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="Bong.jpeg|68" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="1338" ns="6" title="File:BCbud.jpg" />
      <f fromid="878" ns="6" title="File:Balaclavaed dea agent.JPG" />
      <f fromid="849" ns="6" title="File:Balls and sticks of Charas.jpg" />
      <f fromid="1531" ns="6" title="File:Barry McCaffrey.jpg" />
      <f fromid="901" ns="6" title="File:Bill clinton - Weed Depot.jpeg" />
      <f fromid="941" ns="6" title="File:Birmingham peace rally.jpg" />
      <f fromid="1369" ns="6" title="File:Bluedream.jpg" />
      <f fromid="538" ns="6" title="File:Bob marley - Weed Depot.jpg" />
      <f fromid="1531" ns="6" title="File:Bobmartinez.jpg" />
      <f fromid="132" ns="6" title="File:Bogart.png" />
    </allfileusages>
  </query>
</api>