protected function get_messages() {
        global $SESSION;

        $messages = array();
        if (!empty($SESSION->lesson_messages) && is_array($SESSION->lesson_messages) && array_key_exists($this->properties->id, $SESSION->lesson_messages)) {
            $messages = $SESSION->lesson_messages[$this->properties->id];
            unset($SESSION->lesson_messages[$this->properties->id]);
        }

        return $messages;
    }