The element "Buyer post code" (BT-53) shall be provided.
(/ubl-invoice:Invoice/cac:AccountingCustomerParty/cac:Party/cac:PostalAddress | /ubl-creditnote:CreditNote/cac:AccountingCustomerParty/cac:Party/cac:PostalAddress)[$supplierCountryIsDE and $customerCountryIsDE]cbc:PostalZone[boolean(normalize-space(.))]