A65432    AQ32  KQ2  Q7  KQ543  987  765  98  T9876  KJT6  98  KJT  AJ2  54  AJT43

Dealer: South    Vul: EW   MP Scoring West Pass Pass Pass Pass North 1 3 4 East Pass Pass Pass South 1 1N 3 Pass

Here South paused for thought.
What might further bids show?
With maximum support (3+ spades, a 5 card side suit and 14 HCP), given the limiting 1N bid, if 3 was a slam try, and not just a probe for strain, certainly little remained to think of other than checking for at least 2nd round control of diamonds and possibly suggesting 7.

Unfortunately, it occurred to South that North might have had less than a slam try and was checking for control of hearts.
With such as A6543 2 AQ43 Q43, perhaps North would have used 3 instead of New Minor Forcing (or Kantar Two Clubs or other reasonable facsimile).
If South had held such as  KJ  654  765  AKJ43, playing in 5 might have been superior to declaring 3N down at least 1 on a heart lead.

In the actual hand, South intended 3 to show maximum spade support as well as first round control of hearts.
When North bid 4, South decided that North might have held such as
A6543 2 AQ43 Q43 (and that 3 was asking for a heart stopper) and that a 5-2 spade suit would be superior to a surely failing 3N.

Given the range of possible misunderstanding in this 'uncharted' area, South toyed with the idea of an invitational 5 bid after North's 4 'signoff'.

In retrospect, one set of responses after North's game forcing 3 bid include:
3 shows 4 hearts and 5 clubs and a maximum
3 shows 3 spades, a maximum, and tends to deny the A
3N shows a heart stopper and excludes 3 spades and tends to be minimum.
4 shows 3 spades, a maximum, and includes the A
4 shows 3+ diamonds, denies a heart stopper and denies 3 spades
4 shows 3 spades, a maximum, and tends to include the A and tends to deny the A
4 tends to show either 2 spades and no heart stopper or a 3 spade minimum
5 shows 2 spades, 4 diamonds, 5 clubs, 2 hearts and a maximum
5 denies 3 spades, includes 3 or 4 diamonds, no heart stopper, and is a minimum

Suggested Auction

West Pass Pass Pass Pass North 1 3 6 East Pass Pass Pass South 1 1N 3 Pass

Pinpoint World Class Matchpoint Auction after switching Q for K in hand diagram North  - - - 1: 4+ spades 3: 3+ diamonds, game force  4: slam try cuebid 4N: remaining keycards?  5: jack cuebid request 5N: jack cuebid request2 7: matchpoint-itis South 1: 3+ clubs, 10+ HCP 1N: 11-14, no shortness 4: 3+ spades + A 4: A 5: 1 keycard without Q 5: J 6: J Pass How do you justify moving from 1430 Keycard to the ambiguity of remaining keycard asking as in this suggested auction? How do you develop such specific rules as in 'forcing auctions'? How many of your partners would you have to notify?