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6.3. The Wine DocBook System

6.3.1. Writing Documentation with DocBook

DocBook is a flavour of SGML (Standard Generalized Markup Language), a syntax for marking up the contents of documents. HTML is another very common flavour of SGML; DocBook markup looks very similar to HTML markup, although the names of the markup tags differ.

6.3.1.1. Getting Started

Why SGML?: The simple answer to that is that SGML allows you to create multiple formats of a given document from a single source. Currently it is used to create HTML, PDF, PS (PostScript) and text versions of the Wine books.

What do I need?: You need the SGML tools. There are various places where you can get them. The most generic way of getting them is from their source as discussed below.

Quick instructions: These are the basic steps to create the Wine books from the SGML source.

  1. Go to http://www.sgmltools.org

  2. Download all of the sgmltools packages

  3. Install them all and build them (./configure; make; make install)

  4. Switch to your toplevel wine-docs directory

  5. Run ./configure

  6. run make html

  7. View en/wineusr-guide.html, en/winedev-guide.html, etc. in your favorite browser

For more information on building the documentation, please see the README file at the toplevel wine-docs directory.

6.3.1.2. Getting SGML for various distributions

Most Linux distributions have everything you need already bundled up in package form. Unfortunately, each distribution seems to handle its SGML environment differently, installing it into different paths, and naming its packages according to its own whims.

6.3.1.2.1. SGML on Red Hat

The following packages seem to be sufficient for Red Hat 7.1. You will want to be careful about the order in which you install the RPMs.

  • sgml-common-*.rpm

  • openjade-*.rpm

  • perl-SGMLSpm-*.rpm

  • docbook-dtd*.rpm

  • docbook-style-dsssl-*.rpm

  • tetex-*.rpm

  • jadetex-*.rpm

  • docbook-utils-*.rpm

You can also install ghostscript to view the PostScript format output.

6.3.1.2.2. SGML on Debian

This is not a definitive list yet, but it seems you might need the following packages:

  • docbook

  • docbook-dsssl

  • docbook-utils

  • docbook-xml

  • docbook-xsl

  • sgml-base

  • sgml-data

  • tetex-base

  • tetex-bin

  • jade

  • jadetex

6.3.1.3. Terminology

SGML markup contains a number of syntactical elements that serve different purposes in the markup. We'll run through the basics here to make sure we're on the same page when we refer to SGML semantics.

The basic currency of SGML is the tag. A simple tag consists of a pair of angle brackets and the name of the tag. For example, the para tag would appear in an SGML document as <para>. This start tag indicates that the immediately following text should be classified according to the tag. In regular SGML, each opening tag must have a matching end tag to show where the tag contents ends. End tags begin with "</" markup, e.g. </para>.

The combination of a start tag, contents, and an end tag is called an element. SGML elements can be nested inside of each other, or contain only text, or may be a combination of both text and other elements, although in most cases it is better to limit your elements to one or the other.

The XML (eXtensible Markup Language) specification, a modern subset of the SGML specification, adds a so-called empty tag, for elements that contain no text content. The entire element is a single tag, ending with "/>", e.g. <xref/>. However, use of this tag style restricts you to XML DocBook processing, and your document may no longer compile with SGML-only processing systems.

Often a processing system will need more information about an element than you can provide with just tags. SGML allows you to add extra "hints" in the form of SGML attributes to pass along this information. The most common use of attributes in DocBook is giving specific elements a name, or an ID, so you can refer to it from elsewhere. This ID can be used for many things, including file-naming for HTML output, hyper-linking to specific parts of the document, and even pulling text from that element (see the <xref> tag).

An SGML attribute appears inside the start tag, between the '<' and '>' brackets. For example, if you wanted to set the id attribute of the <book> element to "mybook", you would create a start tag like this:

<book id="mybook">

Notice that the contents of the attribute are enclosed in quote marks. These quotes are optional in SGML, but mandatory in XML. It's a good habit to use quotes, as it will make it much easier to migrate your documents to an XML processing system later on.

You can also specify more than one attribute in a single tag:

<book id="mybook" status="draft">

Another commonly used type of SGML markup is the entity. An entity lets you associate a block of text with a name. You declare the entity once, at the beginning of your document, and can invoke it as many times as you like throughout the document. You can use entities as shorthand, or to make it easier to maintain certain phrases in a central location, or even to insert the contents of an entire file into your document.

