I can't seem to find any API support for adding a CNGroup to another CNGroup, although this iOS13 CNChangeHistoryAddSubgroupToGroupEvent class strongly implies it can be done. I have found UX in the macOS contacts app to do this, but iOS and iPadOS don't really seem to reflect it, so it may not actually be something Apple has thought through.
Does any API to do this exist? (I may well have just missed it!)
After creating nested groups I can't seem to find anyway to determine that say group A contains group B, or given group B that it is contained by group A. Does any API exist to do this? I'm hoping I just missed it.