function &_addTextPart(&$obj = null, $text = '')
    {
        $params['content_type'] = 'text/plain';
        $params['encoding']     = $this->_build_params['text_encoding'];
        $params['charset']      = $this->_build_params['text_charset'];
        $params['eol']          = $this->_build_params['eol'];

        if (is_object($obj)) {
            $ret = $obj->addSubpart($text, $params);
        } else {
            $ret = new Mail_mimePart($text, $params);
        }

        return $ret;
    }