At a recent session my RHO opened 4C, alerted by LHO. I asked what it meant and was told it was Gerber. Whatever the merit (or lack of) in this bid, is it legal at level 4?
Blue Book page 24, ref 7D - Opening Bids of 3NT and higher - "These may have any agreed meaning"
My mistake - I looked at section 8C6 page 28 which says 4C and 4D openings can only have one of the described meanings. But I think that's the legacy level 3 restriction.