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>
    <alltransclusions atcontinue="Provenance" />
  </query-continue>
  <query>
    <alltransclusions>
      <t ns="10" title="Template:External Reference Repeater" />
      <t ns="10" title="Template:External References" />
      <t ns="10" title="Template:Gene Ontology Reference Repeater" />
      <t ns="10" title="Template:Gene Synonym Repeater" />
      <t ns="10" title="Template:Gene Synonyms" />
      <t ns="10" title="Template:Ontological References" />
      <t ns="10" title="Template:Ontology Result Format" />
      <t ns="10" title="Template:Ontology Result Format Footer" />
      <t ns="10" title="Template:Ontology Result Format Header" />
      <t ns="10" title="Template:Plant Ontology Reference Repeater" />
    </alltransclusions>
  </query>
</api>