Perhaps their regex engine is insultingly bad. But I assume they would use the basic js/ts which is not that bad.

Some croak on just about anything except basic matching, look ahead, look behind, no capture groups, etc.. pfft. Too advanced

I need to learn regexes

I always just use (?i) at the beginning of everything I don't care about case for. Is that inadvisable compared to this?

Mayybe, the regex matching was case insensitive?