In a Document level charge (ibg-21) where the Tax category code (ibt-102) is "O (Outside of scope of tax)" shall not contain a Document level charge tax rate (ibt-103).
cac:AllowanceCharge[cbc:ChargeIndicator=true()]/cac:TaxCategory[normalize-space(cbc:ID)='O'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT'](not(cbc:Percent))