public function generateElementSortForHolder()
    {
        if (!$this->Sort)
        {
            $holderFilter = ['PageID' => $this->PageID];
            if ($this->ElementID) $holderFilter = ['ElementID' => $this->ElementID];

            $this->Sort = self::get()
                ->filter($holderFilter)
                ->max('Sort') + 1
            ;
        }
        return $this;
    }