Testing nested forms markup. Note that this document is valid XHTML 1.1, except that it's sent as "text/html" (not "application/xhtml+xml"). It is therefore parsed/rendered as HTML in browsers, not as XHTML, with all kinds of consequences.

  <form action="http://example.com/1">
    <div>
      1
      <form action="http://example.com/2">
        <div>
          2
        </div>
      </form>
    </div>
  </form>