\d numeric character [0-9]
\D NOT a numeric character [^0-9]
\w “word” character [a-zA-Z0-9_]
\W NOT a “word” character [^a-zA-Z0-9_]
\s whitespace character [\f\n\r\t\v]
\S NOT a whitespace character [^\f\n\r\t\v]
. Any character except a line break [^\n]
() group
? zero or one
* zero to many
+ one to many
{x} match x times
{x,y} match x to y times
Reference: Regular Expressions: Not as Tricky as They May Seem