You see, in the old days, a regex only returned a boolean: match or not-match. Later, people got serious about actually capturing the matched sections, and they introduced backtracking (versus NFA machines) to get that sort of thing done.

But then, the actual _algorithm_ and internals of what's happening becomes crucial. You now care about more than just a theoretical boolean result: match or not-match.

When internally it matters what the engine is doing, backtracking makes it very hard and unnatural to predict and to think about. That's not how "real" humans actually think about their mother tongue. They don't seem to seriously "backtrack" in their brains while reading a book.

So, are there real-life examples of where that's needed?

Reza.