Where/how do you obtain such confidence in something so wrong? The standard not only doesn't prohibit the implementation from defining something it leaves undef

Where/how do you obtain such confidence in something so wrong? The standard not only doesn't prohibit the implementation from defining something it leaves undefined (surely you don't think even possible behavior becomes invalid as soon as it is documented??), it in fact explicitly permits this possibility to occur -- I suppose to emphasize just how nuts the notion of some kind of 'enforced unpredictability' is: > Permissible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner...