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>
    <alltransclusions>
      <t ns="10" title="Vorlage:Benutzermenü" />
      <t ns="10" title="Vorlage:Benutzermenü/Code" />
      <t ns="10" title="Vorlage:Direktes Anlernen gesperrt" />
      <t ns="10" title="Vorlage:Direktes anlernen gesperrt" />
      <t ns="10" title="Vorlage:Dokumentation" />
      <t ns="10" title="Vorlage:Eingriff in die Elektroinstallation notwendig" />
      <t ns="10" title="Vorlage:Gerät wird nicht mehr produziert" />
      <t ns="10" title="Vorlage:Infobox Komponenten" />
      <t ns="10" title="Vorlage:Method" />
      <t ns="10" title="Vorlage:Method-lc" />
    </alltransclusions>
  </query>
</api>