Parity what?

Parity Key Card Blackwood. Yes, yet another variation of old Blackwood.

"Parity" refers even/odd number of key-cards. Regular RKC uses an either/or variation also of course, but with a discrepancy of 3 (0/3 & 1/4). By reducing this to 2, valuable space is preserved and the need for the 1430-switch is eliminated.

This may lead to problems distinguishing which number to expect. That's why it isn't used all the time, only in cue-bidding situations where ambition, captaincy etc reveals what to expect.

PKC (Parity Key Card) applies when both players have made at least one cuebid (splinter-jumps are by definition not a "cuebid"). Non-serious 3NT (or serious if that's the prefered version) is regarded as a cuebid. Whether non-jump shortness-showing bids should be regarded as a cuebid or not are a matter of partnership definition (I think not). When a minor suit is trumps then 4m (setting trumps or “waiting”) followed by 4NT over cue is also PKC.

Responses:
1step = 0/2/4
2steps = 1/3 no Q (unless ¨ is trumps; then could have Q with 1)
3steps = 1/3 + Q.
Step 4 shows unexpected “max” reply otherwise coinciding with trump suit (don’t want to risk pass from asker).
Continuations as after regular RKCB.

The parity concept has been used in variations of denial-cuebidding within a relay-framework bidding system. This variant is an original idea, I believe. Remember where you saw it first!