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 gafcontinue="BR81_inwendig.JPG" />
  </query-continue>
  <query>
    <pages>
      <page pageid="514" ns="6" title="Bestand:BR151 Gewijzigd.JPG" />
      <page pageid="378" ns="6" title="Bestand:BR200 Drukkap Speaker.JPG" />
      <page pageid="320" ns="6" title="Bestand:BR64 Rookgenerator.JPG" />
      <page pageid="321" ns="6" title="Bestand:BR64 Stroomafnemers voor achterloopas.JPG" />
      <page pageid="313" ns="6" title="Bestand:BR64 stroomafname.JPG" />
      <page pageid="315" ns="6" title="Bestand:BR64 stroomafname 2.JPG" />
      <page pageid="837" ns="6" title="Bestand:BR81.JPG" />
      <page pageid="852" ns="6" title="Bestand:BR81 LED-verlichting.jpg" />
      <page pageid="853" ns="6" title="Bestand:BR81 aangepast.jpg" />
      <page pageid="851" ns="6" title="Bestand:BR81 gestript.jpg" />
    </pages>
  </query>
</api>