You are looking at the HTML representation of the mFormat?> 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>
    <pages>
      <page pageid="1" ns="0" title="Main Page">
        <revisions>
          <rev revid="1" pageid="1" oldid="1" user="MediaWiki default" anon="" timestamp="2005-06-10T20:04:18Z" />
          <rev revid="5" pageid="1" oldid="5" user="Gregory.Szorc" timestamp="2005-06-10T20:29:30Z" />
          <rev revid="31" pageid="1" oldid="31" user="Gregory.Szorc" minor="" timestamp="2005-06-10T21:13:00Z" comment="Added missing link to Wikipedia" />
          <rev revid="46" pageid="1" oldid="46" user="Gregory.Szorc" minor="" timestamp="2005-06-14T20:20:21Z" />
          <rev revid="102" pageid="1" oldid="102" user="Gregory.Szorc" timestamp="2005-06-15T14:57:24Z" />
        </revisions>
      </page>
    </pages>
  </query>
  <query-continue>
    <revisions rvstartid="175" />
  </query-continue>
</api>