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="Cemm4pin.jpg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="270" ns="6" title="File:BasicWireless E-TTL II1.jpg" />
      <page pageid="271" ns="6" title="File:BasicWireless E-TTL II2.jpg" />
      <page pageid="272" ns="6" title="File:BasicWireless E-TTL II3.jpg" />
      <page pageid="966" ns="6" title="File:Beta Firmware 1.63.png" />
      <page pageid="967" ns="6" title="File:Beta Firmware Selection 1.63.png" />
      <page pageid="266" ns="6" title="File:Bluearrow.png" />
      <page pageid="108" ns="6" title="File:Book icoline.png" />
      <page pageid="507" ns="6" title="File:Canon transmitter.JPG" />
      <page pageid="261" ns="6" title="File:Cemm4pin-power.jpg" />
      <page pageid="257" ns="6" title="File:Cemm4pin-zoom.jpg" />
    </pages>
  </query>
</api>