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="B.B.T.Br.Panc._V2_Drawing.jpg|104103" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:B-17G Nose in Detail.jpg" />
      <f ns="6" title="File:B-17G formation on bomb run.jpg" />
      <f ns="6" title="File:B-17 Damage Cologne.jpg" />
      <f ns="6" title="File:B-17 at Mighty 8th Air Force Museum, Pooler, GA, US.jpg" />
      <f ns="6" title="File:B-17 on bomb run.jpg" />
      <f ns="6" title="File:B-17dorsalview.jpg" />
      <f ns="6" title="File:B-38 cannon for MK-5.jpg" />
      <f ns="6" title="File:B.B.T.Br.Panc-003.jpg" />
      <f ns="6" title="File:B.B.T.Br.Panc. V1 Document.png" />
      <f ns="6" title="File:B.B.T.Br.Panc. V2 Document.jpg" />
    </allfileusages>
  </query>
</api>