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>
    <alltransclusions gatcontinue="Birth_date|2671" />
  </query-continue>
  <query>
    <pages>
      <page pageid="139" ns="0" title="Howard Zinn" />
      <page pageid="163" ns="0" title="Ivan Illich" />
      <page pageid="165" ns="0" title="Peter Dale Scott" />
      <page pageid="828" ns="0" title="396 - Toward a Moral Economy (Why Preserving the Status Quo is Not An Option)" />
      <page pageid="1688" ns="0" title="John F. Kennedy" />
      <page pageid="1693" ns="0" title="Bill Hicks" />
      <page pageid="1695" ns="0" title="Martin Luther King" />
      <page pageid="2334" ns="0" title="Richard Grossman" />
      <page pageid="2451" ns="0" title="Morris Berman" />
      <page pageid="6418" ns="0" title="651 - Deep Green Resistance (Earth At Risk Conference)" />
    </pages>
  </query>
</api>