[UBL-SR-31]-Document level charge reason shall occur maximum once
UBL-SR-31
pxs-taxdata:TaxData/pxs-taxdata:ReportedTransaction/pxs-taxdata:ReportedDocument/cac:AllowanceCharge[cbc:ChargeIndicator = true()]
(count(cbc:AllowanceChargeReason) <= 1)