The reason our endless conversations about “formal dress,” “white-tie,” and “daywear” seem to fall on deaf ears or cause more confusion than clarity is perfectly explained by the following ad copy for Tommy John boxer briefs.

’I'm never going back. So comfortable. Also, the pocket at the top is a LIFE SAVER at formal events when you can pee without undoing your belt/shirt tuck.’ - Ryan S.
Words have no meaning if “formal” means only that one can pee without untucking.

I believe the proper term for that condition is in fact “regimental”