Its about maintenance. Things which are "undefined behavior" can actually have a defined behavior if the compiler provides it. By doing something undefined in t

Its about maintenance. Things which are "undefined behavior" can actually have a defined behavior if the compiler provides it. By doing something undefined in the stl, the compiler authors are saying that the compiler will support it and if the compiler changes, they authors will also change the library. If you rely on this behavior, theres no guarantee that the compiler wont change this behavior in a future update thereby breaking your code.