[BR-30]-If both Invoice line period start date (BT-134) and Invoice line period end date (BT-135) are given then the Invoice line period end date (BT-135) shall be later or equal to the Invoice line period start date (BT-134).
Stored validation assertion
(exists(cbc:EndDate) and exists(cbc:StartDate) and xs:date(cbc:EndDate) >= xs:date(cbc:StartDate)) or not(exists(cbc:StartDate)) or not(exists(cbc:EndDate))