Fix compatibility note.

      <p>This command doesn't output anything. Its only use is to

      add comments within a file. These comments are not printed.</p>

      <p>This syntax is available in version 2.5 and later.</p>

      <p>This syntax is available in version 2.4.21 and later.</p>

      <example>

      <!--#comment Blah Blah Blah -->

      <dl>

      <dt><code>echomsg</code> (<em>Apache 2.1 and later</em>)</dt>

      <dd>

      <p>The value is a message that is sent back to the

      <dd><p>The value is a message that is sent back to the

      client if the <code><a href="#element.echo">echo</a></code> element

      attempts to echo an undefined variable. This overrides any <directive

      module="mod_include">SSIUndefinedEcho</directive> directives.</p>

      <example>

      <!--#config sizefmt="abbrev" -->

      </example>

      </dd>

      <dt><code>timefmt</code></dt>

      </example>

      </dd>

      </dl>

    </section> <!-- /config -->

</directivesynopsis>

</modulesynopsis>