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[wine] / documentation / documentation.sgml

  <chapter id="documentation">
    <title>Documenting Wine</title>

    <para>
      This chapter describes how you can help improve Wine's documentation.
    </para>

    <para>
      Like most large scale volunteer projects, Wine is strongest in areas that are rewarding
      for its volunteers to work in. The majority of contributors send code patches either
      fixing bugs, adding new functionality or otherwise improving the software components of
      the distribution. A lesser number contribute in other ways, such as reporting bugs and
      regressions, creating tests, providing organizational assistance, or helping to document
      Wine.
    </para>

    <para>
      Documentation is important for many reasons, and is often the key to the end user having
      a successful experience in installing, setting up and using software. Because Wine is a
      complicated, evolving entity, providing quality up to date documentation is vital to
      encourage more people to persevere with using and contributing to the project.
      The following sections describe in detail how to go about adding to or updating Wine's
      existing documentation.
    </para>

    <sect1 id="doc-overview">
      <title>An Overview Of Wine Documentation</title>

      <para>
        The Wine source code tree comes with a large amount of documentation in the
        <filename>documentation/</filename> subdirectory. This used to be a collection
        of text files culled from various places such as the Wine Weekly News and the wine-devel
        mailing list, but was reorganized some time ago into a number of books, each of which is
        marked up using SGML. You are reading one of these books (the
        <emphasis>Wine Developer's Guide</emphasis>) right now.
      </para>

      <para>
        Since being reorganized, the books have been updated and extended regularly. In their
        current state they provide a good framework which over time can be expanded and kept
        up to date. This means that most of the time when further documentation is added, it is
        a simple matter of updating the content of an already existing file. The books
        available at the time of writing are:

          <itemizedlist>

          <listItem><para>
          The <emphasis>Wine User Guide</emphasis>. This book contains information for end users
          on installing, configuring and running Wine.
          </para></listitem>

          <listItem><para>
          The <emphasis>Wine Developer's Guide</emphasis>. This book contains information and
          guidelines for developers and contributors to the Wine project.
          </para></listitem>

          <listItem><para>
          The <emphasis>Winelib User's Guide</emphasis>. This book contains information for
          developers using Winelib to port Win32 applications to Unix.
          </para></listitem>

          <listItem><para>
          The <emphasis>Wine Packager's Guide</emphasis>. This book contains
          information for anyone who will be distributing Wine to end users
          in a prepackaged format. It is also the exception to the rule as
          it has intentionally been kept in text format.
          </para></listitem>

          <listItem><para>
          The <emphasis>Wine FAQ</emphasis>. This book contains frequently asked questions
          about Wine with their answers.
          </para></listitem>
          </itemizedlist>
      </para>

      <para>
        Another source of documentation is the <emphasis>Wine API Guide</emphasis>. This is
        generated information taken from special comments placed in the Wine source code.
        When you update or add new API calls to Wine you should consider documenting them so
        that developers can determine what the API does and how it should be used.
      </para>

      <para>
        The next sections describe how to create Wine API documentation and how to work with
        SGML so you can add to the existing books.
      </para>
    </sect1>

    <sect1 id="api-docs">
      <title>Writing Wine API Documentation</title>

      <sect2 id="api-docs-intro">
      <title>Introduction to API Documentation</title>
      <para>
        Wine includes a large amount of documentation on the API functions
        it implements. There are several reasons to want to document the Win32
        API:
          <itemizedlist>

          <listItem><para>
          To allow Wine developers to know what each function should do, should
          they need to update or fix it.
          </para></listitem>

          <listItem><para>
          To allow Winelib users to understand the functions that are available
          to their applications.
          </para></listitem>

          <listItem><para>
          To provide an alternative source of free documentation on the Win32 API.
          </para></listitem>

          <listItem><para>
          To provide more accurate documentation where the existing documentation
          is accidentally or deliberately vague or misleading.
          </para></listitem>

          </itemizedlist>
      </para>

      <para>
        To this end, a semi formalized way of producing documentation from the Wine
        source code has evolved. Since the primary users of API documentation are Wine
        developers themselves, documentation is usually inserted into the source code
        in the form of comments and notes. Good things to include in the documentation
        of a function include:
          <itemizedlist>

          <listItem><para>
          The purpose of the function.
          </para></listitem>

          <listItem><para>
          The parameters of the function and their purpose.
          </para></listitem>

          <listItem><para>
          The return value of the function, in success as well as failure cases.
          </para></listitem>

          <listItem><para>
          Additional notes such as interaction with other parts of the system, differences
          between Wine's implementation and Win32s, errors in MSDN documentation,
          undocumented cases and bugs that Wine corrects or is compatible with.
          </para></listitem>

          </itemizedlist>
      </para>

      <para>
        Good documentation helps developers be aware of the effects of making changes. It
        also allows good tests to be written which cover all of the documented cases.
      </para>

      <para>
        Note that you do not need to be a programmer to update the documentation in Wine.
        If you would like to contribute to the project, patches that improve the API
        documentation are welcome. The following describes how to format any documentation
        that you write so that the Wine documentation generator can extract it and make it
        available to other developers and users.
      </para>

      <para>
        In general, if you did not write the function in question, you should be wary of
        adding comments to other peoples code. It is quite possible you may misunderstand
        or misrepresent what the original author intended! Adding API documentation on
        the other hand can be done by anybody, since in most cases there is plenty of
        information about what a function is supposed to do (if it isn't obvious)
        available in books and articles on the internet.
      </para>

