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="Biogold_miner.JPG" />
      <page ns="6" title="File:Beaker.png" missing="" />
      <page pageid="2190" ns="6" title="File:Bacterial counts.pdf" />
      <page pageid="2341" ns="6" title="File:Bdelloid rotifersmaller.png" />
      <page pageid="2241" ns="6" title="File:Beach.jpg" />
      <page pageid="2683" ns="6" title="File:Bear.png" />
      <page pageid="2594" ns="6" title="File:Bernard flyer copy.jpg" />
      <page pageid="1965" ns="6" title="File:Bience Kouros Nebuleuse OpenHackuarium57 050815.pdf" />
      <page pageid="2009" ns="6" title="File:Bience at work WEsessions.jpg" />
      <page pageid="2132" ns="6" title="File:BioInk4Colors.JPG" />
      <page pageid="2180" ns="6" title="File:Biofilia1 xs.png" />