\d - Any digit (0-9)
\w - Word character (a-z, A-Z, 0-9, _)
[A-Z] - Any uppercase letter
[aeiou] - Any vowel
+ - One or more
* - Zero or more
? - Zero or one
{n} - Exactly n times
^ - Start of string
$ - End of string
. - Any character
(a|b) - a or b