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 gafcontinue="Marker_set_2015.jpg" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:Marker set-perspective view-lowres.bmp" missing="" />
      <page pageid="25" ns="6" title="File:Close Smile front view.jpg" />
      <page pageid="72" ns="6" title="File:EM-01 Aid Tray reference frame.jpg" />
      <page pageid="73" ns="6" title="File:EM-02 Coverplates Box reference frame.jpg" />
      <page pageid="56" ns="6" title="File:Example frame atWork.png" />
      <page pageid="39" ns="6" title="File:FBM1 frames.zip" />
      <page pageid="129" ns="6" title="File:Footprint-RoCKIn-AtHome-2015-Rooms.png" />
      <page pageid="38" ns="6" title="File:Lexicon FBM3.zip" />
      <page pageid="128" ns="6" title="File:MarkerFBMArUco.pdf" />
      <page pageid="12" ns="6" title="File:Marker set-top with quote-lowres.png" />
    </pages>
  </query>
</api>