# GNAT Programming Studio Tutorial

## Table of Contents

- 1 Introduction
- 2 Quick overview of the GPS areas
- 3 Editing sources
- 4 Building applications
- 5 Source Navigation
- 6 Search Dialog
- 7 Project View (entities)
- 8 Back to Source Navigation
- 9 Code Completion
- 10 Run
- 11 Debug
- 12 Call Graph
- 13 Locations View
- 14 Projects
  - 14.1 Project Wizard
  - 14.2 Project properties
  - 14.3 Variable editor
  - 14.4 Switch editor
  - 14.5 Source dependencies
  - 14.6 Project dependencies
- 15 Epilogue
- Appendix A GNU Free Documentation License

## 1 Introduction

This document provides a guide through the major capabilities of the GNAT Programming Studio by working on a code example: sdc, a simple desktop calculator.

It is important to realize that the features that you are about to experiment with are available on multiple platforms, using the same user interface and capabilities, providing a user-friendly environment with a tight integration between the tools.

Start GPS in the directory containing the tutorial files, or if the directory is read-only, copy the `tutorial` directory and its subdirectories in a local (writable) area, and start GPS from the `tutorial` directory, so that GPS will load the right context.

By default, the tutorial sources can be found under `<prefix>/share/examples/gps/tutorial`, where `<prefix>` is the prefix directory of the GPS installation.

Alternatively, if you have already started GPS in another directory, you can load the project `sdc.gpr` by using the menu `Project->Open...`

## 2 Quick overview of the GPS areas

Having launched GPS, you should now have access to a main window composed of several areas:

- a menu bar at the top
- a tool bar under the menu bar
- a scenario view under the tool bar, on the left side
- a project view under the scenario view, on the left side
- a working area on the right of the project view
- a messages window under the working area

## 3 Editing sources

In the project view, open the `common` directory by clicking on the `[+]` sign (a triangle under unix systems) on the left of `common`. This will open the directory and display a list of source files located in this directory.

Now, double click on `sdc.adb`: this will open a source editor on this file. The source code is syntax-highlighted: keywords, comments, strings and characters have different colors.

As with many other properties, colors are configurable in GPS:

Select the menu `Edit->Preferences`. This will open a preferences dialog window.

Select the `Editor->Fonts & Colors` page by clicking on the cross next to the item `Editor` and then selecting the `Fonts & Colors` item.

As you go over the various lines and labels, you will notice that by holding the mouse over a label, a tool tip pops up displaying on-line help about the selected item.

Change the background color of the `Keywords` by clicking on the last button, at the right of the `Keywords` line.

Choose a color, e.g a light green. When you're done with the color selection, click on `OK` in the color selection dialog.

Click on the `Apply` button and look at the effects in the source editor. If you like the new display, click on `OK` to confirm the changes, otherwise clicking on `Cancel` will revert to the previous color.

## 4 Building applications

Select the icon `Build Main: sdc.adb` on the toolbar (fourth icon from the right): this will launch a complete build of the sdc application. Note also that you can use a key binding directly instead of this tool bar button (<F4>), or use the corresponding menu item `Build->Project->sdc.adb`. If you use the menu item, an extra intermediate dialog is displayed showing the actual command line that will be used by GPS. Pressing <Enter> will launch also the build.

The build has generated a number of errors in a new window: the Locations tree, displayed in the bottom area. The errors are also highlighted in the corresponding source editor.

GPS has automatically jumped to the first error message (sdc.adb, 28:6 : (style) bad indentation), at the line (28) and column (6) of the error.

Fix the error by hand by inserting a space.

Now you can fix the next error by moving the cursor to the line 30 (press the <down> arrow twice), and by using <Ctrl-Tab> (press first the <Control> key, and then the <Tab> key on your keyboard): this key combination asks the source editor to automatically re-indent the current line.

Note that on some window managers or desktop environments, <Ctrl-Tab> is already defined. If this is the case, you can change this shortcut from the key shortcuts dialog (menu `Edit->Key shortcuts`, `Menus` section, `/Edit/Format Selection` item).

