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Presumably the space, commonly having no meaning in and of itself, could throw you for a moment or two. This isn't a regex `foo_[a-z]`, you have to stop and think about it for a moment.

I don't think it is particularly bad though. It's just not the most trivial of regexes.

Most people would have to check an ASCII table to know what that range is, though.

Which takes for granted the fact that your input stream is even ASCII to begin with. I'm too lazy to check, but I'm pretty sure this isn't going to catch all printable Unicode characters, for example - and then you're left scratching your head over what the hell the original author was trying to achieve.

The main risk in my mind was that it was some sort of control sequence for a feature I hadn't memorized.

I know there's some syntax I can use to create a zero width negative look behind recursive greedy named capture group back reference. Perhaps hyphen-tilde triggers something like that.