pocketmine\level\format\generic\BaseFullChunk::setBlockExtraData PHP Method

    public function setBlockExtraData($x, $y, $z, $data)
    {
        if ($data === 0) {
            unset($this->extraData[Level::chunkBlockHash($x, $y, $z)]);
        } else {
            $this->extraData[Level::chunkBlockHash($x, $y, $z)] = $data;
        }
        $this->setChanged(true);
    }