Entwurf zu DOM

gistfile1.php

<?php

$document = new DomDocument();

$atom = $document->getNamespace('http://www.w3.org/2005/Atom');
$xhtml = $document->getNamespace('http://www.w3.org/1999/xhtml', 'xhtml');

$feed = $atom->createElement('feed');
$document->appendChild($feed);

$entry = $atom->createElement('entry');

$title = $atom->createElement('title')->appendChild('Hello World');
$entry->appendChild($title);

$content = $atom->createElement('content')->setAttribute('type', 'xhtml');
$content->appendChild($xhtml->createElement('p')->appendChild('Hello World'));
$entry->appendChild($content);

$feed->appendChild($entry);

$document->normalizeNamespaces([$atom, $xhtml]);
echo $document;

gistfile2.xml

<?xml version="1.0"?>
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <entry>
    <title>Hello World</title>
    <content type="xhtml">
      <xhtml:p>Hello World</xhtml:p>
    </content>
  </entry>
</feed>