You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allfileusages gafcontinue="Baumriese.jpg|3434" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1413" ns="0" title="Helden" />
      <page pageid="1415" ns="0" title="Rohstoffe" />
      <page pageid="1416" ns="0" title="Trollwelt Baum des Lebens" />
      <page pageid="1554" ns="0" title="Gebäude" />
      <page pageid="2355" ns="0" title="Basar" />
      <page pageid="3488" ns="0" title="Baum des Lebens" />
      <page pageid="3521" ns="0" title="Zentaurenwelt Baum des Lebens" />
      <page pageid="194855" ns="0" title="Guides: Einsteiger Guide" />
    </pages>
  </query>
</api>