In the Wiki, RE2 syntax states:
\s whitespace (== [\t\n\f\r ])
\w word characters (== [0-9A-Za-z_])

... but in Google Apps Scripts, this gives different results:
var char = String.fromCharCode(160); // No-Break Space
var re1 = /[\t\n\f\r 0-9A-Za-z_]/;
var re2 = /[\s\w]/;
var check = ( re1.test(char) == re2.test(char) ) ;
=> false

... also with:
var char = String.fromCharCode(249); // ù

... and many more !

The difference is not there in Google Sheets functions asRegExMatch() and Google Form validation using RegEx. So is Google Apps Script using another engine with different syntax ?
Anyway, it's confusing !