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="Check_mark_23x20_04.svg" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:Blue question mark (italic).svg" missing="" />
      <page ns="6" title="File:Bouncing Snowball.png" missing="" />
      <page ns="6" title="File:Bulbgraph.svg" missing="" />
      <page ns="6" title="File:Cancelled cross.svg" missing="" />
      <page ns="6" title="File:Cancelled process mini.svg" missing="" />
      <page ns="6" title="File:Check mark.svg" missing="" />
      <page ns="6" title="File:Check mark 23x20 02.svg" missing="" />
      <page pageid="1376" ns="6" title="File:Buggered graph.png" />
      <page pageid="1332" ns="6" title="File:Cacti favicon.ico" />
      <page pageid="1331" ns="6" title="File:Cacti favicon demo.png" />
    </pages>
  </query>
</api>