Javascript defines regex ranges in terms of UTF-16 code units w/no consideration for locale, so you can use [a-fA-F0-9] and it will work as expected. The issue

Javascript defines regex ranges in terms of UTF-16 code units w/no consideration for locale, so you can use [a-fA-F0-9] and it will work as expected. The issue discussed in this bug is only relevant to POSIX regular expression ranges. Perhaps you're lamenting that there are so many different flavors of regular expression. I agree. Just the other day I had to give up on using a regex in a CloudFormation template to validate input because I could not get it to work as documented.