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="B2MAN_Fig104.png" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1500" ns="6" title="File:B2BIG.png" />
      <page pageid="1428" ns="6" title="File:B2Delta Tool.png" />
      <page pageid="4602" ns="6" title="File:B2I Tool.png" />
      <page pageid="1875" ns="6" title="File:B2Interval Tool.png" />
      <page pageid="1477" ns="6" title="File:B2Line Tool.png" />
      <page pageid="1767" ns="6" title="File:B2MAN Fig10.png" />
      <page pageid="2028" ns="6" title="File:B2MAN Fig100.png" />
      <page pageid="2029" ns="6" title="File:B2MAN Fig101.png" />
      <page pageid="2030" ns="6" title="File:B2MAN Fig102.png" />
      <page pageid="2031" ns="6" title="File:B2MAN Fig103.png" />
    </pages>
  </query>
</api>