Comment by yunruse

It seems more developer-friendly to me to, at Regex construction, try to parse as linear, and fallback to a backtracking regex if not. The engine is an implementation detail that programmers probably care very little about; a linear engine being default but not raising errors would be the best-of-all-worlds scenario.

(It’s a little weird to see the i flag not working with linear regexes, mind. Surely that’s easily implemented when the regex is compiled?)