      <para>
        A final warning concerns copyright and must be noted. If you read MSDN or any
        publication in order to find out what an API call does, you must be aware that
        the text you are reading is copyrighted and in most cases cannot legally be
        reproduced without the authors permission. If you copy verbatim any information
        from such sources and submit it for inclusion into Wine, you open yourself up
        to potential legal liability. You must ensure that anything you submit is
        your own work, although it can be based on your understanding gleaned from
        reading other peoples work.
      </para>
      </sect2>

      <sect2 id="api-docs-basics">
      <title>Basic API Documentation</title>

      <para>
        The general form of an API comment in Wine is a block comment immediately before a
        function is implemented in the source code. General comments within a function body or
        at the top of an implementation file are ignored by the API documentation generator.
        Such comments are for the benefit of developers only, for example to explain what the
        source code is doing or to describe something that may not be obvious to the person
        reading the source code.
      </para>

      <para>
        The following text uses the function <emphasis>PathRelativePathToA()</emphasis> from
        <filename>SHLWAPI.DLL</filename> as an example. You can find this function in the Wine
        source code tree in the file <filename>dlls/shlwapi/path.c</filename>.
      </para>

      <para>
        The first line of the comment gives the name of the function, the DLL that the
        function is exported from, and its export ordinal number. This is the simplest
        (and most common type of) comment:
      </para>

      <screen>
/*************************************************************************
 * PathRelativePathToW   [SHLWAPI.@]
 */
      </screen>

      <para>
        The functions name and the DLL name are obvious. The ordinal number takes one of
        two forms: Either <command>@</command> as in the above, or a number if the export
        is exported by ordinal. You can see which to use by looking at the DLL's
        <filename>.spec</filename> file. If the line on which the function is listed begins
        with a number, use it, otherwise use the <command>@</command> symbol, which indicates
        that this function is imported only by name.
      </para>

      <para>
        Note also that round or square brackets can be used, and whitespace between the name
        and the DLL/ordinal is free form. Thus the following is equally valid:
      </para>

      <screen>
/*************************************************************************
 *              PathRelativePathToW     (SHLWAPI.@)
 */
      </screen>

      <para>
        This basic comment will not get processed into documentation, since it
        contains no information. In order to produce documentation for the function,
        We must add some of the information listed above.
      </para>

      <para>
        First we add a description of the function. This can be as long as you like, but
        typically contains only a brief description of what the function is meant to do
        in general terms. It is free form text:
      </para>

      <screen>
/*************************************************************************
 * PathRelativePathToW   [SHLWAPI.@]
 *
 * Create a relative path from one path to another.
 */
      </screen>

      <para>
        To be truly useful however we must document the parameters to the function.
        There are two methods for doing this: In the comment, or in the function
        prototype.
      </para>

      <para>
        Parameters documented in the comment should be formatted as follows:
      </para>

      <screen>
/*************************************************************************
 * PathRelativePathToW   [SHLWAPI.@]
 *
 * Create a relative path from one path to another.
 *
 * PARAMS
 *  lpszPath   [O] Destination for relative path
 *  lpszFrom   [I] Source path
 *  dwAttrFrom [I] File attribute of source path
 *  lpszTo     [I] Destination path
 *  dwAttrTo   [I] File attributes of destination path
 *
 */
      </screen>

      <para>
        The parameters section starts with <command>PARAMS</command> on its own line.
        Each parameter is listed in the order they appear in the functions prototype,
        first with the parameters name, followed by its input/output status, followed
        by a free form text description of the comment.
      </para>

      <para>
        The input/output status tells the programmer whether the value will be modified
        by the function (an output parameter), or only read (an input parameter). The
        status must be enclosed in square brackets to be recognized, otherwise, or if it
        is absent, anything following the parameter name is treated as the parameter
        description. This field is case insensitive and can be any of the following:
        <command>[I]</command>, <command>[In]</command>, <command>[O]</command>,
        <command>[Out]</command>, <command>[I/O]</command>, <command>[In/Out]</command>.
      </para>

      <para>
        Following the description and parameters come a number of optional sections, all
        in the same format. A section is defined as the section name, which is an all upper
        case section name on its own line, followed by free form text. You can create any
        sections you like, however for consistency it is recommended you use the following
        section names:
          <orderedlist>

          <listItem><para>
          <command>NOTES</command>. Anything that needs to be noted about the function
          such as special cases and the effects of input arguments.
          </para></listitem>

          <listItem><para>
          <command>BUGS</command>. Any bugs in the function that exist 'by design', i.e.
          those that will not be fixed or exist for compatibility with Windows.
          </para></listitem>

          <listItem><para>
          <command>TODO</command>. Any unhandled cases or missing functionality in the Wine
          implementation of the function.
          </para></listitem>

          <listItem><para>
          <command>FIXME</command>. Things that should be updated or addressed in the implementation
          of the function at some future date (perhaps dependent on other parts of Wine). Note
          that if this information is only relevant to Wine developers then it should probably
          be placed in the relevant code section instead.
          </para></listitem>
          </orderedlist>
      </para>

      <para>
        Following or before the optional sections comes the <command>RETURNS</command> section
        which describes the return value of the function. This is free form text but should include
        what is returned on success as well as possible error return codes. Note that this
        section must be present for documentation to be generated for your comment.
      </para>

