Limiting quantifier size for "efficiency and safety" reasons makes as much sense stopping the following loop

I wasn't proposing a limit on quantifier size, just observing that it's already present (and speculating on why).

Note that the "deep recursion" you are referring to is a warning, perl won't stop the recursion. But the Complex regular subexpression recursion limit makes perl just say "oh well, I had enough - I'll just pretend it doesn't match". That's wrong. It may even be exploitable.

Obviously I didn't read the perldiag page very well, despite linking to it. :-) Now I understand the difference—thanks. (Mainly I missed the fact that the regular expression match fails with a warning, rather than dieing, because I didn't actually run the code myself.)