<html xmlns="http://www.w3.org/1999/xhtml" xmlns:math="http://www.w3.org/1998/Math/MathML">
<head>
<script>
function boom()
{
var ms = document.createElementNS("http://www.w3.org/1998/Math/MathML", "ms");
var textNode = document.getElementById("emptyset").firstChild;
var mrow = document.getElementById("mrow");
ms.appendChild(textNode); // *move* the text node from one place to another!
mrow.appendChild(ms);
}
</script>
</head>
<body onload="boom();">
<math xmlns="http://www.w3.org/1998/Math/MathML">
<merror><emptyset id="emptyset">
<mrow id="mrow"></mrow></emptyset></merror>
</math>
</body>
</html>