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

<head>

<bindings xmlns="http://www.mozilla.org/xbl" xmlns:html="http://www.w3.org/1999/xhtml">
  <binding id="foo">
    <content><html:span>a b<children xmlns="http://www.mozilla.org/xbl"/></html:span></content>
  </binding>
</bindings>

<script type="text/javascript">

function boom()
{
  var cap = document.getElementById("cap"); 
  var lsep = document.createTextNode("\u2028"); // U+2028 LINE SEPARATOR
  cap.insertBefore(lsep, cap.firstChild);
}

</script>

</head>

<body onload="boom();"><caption id="cap" style="-moz-binding: url('#foo');"> </caption></body>

</html>