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="249" ns="0" title="Main Page" />
      <page pageid="250" ns="0" title="2015 New Site Features" />
      <page pageid="252" ns="0" title="Add-on List and Instructions for Use" />
      <page pageid="265" ns="0" title="Developer Public Addons" />
      <page pageid="308" ns="0" title="Contensive SMS Architectural Overview" />
      <page pageid="315" ns="0" title="Supplier Directory" />
      <page pageid="323" ns="0" title="Email Bounce Processing" />
    </pages>
  </query>
</api>