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="Caja.png" />
  </query-continue>
  <query>
    <pages>
      <page pageid="9546" ns="6" title="File:BABS UNSW Australia nswgov.jpg" />
      <page pageid="65335" ns="6" title="File:BBK.pdf" />
      <page pageid="11561" ns="6" title="File:BCAStandard2UCLAiGEM2015.png" />
      <page pageid="66949" ns="6" title="File:Baskus and Walsh.png" />
      <page pageid="64269" ns="6" title="File:Beto.png" />
      <page pageid="41429" ns="6" title="File:Bradford calculation iGEM Goettingen 2015.jpeg" />
      <page pageid="14177" ns="6" title="File:BsaIDig0811.jpg" />
      <page pageid="14175" ns="6" title="File:BsaIDig0812.jpg" />
      <page pageid="54337" ns="6" title="File:CTC in literatrue.png" />
      <page pageid="14671" ns="6" title="File:CWagner.jpg" />
    </pages>
  </query>
</api>