<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, false); ]]> </script></head> <frameset style="-moz-binding: url("#foo");"><frame id="a"></frame></frameset> </html>