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="BasicOptions.png" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:B.JPG" />
      <f ns="6" title="File:BB nano.jpg" />
      <f ns="6" title="File:BCF2000 top.jpg" />
      <f ns="6" title="File:BSsWorking.png" />
      <f ns="6" title="File:Back.jpg" />
      <f ns="6" title="File:Badidea.gif" />
      <f ns="6" title="File:Bare conductive.jpg" />
      <f ns="6" title="File:Bars base 250b.jpg" />
      <f ns="6" title="File:Bars welding 250b.jpg" />
      <f ns="6" title="File:Basic.png" />
    </allfileusages>
  </query>
</api>