The EAN·UCC-13 code of the given gr:ProductOrService or gr:Offering. This code is now officially called GTIN-13 (Global Trade Identifier Number) or EAN·UCC-13. Former 12-digit UPC codes can be converted into EAN·UCC-13 code by simply adding a preceeding zero. Note 1: When using this property for searching by 12-digit UPC codes, you must add a preceeding zero digit. Note 2: As of January 1, 2007, the former ISBN numbers for books etc. have been integrated into the EAN·UCC-13 code. For each old ISBN-10 code, there exists a proper translation into EAN·UCC-13 by adding "978" or "979" as prefix. Since the old ISBN-10 is now deprecated, GoodRelations does not provide a property for ISBNs.