The Unicode Standard assigns various properties and property values to every symbol. For example, to get the set of symbols that are used exclusively in the Greek script, search the Unicode database for symbols whose Script property is set to Greek. Unicode property escapes are a new type of escape sequence available in regular expressions that have the `u` flag set. They enable querying the Unicode database for certain properties and values. E.g. `/\p{Script=Greek}/u.test('π') === true`
Docs: https://mathiasbynens.be/notes/es-unicode-property-escapes https://developers.google.com/web/updates/2017/07/upcoming-regexp-features#unicode_property_escapes