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<chapter id="psgml-mode">
  <title>Using <literal>sgml-mode</literal> with
    <application>Emacs</application></title>
  
  <para>Recent versions of <application>Emacs</application> or <application>XEmacs</application> (available from the ports
    collection) contain a very useful package called PSGML. Automatically
    invoked when a file with the <filename>.sgml</filename> extension is loaded,
    or by typing <command>M-x sgml-mode</command>, it is a major mode for
    dealing with SGML files, elements and attributes.</para>

  <para>An understanding of some of the commands provided by this mode can
    make working with SGML documents such as the Handbook much easier.</para>

  <variablelist>
    <varlistentry>
      <term><command>C-c C-e</command></term>
      
      <listitem>
	<para>Runs <literal>sgml-insert-element</literal>. You will be
	  prompted for the name of the element to insert at the current point.
	  You can use the TAB key to complete the element. Elements that are
	  not valid at the current point will be disallowed.</para>

	<para>The start and end tags for the element will be inserted. If the
	  element contains other, mandatory, elements then these will be
	  inserted as well.</para>
      </listitem>
    </varlistentry>
    
    <varlistentry>
      <term><command>C-c =</command></term>
      
      <listitem>
	<para>Runs <literal>sgml-change-element-name</literal>. Place the
	  point within an element and run this command. You will be prompted
	  for the name of the element to change to. Both the start and end
	  tags of the current element will be changed to the new
	  element.</para>
      </listitem>
    </varlistentry>
    
    <varlistentry>
      <term><command>C-c C-r</command></term>
      
      <listitem>
	<para>Runs <literal>sgml-tag-region</literal>. Select some text (move
	  to start of text, C-space, move to end of text, C-space) and then
	  run this command. You will be prompted for the element to use. This
	  element will then be inserted immediately before and after your
	  marked region.</para>
      </listitem>
    </varlistentry>

    <varlistentry>
      <term><command>C-c -</command></term>
      
      <listitem>
	<para>Runs <literal>sgml-untag-element</literal>. Place the point
	  within the start or end tag of an element you want to remove, and
	  run this command. The element's start and end tags will be
	  removed.</para>
      </listitem>
    </varlistentry>
    
    <varlistentry>
      <term><command>C-c C-q</command></term>
      
      <listitem>
	<para>Runs <literal>sgml-fill-element</literal>. Will recursively fill
	  (i.e., reformat) content from the current element in. The filling
	  <emphasis>will</emphasis> affect content in which whitespace is
	  significant, such as within <sgmltag>programlisting</sgmltag>
	  elements, so run this command with care.</para>
      </listitem>
    </varlistentry>
    
    <varlistentry>
      <term><command>C-c C-a</command></term>
      
      <listitem>
	<para>Runs <literal>sgml-edit-attributes</literal>. Opens a second
	  buffer containing a list of all the attributes for the closest
	  enclosing element, and their current values. Use TAB to navigate
	  between attributes, <command>C-k</command> to remove an existing
	  value and replace it with a new one, <command>C-c C-c</command>
	  to close this buffer and return to the main document.</para>
      </listitem>
    </varlistentry>
    
    <varlistentry>
      <term><command>C-c C-v</command></term>
      
      <listitem>
	<para>Runs <literal>sgml-validate</literal>. Prompts you to save the
	  current document (if necessary) and then runs an SGML validator. The
	  output from the validator is captured into a new buffer, and you can
	  then navigate from one troublespot to the next, fixing markup errors
	  as you go.</para>
      </listitem>
    </varlistentry>
  </variablelist>
  
  <para>Doubtless there are other useful functions of this mode, but those are
    the ones I use most often.</para>

  <para>You can also use the following entries in
    <filename>.emacs</filename> to set proper spacing, indentation,
    and column width for working with the Documentation Project.</para>

  <programlisting>
    (setq sgml-mode-hook
      '(lambda ()
         (setq fill-column 70
               indent-tabs-mode nil
               next-line-add-newlines nil
               standard-indent 2)
         (auto-fill-mode t)))
  </programlisting>

</chapter>


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