> It is not that certain inputs happen to correspond to a configuration solvable by an NFA. It is that if you give it certain inputs it internally generates a d

> It is not that certain inputs happen to correspond to a configuration solvable by an NFA. It is that if you give it certain inputs it internally generates a data structure that actually IS a description of an NFA. And the same is true of most RE engines. All this means is that Perl sometimes evaluates inputs using an NFA algorithm. To describe its matching engine generally as an NFA is extremely misleading. > See for example https://msdn.microsoft.com/en-us/library/e347654k%28v=vs.110.. https://msdn.microsoft.com/en-us/library/e347654k%28v=vs.110.... for yet another non-NFA that is described as one somewhere that programmers are likely to believe it. Yes. It's sad. I frankly can't tell you how much I see this confusion. It happens so much. I point it out when I see it in the hopes that others learn. I don't really buy the argument that we should stop educating others just because the "damage is done." There's certainly a fine line between being an annoying pedant about this and genuinely trying to clarify it for someone who is confused. I thought I was doing the latter in this case initially. Of course, I am hyper sensitive to this topic because I maintain a regex engine! Can you guess which kind? :P