An entity in your document is always surrounded by the '&' and ';' characters. One entity you'll need sooner or later is the one for the '<' character. Since SGML expects all tags to begin with a '<', the '<' is a reserved character. To use it in your document (as I am doing here), you must insert it with the &lt; entity. Each time the SGML processor encounters &lt;, it will place a literal '<' in the output document. Similarly you must use the &gt; and &amp; entities for the '>' and '&' characters.

The final term you'll need to know when writing simple DocBook documents is the DTD (Document Type Declaration). The DTD defines the flavour of SGML a given document is written in. It lists all the legal tag names, like <book>, <para>, and so on, and declares how those tags are allowed to be used together. For example, it doesn't make sense to put a <book> element inside a <para> paragraph element -- only the reverse makes sense.

The DTD thus defines the legal structure of the document. It also declares which attributes can be used with which tags. The SGML processing system can use the DTD to make sure the document is laid out properly before attempting to process it. SGML-aware text editors like Emacs can also use the DTD to guide you while you write, offering you choices about which tags you can add in different places in the document, and beeping at you when you try to add a tag where it doesn't belong.

Generally, you will declare which DTD you want to use as the first line of your SGML document. In the case of DocBook, you will use something like this:

<!doctype book PUBLIC "-//OASIS//DTD DocBook V4.5//EN" []>
<book>
...
</book>

Note that you must specify your toplevel element inside the doctype declaration. If you were writing an article rather than a book, you might use this declaration instead:

<!doctype article PUBLIC "-//OASIS//DTD DocBook V4.5//EN" []>
<article>
...
</article>

6.3.1.4. The Document

Once you're comfortable with SGML, creating a DocBook document is quite simple and straightforward. Even though DocBook contains over 300 different tags, you can usually get by with only a small subset of those tags. Most of them are for inline formatting, rather than for document structuring. Furthermore, the common tags have short, intuitive names.

Below is a (completely nonsensical) example to illustrate how a simple document might be laid out. Notice that all <chapter> and <sect1> elements have id attributes. This is not mandatory, but is a good habit to get into, as DocBook is commonly converted into HTML, with a separate generated file for each <book>, <chapter>, and/or <sect1> element. If the given element has an id attribute, the processor will typically name the file accordingly. Thus, the below document might result in index.html, chapter-one.html, blobs.html, and so on.

Also notice the text marked off with "<!-- " and " -->" strings. These denote SGML comments. SGML processors will completely ignore anything between these markers, similar to "/*" and "*/" comments in C source code.

<!doctype book PUBLIC "-//OASIS//DTD DocBook V4.5//EN" []>
<book id="index">
  <bookinfo>
    <title>A Poet's Guide to Nonsense</title>
  </bookinfo>

  <chapter id="chapter-one">
    <title>Blobs and Gribbles</title>

    <!-- This section contains only one major topic -->
    <sect1 id="blobs">
      <title>The Story Behind Blobs</title>
      <para>
        Blobs are often mistaken for ice cubes and rain
        puddles...
      </para>
    </sect1>

    <!-- This section contains embedded sub-sections -->
    <sect1 id="gribbles">
      <title>Your Friend the Gribble</title>
      <para>
        A Gribble is a cute, unassuming little fellow...
      </para>

      <sect2 id="gribble-temperament">
        <title>Gribble Temperament</title>
        <para>
          When left without food for several days...
        </para>
      </sect2>

      <sect2 id="gribble-appearance">
        <title>Gribble Appearance</title>
        <para>
          Most Gribbles have a shock of white fur running from...
        </para>
      </sect2>
    </sect1>
  </chapter>

  <chapter id="chapter-two">
    <title>Phantasmagoria</title>

    <sect1 id="dretch-pools">
      <title>Dretch Pools</title>

      <para>
        When most poets think of Dretch Pools, they tend to...
      </para>
    </sect>
  </chapter>
</book>

6.3.1.5. Common Elements

Once you get used to the syntax of SGML, the next hurdle in writing DocBook documentation is to learn the many DocBook-specific tag names, and when to use them. DocBook was created for technical documentation, and as such, the tag names and document structure are slanted towards the needs of such documentation.

