The element "VAT category rate" (BT-119) shall be provided.
(/ubl-invoice:Invoice/cac:TaxTotal/cac:TaxSubtotal | /ubl-creditnote:CreditNote/cac:TaxTotal/cac:TaxSubtotal)[$supplierCountryIsDE and $customerCountryIsDE]
cac:TaxCategory/cbc:Percent[boolean(normalize-space(.))]