If one of the VAT codes S, Z, E, AE, K, G, L, or M is used, an invoice shall contain at least one of the following elements: "Seller VAT identifier" (BT-31) or "Seller tax registration identifier" (BT-32) or "SELLER TAX REPRESENTATIVE PARTY" (BG-11).
(/ubl-invoice:Invoice | /ubl-creditnote:CreditNote)[$supplierCountryIsDE and $customerCountryIsDE] (not( ($BT-95-UBL-Inv = $supportedVATCodes or $BT-95-UBL-CN = $supportedVATCodes) or ($BT-102 = $supportedVATCodes) or ($BT-151 = $supportedVATCodes) ) or (cac:TaxRepresentativeParty, $BT-31orBT-32Path))