Earlier quoted context omitted.
It’s not just the syntax. Regex isn’t directly composable (unless you just mash together strings). They cannot define nested structures, I.e. no recursion. They can’t maintain context. We don’t need better language tools. Better parsers can, and already have, been implemented in libraries. I’d have a look at parser combinators.
(?R) is very much recursion in there.
Is true though, or perhaps "state"? I know I had to come up with an algorithm because regexp alone couldn't do what I wanted (not even advanced features like lookahead, lookbehind, etc.)