The element "Seller post code" (BT-38) shall be provided.
(/ubl-invoice:Invoice/cac:AccountingSupplierParty/cac:Party/cac:PostalAddress | /ubl-creditnote:CreditNote/cac:AccountingSupplierParty/cac:Party/cac:PostalAddress)[$supplierCountryIsDE and $customerCountryIsDE]cbc:PostalZone[boolean(normalize-space(.))]