      <para>
        Our final documentation looks like the following:
      </para>

      <screen>
/*************************************************************************
 * PathRelativePathToW   [SHLWAPI.@]
 *
 * Create a relative path from one path to another.
 *
 * PARAMS
 *  lpszPath   [O] Destination for relative path
 *  lpszFrom   [I] Source path
 *  dwAttrFrom [I] File attribute of source path
 *  lpszTo     [I] Destination path
 *  dwAttrTo   [I] File attributes of destination path
 *
 * RETURNS
 *  TRUE  If a relative path can be formed. lpszPath contains the new path
 *  FALSE If the paths are not relative or any parameters are invalid
 *
 * NOTES
 *  lpszTo should be at least MAX_PATH in length.
 *  Calling this function with relative paths for lpszFrom or lpszTo may
 *  give erroneous results.
 *
 *  The Win32 version of this function contains a bug where the lpszTo string
 *  may be referenced 1 byte beyond the end of the string. As a result random
 *  garbage may be written to the output path, depending on what lies beyond
 *  the last byte of the string. This bug occurs because of the behaviour of
 *  PathCommonPrefix() (see notes for that function), and no workaround seems
 *  possible with Win32.
 *  This bug has been fixed here, so for example the relative path from "\\"
 *  to "\\" is correctly determined as "." in this implementation.
 */
      </screen>
      </sect2>

      <sect2 id="api-docs-advanced">
      <title>Advanced API Documentation</title>

      <para>
        There is no markup language for formatting API comments, since they should
        be easily readable by any developer working on the source file. A number of
        constructs are treated specially however, and are noted here. You can use these
        constructs to enhance the usefulness of the generated documentation by making it
        easier to read and referencing related documents.
      </para>

      <para>
        Any valid c identifier that ends with <command>()</command> is taken to
        be an API function and is formatted accordingly. When generating documentation,
        this text will become a link to that API call, if the output type supports
        hyperlinks or their equivalent.
      </para>

      <para>
        Similarly, any interface name starting with a capital I and followed by the
        words "reference" or "object" become a link to that objects documentation.
      </para>

      <para>
        Where an Ascii and Unicode version of a function are available, it is
        recommended that you document only the Unicode version and have the Ascii
        version refer to the Unicode one, as follows:
      </para>
      <screen>
/*************************************************************************
 * PathRelativePathToA   [SHLWAPI.@]
 *
 * See PathRelativePathToW.
 */
      </screen>
      <para>
        Alternately you may use the following form:
      </para>
      <screen>
/*************************************************************************
 * PathRelativePathToA   [SHLWAPI.@]
 *
 * Unicode version of PathRelativePathToW.
 */
      </screen>

      <para>
        You may also use this construct in any other section, such as <command>NOTES</command>.
      </para>

      <para>
        Any numbers and text in quotes (<command>""</command>) are highlighted.
      </para>

      <para>
        Words in all uppercase are assumed to be API constants and are highlighted. If
        you want to emphasize something in the documentation, put it in a section by itself
        rather than making it upper case.
      </para>

      <para>
        Blank lines in a section cause a new paragraph to be started. Blank lines
        at the start and end of sections are ignored.
      </para>

      <para>
        Any comment line starting with (<command>"*|"</command>) is treated as raw text and
        is not pre-processed before being output. This should be used for code listings,
        tables and any text that should remain unformatted.
      </para>

      <para>
        Any line starting with a single word followed by a colon (<command>:</command>)
        is assumed to be case listing and is emphasized and put in its own paragraph. This
        is most often used for return values, as in the example section below.
      </para>
      <screen>
 * RETURNS
 *  Success: TRUE. Something happens that is documented here.
 *  Failure: FALSE. The reasons why this call can fail are listed here.
      </screen>

      <para>
        Any line starting with a (<command>-</command>) is put into a paragraph by itself.
        this allows lists to avoid being run together.
      </para>

      <para>
        If you are in doubt as to how your comment will look, try generating the API
        documentation and checking the output.
      </para>
      </sect2>

      <sect2 id="api-docs-extra">
      <title>Extra API Documentation</title>

      <para>
        Simply documenting the API calls available provides a great deal of information to
        developers working with the Win32 API. However additional documentation is needed
        before the API Guide can be considered truly useful or comprehensive. For example,
        COM objects that are available for developers use should be documented, along with
        the interface(s) that those objects export. Also, it would be helpful to document
        each dll, to provide some structure to the documentation.
      </para>

      <para>
        To facilitate providing extra documentation, you can create comments that provide
        extra documentation on functions, or on keywords such as the name of a COM interface
        or a type definition.
      </para>

      <para>
        These items are generated using the same formatting rules as described earlier. The
        only difference is the first line of the comment, which indicates to the generator
        that the documentation is supplemental and does not describe an export from the dll
        being processed.
      </para>

      <para>
        Lets assume you have implemented a COM interface that you want to document; we'll
        use the name <command>IExample</command> as an example here. Your comment would
        look like the following (assuming you are exporting this object from
        <filename>EXAMPLE.DLL</filename>):
      <screen>
/*************************************************************************
 * IExample   {EXAMPLE}
 *
 * The IExample object provides lots of interesting functionality.
 * ...
 */
      </screen>
      </para>

