<html xmlns="http://www.w3.org/1999/xhtml"><head>
<bindings xmlns="http://www.mozilla.org/xbl"><binding id="foo"><content><optgroup><span><children xmlns="http://www.mozilla.org/xbl"/></span></optgroup></content></binding></bindings>
<script>
<![CDATA[
function boom() { document.getElementById("a").appendChild(document.createElementNS("http://www.w3.org/1999/xhtml", "span")); }
window.addEventListener("load", boom);
]]>
</script></head>
<frameset style="-moz-binding: url("#foo");"><frame id="a"></frame></frameset>
</html>