What everyone forgets is that regexes as implemented in most programming languages are a strict superset of mathematical regular expressions. E.g., PCRE has "su

What everyone forgets is that regexes as implemented in most programming languages are a strict superset of mathematical regular expressions. E.g., PCRE has "subroutine references" that can be used to match balanced brackets, and .NET has "balancing groups" that can similarly be used to do so. In general, most programming languages can recognize at least the context-free languages.