Some modern regex flavors support recursion in Regex: Perl 5.10, PCRE 4.0, Ruby 2.0, and all later versions of these three, support regular expression recursion. Ruby 1.9 supports capturing group recursion (the whole regex can be recursed if wrapped in a capturing group.) .NET does not support recursion, but it supports balancing groups that can be used instead of recursion to match balanced constructs.
