Replying to my own comment to clarify: it is true that you can't express a non-regular language with regular expressions. What I meant is, it is likely we can c

Replying to my own comment to clarify: it is true that you can't express a non-regular language with regular expressions. What I meant is, it is likely we can combine automata and backtracking based techniques to get the best of both worlds. In other words, an automata based engine doesn't necessarily mean you can't also have backreferences and still have efficiency gains.