My LHO opened 2 Clubs with 23 points in 4th seat. My partner passed. Responder bid 2 Diamonds (Alerted by LHO). LHO bid 2 Spades and his partner passed.
After play, I asked what the 2 Diamond bid by RHO was as he showed zero points when the dummy was boarded. The answer was "point system" showing 0-1 pt. I was then advised that there are seven ACBL approved answers to the opening 2Club bid. I am just curious as to this particular "point system" as I cannot find it on the internet.
This allows any artificial responses to this bid. Personally, I play a very unique transfer system where 2d is a transfer to h, 2h to s, 2s to NT, and 2NT as a stayman asking bid. All others are natural. You should never have a problem when using a system over a 2c opening.