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 afcontinue="Cat_wall_4.JPG" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Ballscrews rev b.jpg" />
      <f ns="6" title="File:Bern-muerren.png" />
      <f ns="6" title="File:Bernardo Bellotto, il Canaletto - View of Dresden from the Right Bank of the Elbe with the Augustus Bridge - WGA01824.jpg" />
      <f ns="6" title="File:Cam08-frontdoor.png" />
      <f ns="6" title="File:Camera enclosure.jpg" />
      <f ns="6" title="File:Camera in enclosure.jpg" />
      <f ns="6" title="File:Camera schematics.jpg" />
      <f ns="6" title="File:Cat wall 1.JPG" />
      <f ns="6" title="File:Cat wall 2.JPG" />
      <f ns="6" title="File:Cat wall 3.JPG" />
    </allfileusages>
  </query>
</api>