https://unicode.org/reports/tr18/tr18-5.1.html
https://mathiasbynens.be/notes/javascript-unicode
https://mathiasbynens.be/notes/es6-unicode-regex
https://www.regular-expressions.info/unicode.html
https://regex101.com
https://caniuse.com/#feat=es5
https://github.com/mathiasbynens/regexpu
http://blog.stevenlevithan.com/archives/javascript-regex-and-unicode