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"?>
    <alltransclusions gatcontinue="Blue_1|158" />
      <page pageid="16" ns="0" title="Air Elemental and Storm Elemental" />
      <page pageid="42" ns="0" title="Angel and Archangel" />
      <page pageid="51" ns="0" title="Archer and Marksman" />
      <page pageid="81" ns="0" title="Azure Dragon" />
      <page pageid="90" ns="0" title="Basilisk and Greater Basilisk" />
      <page pageid="99" ns="0" title="Behemoth and Ancient Behemoth" />
      <page pageid="101" ns="0" title="Beholder and Evil Eye" />
      <page pageid="108" ns="0" title="Black Knight and Dread Knight" />
      <page pageid="118" ns="0" title="Boar" />
      <page pageid="121" ns="0" title="Bone Dragon and Ghost Dragon" />