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="Blue_butterfly.jpg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="2894" ns="6" title="File:Balor marilith.jpg" />
      <page pageid="1363" ns="6" title="File:Bariaur2.jpg" />
      <page pageid="774" ns="6" title="File:Batlunch.JPG" />
      <page pageid="2607" ns="6" title="File:BestestGameEvarRuinProgress.png" />
      <page pageid="2102" ns="6" title="File:Big Bone2 0214.JPG" />
      <page pageid="2101" ns="6" title="File:Big Bone 0219.JPG" />
      <page pageid="2440" ns="6" title="File:BiraCoH1.jpg" />
      <page pageid="2441" ns="6" title="File:BiraCoH2.jpg" />
      <page pageid="2095" ns="6" title="File:BlueRose1 0231.JPG" />
      <page pageid="2096" ns="6" title="File:BlueRose2 0235.JPG" />
    </pages>
  </query>
</api>