/**
* add another html message to be concatenated on displaying
*
* @param string $message to be added
* @param string $separator to use between this and previous string/message
*
* @return void
*/
public function addHtml($message, $separator = ' ')
{
if (!is_string($message)) {
trigger_error('Invalid parameter passed to addMessage');
}
$this->_addMessage(Message::rawNotice($message), $separator);
}