[IBR-100-OM] - If Document level charge TAX category code (IBT-102) is 'Z', Document level charge TAX rate (IBT-103) MUST be 0.
IBR-100-OMubl:Invoice/cac:AllowanceCharge[cbc:ChargeIndicator = 'true'] | cn:CreditNote/cac:AllowanceCharge[cbc:ChargeIndicator = 'true']not($cat='Z') or (cac:TaxCategory/cbc:Percent castable as xs:decimal and xs:decimal(cac:TaxCategory/cbc:Percent) = 0)