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="Im_synth_p14_rust.png" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Fry username password.jpg" />
      <f ns="6" title="File:Im synth p10 pm.png" />
      <f ns="6" title="File:Im synth p11 scatter.png" />
      <f ns="6" title="File:Im synth p12 hg.png" />
      <f ns="6" title="File:Im synth p14 combo.png" />
      <f ns="6" title="File:Im synth p14 hg.png" />
      <f ns="6" title="File:Im synth p14 mask.png" />
      <f ns="6" title="File:Im synth p14 metal.png" />
      <f ns="6" title="File:Im synth p14 phong.png" />
      <f ns="6" title="File:Im synth p14 ramp.png" />
    </allfileusages>
  </query>
</api>