新建样式表的问题

<iframe name="iceEditor" id="iceEditor"></iframe>
<SCRIPT LANGUAGE="JavaScript">
document.frames.iceEditor.document.designMode = "On";
alert(document.getElementById("iceEditor").document.styleSheets.length)
document.getElementById("iceEditor").document.createStyleSheet("icebergEditor.css");
alert(document.getElementById("iceEditor").document.styleSheets.length)
</SCRIPT>