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="Bahrain_International_Circuit_-_Paddock_Layout.png" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:B11.png" />
      <f ns="6" title="File:B21.png" />
      <f ns="6" title="File:B31.png" />
      <f ns="6" title="File:BA Racing 2000.png" />
      <f ns="6" title="File:BMW K=Xtreme.jpg" />
      <f ns="6" title="File:BMW SimRace SA Livery2.jpg" />
      <f ns="6" title="File:BackMarker Brigade logo 2015.jpg" />
      <f ns="6" title="File:BackMarker Brigadeside2.png" />
      <f ns="6" title="File:Backmarker1 2015.jpg" />
      <f ns="6" title="File:Bahrain International Circuit.png" />
    </allfileusages>
  </query>
</api>