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="BabbageHouse_011.jpg" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:BabbageHouse 001.jpg" />
      <f ns="6" title="File:BabbageHouse 002.jpg" />
      <f ns="6" title="File:BabbageHouse 003.jpg" />
      <f ns="6" title="File:BabbageHouse 004.jpg" />
      <f ns="6" title="File:BabbageHouse 005.jpg" />
      <f ns="6" title="File:BabbageHouse 006.jpg" />
      <f ns="6" title="File:BabbageHouse 007.jpg" />
      <f ns="6" title="File:BabbageHouse 008.jpg" />
      <f ns="6" title="File:BabbageHouse 009.jpg" />
      <f ns="6" title="File:BabbageHouse 010.jpg" />
    </allfileusages>
  </query>
</api>