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="Hcard-microformat-button.png|1620" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="1380" ns="6" title="File:Bruce County.jpg" />
      <f fromid="1547" ns="6" title="File:Customized Logs Rev 1.11.zip" />
      <f fromid="1468" ns="6" title="File:Daintree History (Fred Morley).doc" />
      <f fromid="1422" ns="6" title="File:Daniel Sarles and grandson Ivan.jpg" />
      <f fromid="1486" ns="6" title="File:Doc.gif" />
      <f fromid="1368" ns="6" title="File:Downtown Tiverton Aug 1989 sml.jpg" />
      <f fromid="1422" ns="6" title="File:Ernest and Flossie Sarles.jpg" />
      <f fromid="1458" ns="6" title="File:Genealogy signature.gif" />
      <f fromid="1422" ns="6" title="File:Grampa&#039;s 70th Birthday May 2, 1957.jpg" />
      <f fromid="1617" ns="6" title="File:Hcard-microformat-button.png" />
    </allfileusages>
  </query>
</api>