An Invoice line (BG-25) where the VAT category code (BT-151) is "Not subject to VAT" shall not contain an Invoiced item VAT rate (BT-152).
cac:InvoiceLine/cac:Item/cac:ClassifiedTaxCategory[normalize-space(cbc:ID) = 'O'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT'] | cac:CreditNoteLine/cac:Item/cac:ClassifiedTaxCategory[normalize-space(cbc:ID) = 'O'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']not(cbc:Percent)