A very strange auction recently resulted in a discussion that may have actually accomplished the development of an interesting treatment.
Assume an auction where a minor is agreed in the middle of a contested auction and where slam is being investigated. A simple example might be 1D-P-2C(GF)-P-2H(one-under, showing four spades)-P-3D(GF, agrees diamonds-3H(interference)-4C(no spade control, heart second-round control, club control, slammish)-4H.
The partnership uses the lowest out-of-focus major as RKCB for diamonds. Thus, had the opponents not intervened, 4H would have been RKCB for diamonds. Plus, undoubtedly we are in a forcing pass auction, when slam is being explored and we are not even to game yet.
So, what should a pass of 4H be? If the heart control has already been shown, and the nature of that heart control (first-round or second-round, for instance), then passing to imply something about the heart suit is of little utility. Passing as a Last Train type of action has some merits. However, the better approach may be for a forcing pass of a call that would have been ace-asking to be ace-asking.
So, in the example, if Responder passes 4H, a call in the clear out-of-focus major, when the heart control situation has already been clarified, then the pass is RKCB.