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="CaseSelectionDmXObj.png" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:COST FORSYS Overview WIKI System.png" />
      <f ns="6" title="File:COST FORSYS WG1 THESSALONIKI France.pdf" />
      <f ns="6" title="File:COST FORSYS WG1 THESSALONIKI Ireland.pdf" />
      <f ns="6" title="File:COST FORSYS WG1 THESSALONIKI MELA.pdf" />
      <f ns="6" title="File:COST FORSYS WG1 THESSALONIKI Portugal.pdf" />
      <f ns="6" title="File:COST FORSYS WG1 THESSALONIKI Russia.pdf" />
      <f ns="6" title="File:COST FORSYS WG1 THESSALONIKI SIMO.pdf" />
      <f ns="6" title="File:COST FORSYS WG1 THESSALONIKI Spain.pdf" />
      <f ns="6" title="File:Capsis415 mac.png" />
      <f ns="6" title="File:Capsis ventoux.png" />
    </allfileusages>
  </query>
</api>