Base quantity MUST be a positive number above zero.
PEPPOL-EN16931-R121pxs-taxdata:TaxData/pxs-taxdata:ReportedTransaction/pxs-taxdata:ReportedDocument/pxs-taxdata:DocumentLinenot(cac:Price/cbc:BaseQuantity) or xs:decimal(cac:Price/cbc:BaseQuantity) > 0