You can then fix all the remaining errors by selecting the whole block (from line 28 to line 40) and pressing <Ctrl-Tab>. To select a block, you can either click on the left mouse button and select the area while holding the button, or using the keyboard by pressing the <Shift> key and moving the cursor using the <Up> or <Down> keys.

Press the <F4> key to build again. GPS will automatically save the modified files, and start a build. This behavior (automatic saving of files before building) can be configured in the preferences dialog.

If you look at the bottom right of the GPS window, you will notice that a progress bar has appeared, displaying the current number of files compiled, and the number of remaining files. This progress bar disappears when the build is finished.

This should now report a successful build.

## 5 Source Navigation

Now let's try to understand a little bit about how the program is working by looking at the `sdc.adb` editor: there's a loop, the main processing is done by the functions Process and Next (at line 30).

Click around line 30, move the mouse over `Process` and let a tool tip appear (`Tokens.Process global procedure declared at tokens.ads:19`): this gives information about the kind of entity and the location (file and line) of the declaration of this procedure, the profile of the parameters, and documentation for this function, as extracted from the comments surrounding the procedure declaration.

Do the same for `Next` (`Tokens.Next global function declared at tokens.ads:15`).

Keeping the mouse over `Next`, display the contextual menu by clicking on the right mouse button, then click on `Goto declaration of Next`: we're now in the package `Tokens`, in file `tokens.ads`; but where is this file in the project?

## 6 Search Dialog

Select the menu `Navigate->Find or Replace...`: this will open a search dialog. In the `Search for:` text entry type `tokens.ads`. Then select `Project view` in the `Look in:` area. The search area provides an easy way to search for text or regular expressions in several contexts including the current file, the project view, ...

Now click on `Find`. The file `tokens.ads`, in directory `struct` is highlighted.

Close the search dialog by clicking on the `Close` button.

Note that in this specific case, a simpler way to locate a file in the project view is to use the contextual menu from the source editor: `Locate in Project View: tokens.ads`.

## 7 Project View (entities)

Click on the `[+]` sign (or triangle) to open `tokens.ads` entities. When you click on a file in the project view, you get language sensitive information about the file, such as `packages`, `subprograms`, `tasks`, ... for `Ada`.

Open the `subprogram` category, click on `Process`: this will open `tokens.ads` and move the cursor on the first line corresponding to the procedure `Process`.

Similarly, click on `Next`, and move your mouse on `Next` in the source editor.

## 8 Back to Source Navigation

Move the mouse over the `Next` identifier in `tokens.ads` editor, and then hold the <Control> key: while you're holding the key, move the mouse over entities: these entities now become clickable hyperlinks. Clicking on the first mouse button will go to the declaration of the entity highlighted (or the body if you are already on the declaration), and clicking on the middle mouse button will go to the body directly: move the mouse back to `Next` and click. Alternatively, you can use the the contextual menu and select `Goto body of Next`; then scroll through the procedure `Next`, move the mouse on `Instructions.Read` at line 46, hold <control> again and click with the middle mouse button (or from the contextual menu, select `Goto body of Read`).

We've now navigated quite a bit through the application source code, which you can verify by clicking on the left arrow in the tool bar, to go back to the previous locations visited.

Repeat the operation until you're back in `sdc.adb`. As with the undo/redo capability in the source editor, the `goto previous/next location` is infinite.

## 9 Code Completion

Go on the line 38 of sdc.adb. You can see that there is a null instruction for the case of Stack.Overflow. We are going to add some code here, using the code assist capabilities.

Type <enter> to create a new line, and then `Scr`, and hit <Ctrl+Space>. A completion popup will be displayed, showing all the entities of the project begining with `Scr`. Select `Screen_Output`. The code will be automatically completed in the editor. Then add a dot in your code. The completion popup will be automatically triggered, and will offer you to complete your code with the entities contained in the `Screen_Output` package. Select `Msg`, add a space, and then an open parenthesis. Once again, the completion windows will pop up, and show you the possible parameters for msg. If you choose the first entry of the completion list ("params of Msg"), the call will be automatically completed by a list of named parameters. Complete the list by giving e.g. `"The stack is full."` for `S1`, `""` for `S2`, and `True` for `End_Line`.

