public function merge($arElementIDList)
    {
        if (empty($arElementIDList)) {
            return $this->returnThis();
        }

        if ($this->isClear()) {
            $this->arElementIDList = $arElementIDList;

            return $this->returnThis();
        }

        $this->arElementIDList = array_merge($this->arElementIDList, $arElementIDList);
        $this->arElementIDList = array_unique($this->arElementIDList);

        return $this->returnThis();
    }