\w represents a "word" character and is equivalent to the expression [A-Za-z0-9].
\W represents the opposite of \w and is equivalent to [^A-Za-z0-9].
\s represents a whitespace character.
\S represents a nonwhitespace character.
\d represents a digit and is equivalent to [0-9].
\D represents a nondigit character and is equivalent to [^0-9].
\n represents a newline character.
\r represents a return character.
\t represents a tab character.