Each Document level allowance (BG-20) shall have a Document level allowance reason (BT-97) or a Document level allowance reason code (BT-98).
/ubl:Invoice/cac:AllowanceCharge[cbc:ChargeIndicator = false()] | /cn:CreditNote/cac:AllowanceCharge[cbc:ChargeIndicator = false()]exists(cbc:AllowanceChargeReason) or exists(cbc:AllowanceChargeReasonCode)