Yeah, regular expressions are great for validating form input on web forms.^(\d{5}$|\d{5}-\d{4}$ would only match input that is in valid US zip code format.^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z]*[a-zA-Z]$ could be used to validate that the user entered in a correctly formated email address.There are many sites on the Internet devoted to regular expressions, I just think it'd be a great addition to this site.