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>
    <abusefilters abfstartid="11" />
  </query-continue>
  <query>
    <abusefilters>
      <filter id="1" description="Large spam pages" />
      <filter id="2" description="Large deletion of articles by new users" />
      <filter id="3" description="Gibber edit summary" />
      <filter id="4" description="Section replacing with URL" />
      <filter id="5" description="Section removal" />
      <filter id="6" description="Too many foreign letters or repeat symbols" />
      <filter id="7" description="Adding too many links in a new page" />
      <filter id="8" description="Spam accounts" />
      <filter id="9" description="Bot URL (url)" />
      <filter id="10" description="disallow certain words in mainspace articles" />
    </abusefilters>
  </query>
</api>