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="Entourage_2004_step8.png" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Cyberduck1.PNG" />
      <f ns="6" title="File:Entourage 2004 step1.png" />
      <f ns="6" title="File:Entourage 2004 step10.png" />
      <f ns="6" title="File:Entourage 2004 step11.png" />
      <f ns="6" title="File:Entourage 2004 step12.png" />
      <f ns="6" title="File:Entourage 2004 step2.png" />
      <f ns="6" title="File:Entourage 2004 step4.png" />
      <f ns="6" title="File:Entourage 2004 step5.png" />
      <f ns="6" title="File:Entourage 2004 step6.png" />
      <f ns="6" title="File:Entourage 2004 step7.png" />
    </allfileusages>
  </query>
</api>