public function addMessage($key, array $args = array())
    {
        // We will only display these messages once.
        if (isset($this->keys[$key]) === false) {
            // Add it to the keys, so the CMS can display it.
            $this->keys[$key] = array('key' => $key, 'params' => $args);
            $this->messages[] = $this->getHelp($key, $args);
        }
    }