Identifying the window under the pointer

Hi all

Does anybody have any idea how to identify which window is at a specific point on the screen? I basically want something like WhichWorkbenchWindow() but for my own windows.

I thought about using layers.library - WhichLayer() looks like a step in the right direction - but how do I find out which layer is associated with which window?

Thanks

layer->Window

Thanks, how embarassing, should have checked the structure.