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="Catamaran-reaching.png" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Battery1.jpg" />
      <f ns="6" title="File:Battery2.jpg" />
      <f ns="6" title="File:Battery switch.jpg" />
      <f ns="6" title="File:BilgepumpCircuit.gif" />
      <f ns="6" title="File:BlueWaterCrewTest.doc" />
      <f ns="6" title="File:Bluewater-dinghy registration-2011 2013 aug.pdf" />
      <f ns="6" title="File:Candc 43 drawing.jpg" />
      <f ns="6" title="File:CatCrew1 May14.jpg" />
      <f ns="6" title="File:CatCrew2 May14.jpg" />
      <f ns="6" title="File:Catamaran-close-hauled.png" />
    </allfileusages>
  </query>
</api>