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="Dronningborg_Herred-Hjoerring_Amt_(cropped).jpg|375" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="1242" ns="6" title="Fil:Bølling Herred-Ringkøbing Amt syd.jpg" />
      <f fromid="1242" ns="6" title="Fil:Bølling Herred.png" />
      <f fromid="1242" ns="6" title="Fil:Bølling Herreds våben 1584.png" />
      <f fromid="376" ns="6" title="Fil:Børglum Herred.jpg" />
      <f fromid="376" ns="6" title="Fil:Børglum Herred Aalborg Amt (cropped).jpg" />
      <f fromid="376" ns="6" title="Fil:Børglum herreds segl 1584 1648.jpg" />
      <f fromid="836" ns="6" title="Fil:DjursNoerreHerred1900.jpg" />
      <f fromid="836" ns="6" title="Fil:DjursNørreHerred.jpg" />
      <f fromid="858" ns="6" title="Fil:DjursSønderHerred.jpg" />
      <f fromid="858" ns="6" title="Fil:Djurs SoenderHerred1900.jpg" />
    </allfileusages>
  </query>
</api>