An Invoice that contains an Invoice line (BG-25) where the Invoiced item VAT category code (BT-151) is "Export outside the EU" shall contain the Seller VAT Identifier (BT-31) or the Seller tax representative VAT identifier (BT-63).
/ubl:Invoice | /cn:CreditNote(exists(//cac:ClassifiedTaxCategory[normalize-space(cbc:ID) = 'G'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']) and (exists(//cac:AccountingSupplierParty/cac:Party/cac:PartyTaxScheme[cac:TaxScheme/(normalize-space(upper-case(cbc:ID)) = 'VAT')]/cbc:CompanyID) or exists(//cac:TaxRepresentativeParty/cac:PartyTaxScheme[cac:TaxScheme/(normalize-space(upper-case(cbc:ID)) = 'VAT')]/cbc:CompanyID))) or not(exists(//cac:ClassifiedTaxCategory[normalize-space(cbc:ID) = 'G'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']))