[ibr-tdd-84] – The cac:BillingReference (BG-03) element MUST NOT contain elements other than cac:InvoiceDocumentReference.
ibr-tdd-84/pxs:TaxData/pxs:ReportedTransaction/pxs:ReportedDocument/cac:BillingReferencecount(*[not(self::cac:InvoiceDocumentReference)]) = 0