public function withExtensionRequest(Extensions $extensions): self
    {
        $obj = clone $this;
        if (!isset($obj->_attributes)) {
            $obj->_attributes = new Attributes();
        }
        $obj->_attributes = $obj->_attributes->withUnique(
            Attribute::fromAttributeValues(
                new ExtensionRequestValue($extensions)));
        return $obj;
    }