CHARACTER CLASSES
\c = control character
\s = white space
\S = non white space
\d = digit
\D = not digit
\w = word
\W = not word
\xhh =hexadecimal character hh
\Oxxx = octal character xxx
QUANTIFIERS
* = 0 or more
+ = 1 or more
? = 1 or 0
{3} = exactly 3
{3,} = 3 or more
{3,5} = 3, 4 or 5
