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="Bong.jpeg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1339" ns="6" title="File:BCbud.jpg" />
      <page pageid="879" ns="6" title="File:Balaclavaed dea agent.JPG" />
      <page pageid="853" ns="6" title="File:Balls and sticks of Charas.jpg" />
      <page pageid="1538" ns="6" title="File:Barry McCaffrey.jpg" />
      <page pageid="1274" ns="6" title="File:Bill clinton - Weed Depot.jpeg" />
      <page pageid="940" ns="6" title="File:Birmingham peace rally.jpg" />
      <page pageid="1368" ns="6" title="File:Bluedream.jpg" />
      <page pageid="1248" ns="6" title="File:Bob marley - Weed Depot.jpg" />
      <page pageid="1534" ns="6" title="File:Bobmartinez.jpg" />
      <page pageid="443" ns="6" title="File:Bogart.png" />
    </pages>
  </query>
</api>