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="Cat_wall_4.JPG" />
  </query-continue>
  <query>
    <pages>
      <page pageid="141" ns="6" title="File:Ballscrews rev b.jpg" />
      <page pageid="178" ns="6" title="File:Bern-muerren.png" />
      <page pageid="189" ns="6" title="File:Bernardo Bellotto, il Canaletto - View of Dresden from the Right Bank of the Elbe with the Augustus Bridge - WGA01824.jpg" />
      <page pageid="228" ns="6" title="File:Cam08-frontdoor.png" />
      <page pageid="27" ns="6" title="File:Camera enclosure.jpg" />
      <page pageid="28" ns="6" title="File:Camera in enclosure.jpg" />
      <page pageid="39" ns="6" title="File:Camera schematics.jpg" />
      <page pageid="115" ns="6" title="File:Cat wall 1.JPG" />
      <page pageid="116" ns="6" title="File:Cat wall 2.JPG" />
      <page pageid="117" ns="6" title="File:Cat wall 3.JPG" />
    </pages>
  </query>
</api>