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>
    <pages>
      <page pageid="1562" ns="6" title="Fil:1120px-Aars Herred Aalborg Amt (cropped).jpg" />
      <page pageid="555" ns="6" title="Fil:Agger Kirke.jpg" />
      <page pageid="1564" ns="6" title="Fil:Andst Herred.png">
        <duplicatefiles>
          <df name="Andst_Herred.png" user="Nico-dk" timestamp="2005-11-09T17:58:23Z" shared="" />
        </duplicatefiles>
      </page>
      <page pageid="1563" ns="6" title="Fil:Anst Herreds segl.jpg">
        <duplicatefiles>
          <df name="Anst_Herreds_segl.jpg" user="Nico-dk" timestamp="2007-04-15T19:36:32Z" shared="" />
        </duplicatefiles>
      </page>
      <page pageid="1561" ns="6" title="Fil:Års Herred.jpg">
        <duplicatefiles>
          <df name="Års_Herred.jpg" user="Nico-dk" timestamp="2005-08-27T23:03:37Z" shared="" />
        </duplicatefiles>
      </page>
      <page pageid="1560" ns="6" title="Fil:Års Herreds segl 1610 1648.jpg" />
    </pages>
  </query>
</api>