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="Buchung_erfassen.png|303" />
  </query-continue>
  <query>
    <pages>
      <page pageid="123" ns="0" title="Faktura Extras Benutzer" />
      <page pageid="125" ns="0" title="Faktura Extras Backup" />
      <page pageid="179" ns="0" title="Faktura Artikel/Leistungen anlegen" />
      <page pageid="241" ns="0" title="Faktura Einkauf/Verkauf Rechnung erstellen" />
      <page pageid="271" ns="0" title="Faktura Einkauf/Verkauf Vorlagen bearbeiten" />
      <page pageid="303" ns="0" title="Faktura Buchhaltung Buchungen erfassen" />
    </pages>
  </query>
</api>