Vampyr, on 2019-October-17, 07:36, said:
Not sure what you are saying here. Opener cannot have a 5-card major when she is 3-1 in the majors.
It's responder who is bidding 3M showing 13(54) game forcing. The 1NT opener might have a 5-card major (at least how many of us play) and if responder bids the splinter rather than the fragment then he avoids wrongsiding a possible game in the 5-3 fit. A "raise" of the splinter is also available for artificial use by opener, for example showing max strength and majors stopped (she uses 4NT to ask for the longer minor).