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="Halle_Bemassung_OG.pdf" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:C-logo claim blacc.png" />
      <f ns="6" title="File:C-logo claim blue.png" />
      <f ns="6" title="File:C-logo claim white.png" />
      <f ns="6" title="File:Club Bemassung.pdf" />
      <f ns="6" title="File:Club Reihe.pdf" />
      <f ns="6" title="File:ColumbiaClub Speks deutsch.pdf" />
      <f ns="6" title="File:Cven 01.jpg" />
      <f ns="6" title="File:Deutsche Specs 2004.pdf" />
      <f ns="6" title="File:Grundriss Rigging EG Ger.pdf" />
      <f ns="6" title="File:Halle Bemassung EG.pdf" />
    </allfileusages>
  </query>
</api>