If opponent doubles
a major suit transfer,
XX = business
accept shows fit, + stopper in opponents suit
pass shows no stopper in opponents suit and or doubleton in major
xx by responder = retransfer (in ♥ auction responder must xx with
4441 etc)
If responder bids new suit it is forcing.
After XX retransfer then if responder bids new suit it is non forcing
If responder accepts his own transfer it is invitational
If responder jumps and accepts his own transfer it is forcing