Tax breakdown (ibg-23) shall be categorized by Tax category rate (ibt-119), except if the Invoice is not subject to tax.
cac:TaxTotal[cbc:TaxAmount/@currencyID=../cbc:DocumentCurrencyCode]/cac:TaxSubtotal
(exists(cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/cbc:ID) and exists(cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/cbc:Percent)) or (cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/normalize-space(cbc:ID)='O')