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"?>
    <allfileusages gafcontinue="BasicOptions.png" />
      <page ns="6" title="File:BSsWorking.png" missing="" />
      <page pageid="3250" ns="6" title="File:B.JPG" />
      <page pageid="1938" ns="6" title="File:BB nano.jpg" />
      <page pageid="2063" ns="6" title="File:BCF2000 top.jpg" />
      <page pageid="3619" ns="6" title="File:Back.jpg" />
      <page pageid="1987" ns="6" title="File:Badidea.gif" />
      <page pageid="3512" ns="6" title="File:Bare conductive.jpg" />
      <page pageid="2597" ns="6" title="File:Bars base 250b.jpg" />
      <page pageid="2598" ns="6" title="File:Bars welding 250b.jpg" />
      <page pageid="2246" ns="6" title="File:Basic.png" />