неопределенное-поведение

In C++, there is an operator reinterpret_cast, the meaning of which is to cast between types that are incompatible with each ... tatic_cast and dynamic_cast. What, then, is the meaning of the existence of this operator, if its use violates the standard?

Looking at the function description system And I noticed two strange places: If command is not a null pointer, the value ... with the executed command at all (unless it is null) - it simply says "Implementation-defined value". And no mention of UB.