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="Csit-system-design-hierarchy.png|558" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Benchmarking-sw-data-planes-Dec5 2017.pdf" />
      <f ns="6" title="File:Building in Containers PoC.pdf" />
      <f ns="6" title="File:CSIT status.PNG" />
      <f ns="6" title="File:Capture LandC.PNG" />
      <f ns="6" title="File:Chinac&#039;s Experience of VPP in OpenStack.pptx" />
      <f ns="6" title="File:Cisco Live VPP and container networking (BRKSDN-2119).pptx" />
      <f ns="6" title="File:Clear Containers+VPP-overview-JuneDevLab.pdf" />
      <f ns="6" title="File:Code.png" />
      <f ns="6" title="File:Connecting two vpp instances with memif.png" />
      <f ns="6" title="File:Create Interface Topology.jpg" />
    </allfileusages>
  </query>
</api>