public function prevNode($nID)
    {
        $nodeOverride = $this->movePrevOverride($nID);
        if ($nodeOverride > 0) {
            return $nodeOverride;
        }
        if (!isset($this->nodesRawIndex[$nID])) {
            return -3;
        }
        $prevNodeInd = $this->nodesRawIndex[$nID]-1;
        if ($prevNodeInd < 0 || !isset($this->nodesRawOrder[$prevNodeInd])) {
            return -3;
        }
        $prevNodeID = $this->nodesRawOrder[$prevNodeInd];
        return $prevNodeID;
    }