createPopup()的小疑问

[guohao0827]

var _oPopup = window.createPopup();
var _oSubPopup = _oPopup.document.parentWindow.createPopup();

第一个好理解

第二个是什么意思？js高手能详细解释一下不？

还有
var oS = _oPopup.document.createStyleSheet();
oS.addRule("body","font-family: 宋体;font-size: 9pt;margin:0px;border: 0px;background-color: #EFEFEB;cursor: default;");
oS.addRule("table","cursor: default;");
oS.addRule("td","font-size: 12px;");
oS.addRule("table.mnuList","border: #00377a 1px solid;display: none;filter: progid:DXImageTransform.Microsoft.Gradient(GradientType=1, StartColorStr=#efefeb, EndColorStr=#ffffff);");
oS.addRule("col.mnuLeft","width: 27px;text-align: center;background-color :#889DC2;");
oS.addRule("col.mnuItm ","padding-top: 5px;padding-left: 10px;");
oS.addRule("tr.mnuSpacer","padding: 0px;font-size: 1px;");
oS.addRule("hr.mnuSpacer","height: 1px;margin-left: 10px;");

oS = _oSubPopup.document.createStyleSheet();
oS.addRule("body","font-family: 宋体;font-size: 9pt;margin:0px;border: 0px;background-color: #EFEFEB;cursor: default;");
oS.addRule("table","cursor: default;");
oS.addRule("td","font-size: 12px;");
oS.addRule("table.mnuList","border: #00377a 1px solid;display: none;filter: progid:DXImageTransform.Microsoft.Gradient(GradientType=1, StartColorStr=#efefeb, EndColorStr=#ffffff);");
oS.addRule("col.mnuLeft","width: 27px;text-align: center;background-color :#889DC2;");
oS.addRule("col.mnuItm ","padding-top: 5px;padding-left: 10px;");
oS.addRule("tr.mnuSpacer","padding: 0px;font-size: 1px;");
oS.addRule("hr.mnuSpacer","height: 1px;margin-left: 10px;");
这个用法比较少见，是什么意思？我看微软CRM里面这样写的。

[hookee]

var _oPopup = window.createPopup();
_oPopup.document.parentWindow就是获得popup的窗口
var _oSubPopup = _oPopup.document.parentWindow.createPopup(); 就是在popup中再popup一个窗口

addRule 是动态添加式样表，
静态的的是用<style>.xxxx{}</style> 其中的.xxx{}就是Rule