Parsing only part of a document with expat in PHP
<xmlroot>
  <page id="home">
    <h1>An HTML Header Tag!</h1>
    <p>This is a paragraph</p>
  </page>
  [...etc]
</xmlroot>

<?php

$doc = new DOMDocument('1.0');

$root = $doc->createElement('html');
$root = $doc->appendChild($root);

$head = $doc->createElement('head');
$head = $root->appendChild($head);

$title = $doc->createElement('title');
$title = $head->appendChild($title);

$text = $doc->createTextNode('< This is the title >');
$text = $title->appendChild($text);

echo $head->ownerDocument->saveXML($head);

<xmlroot>
  <page id="home">
    <![CDATA[
      <h1>An HTML Header Tag!</h1>
      <p>This is a paragraph</p>
    ]]>
  </page>
  [...etc]
</xmlroot>