)
* x-color-values:                        Color Names.         (line  91)
* x-defined-colors:                      Color Names.         (line  43)
* x-display-color-p:                     Display Feature Testing.
                                                              (line  35)
* x-display-list:                        Multiple Displays.   (line  46)
* x-dnd-known-types:                     Drag and Drop.       (line   6)
* x-dnd-test-function:                   Drag and Drop.       (line   6)
* x-dnd-types-alist:                     Drag and Drop.       (line  15)
* x-family-fonts:                        Font Lookup.         (line  27)
* x-font-family-list:                    Font Lookup.         (line  54)
* x-get-cut-buffer:                      Window System Selections.
                                                              (line  52)
* x-get-resource:                        Resources.           (line   8)
* x-get-selection:                       Window System Selections.
                                                              (line  33)
* x-hyper-keysym:                        X11 Keysyms.         (line  32)
* x-list-fonts:                          Font Lookup.         (line   7)
* x-meta-keysym:                         X11 Keysyms.         (line  31)
* x-open-connection:                     Multiple Displays.   (line  52)
* x-parse-geometry:                      Geometry.            (line  10)
* x-pointer-shape:                       Pointer Shape.       (line  28)
* x-popup-dialog:                        Dialog Boxes.        (line  16)
* x-popup-menu:                          Pop-Up Menus.        (line  10)
* x-resource-class:                      Resources.           (line  22)
* x-resource-name:                       Resources.           (line  28)
* x-select-enable-clipboard:             Window System Selections.
                                                              (line  95)
* x-sensitive-text-pointer-shape:        Pointer Shape.       (line  32)
* x-server-vendor:                       Display Feature Testing.
                                                              (line 148)
* x-server-version:                      Display Feature Testing.
                                                              (line 141)
* x-set-cut-buffer:                      Window System Selections.
                                                              (line  56)
* x-set-selection:                       Window System Selections.
                                                              (line  13)
* x-super-keysym:                        X11 Keysyms.         (line  33)
* X11 keysyms:                           X11 Keysyms.         (line   6)
* XBM:                                   XBM Images.          (line   6)
* XPM:                                   XPM Images.          (line   6)
* y-or-n-p:                              Yes-or-No Queries.   (line  24)
* y-or-n-p-with-timeout:                 Yes-or-No Queries.   (line  78)
* yank:                                  Yank Commands.       (line  12)
* yank suppression:                      Changing Key Bindings.
                                                              (line 159)
* yank-pop:                              Yank Commands.       (line  35)
* yank-undo-function:                    Yank Commands.       (line  58)
* yes-or-no questions:                   Yes-or-No Queries.   (line   6)
* yes-or-no-p:                           Yes-or-No Queries.   (line  84)
* zerop:                                 Predicates on Numbers.
                                                              (line  36)
* | in regexp:                           Regexp Backslash.    (line  13)



