<html xmlns="http://www.w3.org/1999/xhtml"><head><script>
<![CDATA[

function boom()
{
  document.execCommand("selectAll", false, null);
  document.execCommand("selectAll", false, null);
  document.execCommand("inserthtml", false, "<span><div>");
  var textarea = document.getElementById("textarea");
  var span = document.createElementNS("http://www.w3.org/1999/xhtml", "span");
  textarea.appendChild(span);
}

]]>
</script></head><div contenteditable="true"></div><body onload="boom();"><textarea id="textarea">f</textarea></body></html>