Google Message Security for Google Apps Administration Guide - Manual (Page 221)

Content Manager 221
[^...] Matches any character not in the set of characters. For
example:
[^a-f] matches any character that’s not a letter from a to f
Note: Regular expressions in Content Manager are not case
sensitive. Therefore, using this formatting to specify a character
set in lowercase letters also excludes the equivalent uppercase
letters.
[:alnum:] Matches alphanumeric characters (letters or digits):
a-z, A-Z, or 0-9
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:almun:]].
[:alpha:] Matches alphabetic characters (letters):
a-z or A-Z
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:alpha:]].
[:digit:] Matches digits:
0-9
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:digit:]].
[:graph:] Matches visible characters only—that is, any characters except
spaces, control characters, and so on.
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:graph:]].
[:punct:] Matches punctuation characters and symbols:
! " # $ % & ' ( ) * + , \ -. / : ; < = > ? @ [ ] ^ _ ` { | }
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:punct:]].
[:print:] Matches visible characters and spaces.
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:print:]].
Character Description