Allowance/charge ChargeIndicator value MUST equal 'true' or 'false'
PEPPOL-EN16931-R043pxs-taxdata:TaxData/pxs-taxdata:ReportedTransaction/pxs-taxdata:ReportedDocument/cac:AllowanceCharge | pxs-taxdata:TaxData/pxs-taxdata:ReportedTransaction/pxs-taxdata:ReportedDocument/pxs-taxdata:DocumentLine/cac:AllowanceChargenormalize-space(cbc:ChargeIndicator/text()) = 'true' or normalize-space(cbc:ChargeIndicator/text()) = 'false'