— Well, if they are truly regular
— Like I said, what you call "regex" today is not necessarily regular anymore but can be context free or even context sensitive
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— For example, using the results of captures inside of your match or using lookahead
— All context free langs can be understood by automata
— I wrote a compiler compiler in C++ that does it :P
— You can't do infinite recursion with a DFA
— You need a stack, so it's a pushdown thing or whatever it's called