Opener has 7-11HCP and no more than 3 controls in a single-suited hand with a 6-card suit somewhere between QT9xxx and AKJXXX, with about 5 or 6 playing tricks.
Within these parameters, opener will be lower range (7-9HCP) or upper range (9-11HCP), and the suit will be treated as either strong (2 of the top 3 honours) or weak
Responder can bid 2NT as a relay; with Spades, he can also use 2S as a relay. Other responses are natural.
Opener rebids over the relay as follows:
Responder can then raise opener's major to 3 ( not forcing), bid game or introduce a new suit, requesting cue bids.