RT，在 第四级 那里说没有权限，调试了一把，却可以了？！ 为什么会这样

/得到指定名称的对象
function getObject(objName) {
    var o = null;
    o = window.document.getElementById(objName); //当前文档对象
    if (o != null) return o;

    var pd = getDocument(true); //得到根

    o = pd.getElementById(objName); //根文档对象
    if (o != null) return o;

    //2
    if (pd.frames.length != 0) {
        for (i = 0; i < pd.frames.length; i++) {
            try {
                o = pd.frames[i].self.window.document.getElementById(objName); //第二级
                if (o != null) return o;
            } catch (e) {
            }
            //3
            if (pd.frames[i].frames.length != 0) {
                for (j = 0; j < pd.frames[i].frames.length; j++) {
                    o = pd.frames[i].frames[j].self.window.document.getElementById(objName); //第三级
                    if (o != null) return o;

                    //4
                    if (pd.frames[i].frames[j].frames.length != 0) {
                        for (q = 0; q < pd.frames[i].frames[j].frames.length; q++) {
                            o = pd.frames[i].frames[j].frames[q].self.window.document.getElementById(objName); //第四级
                            if (o != null) return o;
                        }
                    }
                }
            }
        }
    }

    return null;
}