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="Files_pic4.png|683" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Cia.png" />
      <f ns="6" title="File:Company overview.png" />
      <f ns="6" title="File:Counter.png" />
      <f ns="6" title="File:Counter show.png" />
      <f ns="6" title="File:Counter stat.png" />
      <f ns="6" title="File:Department show.png" />
      <f ns="6" title="File:File ref.png" />
      <f ns="6" title="File:Files pic1.png" />
      <f ns="6" title="File:Files pic10.png" />
      <f ns="6" title="File:Files pic11.png" />
    </allfileusages>
  </query>
</api>