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="Cart_marker_removal.jpg" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Bootmx.jpg" />
      <f ns="6" title="File:Bootmxpb.jpg" />
      <f ns="6" title="File:Bootngh.jpg" />
      <f ns="6" title="File:Bootrepair.jpg" />
      <f ns="6" title="File:Cart clean result back.jpg" />
      <f ns="6" title="File:Cart clean result front.jpg" />
      <f ns="6" title="File:Cart cleaning toolkit.jpg" />
      <f ns="6" title="File:Cart eraser removal.jpg" />
      <f ns="6" title="File:Cart gap dirt removal.jpg" />
      <f ns="6" title="File:Cart inside dirt removal.jpg" />
    </allfileusages>
  </query>
</api>