Tag Table:
Node: Top1145
Node: Introduction66070
Node: Caveats67967
Node: Lisp History69671
Node: Conventions71343
Node: Some Terms72146
Node: nil and t72881
Node: Evaluation Notation74690
Node: Printing Notation75613
Node: Error Messages76422
Node: Buffer Text Notation76864
Node: Format of Descriptions77768
Node: A Sample Function Description78624
Node: A Sample Variable Description82679
Node: Version Info83603
Node: Acknowledgements85461
Node: Lisp Data Types86773
Node: Printed Representation89298
Node: Comments91307
Node: Programming Types92203
Node: Integer Type93995
Node: Floating Point Type94968
Node: Character Type95867
Node: Basic Char Syntax97056
Node: General Escape Syntax100124
Node: Ctl-Char Syntax102046
Node: Meta-Char Syntax103817
Node: Other Char Bits104918
Ref: modifier bits105734
Node: Symbol Type106116
Node: Sequence Type109251
Node: Cons Cell Type110831
Node: Box Diagrams113697
Node: Dotted Pair Notation117322
Node: Association List Type119834
Node: Array Type120836
Node: String Type122561
Node: Syntax for Strings123200
Node: Non-ASCII in Strings124360
Node: Nonprinting Characters126420
Node: Text Props and Strings127863
Node: Vector Type129200
Node: Char-Table Type129974
Node: Bool-Vector Type130981
Node: Hash Table Type132182
Node: Function Type132680
Node: Macro Type133817
Node: Primitive Function Type134717
Node: Byte-Code Type136287
Node: Autoload Type136909
Node: Editing Types137914
Node: Buffer Type138860
Node: Marker Type141003
Node: Window Type141728
Node: Frame Type142938
Node: Window Configuration Type143558
Node: Frame Configuration Type144131
Node: Process Type144706
Node: Stream Type145666
Node: Keymap Type146791
Node: Overlay Type147248
Node: Circular Objects147853
Node: Type Predicates149347
Node: Equality Predicates154597
Node: Numbers158862
Node: Integer Basics160180
Node: Float Basics163272
Node: Predicates on Numbers165564
Node: Comparison of Numbers167146
Node: Numeric Conversions171443
Node: Arithmetic Operations173983
Node: Rounding Operations179493
Node: Bitwise Operations180601
Node: Math Functions189629
Node: Random Numbers191731
Node: Strings and Characters193508
Node: String Basics194778
Node: Predicates for Strings197765
Node: Creating Strings198447
Node: Modifying Strings206449
Node: Text Comparison207729
Node: String Conversion213848
Node: Formatting Strings217980
Node: Case Conversion226389
Node: Case Tables230337
Node: Lists235409
Node: Cons Cells236416
Node: List-related Predicates239086
Node: List Elements240798
Ref: Definition of nth243372
Ref: Definition of safe-length244829
Node: Building Lists246221
Ref: Building Lists-Footnote-1254682
Node: List Variables255156
Node: Modifying Lists258920
Node: Setcar259815
Node: Setcdr262372
Node: Rearrangement264965
Node: Sets And Lists271113
Node: Association Lists278165
Ref: Association Lists-Footnote-1287528
Node: Rings287733
Node: Sequences Arrays Vectors290465
Node: Sequence Functions293109
Node: Arrays296899
Node: Array Functions299363
Node: Vectors301679
Node: Vector Functions303168
Node: Char-Tables305721
Node: Bool-Vectors311613
Node: Hash Tables312933
Node: Creating Hash314555
Node: Hash Access319351
Ref: Definition of maphash320818
Node: Defining Hash321039
Node: Other Hash324100
Node: Symbols325274
Node: Symbol Components326311
Node: Definitions331015
Node: Creating Symbols333330
Ref: Definition of mapatoms339766
Node: Property Lists340906
Node: Plists and Alists342355
Node: Symbol Plists344159
Node: Other Plists346002
Node: Evaluation348198
Node: Intro Eval348996
Ref: Intro Eval-Footnote-1352357
Node: Forms352492
Node: Self-Evaluating Forms353668
Node: Symbol Forms355188
Node: Classifying Lists356259
