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 afcontinue="Setup_amplitude.png|37" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="6" ns="6" title="File:Create Job 1.png" />
      <f fromid="6" ns="6" title="File:Create Job 2.png" />
      <f fromid="2" ns="6" title="File:Job Monitor 0.png" />
      <f fromid="2" ns="6" title="File:Job monitor.png" />
      <f fromid="57" ns="6" title="File:Licensing dialog.png" />
      <f fromid="37" ns="6" title="File:Property airfoil.png" />
      <f fromid="18" ns="6" title="File:Pviewer default v360.png" />
      <f fromid="18" ns="6" title="File:Pviewer multiple.png" />
      <f fromid="9" ns="6" title="File:Pviewer sg6043.png" />
      <f fromid="18" ns="6" title="File:Pviewer v360.png" />
    </allfileusages>
  </query>
</api>