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="Bedrock|59" />
  </query-continue>
  <query>
    <pages>
      <page pageid="59" ns="0" title="Blocks" />
      <page pageid="513" ns="0" title="Back Stone Wall" />
      <page pageid="1341" ns="0" title="Back Wood Wall" />
      <page pageid="2687" ns="0" title="Ballista" />
      <page pageid="2797" ns="0" title="Factories" />
      <page pageid="2852" ns="0" title="Ballista Factory" />
      <page pageid="2857" ns="0" title="Bakery" />
      <page pageid="2883" ns="0" title="Ballista Bolts" />
    </pages>
  </query>
</api>