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>
    <pages>
      <page pageid="3" ns="0" title="Star Trek: The Next Generation - Birth of the Federation" />
      <page pageid="13" ns="0" title="Radio Pulsar" />
      <page pageid="14" ns="0" title="X-ray Pulsar" />
      <page pageid="29" ns="0" title="Large Map Generation Chart and tutorial for UE" />
    </pages>
  </query>
</api>