The description of the Rabbit 4000 cbm instruction states calls (de) "address of I/O register" and states "only (de) is affected by ioi or ioe".
What happens if neither ioi or ioe is used? What will (de) refer to? Internal I/O? External I/O? Memory?
If the latter, will the instruction work normally for (de) == (hl)?
If yes, it could be very useful for setting or resetting bits in memory, in particular for implementing bitfields.