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 gatcontinue="CategoryTOC|1557" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1169" ns="14" title="Category:Pets" />
      <page pageid="1197" ns="14" title="Category:Politics and Society" />
      <page pageid="1202" ns="14" title="Category:Popular Science" />
      <page pageid="1285" ns="14" title="Category:Reviewed by Jill Murphy" />
      <page pageid="1287" ns="14" title="Category:Reviewed by John Lloyd" />
      <page pageid="1293" ns="14" title="Category:Reviewed by Keith Dudhnath" />
      <page pageid="1297" ns="14" title="Category:Reviewed by Lesley Mason" />
      <page pageid="1303" ns="14" title="Category:Reviewed by Magda Healey" />
      <page pageid="1324" ns="14" title="Category:Reviewed by Sue Magee" />
      <page pageid="1334" ns="14" title="Category:Reviews" />
    </pages>
  </query>
</api>