Node: Function Indirection357017
Ref: Definition of indirect-function359666
Node: Function Forms360487
Node: Macro Forms361486
Node: Special Forms363088
Node: Autoloading365396
Node: Quoting365895
Node: Eval367268
Ref: Definition of eval-region369130
Ref: Definition of max-lisp-eval-depth371207
Node: Control Structures373601
Node: Sequencing375256
Node: Conditionals378159
Node: Combining Conditions382130
Node: Iteration385747
Node: Nonlocal Exits388638
Node: Catch and Throw389338
Node: Examples of Catch393418
Node: Errors395342
Node: Signaling Errors396832
Ref: Definition of signal398917
Node: Processing of Errors400839
Node: Handling Errors402743
Node: Error Symbols410428
Node: Cleanups414105
Node: Variables417834
Node: Global Variables420020
Node: Constant Variables421109
Node: Local Variables422057
Ref: Definition of max-specpdl-size426576
Node: Void Variables427314
Node: Defining Variables430798
Ref: Defining Variables-Footnote-1437854
Node: Tips for Defining437920
Node: Accessing Variables441157
Node: Setting Variables442537
Node: Variable Scoping445918
Node: Scope447523
Node: Extent449489
Node: Impl of Scope450962
Node: Using Scoping452948
Node: Buffer-Local Variables454474
Node: Intro to Buffer-Local455383
Node: Creating Buffer-Local459437
Node: Default Value467665
Node: Future Local Variables471077
Node: File Local Variables472123
Node: Variable Aliases477677
Node: Variables with Restricted Values481024
Node: Functions482285
Node: What Is a Function483505
Node: Lambda Expressions488233
Node: Lambda Components489142
Node: Simple Lambda490974
Node: Argument List492635
Node: Function Documentation496552
Node: Function Names499180
Node: Defining Functions502121
Ref: Definition of defalias504320
Node: Calling Functions505876
Node: Mapping Functions509734
Ref: Definition of mapcar510655
Node: Anonymous Functions512986
Node: Function Cells516838
Node: Obsolete Functions521757
Node: Inline Functions523203
Node: Function Safety525266
Node: Related Topics526867
Node: Macros528108
Node: Simple Macro529460
Node: Expansion530223
Node: Compiling Macros533726
Node: Defining Macros535579
Ref: Definition of declare537163
Node: Backquote538372
Node: Problems with Macros540975
Node: Wrong Time541769
Node: Argument Evaluation542820
Node: Surprising Local Vars545751
Node: Eval During Expansion547820
Node: Repeated Expansion549614
Node: Indenting Macros551988
Node: Customization554310
Node: Common Keywords555040
Node: Group Definitions561483
Node: Variable Definitions564807
Node: Customization Types573166
Node: Simple Types574765
Node: Composite Types582084
Node: Splicing into Lists590629
Node: Type Keywords592496
Node: Defining New Types596618
Node: Loading600030
Node: How Programs Do Loading601961
Ref: Definition of load-read-function606976
Node: Load Suffixes607568
Node: Library Search609744
Node: Loading Non-ASCII614640
Node: Autoload616810
Ref: autoload cookie621481
Node: Repeated Loading624162
Node: Named Features626275
Node: Where Defined632423
Node: Unloading634476
Node: Hooks for Loading636921
Node: Byte Compilation639417
Node: Speed of Byte-Code641460
Node: Compilation Functions642530
Node: Docs and Compilation649619
Node: Dynamic Loading652277
Node: Eval During Compile654884
Node: Compiler Errors658093
Node: Byte-Code Objects659790
Node: Disassembly662155
Node: Advising Functions670586
Node: Simple Advice673047
Node: Defining Advice675785
Node: Around-Advice681919
Node: Computed Advice683435
Node: Activation of Advice684940
Node: Enabling Advice689852
Node: Preactivation691396
Node: Argument Access in Advice694047
Node: Advising Primitives697139
Node: Combined Definition698399
Node: Debugging700853
Node: Debugger702426
Node: Error Debugging703572
