Google Message Security for Google Apps Administration Guide - Manual (Page 222)

222 Message Security for Google Apps Administration Guide
[:space:] Matches all whitespace characters, including spaces, tabs, and
line breaks.
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:space:]].
[:word:] Matches any word character—that is, any letter, digit, or
underscore:
a-z, A-Z, 0-9, or _
Note: This character class must be surrounded with another set
of square brackets when you use it in a regular expression, for
example: [[:word:]].
Shorthand Character Classes
\w Matches any word character—that is, any letter, digit, or
underscore:
a-z, A-Z, 0-9, or _
Equivalent to [:word:]
\W Matches any non-word character—that is, any character that’s
not a letter, digit, or underscore.
Equivalent to [^[:word:]]
\s Matches any whitespace character. For example, use this
character to specify a space between words in a phrase:
stock\stips matches the phrase stock tips
Equivalent to [:space:]
\S Matches any character that’s not a whitespace.
Equivalent to [^[:space:]]
\d Matches any digit from 0-9.
Equivalent to [:digit:]
\D Matches any character that’s not a digit from 0-9.
Equivalent to [^[:digit:]]
Character Description