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="Drcarls-layout2013.png|3613" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Bm button.jpg" />
      <f ns="6" title="File:Brc sun wind map.jpg" />
      <f ns="6" title="File:Button template.pdf" />
      <f ns="6" title="File:Carl-approved.png" />
      <f ns="6" title="File:Circle-of-tiles.png" />
      <f ns="6" title="File:Dome Construction Diagram.gif" />
      <f ns="6" title="File:Dr carls invite.jpg" />
      <f ns="6" title="File:Drcarl layout 2007.png" />
      <f ns="6" title="File:Drcarl layout 2008.png" />
      <f ns="6" title="File:Drcarls-layout2010.png" />
    </allfileusages>
  </query>
</api>