Tax category tax amount (ibt-117) shall be 0 (zero) if Tax category code (ibt-118) equals to E (Exempt from tax).
/*/cac:TaxTotal/cac:TaxSubtotal/cac:TaxCategory[normalize-space(cbc:ID) = 'G'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT'](xs:decimal(../cbc:TaxAmount) = 0)