      <para>
        Format this documentation exactly as you would a standard export. The only
        difference is the use of curly brackets to mark this documentation as supplemental.
        The generator will output this documentation using the name given before the
        DLL name, and will link to it from the main DLL page. In addition, if you have
        referred to the comment name in other documentation using "IExample interface",
        "IExample object", or "IExample()", those references will point to this documentation.
      </para>

      <para>
        If you document you COM interfaces this way then all following extra comments that
        follow in the same source file that begin with the same document title will be added
        as references to this comment before it is output. For an example of this see
        <filename>dlls/oleaut32/safearray.c</filename>. This uses an extra comment to document
        The SafeArray functions and link them together under one heading.
      </para>

       <para>
        As a special case, if you use the DLL name as the comment name, the comment will
        be treated as documentation on the DLL itself. When the documentation for the DLL
        is processed, the contents of the comment will be placed before the generated
        statistics, exports and other information that makes up a DLL's documentation page.
      </para>
      </sect2>

      <sect2 id="api-docs-generating">
      <title>Generating API Documentation</title>

      <para>
        Having edited or added new API documentation to a source code file, you
        should generate the documentation to ensure that the result is what you
        expected. Wine includes a tool (slightly misleadingly) called
        <command>c2man.pl</command> in the <filename>tools/</filename> directory
        which is used to generate the documentation from the source code.
      </para>

      <para>
        You can run <command>c2man.pl</command> manually for testing purposes; it is
        a fairly simple perl script which parses <filename>.c</filename> files
        to create output in several formats. If you wish to try this you may want
        to run it with no arguments, which will cause it to print usage information.
      </para>

      <para>
        An easier way is to use Wine's build system. To create man pages for a given
        dll, just type <command>make man</command> from within the dlls directory
        or type <command>make manpages</command> in the root directory of the Wine
        source tree. You can then check that a man page was generated for your function,
        it should be present in the <filename>documentation/man3w</filename> directory
        with the same name as the function.
      </para>

      <para>
        Once you have generated the man pages from the source code, running
        <command>make install</command> will install them for you. By default they are
        installed in section 3w of the manual, so they don't conflict with any existing
        man page names. So, to read the man page you should use
        <command>man -S 3w {name}</command>. Alternately you can edit
        <filename>/etc/man.config</filename> and add 3w to the list of search paths
        given in the variable <emphasis>MANSECT</emphasis>.
      </para>

      <para>
        You can also generate HTML output for the API documentation, in this case the
        make command is <command>make doc-html</command> in the dll directory,
        or <command>make htmlpages</command> from the root. The output will be
        placed by default under <filename>documentation/html</filename>. Similarly
        you can create SGML source code to produce the <emphasis>Wine Api Guide</emphasis>
        with the command <command>make sgmlpages</command>.
      </para>
      </sect2>
    </sect1>

    <sect1 id="wine-docbook">
      <title>The Wine DocBook System</title>

      <sect2 id="writing-docbook">
        <title>Writing Documentation with DocBook</title>

        <para>
          DocBook is a flavour of <acronym>SGML</acronym>
          (<firstterm>Standard Generalized Markup
          Language</firstterm>), 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.
        </para>
        <sect3>
          <title>Getting Started</title>
            <note>
            <title>Why SGML?</title>
              <para>
               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.
              </para>
            </note>

            <note>
            <title>What do I need?</title>
              <para>
               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.
              </para>
            </note>

            <note>
            <title>Quick instructions</title>
              <para>
               These are the basic steps to create the Wine books from the SGML source.
              </para>
            </note>

          <orderedlist>

          <listItem><para>
          Go to <ulink url="http://www.sgmltools.org">http://www.sgmltools.org</ulink>
          </para></listitem>

          <listItem><para>
          Download all of the sgmltools packages
          </para></listitem>

          <listItem><para>
          Install them all and build them (<command>./configure; make; make install</command>)
          </para></listitem>

          <listItem><para>
          Switch to your toplevel Wine directory
          </para></listitem>

          <listItem><para>
          Run <command>./configure</command> (or <command>make distclean && ./configure</command>)
          </para></listitem>

          <listItem><para>
          Switch to the <filename>documentation/</filename> directory
          </para></listitem>

          <listItem><para>
          run <command>make html</command>
          </para></listitem>

          <listItem><para>
          View <filename>wine-user.html</filename>, <filename>wine-devel.html</filename>, etc. in your favorite browser
          </para></listitem>

          </orderedlist>

        </sect3>

        <sect3>
          <title>Getting SGML for various distributions</title>
          <para>
            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.
          </para>

          <sect4>
          <title>SGML on Red Hat</title>
          <para>
            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.
            <itemizedlist>
              <listitem>
                <para>
                  sgml-common-*.rpm
                </para>
              </listitem>
              <listitem>
                <para>
                  openjade-*.rpm
                </para>
              </listitem>
              <listitem>
                <para>
                  perl-SGMLSpm-*.rpm
                </para>
              </listitem>
              <listitem>
                <para>
                  docbook-dtd*.rpm
                </para>
              </listitem>
              <listitem>
                <para>
                  docbook-style-dsssl-*.rpm
                </para>
              </listitem>
              <listitem>
                <para>
                  tetex-*.rpm
                </para>
              </listitem>
              <listitem>
                <para>
                  jadetex-*.rpm
                </para>
              </listitem>
              <listitem>
                <para>
                  docbook-utils-*.rpm
                </para>
              </listitem>
            </itemizedlist>
            You can also use ghostscript to view the ps format output and
            Adobe Acrobat 4 to view the pdf file.
          </para>
        </sect4>

