I'm thinking about making a doubly-linked list class its own SubSequence.
If I do RangeReplaceableCollection code on a SubSequence that changes one or both endpoints, how can that cascade to other SubSequences that share that data? Or equivalently, what happens if I change endpoint(s) from the primary instance (i.e. the collection that the sub-sequences are subbing)? Or can I assume that sub-sequences are totally temporary and let them crash-and-burn, since I shouldn't have multiple sub-sequences on a data block active at once?