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="CC_Basic_NC.png|534" />
  </query-continue>
  <query>
    <pages>
      <page pageid="447" ns="0" title="Interdimensional Transit Authority" />
      <page pageid="462" ns="0" title="Worlds of the ITA" />
      <page pageid="468" ns="0" title="Marketplace Earth" />
      <page pageid="477" ns="0" title="Earth Prime" />
      <page pageid="479" ns="0" title="ITA Travel Advisories and Ratings" />
      <page pageid="499" ns="10" title="Template:CC License" />
      <page pageid="500" ns="10" title="Template:ITA License" />
      <page pageid="522" ns="0" title="Roman Republic Earth I" />
      <page pageid="523" ns="0" title="Empires Earth" />
      <page pageid="526" ns="0" title="Empires Earth history" />
    </pages>
  </query>
</api>