In a game-forcing auction, when (a) a minor-suit has already been agreed or (b) the suit-agreement bid is a jump, a bid of four of this agreed minor suit is asking about key cards, just like RKC Blackwood.
Continuations after partner's response:
|cheapest bid that's not trumps||Asking about the trump queen if it hasn't already been shown. There is no king-asking equivalent of the Blackwood 5NT and the partnership will have to cue-bid instead.|
If a 4m bid agrees that minor and so isn't Minorwood (which would have needed suit agreement before that bid), then a continuation of the cheapest next bid takes that meaning instead.
4m isn't Minorwood in any of the following situations:
(a) the minor hadn't ALREADY been agreed, unless the 4m bid is a jump.
(b) it's not a game-forcing situation, e.g. the partnership's pre-empting or being pushed up in a competitive auction, or after 1m 3m (Inverted) game try. Raising partner's minor-suit pre-empt to 4m is also merely competitive.
(c) the 4m bidder opened the bidding with a strong balanced opening call (e.g. 1NT, 2D, 2NT) and Blackwood hasn't yet been unlocked, e.g. with a splinter, by implication asking partner to consider slam if they don't have wasted values in the suit. It's a fundamental principle of bidding that after such an immediately informative opening, it's normally responder who asks all the questions because they have much more information about the partnership's combined holding.