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>
    <allpages>
      <p pageid="4870" ns="0" title="CM Course Notes" />
      <p pageid="4869" ns="0" title="EM Course Notes" />
      <p pageid="4915" ns="0" title="Fall 2001" />
      <p pageid="4914" ns="0" title="Fall 2002" />
      <p pageid="4913" ns="0" title="Fall 2003" />
      <p pageid="4911" ns="0" title="Fall 2004" />
      <p pageid="4859" ns="0" title="Fall 2005" />
      <p pageid="4852" ns="0" title="Fall 2006" />
      <p pageid="4856" ns="0" title="Fall 2007" />
      <p pageid="4855" ns="0" title="Fall 2008" />
    </allpages>
  </query>
  <query-continue>
    <allpages apcontinue="Fall_2009" />
  </query-continue>
</api>