AFAIR

After partner opens a strong notrump, responder bids as follows:

2C -> Stayman
2D -> 2H
2H -> 2S
2S -> 5-5 or better in two TOUCHING suits (includes S&C)
2NT -> weak takeout in a minor or 5-5 or better in two NON-TOUCHING
suits or a raise to 3NT with two small doubletons in the majors.

To make an invitational raise that would previously be used by bidding 2NT directly, then Stayman must be bid first, then rebid 2NT.

Over 2NT, opener must rebid 3C. Responder may apss passed with weak Clubs, corrected to 3D with weak Diamonds, bids the major for a non-touching 2 suited hand (C&H or D&S), and bid 3NT to show the raise to 3NT with small doubletons in the majors.

Over 2S, opener must rebid 2NT, and responder would bid the lower of the two touching suits, 3S showing S and C.

You take your choice as to the strength of the 2S and 2NT bids, whether invitational or game forcing.

Source:Brian Meadows