key into a larger object that you have not closed yet, the smaller object is subtracted from the larger one, thus appearing as a hole in the larger one.
键的同时，在一个尚未封闭的较大对象中绘制了一个较小的对象，则会从较大对象中减去较小对象，这样看上去就像是较大对象中出现一个洞一样。