\d [0-9] Digits 0 to 9.
\w [0-9A-Za-z_] A 'word' character allowable in a Perl variable name.
\s [ \t\n\r] A whitespace character that is, a space, a tab, a newline or a return.
\D [^0-9] Any non-digit.
\W [^0-9A-Za-z_] A non-'word' character.
\S [^ \t\n\r] A non-blank character.