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="Bandwidth_utilization_SNMP.pdf|4304" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:BGP-overall.png" />
      <f ns="6" title="File:BGP and PCEP Kibana.png" />
      <f ns="6" title="File:BIER APP Figure.jpeg" />
      <f ns="6" title="File:BIER Figure1.jpeg" />
      <f ns="6" title="File:BIER Figure2.jpeg" />
      <f ns="6" title="File:BIER Figure3.jpeg" />
      <f ns="6" title="File:BIER Figure4.jpeg" />
      <f ns="6" title="File:BMP.png" />
      <f ns="6" title="File:BS.png" />
      <f ns="6" title="File:BS NBR invite.png" />
    </allfileusages>
  </query>
</api>