Selection.AddToContainers Method (Visio)
Adds the selection of shapes to all underlying containers that allow it as a member.
expression A variable that represents a Selection object.
When you call the AddToContainers method, Microsoft Visio uses the setting of the ContainerProperties.ResizeAsNeeded property for each container to determine how the container resizes.
Each shape in the selection is added to its underlying containers according to the position of the shape. As a result, different shapes may end up being contained by different containers. If the underlying container is a list, the shape is added as normal container member, not list member.
The AddToContainers method works only if the selection sits at least partially on top of a container that does not already contain it.