OK465 you are actually incorrect, the format given is indeed supported for speed when entering a B, however not when entering A. Using a hard speed in FMC will result in attempt to achieve actual speed, thus a DRAG REQUIRED can be a direct result if leaving 210/ at a waypoint on 5nm from RWxx
Turkish Delight was correct in his example as the statement provided 220B/12000A is factually correctly used during a descent profile: crossing waypoint XXXXX at KIAS 220 or less and above 12000'.
The NG box always treats a waypoint speed as at or below. The obvious example being a waypoint coded for 250 below 10,000. The NG FMS will cross this waypoint at 240 unless you go in and change the descent default.
What you are quoting here is the VNAV PTH speed restriction which is always obeyed when used. Thus if high on profile the path will be "lost" in favour of maintaining a speed restriction below the altitude with deviation of -15kts/+10kts to the target speed. Hence the default of 240/100 as this commands "no more" than KIAS 250 below FL100. Thus VNAV PTH will maintain KIAS 250 until the path is regained from above. Simultaneously it displays the message UNABLE NEXT ALTITUDE when it calculates that (even with 250kts) the commanded target altitude cannot be achieved at the next hard altitude of a waypoint, so crews need to do act and do something like using speed brake, flaps or landing gear, which results in VNAV PTH recalculating the possibility of reaching the waypoint at the desired altitude, prompting further if unable to comply.