To my knowledge, in case of unspecified behaviour, it's not required to pick and document a particular choice. Behaviour may even vary on a case by case basis w

To my knowledge, in case of unspecified behaviour, it's not required to pick and document a particular choice. Behaviour may even vary on a case by case basis where it makes sense (eg order of evaluation of function arguments, whether an inline or external definition of an inline function gets used, etc). The need to properly document the choice is the defining characteristic of implementation-defined behaviour.