In a Document level charge (BG-21) where the Document level charge VAT category code (BT-102) is "Export outside the EU" the Document level charge VAT rate (BT-103) shall be 0 (zero).
cac:AllowanceCharge[cbc:ChargeIndicator=true()]/cac:TaxCategory[normalize-space(cbc:ID)='G'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT'](xs:decimal(cbc:Percent) = 0)