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HTML is good for debugging, but probably is not suitable for your application.
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<?xml version="1.0"?>
<api>
  <query>
    <pages>
      <page pageid="1" ns="0" title="Main Page">
        <revisions>
          <rev user="MediaWiki default" anon="" timestamp="2011-12-16T17:21:28Z" comment="" />
        </revisions>
      </page>
    </pages>
  </query>
</api>