public function append($name, $value = null)
    {
        if (is_array($name)) {
            foreach ($name as $key => $val) {
                if (isset($this->_vars[$key])) {
                    $this->_vars[$key] .= $val;
                } else {
                    $this->_vars[$key] = $val;
                }
            }
        } else {
            if (isset($this->_vars[$name])) {
                $this->_vars[$name] .= $value;
            } else {
                $this->_vars[$name] = $value;
            }
        }
    }