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## Using PSGML mode in Emacs

By David Lutterkort

OpenACS docs are written by the named authors, and may be edited by OpenACS documentation staff.

Note: `nxml` mode replaces and/or complements psgml mode. More information.

### What it is

PSGML Mode is a mode for editing, umm, SGML and XML documents in emacs. It can parse a DTD and help you insert the right tags in the right place, knows about tags' attributes and can tell you in which contexts a tag can be used. If you give it the right DTD, that is. But even without a DTD, it can save you some typing since pressing `C-c/` will close an open tag automatically.

### Where to get it

Most newer emacsen come with PSGML mode preinstalled. You can find out whether your emacs has it with the `locate-library` command. In Emacs, type `M-x locate-library` and enter `psgml`. Emacs will tell you if it found it or not.

If you don't have PSGML preinstalled in your Emacs, there are two things you can do:

1. On Linux: Get the psgml rpm from RedHat's docbook-tools and install it as usual.

2. On other systems: Get the tarball from the PSGML Website. Unpack it and follow the install instructions.

### Using `CATALOG` files

The easiest way to teach PSGML mode about a DTD is by adding it to your own `CATALOG`. Here is an example of how you can set that up for the Docbook XML DTD.

1. Get the Docbook XML DTD zip archive from docbook.org

2. Go somewhere in your working directory and do

             mkdir -p dtd/docbook-xml
             cd dtd/docbook-xml
             unzip -a <docbook XML DTD zip archive>

3. Create a file with the name `CATALOG` in the `dtd` directory and put the line

             CATALOG "docbook-xml/docbook.cat"

   in it. By maintaining your own `CATALOG`, it is easy to add more DTD's without changing your emacs settings. (How about that HTML 4.01 DTD you always wanted to get from W3C ? The DTD is in the zip archives and tarballs available on the site.)

That's it. Now you are ready to tell emacs all about PSGML mode and that funky `CATALOG`

### What to tell emacs

If you installed PSGML mode in a non-standard location, e.g., somewhere in your home directory, you need to add this to the `load-path` by adding this line to your `.emacs` file:

          (add-to-list 'load-path "/some/dir/that/contains/psgml.elc")

To let PSGML mode find your `CATALOG` and to enable PSGML mode for all your editing, add these lines to your `.emacs`:

          (require 'psgml)

          (add-to-list 'auto-mode-alist '("\\.html" . sgml-mode))
          (add-to-list 'auto-mode-alist '("\\.adp" . xml-mode))
          (add-to-list 'auto-mode-alist '("\\.xml" . xml-mode))
          (add-to-list 'auto-mode-alist '("\\.xsl" . xml-mode))

          (add-to-list 'sgml-catalog-files "/path/to/your/dtd/CATALOG")

If you want font-locking and indentation, you can also add these lines into the `.emacs` file:

          (setq sgml-markup-faces '((start-tag . font-lock-function-name-face)
                                    (end-tag . font-lock-function-name-face)
                    (comment . font-lock-comment-face)
                    (pi . bold)
                    (sgml . bold)
                    (doctype . bold)
                    (entity . font-lock-type-face)
                    (shortref . font-lock-function-name-face)))
          (setq sgml-set-face t)
          (setq-default sgml-indent-data t)
          ;; Some convenient key definitions:
          (define-key sgml-mode-map "\C-c\C-x\C-e" 'sgml-describe-element-type)
          (define-key sgml-mode-map "\C-c\C-x\C-i" 'sgml-general-dtd-info)
          (define-key sgml-mode-map "\C-c\C-x\C-t" 'sgml-describe-entity)

### What is a `DOCTYPE` ?

All SGML and XML documents that should conform to a DTD have to declare a doctype. For the docbook XML, all your `.xml` files whould start with the line

          <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" "docbookx.dtd">

If your document is only part of a larger XML document, you can tell PSGML mode about it by appending the following lines to your file. In this case, do not include a DOCTYPE declaration in your file.

          <!--
           Local Variables:
           sgml-parent-document: ("top.xml" "book" "sect1")
           End:
          -->

Which says that the parent of this document can be found in the file `top.xml`, that the element in the parent that will enclose the current document is a `book` and that the current file's topmost element is a `sect1`.

### How to use it

Of course, you should read the emacs texinfo pages that come with PSGML mode from start to finish. Barring that, here are some handy commands:

Key | Command
--- | ---
`C-c C-e` | Insert an element. Uses completion and only lets you insert elements that are valid
`C-c C-a` | Edit attributes of enclosing element.
`C-c C-x C-i` | Show information about the document's DTD.
`C-c C-x C-e` | Describe element. Shows for one element which elements can be parents, what its contents can be and lists its attributes.

### Further reading

Start with the the section called “OpenACS Documentation Guide”

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