Message

Each Tax Category SHALL have a VAT category rate, except if the order is not subject to VAT.

Context
cac:TaxCategory | cac:ClassifiedTaxCategory
Test
cbc:Percent or (normalize-space(cbc:ID)='O')
Usage
/ ubl:OrderChange / cac:AllowanceCharge / cac:TaxCategory / cbc:Percent
/ ubl:OrderChange / cac:OrderLine / cac:LineItem / cac:Item / cac:ClassifiedTaxCategory / cbc:Percent