请各位高手帮忙呀！！一个另我头痛的问题！

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
var objWin;
function setValue(){
document.Form1.txt1.value= "changed" ;
newoption = new Option("changed","changed");
document.Form1.sel1.add(newoption);
}function openWin(){ objWin = window.open('','');
objWin.document.open();
objWin.document.write ("<body bgcolor=#cccccc></body>");
objWin.document.write ("<input type='button' value='SetValue' onclick='opener.setValue();window.opener=null;window.close()'>");
objWin.document.write ("<input type='button' value='CloseMe' onclick='if(opener.closed){window.opener=null;window.close()}'>");
objWin.document.write ("<input type='button' value='CloseMeAndParent' onclick='window.opener.opener=null;window.opener.close();window.opener=null;window.close()'>");
objWin.document.close;
}
function closesubwin(){
if(objWin.closed == false){
objWin.close();
}
}
//-->
</SCRIPT>
</HEAD><BODY onunload="closesubwin()">
<FORM name="Form1" METHOD=POST ACTION="">
<INPUT TYPE="text" NAME="txt1" value="default">
<INPUT TYPE="button" NAME="abc" onclick="openWin()" value="openWin">
<select name="sel1"></select>
</FORM>
</BODY>
</HTML>