form validation using php

hi i need to validate a field in a form where a user enters their lodgement number as part of a registration form. this lodgement number can have letters, numbers, spaces and special characters. i do not know exactly what those special characters are, so do i have to define the type of special characters and validate accordingly. presently my php code for validating the lodgement number is $lodgementtf = $_POST["lodgementtf"]; if($lodgementtf == "" || !preg_match("/^[a-zA-Z0-9_ <]+$/", $lodgementtf) ) { echo "display error message": } i also have another way of validating if($lodgementnumber == "" || !preg_match("/^[a-zA-Z0-9_ !-@£$%^&*()]+$/", $lodgementnumber) ) does this mean that the special characters can only be = a space AND _!-@£$%^&*() and no other special characters. please advice. thanks.