So as I understand it an example might be that you have a map with two sheets and many layers one of which is a mountain layer.

You have mountain 'a' on sheet 1 and a mountain 'b' on sheet 2 (which is above sheet 1), but both mountains can be assigned to a single mountain layer.

By selecting the mountain layer you can edit all the mountains regardless of what sheet they are on. By selecting sheet 1 you can edit mountain 'a' only and by selecting sheet 2 you can edit mountain 'b' only... is that right?