javascript如何获得flash引用的swf地址

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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>

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<body>
<OBJECT id="fl" title=dg codeBase=http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,28,0 height=460 width=622
classid=clsid:d27cdb6e-ae6d-11cf-96b8-444553540000>
<PARAM NAME="_cx" VALUE="847">
<PARAM NAME="_cy" VALUE="847">
<PARAM NAME="FlashVars" VALUE="">
<PARAM NAME="Movie" VALUE="http://upload.china228.com/flash/11d2.swf">
<PARAM NAME="Src" VALUE="http://upload.china228.com/flash/11d2.swf">
<PARAM NAME="WMode" VALUE="Window">
<PARAM NAME="Play" VALUE="-1">
<PARAM NAME="Loop" VALUE="-1">
<PARAM NAME="Quality" VALUE="High">
<PARAM NAME="SAlign" VALUE="">
<PARAM NAME="Menu" VALUE="-1">
<PARAM NAME="Base" VALUE="">
<PARAM NAME="AllowScriptAccess" VALUE="">
<PARAM NAME="Scale" VALUE="ShowAll">
<PARAM NAME="DeviceFont" VALUE="0">
<PARAM NAME="EmbedMovie" VALUE="0">
<PARAM NAME="BGColor" VALUE="">
<PARAM NAME="SWRemote" VALUE="">
<PARAM NAME="MovieData" VALUE="">
<PARAM NAME="SeamlessTabbing" VALUE="1">
<PARAM NAME="Profile" VALUE="0">
<PARAM NAME="ProfileAddress" VALUE="">
<PARAM NAME="ProfilePort" VALUE="0">
<PARAM NAME="AllowNetworking" VALUE="all">
<PARAM NAME="AllowFullScreen" VALUE="false">
</OBJECT>
<button onclick="javascript:alert(document.getElementById('fl').Movie);">查看flash地址</button>
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