Thanks @AkimasaKajitani: this helps.
Of note: the formula should be used as REGEX_Match(String, pattern, icase) and does not allow reversal of String and pattern arguments it seems.
I sometimes over-think them!!!
Well, in attempting to create an app in App Builder for extra credit, this helped me uncover a potential defect in App Builder. Win Win!
This one took me a minute to get started but once I got started, I was able to find a fairly simple solution: