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="IK_MT375.png" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="Bestand:Hubbert peak oil plot.svg" missing="" />
      <page pageid="4078" ns="6" title="Bestand:Belgium icon.png" />
      <page pageid="4017" ns="6" title="Bestand:Centrosolar.png" />
      <page pageid="4082" ns="6" title="Bestand:Checkmark 12x12.png" />
      <page pageid="10" ns="6" title="Bestand:DeWiki-Logo.jpg" />
      <page pageid="113" ns="6" title="Bestand:Delta Solivia 3.3.jpg" />
      <page pageid="109" ns="6" title="Bestand:Eenfase-vs-driefase-invoeding.png" />
      <page pageid="101" ns="6" title="Bestand:Enercon E-126 CC-attribute JakoJellema@Flickr.jpg" />
      <page pageid="85" ns="6" title="Bestand:Ferraris meter dubbel tarief.jpg" />
      <page pageid="4089" ns="6" title="Bestand:Germany icon.png" />
    </pages>
  </query>
</api>