        <sect4>
          <title>SGML on Debian</title>
          <para>
           This is not a definitive list yet, but it seems
           you might need the following packages:
            <itemizedlist>
              <listitem>
                <para>
                  docbook
                </para>
              </listitem>
              <listitem>
                <para>
                  docbook-dsssl
                </para>
              </listitem>
              <listitem>
                <para>
                  docbook-utils
                </para>
              </listitem>
              <listitem>
                <para>
                  docbook-xml
                </para>
              </listitem>
              <listitem>
                <para>
                  docbook-xsl
                </para>
              </listitem>
              <listitem>
                <para>
                  sgml-base
                </para>
              </listitem>
              <listitem>
                <para>
                  sgml-data
                </para>
              </listitem>
              <listitem>
                <para>
                  tetex-base
                </para>
              </listitem>
              <listitem>
                <para>
                  tetex-bin
                </para>
              </listitem>
              <listitem>
                <para>
                  jade
                </para>
              </listitem>
              <listitem>
                <para>
                  jadetex
                </para>
              </listitem>
            </itemizedlist>
          </para>
        </sect4>

        </sect3>
        <sect3>
          <title>Terminology</title>

          <para>
            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.
          </para>
          <para>
            The basic currency of SGML is the
            <firstterm>tag</firstterm>.  A simple tag consists of a
            pair of angle brackets and the name of the tag.  For
            example, the <sgmltag>para</sgmltag> tag would appear in
            an SGML document as <sgmltag
            class="starttag">para</sgmltag>.  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 start tag's
            contents end.  End tags begin with
            <quote><literal>&lt;/</literal></quote> markup, e.g.,
            <sgmltag class="endtag">para</sgmltag>.
          </para>
          <para>
            The combination of a start tag, contents, and an end tag
            is called an <firstterm>element</firstterm>.  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.
          </para>
          <para>
            The <acronym>XML</acronym> (<firstterm>eXtensible Markup
            Language</firstterm>) specification, a modern subset of
            the SGML specification, adds a so-called <firstterm>empty
            tag</firstterm>, for elements that contain no text
            content.  The entire element is a single tag, ending with
            <quote><literal>/&gt;</literal></quote>, e.g.,
            <sgmltag>&lt;xref/&gt;</sgmltag>.  However, use of this
            tag style restricts you to XML DocBook processing, and
            your document may no longer compile with SGML-only
            processing systems.
          </para>
          <!-- *** Note: We could normally use the "emptytag"
            attribute for XML empty tags, but that's only a recent
            addition, and we don't want to screw up documents
            generated against older stylesheets.
          *** -->
          <para>
            Often a processing system will need more information about
            an element than you can provide with just tags.  SGML
            allows you to add extra <quote>hints</quote> in the form
            of SGML <firstterm>attributes</firstterm> 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 <sgmltag
            class="starttag">xref</sgmltag> tag).
          </para>
          <para>
            An SGML attribute appears inside the start tag, between
            the &lt; and &gt; brackets.  For example, if you wanted to
            set the <sgmltag class="attribute">id</sgmltag> attribute
            of the <sgmltag class="starttag">book</sgmltag> element to
            <quote>mybook</quote>, you would create a start tag like
            this: <programlisting>&lt;book id="mybook"></programlisting>
          </para>
          <para>
            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.
          </para>
          <para>
            You can also specify more than one attribute in a single
            tag: <programlisting>&lt;book id="mybook" status="draft"></programlisting>
          </para>
          <para>
            Another commonly used type of SGML markup is the
            <firstterm>entity</firstterm>.  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.
          </para>
          <para>
            An entity in your document is always surrounded by the
            <quote>&amp;</quote> and <quote>;</quote> characters.  One
            entity you'll need sooner or later is the one for the
            <quote>&lt;</quote> character.  Since SGML expects all
            tags to begin with a <quote>&lt;</quote>, the
            <quote>&lt;</quote> is a reserved character.  To use it in
            your document (as I am doing here), you must insert it
            with the <literal>&amp;lt;</literal> entity.  Each time
            the SGML processor encounters <literal>&amp;lt;</literal>,
            it will place a literal <quote>&lt;</quote> in the output
            document. Similarly you must use the <literal>&amp;gt;</literal> 
            and <literal>&amp;amp;</literal> entities for the 
            <quote>&gt;</quote> and <quote>&amp;</quote> characters.
          </para>
          <para>
            The final term you'll need to know when writing simple
            DocBook documents is the <acronym>DTD</acronym>
            (<firstterm>Document Type Declaration</firstterm>).  The
            DTD defines the flavour of SGML a given document is written
            in.  It lists all the legal tag names, like <sgmltag
            class="starttag">book</sgmltag>, <sgmltag
            class="starttag">para</sgmltag>, and so on, and declares
            how those tags are allowed to be used together.  For
            example, it doesn't make sense to put a <sgmltag
            class="starttag">book</sgmltag> element inside a <sgmltag
            class="starttag">para</sgmltag> paragraph element -- only
            the reverse makes sense.
          </para>
          <para>
            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.
          </para>
          <para>
            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:
            <programlisting>&lt!doctype book PUBLIC "-//OASIS//DTD
            DocBook V3.1//EN" []> &lt;book> ...
            &lt;/book></programlisting>
          </para>
          <para>
            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:
            <programlisting>&lt!doctype article PUBLIC "-//OASIS//DTD DocBook V3.1//EN" []>
&lt;article>
...
&lt;/article></programlisting>
          </para>
        </sect3>

