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>
    <allfileusages>
      <f ns="6" title="Fil:Carl Barks a Finnland 94.jpg" />
      <f ns="6" title="Fil:Donald Duck Star on the Walk of Fame.JPG" />
      <f ns="6" title="Fil:Furrysnowleopard.jpg" />
      <f ns="6" title="Fil:FursuitHoneybunny.jpg" />
      <f ns="6" title="Fil:Nero and Rotanes.JPG" />
      <f ns="6" title="Fil:Robin Hood Memorial.jpg" />
      <f ns="6" title="Fil:The Spirit of 43-Donald Duck, cropped version.jpg" />
      <f ns="6" title="Fil:The original Winnie the Pooh toys.jpg" />
      <f ns="6" title="Fil:Zibafursonas.jpg" />
    </allfileusages>
  </query>
</api>