public function extend() 
    {
        return [
            "rentalFeeSink" => $this->rentalFeeSink()->address()->toClean(),
            "rentalFee" => empty($this->parent) ? Fee::ROOT_PROVISION_NAMESPACE : Fee::SUB_PROVISION_NAMESPACE,
            "parent" => $this->parent,
            "newPart" => $this->newPart,
            // transaction type specialization
            "type" => TransactionType::PROVISION_NAMESPACE,
        ];
    }