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="BAC_Inside_1990.jpg|209" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:BAC 2002-2003.png" />
      <f ns="6" title="File:BAC Big Top (2007).jpg" />
      <f ns="6" title="File:BAC Clowns 1987.jpg" />
      <f ns="6" title="File:BAC Clowns 1987.jpg" />
      <f ns="6" title="File:BAC Clowns 1987.jpg" />
      <f ns="6" title="File:BAC Clowns 1987.jpg" />
      <f ns="6" title="File:BAC Founders 1997.JPG" />
      <f ns="6" title="File:BAC Founders 1997.JPG" />
      <f ns="6" title="File:BAC Founders 1997.JPG" />
      <f ns="6" title="File:BAC Fron 1987.jpg" />
    </allfileusages>
  </query>
</api>