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

<style type="text/css">
mover { font-size: 326590449211mm; }
</style>

<script type="text/javascript">

function boom()
{
  document.getElementById("r").setAttribute("accentunder", "4");
}

</script>
</head>

<body onload="boom();">

<mover xmlns="http://www.w3.org/1998/Math/MathML" id="mover"><munderover id="r"><merror/><msqrt/></munderover></mover>

</body>
</html>