        <sect3 id="sgml-document">
          <title>The Document</title>
          <para>
            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.
          </para>
          <para>
            Below is a (completely nonsensical) example to illustrate
            how a simple document might be laid out.  Notice that all
            <sgmltag class="starttag">chapter</sgmltag> and <sgmltag
            class="starttag">sect1</sgmltag> elements have <sgmltag
            class="attribute">id</sgmltag> 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 <sgmltag class="starttag">book</sgmltag>,
            <sgmltag class="starttag">chapter</sgmltag>, and/or <sgmltag
            class="starttag">sect1</sgmltag> element.  If the given
            element has an <sgmltag class="attribute">id</sgmltag>
            attribute, the processor will typically name the file
            accordingly.  Thus, the below document might result in
            <filename>index.html</filename>,
            <filename>chapter-one.html</filename>,
            <filename>blobs.html</filename>, and so on.
          </para>
          <para>
            Also notice the text marked off with <quote>&lt;!--
            </quote> and <quote> --&gt;</quote> characters.  These
            denote SGML comments.  SGML processors will completely
            ignore anything between these markers, similar to
            <quote>/*</quote> and <quote>*/</quote> comments in C
            source code.
          </para>

          <!-- Encase the following SGML excerpt inside a CDATA
               block so we don't have to bother converting all
               brackets to entities
          -->
          <programlisting>
<![CDATA[
<!doctype book PUBLIC "-//OASIS//DTD DocBook V3.1//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>
]]>
</programlisting>
        </sect3>

        <sect3>
          <title>Common Elements</title>
          <para>
            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.
          </para>
          <para>
            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.
          </para>
          <para>
            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 <ulink
            url="http://docbook.org">http://docbook.org</ulink>.  To
            see how they are used in practice, download the SGML
            source for this manual (the Wine Developer Guide) and
            browse through it, comparing it to the generated HTML (or
            PostScript or PDF).
          </para>
          <para>
            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 <sgmltag
            class="starttag">systemitem</sgmltag> tag doesn't produce
            any formatting by default, you should fix the stylesheets,
            not change the valid <sgmltag
            class="starttag">systemitem</sgmltag> tag to, for example,
            an <sgmltag class="starttag">emphasis</sgmltag> tag.
          </para>
          <para>
            Here are the common SGML elements:
          </para>

          <variablelist>
            <title>Structural Elements</title>
            <varlistentry>
              <term><sgmltag class="starttag">book</sgmltag></term>
              <listitem>
                <para>
                  The book is the most common toplevel element, and is
                  probably the one you should use for your document.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">set</sgmltag></term>
              <listitem>
                <para>
                  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 
                  <sgmltag class="starttag">book</sgmltag> to
                  put each Wine guide into a separate directory (see
                  <filename>documentation/wine-devel.sgml</filename>,
                  etc.).
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">chapter</sgmltag></term>
              <listitem>
                <para>
                  A <sgmltag class="starttag">chapter</sgmltag>
                  element includes a single entire chapter of the
                  book.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">part</sgmltag></term>
              <listitem>
                <para>
                  If the chapters in your book fall into major
                  categories or groupings (as in the Wine Developer
                  Guide), you can place each collection of chapters
                  into a <sgmltag class="starttag">part</sgmltag>
                  element.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">sect?</sgmltag></term>
              <listitem>
                <para>
                  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, <sgmltag class="starttag">sect1</sgmltag>,
                  <sgmltag class="starttag">sect2</sgmltag>, <sgmltag
                  class="starttag">sect3</sgmltag>, <sgmltag
                  class="starttag">sect4</sgmltag>, and <sgmltag
                  class="starttag">sect5</sgmltag> (if necessary).
                  These tags must be nested in order: you can't place
                  a <sgmltag class="starttag">sect3</sgmltag> directly
                  inside a <sgmltag class="starttag">sect1</sgmltag>.
                  You have to nest the <sgmltag
                  class="starttag">sect3</sgmltag> inside a <sgmltag
                  class="starttag">sect2</sgmltag>, 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
                  <sgmltag class="starttag">section</sgmltag> element
                  which you can nest inside itself, but its use is
                  discouraged in favor of the numbered section tags.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">title</sgmltag></term>
              <listitem>
                <para>
                  The title of a book, chapter, part, section, etc.
                  In most of the major structural elements, like
                  <sgmltag class="starttag">chapter</sgmltag>,
                  <sgmltag class="starttag">part</sgmltag>, and the
                  various section tags, <sgmltag
                  class="starttag">title</sgmltag> is mandatory.  In
                  other elements like <sgmltag
                  class="starttag">book</sgmltag> and <sgmltag
                  class="starttag">note</sgmltag>, it's optional.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">para</sgmltag></term>
              <listitem>
                <para>
                  The basic unit of text is the paragraph, represented
                  by the <sgmltag class="starttag">para</sgmltag> 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 <sgmltag
                  class="starttag">book</sgmltag>, <sgmltag
                  class="starttag">chapter</sgmltag>, <sgmltag
                  class="starttag">title</sgmltag>, and <sgmltag
                  class="starttag">para</sgmltag>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">article</sgmltag></term>
              <listitem>
                <para>
                  For shorter, more targeted documents, like topic
                  pieces and whitepapers, you can use <sgmltag
                  class="starttag">article</sgmltag> as your toplevel
                  element.
                </para>
              </listitem>
            </varlistentry>
          </variablelist>

