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="CRAM_3.jpg|118" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:CMake Installer 01.png" />
      <f ns="6" title="File:CMake Installer 02.png" />
      <f ns="6" title="File:CMake Installer 03.png" />
      <f ns="6" title="File:CMake Installer 04.png" />
      <f ns="6" title="File:CMake Installer 05.png" />
      <f ns="6" title="File:CMake Installer 06.png" />
      <f ns="6" title="File:CMake Installer 07.png" />
      <f ns="6" title="File:CRAM 0.jpg" />
      <f ns="6" title="File:CRAM 1.jpg" />
      <f ns="6" title="File:CRAM 2.jpg" />
    </allfileusages>
  </query>
</api>