To cover its target audience, DocBook declares a wide variety of specialized tags, including tags for formatting source code (with somewhat of a C/C++ bias), computer prompts, GUI application features, keystrokes, and so on. DocBook also includes tags for universal formatting needs, like headers, footnotes, tables, and graphics.

We won't cover all of these elements here (over 300 DocBook tags exist!), but we will cover the basics. To learn more about the other tags, check out the official DocBook guide at http://docbook.org. To see how they are used in practice, download the SGML source for this manual (the Wine Developer's Guide) and browse through it, comparing it to the generated HTML (or PostScript or PDF).

There are often many correct ways to mark up a given piece of text, and you may have to make guesses about which tag to use. Sometimes you'll have to make compromises. However, remember that it is possible to further customize the output of the SGML processors. If you don't like the way a certain tag looks in HTML, that doesn't mean you should choose a different tag based on its output formatting. The processing stylesheets can be altered to fix the formatting of that same tag everywhere in the document (not just in the place you're working on). For example, if you're frustrated that the <systemitem> tag doesn't produce any formatting by default, you should fix the stylesheets, not change the valid <systemitem> tag to, for example, an <emphasis> tag.

Here are the common SGML elements:

Structural Elements

<book>

The book is the most common toplevel element, and is probably the one you should use for your document.

<set>

If you want to group more than one book into a single unit, you can place them all inside a set. This is useful when you want to bundle up documentation in alternate ways. We do this with the Wine documentation, using <book> to put each Wine guide into a separate directory (see documentation/wine-devel.sgml, etc.).

<chapter>

A <chapter> element includes a single entire chapter of the book.

<part>

If the chapters in your book fall into major categories or groupings (as in the Wine Developer's Guide), you can place each collection of chapters into a <part> element.

<sectN>

DocBook has many section elements to divide the contents of a chapter into smaller chunks. The encouraged approach is to use the numbered section tags, <sect1>, <sect2>, <sect3>, <sect4>, and <sect5> (if necessary). These tags must be nested in order: you can't place a <sect3> directly inside a <sect1>. You have to nest the <sect3> inside a <sect2>, and so forth. Documents with these explicit section groupings are easier for SGML processors to deal with, and lead to better organized documents. DocBook also supplies a <section> element which you can nest inside itself, but its use is discouraged in favor of the numbered section tags.

<title>

The title of a book, chapter, part, section, etc. In most of the major structural elements, like <chapter>, <part>, and the various section tags, <title> is mandatory. In other elements like <book> and <note>, it's optional.

<para>

The basic unit of text is the paragraph, represented by the <para> tag. This is probably the tag you'll use most often. In fact, in a simple document, you can probably get away with using only <book>, <chapter>, <title>, and <para>.

<article>

For shorter, more targeted documents, like topic pieces and whitepapers, you can use <article> as your toplevel element.

Inline Formatting Elements

<filename>

The name of a file. You can optionally set the class attribute to Directory, HeaderFile, and SymLink to further classify the filename.

<userinput>

Literal text entered by the user.

<computeroutput>

Literal text output by the computer.

<literal>

A catch-all element for literal computer data. Its use is somewhat vague; try to use a more specific tag if possible, like <userinput> or <computeroutput>.

<quote>

An inline quotation. This tag typically inserts quotation marks for you, so you would write <quote>This is a quote</quote> rather than "This is a quote". This usage may be a little bulkier, but it does allow for automated formatting of all quoted material in the document. Thus, if you wanted all quotations to appear in italic, you could make the change once in your stylesheet, rather than doing a search and replace throughout the document. For larger chunks of quoted text, you can use <blockquote>.

<note>

Insert a side note for the reader. By default, the SGML processor usually prefixes the content with "Note:". You can change this text by adding a <title> element. Thus, to add a visible FIXME comment to the documentation, you might write:

<note>
  <title>EXAMPLE</title>
  <para>This is an example note...</para>
</note>

The results will look something like this:

EXAMPLE: This is an example note...

