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="ExportData.png|30" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="30" ns="6" title="File:BB.png" />
      <f fromid="90" ns="6" title="File:CEDEUS Detailed Architecture with GeoNode - single db.png" />
      <f fromid="78" ns="6" title="File:CEDEUS Physical Architecture-central.png" />
      <f fromid="78" ns="6" title="File:CEDEUS Physical Architecture-multi-server decentral.png" />
      <f fromid="65" ns="6" title="File:Dataenrichment v4 150g.jpg" />
      <f fromid="30" ns="6" title="File:Date.png" />
      <f fromid="30" ns="6" title="File:DayTravel.png" />
      <f fromid="27" ns="6" title="File:Delete.png" />
      <f fromid="30" ns="6" title="File:DisplayXYData.png" />
      <f fromid="30" ns="6" title="File:Editable.png" />
    </allfileusages>
  </query>
</api>