Don't forget to add a semicolon at the end of the instruction. Then hit <F4> in order to rebuild the application.

## 10 Run

It is now time to run the application: select the menu `Build->Run->sdc`, which will open a dialog window. In the text input field (selected by default), press the right arrow key and then insert `input.txt`: this is the name of a text file that will be passed as argument to the sdc program.

The text input should now read: `%E input.txt` and the full command that will be executed is displayed underneath: `.../gps/tutorial/obj/sdc input.txt`

Now click on `Execute`: a new window titled `Run: sdc` is created at the bottom of the main window where the sdc application runs and displays an unexpected internal error: this is a good opportunity to use the integrated debugger.

Close the execution window by clicking on the x icon on the top right corner of this window.

## 11 Debug

Open the preferences dialog (menu `Edit->Preferences`) and click on the `Debugger` item on the left; set the button `Break on exceptions` to Enabled: this will enable by default a special breakpoint every time an exception is raised. Click on `OK` to confirm your change.

Now select the menu `Debug->Initialize->sdc`: GPS automatically switches to the Debug perspective as shown in the menu `Window->Perspectives`, and new windows have appeared: the debugger data window on top, the call stack window on the right, and the debugger console at the bottom.

You can also look at the various debug menu item and tool bar buttons which are now activated.

On the call stack window (you can use the menu `Debug->Data->Call Stack` to open it if you do not have it displayed), select the contextual menu: various pieces of information can be displayed or removed in the call stack. From this contextual menu, add the `Frame Number` info by clicking on it.

Now select the menu `Debug->Run...` and type `input.txt` in the text input field. Click on `OK`: the debugger should stop on an exception (`Constraint_Error` in the file `stack.adb`, at line 49).

Go up in the call stack by clicking on the `tokens.process` line (frame number 6 or 7, depending on your GNAT version).

If you move the mouse over the parameter `T` at line 64, a tool tip is displayed showing the value of `T`. You have probably noticed that tool tips, like menus, are contextual: depending on the current session and on the entity selected, different information is displayed.

Select the contextual menu `Debug->Display T`: this will open a new window: the data window, with a box displaying graphically the contents of the different fields of `T`, each clearly separated.

On `T` data display, select the contextual menu `Display->Show Value + Type`: this displays for all fields both their type and value.

Special colors are used in the data display: blue for pointers that can be dereferenced by a double-click (double click on `T.val`); red for fields that have been modified since last step.

From the T box, right-click to display the contextual menu and select `View memory at address of T`: a memory view is opened on top of the source editors. Use the `up` and `down` arrows on the right to visit memory.

Click in the memory dump, and modify it by typing numbers. Notice the red color for modified values; click on `Undo Changes` to cancel the modifications; then close the memory window by e.g. clicking on the `x` icon or pressing <Ctrl-W>.

In the call stack, go back to `stack.push` frame (num 4 or 5). Move the mouse over `Last` and let the debugger display its value: 0. From the contextual menu, select `Goto declaration of Last`: this will jump to the line 16 of `stack.adb`, where you can see that `Last` is a `Natural`. Now click on the `Goto Previous Location` button in the tool bar: we're now back at line 49 where we can see that for a `Push` procedure, `Last` should be incremented, and not decremented.

Fix the line to `Last := Last + 1;`

Save the file (<Ctrl-S>); End the debug session: menu `Debug->Terminate`; Rebuild (press <F4> key); Rerun (menu `Build->Run->sdc`, click on `Execute`): the program now completes as expected. Close the execution window.

## 12 Call Graph

Now go back to the file `sdc.adb`, move the mouse over the procedure sdc at line 8, select the contextual menu `Browsers->Sdc calls`: this will open a new window titled Call graph browser.

Note that there is also a top level contextual menu (`Sdc calls`) which provides a tree view of the callers/callees.

In the call graph, click on the right arrow of `Process` (one of the first items on the top). Also click on the right arrow of `error_msg`.

Select `Orthogonal links` in the contextual menu of the graph to change the way links are displayed in the graph. You may then play with the zoom (<=> and <-> keys).

