Used in various point count range such as 11-15 HCP
2 (Mini Roman) shows 4,4,4,1 or 5,4,4,0 distribution .
Responder can pass with long diamonds or bid 2 with a weak hand and opener will pass unless it is his singleton. If you play that Mini Roman guarantees 4 spades a weak responder with a fit can bid 2.
If responder wants to know opener's shortness he bids 2NT.
Some play that Mini Roman guarantees 4 spades with any point count while others guarantee 4 spades unless they have 13-15 HCP
Others do not guarantee spades.Everything is up to partnership agreement.
Mini/Maxi combination
Some like to play Mini Roman/Maxi Roman combination bid. The Maxi Roman point count is also partnership agreement but we have been experimenting with 20 or more HCP in conjunction with Mini Roman 11-15 with 4 spades.
When played this way the only disadvantage is responder cannot pass 2.
2NT is still the asking bid. Opener need not jump at this time to show Maxi Roman hand because responder will never pass when Opener shows his shortness. If responder signs off below game Opener will bid game with the Maxi hand and pass with the Mini hand.If responder bids game and Opener has Maxi hand chances are the bidding will continue. In any event it will become clear to responder what his partner has.
What happens when responder bids 2/2 and opener has Maxi hand.
If responder bids 2/2 then opener will raise THE SUIT unless it is his shortness which in that case he bids 2NT. That tells responder that he has a Maxi hand and shortness in the bid suit.Knowing his partner has a Maxi hand it is up to responder to pick a game contract unless he has an absolutely bust hand in which case he bails at the 3 level. If he does not bid game any further action is up to opener.