Regular expressions in Find and Replace

I may have made this suggestion earlier but cannot find it. Adding regular expressions (regex or regexp) making it possible to search for patterns, as in Word, would be an immense improvement for writers, one that alone would justify updating. I currently need to review all uses of "this", "that", "these", and "those" in several files. Word allows one to search for "th[aeiost]{2;3}" when checking the appropriate option, and the programme locates all four words in a single operation. Just imagine the power and the flexibility. This is absolutely impossible in WordPerfect. Using "th[* (Many Char)]" finds irrelevant hits, such as "the", "them", etc., making this very limited technique impossible to work with. There are surely ready-made code libraries that can be used to implement regex rather than doing it from scratch.