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="Powercannon_render3.png" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:Octree2.svg" missing="" />
      <page pageid="66" ns="6" title="File:Forum idea.png" />
      <page pageid="48" ns="6" title="File:GravitySuitIcon.png" />
      <page pageid="70" ns="6" title="File:Morph modelrender.png" />
      <page pageid="69" ns="6" title="File:Morph wiremodel.png" />
      <page pageid="61" ns="6" title="File:Morphball model.png" />
      <page pageid="62" ns="6" title="File:Morphball render.png" />
      <page pageid="60" ns="6" title="File:Morphball wire.png" />
      <page pageid="71" ns="6" title="File:Morphball wirerender.png" />
      <page pageid="63" ns="6" title="File:Mrsinistar avatar.jpg" />
    </pages>
  </query>
</api>