public function unshift($iElementID)
    {
        if (empty($iElementID)) {
            return $this->returnThis();
        }

        if ($this->isEmpty()) {
            $this->arElementIDList = [$iElementID];

            return $this->returnThis();
        }

        array_unshift($this->arElementIDList, $iElementID);

        return $this->returnThis();
    }