[UBL-SR-12]-Seller VAT identifier shall occur maximum once
UBL-SR-12pxs-taxdata:TaxData/pxs-taxdata:ReportedTransaction/pxs-taxdata:ReportedDocument(count(cac:AccountingSupplierParty/cac:Party/cac:PartyTaxScheme[cac:TaxScheme/upper-case(cbc:ID)='VAT']/cbc:CompanyID) <= 1)