[ibr-tdd-57] The Invoice XML (tdt-012) MUST contain either a UBL 2.1 Invoice or a UBL 2.1 Credit Note
ibr-tdd-57
/pxs:TaxData/pxs:ReportedTransaction/pxs:SourceDocument/cec:ExtensionContent
exists(inv:Invoice) or exists(cn:CreditNote)