Node: Infinite Loops707881
Node: Function Debugging709134
Node: Explicit Debug712180
Node: Using Debugger713055
Node: Debugger Commands715277
Node: Invoking the Debugger719444
Node: Internals of Debugger723426
Node: Edebug727879
Node: Using Edebug729961
Node: Instrumenting732553
Node: Edebug Execution Modes735648
Node: Jumping739117
Node: Edebug Misc741999
Node: Breaks743408
Node: Breakpoints743917
Node: Global Break Condition746582
Node: Source Breakpoints747638
Node: Trapping Errors748591
Node: Edebug Views749720
Node: Edebug Eval751843
Node: Eval List752932
Node: Printing in Edebug756896
Node: Trace Buffer758600
Node: Coverage Testing760534
Node: The Outside Context763303
Node: Checking Whether to Stop764026
Node: Edebug Display Update764735
Node: Edebug Recursive Edit766893
Node: Edebug and Macros768557
Node: Instrumenting Macro Calls769097
Node: Specification List772125
Node: Backtracking780216
Node: Specification Examples782383
Node: Edebug Options784442
Node: Syntax Errors788602
Node: Excess Open789948
Node: Excess Close791709
Node: Test Coverage792971
Node: Compilation Errors794585
Node: Read and Print795858
Node: Streams Intro796831
Node: Input Streams798895
Node: Input Functions803939
Node: Output Streams806053
Node: Output Functions810261
Node: Output Variables815017
Node: Minibuffers820087
Node: Intro to Minibuffers821643
Node: Text from Minibuffer825004
Ref: Definition of minibuffer-local-map830496
Node: Object from Minibuffer832345
Node: Minibuffer History835590
Node: Initial Input840768
Node: Completion842536
Node: Basic Completion844496
Ref: Definition of test-completion850809
Node: Minibuffer Completion852805
Node: Completion Commands856474
Node: High-Level Completion862465
Ref: Definition of read-variable866733
Node: Reading File Names868041
Node: Programmed Completion875522
Node: Yes-or-No Queries878322
Node: Multiple Queries883468
Node: Reading a Password887688
Node: Minibuffer Commands888612
Node: Minibuffer Windows889943
Ref: Definition of minibuffer-window890391
Node: Minibuffer Contents891661
Node: Recursive Mini893396
Node: Minibuffer Misc894818
Ref: Definition of minibuffer-help-form895442
Ref: Definition of minibuffer-scroll-window895613
Node: Command Loop896462
Node: Command Overview898025
Node: Defining Commands901008
Node: Using Interactive901756
Node: Interactive Codes907384
Node: Interactive Examples914692
Node: Interactive Call915995
Node: Distinguish Interactive920796
Node: Command Loop Info923267
Ref: Definition of this-command-keys-vector927202
Node: Adjusting Point929178
Node: Input Events930360
Node: Keyboard Events932321
Node: Function Keys935027
Node: Mouse Events937889
Node: Click Events939008
Node: Drag Events943635
Node: Button-Down Events945170
Ref: Button-Down Events-Footnote-1946361
Node: Repeat Events946421
Node: Motion Events950787
Node: Focus Events951535
Node: Misc Events953090
Node: Event Examples956807
Node: Classifying Events958310
Node: Accessing Mouse962274
Node: Accessing Scroll967448
Node: Strings of Events968634
Node: Reading Input972464
Node: Key Sequence Input973487
Node: Reading One Event978597
Node: Event Mod982957
Node: Invoking the Input Method986577
Node: Quoted Character Input988541
Node: Event Input Misc990066
Node: Special Events994824
Node: Waiting996068
Node: Quitting998833
Node: Prefix Command Arguments1004427
Node: Recursive Editing1009358
Node: Disabling Commands1014407
Node: Command History1016580
Node: Keyboard Macros1018289
Node: Keymaps1021368
Node: Key Sequences1023218
Node: Keymap Basics1025719
Node: Format of Keymaps1028253
Node: Creating Keymaps1032673
Node: Inheritance and Keymaps1035180
Node: Prefix Keys1037264
Ref: Definition of define-prefix-command1040759
