[[Common interface for objects (containers) that can have multiple contents (sub-objects).
APIs in this interface deal with containers of multiple sub-objects, not
with individual parts.
[[Begin iterating over this object's contents.]]
return: iterator<Efl.Gfx.Entity> @owned @warn_unused; [[Iterator on object's content.]]
[[Returns the number of contained sub-objects.]]
return: int; [[Number of sub-objects.]]
content,added: Efl.Gfx.Entity; [[Sent after a new sub-object was added.]]
content,removed: Efl.Gfx.Entity; [[Sent after a sub-object was removed, before unref.]]