If you select `Hide links` from `error_msg` contextual menu, this will hide all the links that are related to this item: the link between the callers and callees of `error_msg` are no longer displayed. This can be useful when the graph becomes complex, to hide some parts. If you go back to the contextual menu, you can now select `Show links` to show the links again.

Click on right arrow of `process` (`(Decl) instructions.ads:12`).

The items can also be moved: move e.g `msg` item around.

You can also recompute the layout of all the current items by using the browser's contextual menu `Refresh layout` (move the mouse on the browser's background, with no box underneath, and right click).

Click on left arrow of `msg` to display who is calling `msg`. Notice that `view` calls `msg`.

Click on left arrow of `view`: the arrow disappears, and no new items are created, which means that `view` isn't called by anyone, so we're now going to remove this procedure.

## 13 Locations View

From view, click on the blue link: `stack.ads:32`, this will open the file `stack.ads` at line 32. Then from the source editor (file `stack.ads`), select the contextual menu `References->Find all references to View`: this highlights the `Locations` tree which now contains all the references for `view`, grouped by files (`stack.ads` and `stack.adb`).

The first location is highlighted automatically: this is the spec of the procedure `View`. Now click in the tree on the `+` sign (or triangle) at the left of `stack.adb`: two locations are listed, at line 90 and 97. Click on each of these locations: they correspond to the procedure body.

The `Find all references` capability is another way to list all the uses of an entity, and it confirms that `View` isn't called in our project.

Remove View body by e.g selecting it, and pressing the <Delete> key, then save the file (<Ctrl-S>).

Do the same for the spec, save the file.

Close the `stack.ads` and `stack.adb` files (menu File->Close, or using the shortcut <Ctrl-W>). Rebuild by pressing the <F4> key.

Let's now see how to create a project corresponding to the sdc project we've used in this tutorial.

## 14 Projects

Next: Project properties, Up: Projects

### 14.1 Project Wizard

Go to the menu `Project->New...`: this is a standard wizard, with various steps listed on the left area of the window.

The first page of the wizard allows you to select what kind of project you want to build, depending on the information you have. Select the default choice `Single Project`, and press `Forward`.

Type sdc2 in the project name field.

Click on `Forward`: we are now on the language selection page. It is possible to create a multi-language project by e.g. selecting the C or C++ check box.

Click on `Forward`: we are now on the `VCS page`. VCS stands for Version Control System. GPS provides a generic framework for VCS which allows it to support new systems easily. Systems supported by default are CVS, ClearCase, Subversion and GIT. Select `Auto`, which means that GPS will automatically detect the version control system used, if any.

Click on `Forward`: this is the source directories selection, used to specify the project's sources. Click on the `Add` button, and select the `struct` directory, then click on `OK` to validate.

Click on `Forward`: this is the `Build` and `Exec` directory selection, used to store object, ali files, ...

Click on the first `Browse` button, then click on `obj`, and finally click on `OK`.

Click on `Forward`: this is the main units selection, used mainly for building executables and debugging.

Click on `Add`, open the `common` directory and select `sdc.adb`.

Click on `Forward`: this is the naming scheme editor. GNAT is very flexible and can use any kind of naming scheme for Ada files. In particular, you can easily set the default file extensions (e.g by using one of the predefined schemes) and you can also specify exceptions that use non standard file names.

Click on `Forward`: we're now in the switch selector. Select `Recompile if switches changed`.

Click on `Ada` page.

Select `Full errors` and `Overflow checking`. The boxes and the command line (the text entry at the bottom of the page) are fully synchronized, e.g if you click on the command line, and change `-gnatf` to `-gnat`, the `Full errors` check box is unselected; now type `a` to get `-gnata`, and notice that `Enable assertions` is now selected.

We've now created a project similar to the one used in this tutorial.

Click on `Cancel` to close the wizard.

Clicking on `Apply` instead would have created the project file and loaded it in GPS.

Next: Variable editor, Previous: Project Wizard, Up: Projects

### 14.2 Project properties

In the project view, on the project sdc, use the contextual menu `Project->Properties`. All the properties set in the project wizard can be found here as well. You can switch between pages by clicking on the tabs located along the left side of the window.

Once you're done exploring the property pages, click on the `Cancel` button to close the properties window.

