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="Dronningborg_Herred-Hjoerring_Amt_(cropped).jpg" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="Fil:Bølling Herred-Ringkøbing Amt syd.jpg" missing="" />
      <page ns="6" title="Fil:Bølling Herred.png" missing="" />
      <page ns="6" title="Fil:Bølling Herreds våben 1584.png" missing="" />
      <page ns="6" title="Fil:Børglum Herred.jpg" missing="" />
      <page ns="6" title="Fil:Børglum Herred Aalborg Amt (cropped).jpg" missing="" />
      <page ns="6" title="Fil:Børglum herreds segl 1584 1648.jpg" missing="" />
      <page ns="6" title="Fil:DjursNoerreHerred1900.jpg" missing="" />
      <page ns="6" title="Fil:DjursNørreHerred.jpg" missing="" />
      <page ns="6" title="Fil:DjursSønderHerred.jpg" missing="" />
      <page ns="6" title="Fil:Djurs SoenderHerred1900.jpg" missing="" />
    </pages>
  </query>
</api>