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="Domain-model-0.png|375" />
  </query-continue>
  <query>
    <pages>
      <page pageid="307" ns="0" title="Technical Team/Old/Sandbox for Sharing Examples/Sample RDF File for Apache Tomcat (section 3)" />
      <page pageid="320" ns="0" title="Technical Team/Old/Sandbox for Sharing Examples/OpenLogic SPDX 1.0 beta examples" />
      <page pageid="325" ns="0" title="Technical Team/Proposals/2010-10-21/Composite licensing" />
      <page pageid="358" ns="0" title="Business Team/Minutes/2011-01-20" />
      <page pageid="359" ns="0" title="Business Team/Beta Program/Draft Orientation Slides" />
      <page pageid="362" ns="0" title="Technical Team/Minutes/2011-02-01" />
      <page pageid="520" ns="0" title="Technical Team/Proposals/Yet another rough proposal for conceptual model of SPDX 2" />
      <page pageid="863" ns="0" title="Technical Team/Minutes/2014-05-06" />
    </pages>
  </query>
</api>