UB is also very much based around software incompatibilities though, not just the ability to optimise stuff.
But where IB can have useful definitions to document, UB was defined so because the behaviours were considered sufficiently divergent that allowing them was useless, and so it was much easier to just forbid them all.
But where IB can have useful definitions to document, UB was defined so because the behaviours were considered sufficiently divergent that allowing them was useless, and so it was much easier to just forbid them all.