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="Pillar_2-Cog_Code.png" />
  </query-continue>
  <query>
    <pages>
      <page pageid="4" ns="6" title="File:Information Plaque.jpg" />
      <page pageid="6" ns="6" title="File:Map.png" />
      <page pageid="12" ns="6" title="File:P7-T1.jpg" />
      <page pageid="55" ns="6" title="File:Pillar-set-thumb.jpg" />
      <page pageid="5" ns="6" title="File:Pillar 01-Night01.jpg" />
      <page pageid="9" ns="6" title="File:Pillar 01-Text 01.jpg" />
      <page pageid="8" ns="6" title="File:Pillar 01-Text 02.jpg" />
      <page pageid="13" ns="6" title="File:Pillar 07-Daytime.jpg" />
      <page pageid="44" ns="6" title="File:Pillar 2-Base.jpg" />
      <page pageid="21" ns="6" title="File:Pillar 2-Cog Code.jpg" />
    </pages>
  </query>
</api>