Node: Active Keymaps1041381
Node: Searching Keymaps1046394
Node: Controlling Active Maps1048536
Ref: Definition of minor-mode-map-alist1050708
Node: Key Lookup1054658
Node: Functions for Key Lookup1060378
Node: Changing Key Bindings1065719
Node: Remapping Commands1074104
Node: Translation Keymaps1076467
Node: Key Binding Commands1081515
Node: Scanning Keymaps1084553
Node: Menu Keymaps1091234
Node: Defining Menus1092044
Ref: Defining Menus-Footnote-11094317
Node: Simple Menu Items1094397
Ref: Simple Menu Items-Footnote-11096845
Node: Extended Menu Items1096974
Node: Menu Separators1101996
Node: Alias Menu Items1104248
Node: Mouse Menus1105484
Node: Keyboard Menus1107347
Node: Menu Example1108646
Node: Menu Bar1111275
Node: Tool Bar1114698
Node: Modifying Menus1122583
Node: Modes1124090
Node: Hooks1125323
Node: Major Modes1131459
Node: Major Mode Basics1132626
Node: Major Mode Conventions1135516
Node: Auto Major Mode1145848
Node: Mode Help1153688
Node: Derived Modes1154809
Node: Generic Modes1159053
Node: Mode Hooks1161203
Node: Example Major Modes1163469
Node: Minor Modes1172211
Node: Minor Mode Conventions1173766
Node: Keymaps and Minor Modes1178538
Node: Defining Minor Modes1179608
Node: Mode Line Format1186176
Node: Mode Line Basics1187489
Node: Mode Line Data1189223
Node: Mode Line Top1193483
Node: Mode Line Variables1195947
Ref: Definition of minor-mode-alist1200103
Node: %-Constructs1202382
Node: Properties in Mode1206013
Node: Header Lines1207545
Node: Emulating Mode Line1208688
Node: Imenu1210341
Node: Font Lock Mode1217108
Node: Font Lock Basics1218910
Node: Search-based Fontification1222289
Node: Customizing Keywords1231692
Node: Other Font Lock Variables1234738
Node: Levels of Font Lock1237125
Node: Precalculated Fontification1238401
Node: Faces for Font Lock1239219
Node: Syntactic Font Lock1241286
Node: Setting Syntax Properties1244159
Node: Multiline Font Lock1246463
Node: Font Lock Multiline1249650
Node: Region to Fontify1252022
Node: Desktop Save Mode1253391
Node: Documentation1255154
Node: Documentation Basics1256677
Node: Accessing Documentation1259880
Ref: describe-symbols example1262440
Ref: Definition of Snarf-documentation1265555
Node: Keys in Documentation1266648
Node: Describing Characters1269446
Node: Help Functions1273322
Ref: Definition of data-directory1279391
Node: Files1280953
Node: Visiting Files1283038
Node: Visiting Functions1284542
Node: Subroutines of Visiting1290936
Node: Saving Buffers1293608
Ref: Definition of save-some-buffers1295147
Ref: Definition of write-file1296274
Node: Reading from Files1301843
Node: Writing to Files1304764
Ref: Definition of with-temp-file1308700
Node: File Locks1309287
Node: Information about Files1312754
Node: Testing Accessibility1313595
Node: Kinds of Files1318463
Node: Truenames1320295
Node: File Attributes1322886
Ref: Definition of file-attributes1325391
Node: Locating Files1329207
Node: Changing Files1332162
Node: File Names1339465
Node: File Name Components1341305
Node: Relative File Names1346041
Node: Directory Names1348309
Ref: Definition of abbreviate-file-name1352483
Node: File Name Expansion1352756
Ref: Definition of substitute-in-file-name1356178
Node: Unique File Names1358026
Node: File Name Completion1362471
Node: Standard File Names1365621
Node: Contents of Directories1367874
Node: Create/Delete Dirs1372912
Node: Magic File Names1373998
Node: Format Conversion1383399
Node: Backups and Auto-Saving1389769
Node: Backup Files1390439
Node: Making Backups1391822
Node: Rename or Copy1396459
Node: Numbered Backups1399506
Node: Backup Names1401836
Node: Auto-Saving1405564
Node: Reverting1414768
Ref: Definition of revert-buffer-function1417289
Node: Buffers1418878
Node: Buffer Basics1420339
