include('system/language/english/form_validation_lang.php');
-$lang['_valid_username'] = "You must enter an e-mail address or a valid username.";
+$lang['_valid_username'] = 'You must enter a valid username with letters, numbers, . (dots) or _ (underscores).';
+$lang['_valid_username_or_email'] = "You must enter an e-mail address or a valid username.";
$lang['_do_login'] = "Wrong %s, or wrong %s.";