You are looking at the HTML representation of the XML format.
HTML is good for debugging, but probably is not suitable for your application.
Please see "format" parameter documentation at the API help for more information.
<?xml version="1.0" encoding="utf-8"?>
<api>
  <query>
    <general mainpage="Welcome" base="http://www.birdforum.net/opus/Welcome" sitename="Opus" generator="MediaWiki 1.9.3" case="first-letter" rights="" />
  </query>
</api>