At least 6 chars with 1 upper/lower case letter and 1 special char

Contains between 6 and 20 characters

Email Validation regex for RFC-2822

\b can be replicated as (?<=\w)(?=\W)|(?<=\W)(?=\w) Understanding how to create these class transitions can be beneficial for several reasons. In this instance, counting the results of this regex can be used to measure randomness within strings containing multiple character classes.