<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script>
function boom()
{
  document.getElementById("mo").appendChild(document.getElementById("mo2"));
  document.body.offsetWidth;
  document.getElementById("span").appendChild(document.createTextNode("baz"));
}
</script>
</head>

<body onload="boom();">

<p>Foo <math xmlns="http://www.w3.org/1998/Math/MathML"><mo id="mo2">-</mo></math></p>

<p><math xmlns="http://www.w3.org/1998/Math/MathML"><msub id="msub"><mo id="mo">+</mo></msub></math> <span id="span">bar</span></p>

</body>
</html>