[MoonZ]

> In fact lookbehinds require a fixed-length pattern

Just a small note: some regex engines support "variable length lookbehind", check the last column on this wikipedia article : https://en.wikipedia.org/wiki/Comparison_of_regular_expressi...

[zahlman]

Good to know. Although a lookbehind for `\d+` doesn't really gain anything over a lookbehind for `\d` anyway; they match in the same circumstances, just with different results.