"Separate" containers

[SPP SciO]

"The specific design and material of the sides and base can vary greatly depending on the container's purpose" - I think this grants broad leeway. For example, a bag is a container, and it doesn't have walls. At a recent invitational, I only discredited two "containers" - one was a flat tray with magnets underneath (if it had a lip I probably would have counted it, but there were no discernible "sides") and another was a PVC ring that had no base.