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="BukiCruiseDate.jpg|1623" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1" ns="0" title="Main Page" />
      <page pageid="28" ns="0" title="Fate Testarossa" />
      <page pageid="46" ns="0" title="Sayaka Miki" />
      <page pageid="436" ns="0" title="Theme" />
      <page pageid="1264" ns="0" title="Uniform Voting" />
      <page pageid="1644" ns="0" title="Chihaya Izumi" />
      <page pageid="1866" ns="0" title="Homura Akemi" />
      <page pageid="2488" ns="0" title="Batiste" />
      <page pageid="2566" ns="0" title="Black Rose Dueling" />
    </pages>
  </query>
</api>