Nice question - and a reminder to me to use STUFF more often.

I don't understand why the explanation worries about the result length. . I agree with John Arnott's comments above about this. String functions either do or don't have a length parameter, and the ones that don't have a resulting length that can be any valid length (except MAX, unless a parameter of the function is declared with length MAX). Why should anyone expect STUFF to behave differently from + in this respect?