Node: Current Buffer1422391
Ref: Definition of with-temp-buffer1428285
Node: Buffer Names1429150
Node: Buffer File Name1432797
Node: Buffer Modification1438897
Node: Modification Time1441973
Node: Read Only Buffers1446565
Node: The Buffer List1449382
Node: Creating Buffers1454623
Node: Killing Buffers1457001
Node: Indirect Buffers1461493
Node: Buffer Gap1464510
Node: Windows1465507
Node: Basic Windows1467363
Node: Splitting Windows1470661
Node: Deleting Windows1477350
Node: Selecting Windows1480200
Node: Cyclic Window Ordering1484963
Node: Buffers and Windows1489980
Node: Displaying Buffers1493517
Node: Choosing Window1499299
Ref: Definition of special-display-frame-alist1507829
Node: Window Point1509659
Node: Window Start1511882
Node: Textual Scrolling1520007
Node: Vertical Scrolling1528947
Node: Horizontal Scrolling1531545
Node: Size of Window1537140
Node: Resizing Windows1542289
Node: Coordinates and Windows1548719
Node: Window Tree1550994
Node: Window Configurations1552154
Node: Window Hooks1556802
Node: Frames1560472
Node: Creating Frames1563775
Node: Multiple Displays1565422
Node: Frame Parameters1568898
Node: Parameter Access1569961
Node: Initial Parameters1571408
Node: Window Frame Parameters1574297
Node: Basic Parameters1575468
Node: Position Parameters1576914
Node: Size Parameters1579723
Node: Layout Parameters1580909
Node: Buffer Parameters1583168
Node: Management Parameters1584342
Node: Cursor Parameters1585925
Node: Color Parameters1587946
Node: Size and Position1591442
Node: Geometry1595612
Node: Frame Titles1597545
Node: Deleting Frames1599177
Node: Finding All Frames1600545
Node: Frames and Windows1602260
Node: Minibuffers and Frames1604165
Node: Input Focus1605439
Node: Visibility of Frames1611222
Node: Raising and Lowering1613275
Node: Frame Configurations1614910
Node: Mouse Tracking1615799
Node: Mouse Position1617466
Node: Pop-Up Menus1619306
Node: Dialog Boxes1622770
Node: Pointer Shape1625142
Node: Window System Selections1626994
Ref: Definition of x-set-cut-buffer1629647
Node: Drag and Drop1631918
Node: Color Names1633228
Node: Text Terminal Colors1637433
Node: Resources1640164
Node: Display Feature Testing1642114
Ref: Display Face Attribute Testing1644086
Node: Positions1649084
Node: Point1650590
Node: Motion1653294
Node: Character Motion1654061
Node: Word Motion1655760
Node: Buffer End Motion1657774
Node: Text Lines1659524
Ref: Definition of count-lines1664299
Node: Screen Lines1665312
Node: List Motion1672345
Node: Skipping Characters1676168
Node: Excursions1678763
Node: Narrowing1681612
Node: Markers1685917
Node: Overview of Markers1686939
Node: Predicates on Markers1690145
Node: Creating Markers1691041
Node: Information from Markers1694373
Node: Marker Insertion Types1695465
Node: Moving Markers1696624
Node: The Mark1697996
Node: The Region1706348
Node: Text1707595
Node: Near Point1710650
Node: Buffer Contents1713888
Node: Comparing Text1719312
Node: Insertion1720742
Node: Commands for Insertion1725451
Node: Deletion1728528
Node: User-Level Deletion1733067
Node: The Kill Ring1737382
Node: Kill Ring Concepts1739604
Node: Kill Functions1740655
Node: Yanking1743028
Node: Yank Commands1745397
Node: Low-Level Kill Ring1748328
Node: Internals of Kill Ring1752793
Node: Undo1755688
Node: Maintaining Undo1761057
Node: Filling1764361
Ref: Definition of sentence-end-double-space1770448
Node: Margins1771869
Node: Adaptive Fill1776367
Node: Auto Filling1780469
Node: Sorting1782170
Node: Columns1792516
Node: Indentation1795130
Node: Primitive Indent1795911
Node: Mode-Specific Indent1797380
Node: Region Indent1799773
Node: Relative Indent1802800
Node: Indent Tabs1805196
Node: Motion by Indent1806575
Node: Case Changes1807487
