A Document level allowance (BG-20) where VAT category code (BT-95) is "Not subject to VAT" shall not contain a Document level allowance VAT rate (BT-96).
cac:AllowanceCharge[cbc:ChargeIndicator=false()]/cac:TaxCategory[normalize-space(cbc:ID)='O'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']not(cbc:Percent)