https://www.scirra.com/manual/150/containers
What containers do
Placing objects in a container has the following effects:
1.If one object in a container is created, every other object in its container is also automatically created.
2.If one object in a container is destroyed, every other associated object in its container is also destroyed.
3.If a condition picks one object in a container, every other associated object in its container is also picked.