Proper shared objects

Hi.

Omnigraffle is one instrument on my Mac I love most. Nevertheless, there is few things I can't figure out. I will be very grateful for any help.

Suppose you have two canvases with mockups of web pages on them. Suppose, you have same block on them, that represents header of web page (logo, menu, etc). Seems like job for shared layers, eh? 

Now, suppose, that you have footer as well. And length of this two pages is different. Is there any way to use same footer on both canvases, but with different positioning?

In fact, question is a little bit wider: is there any way to have something like stencil library of building blocks, or "includes". Some way to define "block: list-with-suggest" and use it in different canvases. But not like stencil library — when I change block definition, it should change everywhere (like with shared layers).

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Sergey Petrov