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="BR81_inwendig.JPG|836" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="504" ns="6" title="Bestand:BR151 Gewijzigd.JPG" />
      <f fromid="343" ns="6" title="Bestand:BR200 Drukkap Speaker.JPG" />
      <f fromid="304" ns="6" title="Bestand:BR64 Rookgenerator.JPG" />
      <f fromid="304" ns="6" title="Bestand:BR64 Stroomafnemers voor achterloopas.JPG" />
      <f fromid="304" ns="6" title="Bestand:BR64 stroomafname.JPG" />
      <f fromid="304" ns="6" title="Bestand:BR64 stroomafname 2.JPG" />
      <f fromid="836" ns="6" title="Bestand:BR81.JPG" />
      <f fromid="836" ns="6" title="Bestand:BR81 LED-verlichting.jpg" />
      <f fromid="836" ns="6" title="Bestand:BR81 aangepast.jpg" />
      <f fromid="836" ns="6" title="Bestand:BR81 gestript.jpg" />
    </allfileusages>
  </query>
</api>