Node: Text Properties1810728
Node: Examining Properties1813203
Node: Changing Properties1816951
Node: Property Search1822276
Node: Special Properties1828734
Ref: Text help-echo1832103
Ref: Help display1840051
Node: Format Properties1841280
Node: Sticky Properties1842275
Node: Saving Properties1846280
Node: Lazy Properties1849503
Node: Clickable Text1851686
Node: Links and Mouse-11855324
Node: Fields1859374
Node: Not Intervals1864752
Node: Substitution1867253
Node: Registers1869118
Node: Transposition1872352
Node: Base 641873249
Ref: Base 64-Footnote-11875437
Node: MD5 Checksum1875712
Ref: MD5 Checksum-Footnote-11877800
Node: Atomic Changes1877883
Node: Change Hooks1881469
Node: Non-ASCII Characters1885045
Node: Text Representations1886396
Node: Converting Representations1890107
Node: Selecting a Representation1895551
Node: Character Codes1898215
Node: Character Sets1899476
Node: Chars and Bytes1901453
Node: Splitting Characters1902737
Node: Scanning Charsets1905305
Node: Translation of Characters1906852
Node: Coding Systems1910687
Node: Coding System Basics1911927
Node: Encoding and I/O1916013
Node: Lisp and Coding Systems1920048
Node: User-Chosen Coding Systems1925081
Node: Default Coding Systems1929061
Node: Specifying Coding Systems1936469
Node: Explicit Encoding1938883
Node: Terminal I/O Encoding1942803
Node: MS-DOS File Types1944063
Node: Input Methods1946642
Node: Locales1949554
Node: Searching and Matching1951785
Node: String Search1953009
Node: Searching and Case1958146
Node: Regular Expressions1960198
Node: Syntax of Regexps1961315
Node: Regexp Special1963140
Node: Char Classes1974051
Node: Regexp Backslash1976090
Node: Regexp Example1984307
Node: Regexp Functions1986881
Node: Regexp Search1989122
Node: POSIX Regexps1995903
Node: Match Data1997797
Node: Replacing Match1998926
Node: Simple Match Data2001740
Node: Entire Match Data2006830
Node: Saving Match Data2009804
Node: Search and Replace2011185
Node: Standard Regexps2016797
Node: Syntax Tables2019362
Node: Syntax Basics2020619
Node: Syntax Descriptors2022898
Node: Syntax Class Table2024840
Node: Syntax Flags2032401
Node: Syntax Table Functions2035872
Node: Syntax Properties2040339
Node: Motion and Syntax2041586
Node: Parsing Expressions2043175
Node: Motion via Parsing2045008
Node: Position Parse2047884
Node: Parser State2049776
Node: Low-Level Parsing2052729
Node: Control Parsing2054505
Node: Standard Syntax Tables2055379
Node: Syntax Table Internals2056226
Node: Categories2059012
Node: Abbrevs2063974
Node: Abbrev Mode2066120
Node: Abbrev Tables2066870
Node: Defining Abbrevs2069356
Node: Abbrev Files2072131
Node: Abbrev Expansion2074200
Node: Standard Abbrev Tables2080182
Node: Processes2081259
Node: Subprocess Creation2083817
Node: Shell Arguments2087612
Node: Synchronous Processes2089254
Ref: Synchronous Processes-Footnote-12099457
Node: Asynchronous Processes2099557
Node: Deleting Processes2103976
Node: Process Information2106021
Ref: Coding systems for a subprocess2110027
Node: Input to Processes2111209
Node: Signals to Processes2114398
Node: Output from Processes2118728
Node: Process Buffers2121170
Node: Filter Functions2124181
Node: Decoding Output2129378
Node: Accepting Output2131621
Node: Sentinels2133706
Node: Query Before Exit2138415
Node: Transaction Queues2140117
Node: Network2142072
Node: Network Servers2146928
Node: Datagrams2148851
Node: Low-Level Network2150109
Node: Network Processes2150712
Node: Network Options2157196
Node: Network Feature Testing2160462
Node: Misc Network2161828
Node: Byte Packing2163602
Node: Bindat Spec2164463
Node: Bindat Functions2170074
Node: Bindat Examples2172860
Node: Display2178932
Node: Refresh Screen2180669
Node: Forcing Redisplay2181973
