Code Meaning
\a Alarm
\b Word boundary
\B Not word boundary
\d Digit
\D Not digit
\e Escape
\f Form feed
\n Newline
\r Carriage return
\s Space character (space, \t, \n, \r, \f)
\S Not space character
\t Tab
\w Word
\W Not word
\oNN Octal
\xNN Hexadecimal
\cC Control character