Next: Switch editor, Previous: Project properties, Up: Projects

### 14.3 Variable editor

Select the window titled "Scenario". If not available, you can open it using the menu `Tools->Views->Scenario`. This window contains a `Build` label.

This is a configuration variable. With GPS and the GNAT project facility, you can define as many configuration variables as you want, and modify any project settings (e.g. switches, sources, ...) based on the values of configuration variables. These variables can also take any number of different values.

The `Build` variable demonstrates a typical `Debug/Production` configuration where we've set different switches for the two modes.

Right click on the `Build` label and select `Edit properties of Build...`: this opens the variable editor, where values can be added or renamed. Close the variable editor by clicking on the `Cancel` button.

Now, let's take a look at the switches set in the project.

Next: Source dependencies, Previous: Variable editor, Up: Projects

### 14.4 Switch editor

Select the menu item `Project->Edit File Switches`: a global switch editor is displayed in the working area, showing the switches associated with each file in the `sdc` project.

The editor lists the switches associated with each file in the project. Gray entries indicate default (global) switches. Notice that `screen_output.adb` has specific switches, which are highlighted using a different font.

Switch between `Debug` and `Production` mode in the `Build` combo box: the switches are updated automatically.

Back to our project, let's now examine the dependencies between sources.

Next: Project dependencies, Previous: Switch editor, Up: Projects

### 14.5 Source dependencies

Select `sdc.adb` in the `Project View` and then the contextual menu item `Show dependencies for sdc.adb`: this will open a new graph showing the dependencies between sources of the project.

Click on the right arrow of `tokens.ads` to display the files that `tokens.ads` depends on. Similarly, click on the right arrow of `stack.ads`.

Previous: Source dependencies, Up: Projects

### 14.6 Project dependencies

Back in the project view, on the Sdc project, select the contextual menu `Project->Dependencies`, then on the `Add From File`, then open the tutorial directory and click on the `projects` subdirectory. Select the file `prj1.gpr`. Click on `Apply` to validate the change.

You can see the new dependency added in the project view, as a tree of projects. In particular, project dependencies are duplicated: if you open the `prj1` icon by clicking on the `[+]` sign (or triangle), and then similarly open the `prj2` icon, you will notice that the project `prj4` is displayed twice: once as a dependency of `prj2`, and once as a dependency of `prj1`.

GPS can also display the graph of dependencies between projects: on Sdc project, use the contextual menu `Show projects imported by Sdc`: this will open a project hierarchy browser.

On the `Sdc.gpr` project, select the contextual menu `Show projects imported by Sdc recursively`.

In the browser, you can move the project items, and select them to highlight the dependencies.

## 15 Epilogue

This terminates our tour of GPS, the GNAT Programming Studio. We hope this tutorial gave you a good overview of the general capabilities available with GPS. A non exhaustive list of the features not mentioned in this document includes:

- Documentation generation
- Automatic generation of body files
- Pretty printing
- Visual comparison of files
- Version control
- Flexible multiple document interface
- Code coverage

For more information, please look at the User's Guide (gps.html), and also look at the `Tools` menu which gives access to most of these capabilities.

## Appendix A GNU Free Documentation License

Version 1.1, March 2000

Copyright © 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 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 written 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 that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”.

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. (For example, 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.

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 “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, whose contents can be viewed and edited directly and 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 has been designed to thwart or discourage subsequent modification by readers is not Transparent. 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 designed for human modification. Opaque formats include PostScript, PDF, 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 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.

### 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 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 publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. 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:

1. 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.
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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.

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.”

Heading 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, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an “aggregate”, and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they 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 quarter of the entire aggregate, the Document's Cover Texts may be placed on covers that surround only the Document within the aggregate. Otherwise they must appear on covers around 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 provided that you also include the original English version of this License. In case of a disagreement between the translation and the original English version of this License, the original English version will prevail.

### 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 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. A copy of the license is included in the section entitled “GNU Free Documentation License”.

If you have no Invariant Sections, write “with no Invariant Sections” instead of saying which ones are invariant. If you have no Front-Cover Texts, write “no Front-Cover Texts” instead of “Front-Cover Texts being LIST”; likewise for Back-Cover Texts.

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.