          <variablelist>
            <title>Inline Formatting Elements</title>
            <varlistentry>
              <term><sgmltag class="starttag">filename</sgmltag></term>
              <listitem>
                <para>
                  The name of a file.  You can optionally set the
                  <sgmltag class="attribute">class</sgmltag> attribute
                  to <literal>Directory</literal>,
                  <literal>HeaderFile</literal>, and
                  <literal>SymLink</literal> to further classify the
                  filename.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">userinput</sgmltag></term>
              <listitem>
                <para>
                  Literal text entered by the user.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">computeroutput</sgmltag></term>
              <listitem>
                <para>
                  Literal text output by the computer.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">literal</sgmltag></term>
              <listitem>
                <para>
                  A catch-all element for literal computer data.  Its
                  use is somewhat vague; try to use a more specific
                  tag if possible, like <sgmltag
                  class="starttag">userinput</sgmltag> or <sgmltag
                  class="starttag">computeroutput</sgmltag>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">quote</sgmltag></term>
              <listitem>
                <para>
                  An inline quotation.  This tag typically inserts
                  quotation marks for you, so you would write <sgmltag
                  class="starttag">quote</sgmltag>This is a
                  quote<sgmltag class="endtag">quote</sgmltag> 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 <sgmltag
                  class="starttag">blockquote</sgmltag>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">note</sgmltag></term>
              <listitem>
                <para>
                  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
                  <sgmltag class="starttag">title</sgmltag> element.
                  Thus, to add a visible FIXME comment to the
                  documentation, you might write:
                </para>
<programlisting>
<![CDATA[
<note>
  <title>EXAMPLE</title>
  <para>This is an example note...</para>
</note>
]]></programlisting>
                <para>
                  The results will look something like this:
                </para>
                  <note>
                    <title>EXAMPLE</title>
                    <para>This is an example note...</para>
                  </note>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">sgmltag</sgmltag></term>
              <listitem>
                <para>
                  Used for inserting SGML tags, etc., into a SGML
                  document without resorting to a lot of entity
                  quoting, e.g., &amp;lt;.  You can change the
                  appearance of the text with the <sgmltag
                  class="attribute">class</sgmltag> attribute.  Some
                  common values of this are
                  <literal>starttag</literal>,
                  <literal>endtag</literal>,
                  <literal>attribute</literal>,
                  <literal>attvalue</literal>, and even
                  <literal>sgmlcomment</literal>.  See this SGML file,
                  <filename>documentation/documentation.sgml</filename>,
                  for examples.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">prompt</sgmltag></term>
              <listitem>
                <para>
                  The text used for a computer prompt, for example a
                  shell prompt, or command-line application prompt.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">replaceable</sgmltag></term>
              <listitem>
                <para>
                  Meta-text that should be replaced by the user, not
                  typed in literally, e.g., in command descriptions
                  and <parameter>--help</parameter> outputs.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">constant</sgmltag></term>
              <listitem>
                <para>
                  A programming constant, e.g.,
                  <constant>MAX_PATH</constant>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">symbol</sgmltag></term>
              <listitem>
                <para>
                  A symbolic value replaced, for example, by a
                  pre-processor.  This applies primarily to C macros,
                  but may have other uses.  Use the <sgmltag
                  class="starttag">constant</sgmltag> tag instead of
                  <sgmltag class="starttag">symbol</sgmltag> where
                  appropriate.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">function</sgmltag></term>
              <listitem>
                <para>
                  A programming function name.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">parameter</sgmltag></term>
              <listitem>
                <para>
                  Programming language parameters you pass with a
                  function.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">option</sgmltag></term>
              <listitem>
                <para>
                  Parameters you pass to a command-line executable.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">varname</sgmltag></term>
              <listitem>
                <para>
                  Variable name, typically in a programming language.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">type</sgmltag></term>
              <listitem>
                <para>
                  Programming language types, e.g., from a typedef
                  definition.  May have other uses, too.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">structname</sgmltag></term>
              <listitem>
                <para>
                  The name of a C-language <type>struct</type>
                  declaration, e.g., <structname>sockaddr</structname>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">structfield</sgmltag></term>
              <listitem>
                <para>
                  A field inside a C <type>struct</type>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">command</sgmltag></term>
              <listitem>
                <para>
                  An executable binary, e.g., <command>wine</command>
                  or <command>ls</command>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">envar</sgmltag></term>
              <listitem>
                <para>
                  An environment variable, e.g, <envar>$PATH</envar>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">systemitem</sgmltag></term>
              <listitem>
                <para>
                  A generic catch-all for system-related things, like
                  OS names, computer names, system resources, etc.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">email</sgmltag></term>
              <listitem>
                <para>
                  An email address.  The SGML processor will typically
                  add extra formatting characters, and even a
                  <literal>mailto:</literal> link for HTML pages.
                  Usage: <sgmltag
                  class="starttag">email</sgmltag>user@host.com<sgmltag
                  class="endtag">email</sgmltag>
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">firstterm</sgmltag></term>
              <listitem>
                <para>
                  Special emphasis for introducing a new term.  Can
                  also be linked to a <sgmltag
                  class="starttag">glossary</sgmltag> entry, if
                  desired.
                </para>
              </listitem>
            </varlistentry>
          </variablelist>

