模式窗口问题: 如何打开另一个模式窗口, 从模式窗口打开另一模式窗口, 返回值时返回到原来的窗口.

index.htm
-------------------------------------
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=gb2312">
<SCRIPT language="javascript">
function hello()
{
    alert("hello world!");
}
</SCRIPT>
</HEAD><BODY>
<A href="#" onClick="showModalDialog('a.htm',window)">open</A>
</BODY>
</HTML>a.htm
------------------------------------------------------------
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=gb2312">
<TITLE>无标题文档</TITLE>
</HEAD><BODY>
<A href="#" onClick="showModalDialog('b.htm',window)">open</A>
</BODY>
</HTML>
b.htm
------------------------------------------------------
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=gb2312">
<SCRIPT language="javascript">
function test()
{
    var parentWin = dialogArguments;
var grandParentWin  = dialogArguments.dialogArguments;
self.close();
parentWin.close();
grandParentWin.hello();
}
</SCRIPT>
</HEAD><BODY>
<A href="#" onClick="test()">close</A>
</BODY>
</HTML>