如何使用“界面”构建器中的“对象库”窗口

I've been doing iOS developement for a while but never used or seen someone using the Window object. I tried googling about it but I did not found any relevant articles. I know about 'UIWindow' object and how it can be used from code. So what can be done with the Window object from Interface Builder? When and why whould I choose to use it?I've been doing iOS developement for a while bu