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="Shutterstock_102071002.jpg|1146" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Capitol Building 4.jpg" />
      <f ns="6" title="File:Disrupted Adoptions.jpg" />
      <f ns="6" title="File:Exhibit S-1 Statistics at a Glance, 2012.jpg" />
      <f ns="6" title="File:Incoming Adoptions By State.jpg" />
      <f ns="6" title="File:Incoming Adoptions by Country of Origin.jpg" />
      <f ns="6" title="File:Outgoing Adoption.jpg" />
      <f ns="6" title="File:Ovulation to Implantation.jpg" />
      <f ns="6" title="File:Shutterstock 100344428.jpg" />
      <f ns="6" title="File:Shutterstock 101701792.jpg" />
      <f ns="6" title="File:Shutterstock 101701792.jpg" />
    </allfileusages>
  </query>
</api>