svg element in a xul file

"xiongh" <[email protected]>
Newsgroups gmane.comp.mozilla.devel.xml
Organization http://groups.google.com
Message-ID <[email protected]>
how can I insert a SVG element in a Xul file?

for example: my file.xul it's :

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>

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

xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
	xmlns:svg="http://www.w3.org/2000/svg" >


<button label="add" />
	<svg:svg>
		<svg:ellipse cx="100" cy="100" rx="70" ry="50" style="fill:red"/>

	</svg:svg>


</window>

but i don't visualize anything!!!!
Why?
I must use,xbl?or?
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