Playing transfers and Stayman, 3S: is sometimes idle after a 2NT opening. Some Puppet Stayman types prefer it to be reverse Flannery, that is 5S:+4H:, as this shape is hard to show using Puppet. Most seem to use it as a puppet to 3NT with rebids thus:
4C: = single suiter in clubs
4D: = single suiter in diamonds
4H: = both minors, short hearts
4S: = both minors, short spades
4NT = 2254 or 2245 slam try values
5C: = both minors, no slam interest
Some prefer to reverse the meanings of 4C: and 4D: so that opener is always playing the hand.

How strong one plays this bid also varies. Some play that it shows a minimum of a slam try; others prefer it can be a choice of games. In either case, opener's 4NT rebid is nonforcing. If you use the 5C: bid, which most do not, then all the other two-suited bids show slam interest. I recommend this method.

Some non-standard, but interesting extra later bids I play in some partnerships:

2NT-3S:; 3NT-4M; 5m-next step = key card
2NT-3S:; 3NT-4M; other-5M = RKCB in the corresponding minor
2NT-3S:; 3NT-5m = key card in that minor. Then 6m+1 = specific kings
2NT-3S:; 3NT-4m; next step = key card

Many play this convention in conjunction with a non-standard 3NT response. It is highly recommended that one does not do this. 2NT-3NT will frequently get passed regardless of one's agreements about its forcing status. I know lots of partnerships who gave this up after the third catastrophe.

Jeff Goldsmith, jeff@gg.caltech.edu, August 3rd, 2002