private function check_username($username)
{
$return = '';
if ($username == '') {
$return .= 'Username cannot be left blank.<br />';
}
if (User::check_alphanumeric($username) != TRUE) {
$return .= 'Username must only contain letters and numbers.<br />';
}
if (User::check_username_available($username) != TRUE) {
$return .= 'Username not available.<br />';
}
return strlen($return) > 0 ? $return : TRUE;
}
