Brackets are character classes. They match any single character between them--specific meta characters are interpretted differently. They allow ranges such as a-z for matching the english alphabet (lowercase), for example. They also support negation by placing ^ as the first character, ie, match anything BUT the following. You might want to play around here: https://regexr.com/

This solution looks very clear and excellent to me!
May I ask: Do the square brackets prevent any content from being interpreted as Regex escape chars?

Is there any particular reason to use strict (in)equality here?

You're right. \w is equivalent to [A-Za-z0-9_]

interesting~

It's just for fun, a personal challenge: see Code Golfing

why compress code like this?

I think i(ignore case) isnt necessary in this case

I think it might be better using === or !==.