. Matches any character.
^ Matches start of line.
$ Matches end of line.
*<\|> Matches 0 or more of the preceding element.
+ Matches 1 or more of the preceding element.
? Matches 0 or 1 of the preceding element.
+ Matches 1 or more of the preceding element.
! Matches any character that is NOT in the preceding class.
^ Matches any character that is NOT in the preceding class.
- Matches a hyphen.
[ Matches an opening bracket.
] Matches a closing bracket.
{ Matches an opening curly bracket.
} Matches a closing curly bracket.
| Matches a vertical bar or pipe.
\ Matches an escape character.
. Matches a period.
\ Matches a backslash.
/ Matches a forward slash.
\n Matches a line feed.
\t Matches a tab.
\r Matches a carriage return.
\b Matches a word boundary.
\B Matches a non-word boundary.
\d Matches any digit.
\D Matches any non-digit.
\w Matches any word character.
\W Matches any non-word character.
[a-z] Matches any lowercase letter "a" or "z".
A-Z Matches any uppercase letter "A" or "Z".
[0-9] Matches any digit "0" or "9".
[a-z] Matches any lowercase letter.
[A-Z] Matches any uppercase letter.
[0-9] Matches any digit.
[0-9a-zA-Z] Matches any digit or letter.