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<a name="HTML-Xref-Link-Basics"></a>
<div class="header">
<p>
Next: <a href="HTML-Xref-Node-Name-Expansion.html#HTML-Xref-Node-Name-Expansion" accesskey="n" rel="next">HTML Xref Node Name Expansion</a>, Up: <a href="HTML-Xref.html#HTML-Xref" accesskey="u" rel="up">HTML Xref</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html#Command-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="HTML-Cross-Reference-Link-Basics"></a>
<h4 class="subsection">24.4.1 HTML Cross Reference Link Basics</h4>
<a name="index-HTML-cross-reference-link-basics"></a>

<p>For our purposes, an HTML link consists of four components: a host
name, a directory part, a file part, and a target part.  We
always assume the <code>http</code> protocol.  For example:
</p>
<div class="example">
<pre class="example">http://<var>host</var>/<var>dir</var>/<var>file</var>.html#<var>target</var>
</pre></div>

<p>The information to construct a link comes from the node name and
manual name in the cross reference command in the Texinfo source
(see <a href="Cross-References.html#Cross-References">Cross References</a>), and from <em>external information</em>
(see <a href="HTML-Xref-Configuration.html#HTML-Xref-Configuration">HTML Xref Configuration</a>).
</p>
<p>We now consider each part in turn.
</p>
<p>The <var>host</var> is hardwired to be the local host.  This could either
be the literal string &lsquo;<samp>localhost</samp>&rsquo;, or, according to the rules for
HTML links, the &lsquo;<samp>http://localhost/</samp>&rsquo; could be omitted entirely.
</p>
<p>The <var>dir</var> and <var>file</var> parts are more complicated, and depend on
the relative split/mono nature of both the manual being processed and
the manual that the cross reference refers to.  The underlying idea is
that there is one directory for Texinfo manuals in HTML, and a given
<var>manual</var> is either available as a monolithic file
<samp><var>manual</var>.html</samp>, or a split subdirectory
<samp><var>manual</var>/*.html</samp>.  Here are the cases:
</p>
<ul>
<li> If the present manual is split, and the referent manual is also split,
the directory is &lsquo;<samp>../<var>referent/</var></samp>&rsquo; and the file is the
expanded node name (described later).

</li><li> If the present manual is split, and the referent manual is mono, the
directory is &lsquo;<samp>../</samp>&rsquo; and the file is <samp><var>referent</var>.html</samp>.

</li><li> If the present manual is mono, and the referent manual is split, the
directory is <samp><var>referent</var>/</samp> and the file is the expanded node
name.

</li><li> If the present manual is mono, and the referent manual is also mono,
the directory is <samp>./</samp> (or just the empty string), and the file is
<samp><var>referent</var>.html</samp>.

</li></ul>

<a name="index-BASEFILENAME_005fLENGTH-1"></a>
<p>Another rule, that only holds for filenames, is that base filenames
are truncated to 245 characters, to allow for an extension to be
appended and still comply with the 255-character limit which is common
to many filesystems.  Although technically this can be changed with
the <code>BASEFILENAME_LENGTH</code> customization variable (see <a href="Other-Customization-Variables.html#Other-Customization-Variables">Other Customization Variables</a>), doing so would make cross-manual references
to such nodes invalid.
</p>
<p>Any directory part in the filename argument of the source cross
reference command is ignored.  Thus, <code>@xref{,,,../foo}</code> and
<code>@xref{,,,foo}</code> both use &lsquo;<samp>foo</samp>&rsquo; as the manual name.  This
is because any such attempted hardwiring of the directory is very
unlikely to be useful for both Info and HTML output.
</p>
<p>Finally, the <var>target</var> part is always the expanded node name.
</p>
<p>Whether the present manual is split or mono is determined by user
option; <code>makeinfo</code> defaults to split, with the
<samp>--no-split</samp> option overriding this.
</p>
<p>Whether the referent manual is split or mono, however, is another bit
of the external information (see <a href="HTML-Xref-Configuration.html#HTML-Xref-Configuration">HTML Xref Configuration</a>).  By
default, <code>makeinfo</code> uses the same form of the referent manual
as the present manual.
</p>
<p>Thus, there can be a mismatch between the format of the referent
manual that the generating software assumes, and the format it&rsquo;s
actually present in.  See <a href="HTML-Xref-Mismatch.html#HTML-Xref-Mismatch">HTML Xref Mismatch</a>.
</p>

<hr>
<div class="header">
<p>
Next: <a href="HTML-Xref-Node-Name-Expansion.html#HTML-Xref-Node-Name-Expansion" accesskey="n" rel="next">HTML Xref Node Name Expansion</a>, Up: <a href="HTML-Xref.html#HTML-Xref" accesskey="u" rel="up">HTML Xref</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html#Command-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
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