My mistake. I knew you were big-time on volumes, but I thought containers/partitions entered into your scheme too.
Containers, Volume Groups, and Volumes are all part of APFS's hierarchy of virtual structures and are free to expand or shrink to fill the immediate data storage needs. None of them are anchored to a specific physical location on the drive and by default each of them has access to the entire capacity of the drive (or partition) they are mounted on, unless they are specifically created with limits.
If we knew what it was we were doing, it wouldn't be called research, would it?
