Each Document level charge (BG-21) shall contain a Document level charge reason (BT-104) or a Document level charge reason code (BT-105), or both.
/ubl:Invoice/cac:AllowanceCharge[cbc:ChargeIndicator = true()] | /cn:CreditNote/cac:AllowanceCharge[cbc:ChargeIndicator = true()]exists(cbc:AllowanceChargeReason) or exists(cbc:AllowanceChargeReasonCode)