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<html lang="en">
<head>
<title>HTML Xref Node Name Expansion - GNU Texinfo 4.13</title>
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Next:&nbsp;<a rel="next" accesskey="n" href="HTML-Xref-Command-Expansion.html#HTML-Xref-Command-Expansion">HTML Xref Command Expansion</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="HTML-Xref-Link-Basics.html#HTML-Xref-Link-Basics">HTML Xref Link Basics</a>,
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<hr>
</div>

<h4 class="subsection">22.4.2 HTML Cross-reference Node Name Expansion</h4>

<p><a name="index-HTML-cross_002dreference-node-name-expansion-1376"></a><a name="index-node-name-expansion_002c-in-HTML-cross_002dreferences-1377"></a><a name="index-expansion_002c-of-node-names-in-HTML-cross_002dreferences-1378"></a>
As mentioned in the previous section, the key part of the HTML
cross-reference algorithm is the conversion of node names in the
Texinfo source into strings suitable for XHTML identifiers and
filenames.  The restrictions are similar for each: plain ASCII
letters, numbers, and the &lsquo;<samp><span class="samp">-</span></samp>&rsquo; and &lsquo;<samp><span class="samp">_</span></samp>&rsquo; characters are all
that can be used.  (Although HTML anchors can contain most characters,
XHTML is more restrictive.)

  <p>Cross-references in Texinfo can actually refer either to nodes or
anchors (see <a href="anchor.html#anchor">anchor</a>), but anchors are treated identically to nodes
in this context, so we'll continue to say &ldquo;node&rdquo; names for
simplicity.

  <p>(@-commands and 8-bit characters are not presently handled by
<samp><span class="command">makeinfo</span></samp> for HTML cross-references.  See the next section.)

  <p>A special exception: the Top node (see <a href="The-Top-Node.html#The-Top-Node">The Top Node</a>) is always
mapped to the file <samp><span class="file">index.html</span></samp>, to match web server software. 
However, the HTML <em>target</em> is &lsquo;<samp><span class="samp">Top</span></samp>&rsquo;.  Thus (in the split case):

<pre class="example">     @xref{Top, Introduction,, emacs, The GNU Emacs Manual}.
     &rArr; &lt;a href="emacs/index.html#Top"&gt;
</pre>
     <ol type=1 start=1>
<li>The standard ASCII letters (a-z and A-Z) are not modified.  All other
characters are changed as specified below.

     <li>The standard ASCII numbers (0-9) are not modified except when a number
is the first character of the node name.  In that case, see below.

     <li>Multiple consecutive space, tab and newline characters are transformed
into just one space.  (It's not possible to have newlines in node
names with the current implementation, but we specify it anyway, just
in case.)

     <li>Leading and trailing spaces are removed.

     <li>After the above has been applied, each remaining space character is
converted into a &lsquo;<samp><span class="samp">-</span></samp>&rsquo; character.

     <li>Other ASCII 7-bit characters are transformed into &lsquo;<samp><span class="samp">_00</span><var>xx</var></samp>&rsquo;,
where <var>xx</var> is the ASCII character code in (lowercase) hexadecimal. 
This includes &lsquo;<samp><span class="samp">_</span></samp>&rsquo;, which is mapped to &lsquo;<samp><span class="samp">_005f</span></samp>&rsquo;.

     <li>If the node name does not begin with a letter, the literal string
&lsquo;<samp><span class="samp">g_t</span></samp>&rsquo; is prefixed to the result.  (Due to the rules above, that
string can never occur otherwise; it is an arbitrary choice, standing
for &ldquo;GNU Texinfo&rdquo;.)  This is necessary because XHTML requires that
identifiers begin with a letter.

       </ol>

  <p>For example:

<pre class="example">     @node A  node --- with _'%
     &rArr; A-node-_002d_002d_002d-with-_005f_0027_0025
</pre>
  <p>Notice in particular:

     <ul>
<li>&lsquo;<samp><span class="samp">_</span></samp>&rsquo; &rArr; &lsquo;<samp><span class="samp">_005f</span></samp>&rsquo;
<li>&lsquo;<samp><span class="samp">-</span></samp>&rsquo; &rArr; &lsquo;<samp><span class="samp">_002d</span></samp>&rsquo;
<li>&lsquo;<samp><span class="samp">A  node</span></samp>&rsquo; &rArr; &lsquo;<samp><span class="samp">A-node</span></samp>&rsquo;
</ul>

  <p>On case-folding computer systems, nodes differing only by case will be
mapped to the same file.

  <p>In particular, as mentioned above, Top always maps to the file
<samp><span class="file">index.html</span></samp>.  Thus, on a case-folding system, Top and a node
named `Index' will both be written to <samp><span class="file">index.html</span></samp>.

  <p>Fortunately, the targets serve to distinguish these cases, since HTML
target names are always case-sensitive, independent of operating
system.

  </body></html>