A regular expression (shortened as regex or regexp or rational expression) is a sequence of characters that specifies a search pattern in the text.A good testing site is https://infoheap.com/php-preg_match-online/ Examples of regex for passwordPHP Version/^(?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[a-zA-Z])(?=\S*[\W]).{8,}$/Must have special characters(?=\S*[\W])Must have a number(?=.*\\d)Must...