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="Book_link|668" />
  </query-continue>
  <query>
    <pages>
      <page pageid="32" ns="10" title="Template:Dead link" />
      <page pageid="405" ns="10" title="Template:Book link" />
      <page pageid="455" ns="0" title="Mano Singham" />
      <page pageid="419" ns="10" title="Template:Book link/doc" />
      <page pageid="490" ns="0" title="Daniel Dennett" />
      <page pageid="460" ns="0" title="Richard Dawkins" />
      <page pageid="489" ns="0" title="Christopher Hitchens" />
      <page pageid="33" ns="10" title="Template:Fix" />
      <page pageid="10" ns="0" title="American Atheists" />
      <page pageid="423" ns="0" title="Wiki template" />
    </pages>
  </query>
</api>