public function add($key, $value)
    {
        if (empty($key)) return false;

        if (empty($this->engineVarList->$key)) {
            $this->engineVarList->$key = $value;

            return $this;
        }

        if (is_array($this->engineVarList->$key)) {
            array_merge($this->engineVarList->$key, $value);
        }

        return $this;
    }