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>
    <allfileusages>
      <f ns="6" title="File:Case studies.svg" />
      <f ns="6" title="File:H2o icon.svg" />
      <f ns="6" title="File:Help icon4.svg" />
      <f ns="6" title="File:Lin-Cyber Conflict and National Security 2012.pdf" />
      <f ns="6" title="File:NRC-Cyberattack Capabilities-2009.pdf" />
      <f ns="6" title="File:Toc icon.svg" />
    </allfileusages>
  </query>
</api>