$(document).ready(function() {


	
	$.validator.addMethod("alphaNumeric", function(value, element) {
		return this.optional(element) || /^([a-zA-Z0-9]+)$/i.test(value);
	});
	
	$("#login_form").validate({
		rules: {
			username: {
					required: true,
					alphaNumeric: true,
					maxlength: 20
				},
			userpwd: {
					required: true,
					alphaNumeric: true,
					maxlength: 12
				}
		},
		messages: {
			username: "*",
			userpwd: "*"
		}
	});
});