Node: Truncation2184885
Node: The Echo Area2187645
Node: Displaying Messages2188672
Ref: message-box2191375
Node: Progress2192847
Node: Logging Messages2197998
Node: Echo Area Customization2199864
Node: Warnings2201754
Node: Warning Basics2202234
Node: Warning Variables2205009
Node: Warning Options2208318
Node: Invisible Text2209655
Node: Selective Display2215181
Node: Temporary Displays2219340
Node: Overlays2224797
Node: Managing Overlays2225802
Node: Overlay Properties2231245
Node: Finding Overlays2239350
Node: Width2241855
Node: Line Height2244162
Node: Faces2248392
Node: Defining Faces2250058
Node: Face Attributes2256068
Node: Attribute Functions2263338
Node: Displaying Faces2271365
Node: Font Selection2273285
Node: Face Functions2277954
Node: Auto Faces2279921
Node: Font Lookup2281389
Node: Fontsets2284423
Node: Fringes2289487
Node: Fringe Size/Pos2290207
Node: Fringe Indicators2292108
Node: Fringe Cursors2296682
Node: Fringe Bitmaps2298583
Node: Customizing Bitmaps2300360
Node: Overlay Arrow2302421
Node: Scroll Bars2304856
Node: Display Property2308805
Node: Replacing Specs2310134
Node: Specified Space2312563
Node: Pixel Specification2315117
Node: Other Display Specs2317835
Node: Display Margins2321991
Node: Images2324385
Node: Image Descriptors2328079
Node: XBM Images2335341
Node: XPM Images2337514
Node: GIF Images2338066
Node: PostScript Images2338531
Node: Other Image Types2339551
Node: Defining Images2340546
Node: Showing Images2346036
Node: Image Cache2350605
Node: Buttons2352941
Node: Button Properties2354608
Node: Button Types2356722
Node: Making Buttons2358065
Node: Manipulating Buttons2360477
Node: Button Buffer Commands2362412
Node: Abstract Display2365309
Node: Abstract Display Functions2368014
Node: Abstract Display Example2373018
Node: Blinking2377651
Node: Usual Display2379595
Node: Display Tables2383155
Node: Display Table Format2384139
Node: Active Display Table2387565
Node: Glyphs2389373
Node: Beeping2391549
Node: Window Systems2392854
Node: System Interface2394157
Node: Starting Up2395920
Node: Startup Summary2396509
Node: Init File2400586
Node: Terminal-Specific2404175
Node: Command-Line Arguments2407384
Node: Getting Out2411044
Node: Killing Emacs2411603
Node: Suspending Emacs2413959
Node: System Environment2417116
Node: User Identification2426036
Node: Time of Day2429308
Node: Time Conversion2433121
Node: Time Parsing2437193
Node: Processor Run Time2442443
Node: Time Calculations2443151
Node: Timers2444272
Node: Idle Timers2450772
Node: Terminal Input2455163
Node: Input Modes2455581
Node: Recording Input2457978
Node: Terminal Output2459437
Node: Sound Output2462295
Node: X11 Keysyms2464503
Node: Batch Mode2466023
Node: Session Management2467259
Node: Antinews2469130
Node: GNU Free Documentation License2485532
Node: GPL2507755
Node: Tips2545322
Node: Coding Conventions2546527
Ref: Coding Conventions-Footnote-12557069
Node: Key Binding Conventions2557170
Node: Programming Tips2560143
Node: Compilation Tips2564266
Node: Warning Tips2566222
Node: Documentation Tips2567610
Ref: Docstring hyperlinks2572207
Node: Comment Tips2578674
Node: Library Headers2582539
Node: GNU Emacs Internals2587755
Node: Building Emacs2588539
Node: Pure Storage2593264
Node: Garbage Collection2596272
Node: Memory Usage2605359
Node: Writing Emacs Primitives2607011
Ref: Defining Lisp variables in C2615253
Ref: Writing Emacs Primitives-Footnote-12618512
Node: Object Internals2618657
Node: Buffer Internals2619978
Node: Window Internals2631450
Node: Process Internals2638303
Node: Standard Errors2640834
Node: Standard Buffer-Local Variables2646415
Node: Standard Keymaps2650558
Node: Standard Hooks2655767
Node: Index2662595

End Tag Table
