Ukramedia shows how to make a responsive mask in Ae that can adjust around elements on a layer.
Check out this new tutorial from Ukramedia that shows how to set up a smart mask with After Effects and some expressions. Sergei Prokhnevskiy shows how to create these smart masks, a system that can help with a lot of animation and effects in Ae.
More on Smart Elements and Expressions.
Responsive or “smart” boundaries are a popular topic for After Effects users.
You can easily make a responsive behavior in After Effects. Check out this tutorial from VinhSon Nguyen (Creative Dojo) that shows how to make such a system as a preset in After Effects.
Also, look at the free Danim Box and Danim Creator and see how you can create better templates in After Effects. Get Danim Box here for free.
Another tool from Arne Breusing lets users span rectangles in Adobe After Effects between two controller layers. The script allows a simple and easy workflow for building dynamic and flexible layouts with a few clicks.