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="XLS_File_Example.jpg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="84" ns="6" title="File:Canvas.jpg" />
      <page pageid="37" ns="6" title="File:Color Legend.jpg" />
      <page pageid="35" ns="6" title="File:Comment feature.jpg" />
      <page pageid="19" ns="6" title="File:Double click on arrow to add R or I.jpg" />
      <page pageid="10" ns="6" title="File:File menu.jpg" />
      <page pageid="28" ns="6" title="File:Intervention .jpg" />
      <page pageid="36" ns="6" title="File:Outcome editor.jpg" />
      <page pageid="50" ns="6" title="File:Outcome group.jpg" />
      <page pageid="29" ns="6" title="File:Rationale Full text .jpg" />
      <page pageid="67" ns="6" title="File:Software-box.jpg" />
    </pages>
  </query>
</api>