A Global Trade Item Number (GTIN). GTINs identify trade items, including products and services, using numeric identification codes. The [[gtin]] property generalizes the earlier [[gtin8]], [[gtin12]], [[gtin13]], and [[gtin14]] properties. The GS1 digital link specifications express GTINs as URLs. A correct [[gtin]] value should be a valid GTIN, which means that it should be an all-numeric string of either 8, 12, 13 or 14 digits, or a "GS1 Digital Link" URL based on such a string. The numeric component should also have a valid GS1 check digit and meet the other rules for valid GTINs. See also GS1's GTIN Summary and Wikipedia for more details. Left-padding of the gtin values is not required or encouraged.