<sgmltag>

Used for inserting SGML tags, etc., into a SGML document without resorting to a lot of entity quoting, e.g. &lt;. You can change the appearance of the text with the class attribute. Some common values of this are starttag, endtag, attribute, attvalue, and even sgmlcomment. See this SGML file, documentation/documentation.sgml, for examples.

<prompt>

The text used for a computer prompt, for example a shell prompt, or command-line application prompt.

<replaceable>

Meta-text that should be replaced by the user, not typed in literally, e.g. in command descriptions and --help outputs.

<constant>

A programming constant, e.g. MAX_PATH.

<symbol>

A symbolic value replaced, for example, by a pre-processor. This applies primarily to C macros, but may have other uses. Use the <constant> tag instead of <symbol> where appropriate.

<function>

A programming function name.

<parameter>

Programming language parameters you pass with a function.

<option>

Parameters you pass to a command-line executable.

<varname>

Variable name, typically in a programming language.

<type>

Programming language types, e.g. from a typedef definition. May have other uses, too.

<structname>

The name of a C-language struct declaration, e.g. sockaddr.

<structfield>

A field inside a C struct.

<command>

An executable binary, e.g. wine or ls.

<envar>

An environment variable, e.g. $PATH.

<systemitem>

A generic catch-all for system-related things, like OS names, computer names, system resources, etc.

<email>

An email address. The SGML processor will typically add extra formatting characters, and even a mailto: link for HTML pages. Usage: <email>user@host.com</email>

<firstterm>

Special emphasis for introducing a new term. Can also be linked to a <glossary> entry, if desired.

Item Listing Elements

<itemizedlist>

For bulleted lists, no numbering. You can tweak the layout with SGML attributes.

<orderedlist>

A numbered list; the SGML processor will insert the numbers for you. You can suggest numbering styles with the numeration attribute.

<simplelist>

A very simple list of items, often inlined. Control the layout with the type attribute.

<variablelist>

A list of terms with definitions or descriptions, like this very list!

Block Text Quoting Elements

<programlisting>

Quote a block of source code. Typically highlighted in the output and set off from normal text.

<screen>

Quote a block of visible computer output, like the output of a command or chunks of debug logs.

Hyperlink Elements

<link>

Generic hypertext link, used for pointing to other sections within the current document. You supply the visible text for the link, plus the name of the id attribute of the element that you want to link to. For example:

<link linkend="configuring-wine">the section on configuring wine</link>
...
<sect2 id="configuring-wine">
...

<xref>

In-document hyperlink that can generate its own text. Similar to the <link> tag, you use the linkend attribute to specify which target element you want to jump to:

<xref linkend="configuring-wine">
...
<sect2 id="configuring-wine">
...

By default, most SGML processors will auto generate some generic text for the <xref> link, like "Section 2.3.1". You can use the endterm attribute to grab the visible text content of the hyperlink from another element:

<xref linkend="configuring-wine" endterm="config-title">
...
<sect2 id="configuring-wine">
  <title id="config-title">Configuring Wine</title>
...

This would create a link to the configuring-wine element, displaying the text of the config-title element for the hyperlink. Most often, you'll add an id attribute to the <title> of the section you're linking to, as above, in which case the SGML processor will use the target's title text for the link text.

Alternatively, you can use an xreflabel attribute in the target element tag to specify the link text:

<sect1 id="configuring-wine" xreflabel="Configuring Wine">

Note: <xref> is an empty element. You don't need a closing tag for it (this is defined in the DTD). In SGML documents, you should use the form <xref>, while in XML documents you should use <xref/>.

<anchor>

An invisible tag, used for inserting id attributes into a document to link to arbitrary places (i.e., when it's not close enough to link to the top of an element).

<ulink>

Hyperlink in URL form, e.g. http://www.winehq.org.

<olink>

Indirect hyperlink; can be used for linking to external documents. Not often used in practice.

6.3.2. Editing SGML Documents

You can write SGML/DocBook documents in any text editor you might find although some editors are more friendly for this task than others.

The most commonly used open source SGML editor is Emacs, with the PSGML mode, or extension. Emacs does not supply a GUI or WYSIWYG (What You See Is What You Get) interface, but it does provide many helpful shortcuts for creating SGML, as well as automatic formatting, validity checking, and the ability to create your own macros to simplify complex, repetitive actions.