          <variablelist>
            <title>Item Listing Elements</title>
            <varlistentry>
              <term><sgmltag class="starttag">itemizedlist</sgmltag></term>
              <listitem>
                <para>
                  For bulleted lists, no numbering.  You can tweak the
                  layout with SGML attributes.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">orderedlist</sgmltag></term>
              <listitem>
                <para>
                  A numbered list; the SGML processor will insert the
                  numbers for you.  You can suggest numbering styles
                  with the <sgmltag
                  class="attribute">numeration</sgmltag> attribute.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">simplelist</sgmltag></term>
              <listitem>
                <para>
                  A very simple list of items, often inlined.  Control
                  the layout with the <sgmltag
                  class="attribute">type</sgmltag> attribute.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">variablelist</sgmltag></term>
              <listitem>
                <para>
                  A list of terms with definitions or descriptions,
                  like this very list!
                </para>
              </listitem>
            </varlistentry>
          </variablelist>

          <variablelist>
            <title>Block Text Quoting Elements</title>
            <varlistentry>
              <term><sgmltag class="starttag">programlisting</sgmltag></term>
              <listitem>
                <para>
                  Quote a block of source code.  Typically highlighted
                  in the output and set off from normal text.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">screen</sgmltag></term>
              <listitem>
                <para>
                  Quote a block of visible computer output, like the
                  output of a command or chunks of debug logs.
                </para>
              </listitem>
            </varlistentry>
          </variablelist>

          <variablelist>
            <title>Hyperlink Elements</title>
            <varlistentry>
              <term><sgmltag class="starttag">link</sgmltag></term>
              <listitem>
                <para>
                  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 <sgmltag
                  class="attribute">id</sgmltag> attribute of the
                  element that you want to link to.  For example:
<programlisting>&lt;link linkend="configuring-wine">the section on configuring wine&lt;/link>
...
&lt;sect2 id="configuring-wine">
...</programlisting>
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">xref</sgmltag></term>
              <listitem>
                <para>
                  In-document hyperlink that can generate its own
                  text.  Similar to the <sgmltag
                  class="starttag">link</sgmltag> tag, you use the
                  <sgmltag class="attribute">linkend</sgmltag>
                  attribute to specify which target element you want
                  to jump to:
                </para>
                <para>
<programlisting>&lt;xref linkend="configuring-wine">
...
&lt;sect2 id="configuring-wine">
...</programlisting>
                </para>
                <para>
                  By default, most SGML processors will auto generate
                  some generic text for the <sgmltag
                  class="starttag">xref</sgmltag> link, like
                  <quote>Section 2.3.1</quote>.  You can use the
                  <sgmltag class="attribute">endterm</sgmltag>
                  attribute to grab the visible text content of the
                  hyperlink from another element:
                </para>
                <para>
<programlisting>&lt;xref linkend="configuring-wine" endterm="config-title">
...
&lt;sect2 id="configuring-wine">
  &lt;title id="config-title">Configuring Wine&lt;/title>
...</programlisting>
                </para>
                <para>
                  This would create a link to the
                  <symbol>configuring-wine</symbol> element,
                  displaying the text of the
                  <symbol>config-title</symbol> element for the
                  hyperlink.  Most often, you'll add an <sgmltag
                  class="attribute">id</sgmltag> attribute to the
                  <sgmltag class="starttag">title</sgmltag> 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.
                </para>
                <para>
                  Alternatively, you can use an <sgmltag
                  class="attribute">xreflabel</sgmltag> attribute in
                  the target element tag to specify the link text:
                </para>
<programlisting>&lt;sect1 id="configuring-wine" xreflabel="Configuring Wine"></programlisting>
                <note>
                  <para>
                    <sgmltag class="starttag">xref</sgmltag> 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 <sgmltag
                    class="starttag">xref</sgmltag>, while in XML
                    documents you should use
                    <sgmltag>&lt;xref/></sgmltag>.
                  </para>
                </note>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">anchor</sgmltag></term>
              <listitem>
                <para>
                  An invisible tag, used for inserting <sgmltag
                  class="attribute">id</sgmltag> 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).
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">ulink</sgmltag></term>
              <listitem>
                <para>
                  Hyperlink in URL form, e.g., <ulink
                  url="http://www.winehq.org">http://www.winehq.org</ulink>.
                </para>
              </listitem>
            </varlistentry>
            <varlistentry>
              <term><sgmltag class="starttag">olink</sgmltag></term>
              <listitem>
                <para>
                  Indirect hyperlink; can be used for linking to
                  external documents.  Not often used in practice.
                </para>
              </listitem>
            </varlistentry>
          </variablelist>
        </sect3>
      </sect2>

      <sect2 id="sgml-environment">
        <title>Editing SGML Documents</title>

        <para>
          You can write SGML/DocBook documents in any text editor you
          might find although some editors are more friendly for
          this task than others.
        </para>
        <para>
          The most commonly used open source SGML editor is Emacs,
          with the PSGML <firstterm>mode</firstterm>, 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.
        </para>
      </sect2>

    </sect1>
  </chapter>

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