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="Illustration_glow_4.png" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:ConeyIsland.png" missing="" />
      <page ns="6" title="File:Construction 16.png" missing="" />
      <page ns="6" title="File:Illustration background.png" missing="" />
      <page ns="6" title="File:Illustration cab coordinates.png" missing="" />
      <page ns="6" title="File:Illustration center origin.png" missing="" />
      <page ns="6" title="File:Illustration digitalgauge 1.png" missing="" />
      <page ns="6" title="File:Illustration digitalgauge 2.png" missing="" />
      <page ns="6" title="File:Illustration glow 1.png" missing="" />
      <page ns="6" title="File:Illustration glow 2.png" missing="" />
      <page ns="6" title="File:Illustration glow 3.png" missing="" />
    </pages>
  </query>
</api>