[BR-CO-03-GST-SG]-Tax point date (IBT-007) and Value added tax point date code (IBT-008) are mutually exclusive.
BR-CO-03-GST-SG/ubl:Invoice | /cn:CreditNote(exists(cbc:TaxPointDate) and not(cac:InvoicePeriod/cbc:DescriptionCode)) or (not(cbc:TaxPointDate) and exists(cac:InvoicePeriod/cbc:DescriptionCode)) or (not(cbc:TaxPointDate) and not(cac:InvoicePeriod/cbc:DescriptionCode))