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="Babesia-canis-dog.jpg" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="Bestand:BSC Canine1.svg" />
      <f ns="6" title="Bestand:BSC Canine3.svg" />
      <f ns="6" title="Bestand:BSC Canine5.svg" />
      <f ns="6" title="Bestand:BSC Canine7.svg" />
      <f ns="6" title="Bestand:BSC Canine9.svg" />
      <f ns="6" title="Bestand:BSC Feline1.svg" />
      <f ns="6" title="Bestand:BSC Feline3.svg" />
      <f ns="6" title="Bestand:BSC Feline5.svg" />
      <f ns="6" title="Bestand:BSC Feline7.svg" />
      <f ns="6" title="Bestand:BSC Feline9.svg" />
    </allfileusages>
  </query>
</api>