A regular expression is really just a sequence or pattern of characters that is matched against a string of text when performing searches and replacements . A simple regular expression consists of a character or set of characters that matches itself. The regular expression is normally delimited by forward slashes ; for example, /abc/ .
The first part of this chapter delves into the construction of regular expressions and how to use regular expression metacharacters. The second part of the chapter applies this information to validating form input.