http://en.wikipedia.org/wiki/Regular_expression
http://lt.php.net/manual/en/function.preg-replace.php
http://lt.php.net/manual/en/function.preg-match.php
http://lt.php.net/manual/en/reference.pcre.pattern.syntax.php
http://lt.php.net/manual/en/reference.pcre.pattern.modifiers.php
