Already, above the fold, you see the problem: Text Description: three-letter word starting with 'X'. Regular Expression: \bX[A-Za-z]}{2}\b "été"

Already, above the fold, you see the problem: Text Description: three-letter word starting with 'X'. Regular Expression: \bX[A-Za-z]}{2}\b "été" is a word too. Without going out of English, "'em" is an English word, granted, not starting with a X, but demonstrating that letters are not [A-Za-z]. So once you've specified what you really meant: Sequences of three characters, the first being 'X', and the two others being any letter in the set "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" (and therefore excluding accented letters, ideograms, greek, russian, etc). you realise that you really want to be able to write \bX[A-Za-z]}{2}\b instead. DUH.