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="B|500" />
  </query-continue>
  <query>
    <pages>
      <page pageid="13" ns="0" title="Gnawing Zombie" />
      <page pageid="89" ns="0" title="Nantuko Shade" />
      <page pageid="94" ns="0" title="Nightwing Shade" />
      <page pageid="186" ns="0" title="Stonefare Crocodile" />
      <page pageid="283" ns="0" title="Evil Twin" />
      <page pageid="294" ns="0" title="Erebos&#039;s Emissary" />
      <page pageid="367" ns="0" title="Stensia Bloodhall" />
      <page pageid="406" ns="0" title="Searchlight Geist" />
      <page pageid="416" ns="0" title="Erebos, God of the Dead" />
      <page pageid="429" ns="0" title="Cavern Lampad" />
    </pages>
  </query>
</api>