Modifier Semantics \w \s \d /u Unicode \p{IsWord} \p{IsSpace} [0-9] /a ASCII/Perl [A-Za-z0-9_] [ \t\r\n] [0-9] /b Broken/Legacy same as perl 5.8 [0-9] /l "use locale" same semantics as under use locale in 5.8.x