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="B212.jpg|17594" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1380" ns="0" title="Marilyn Manson discography" />
      <page pageid="6430" ns="0" title="Born Villain (album)" />
      <page pageid="8727" ns="0" title="1996-1997 Antichrist Superstar imagery" />
      <page pageid="8832" ns="0" title="2006-2008 Eat Me, Drink Me imagery" />
      <page pageid="24296" ns="0" title="2014-2016 The Pale Emperor imagery" />
      <page pageid="24420" ns="0" title="Antichrist Superstar merchandise" />
      <page pageid="25219" ns="0" title="2016-2018 Heaven Upside Down imagery" />
    </pages>
  </query>
</api>