[ibr-030]-If both Invoice line period start date (ibt-134) and Invoice line period end date (ibt-135) are given then the Invoice line period end date (ibt-135) MUST be later or equal to the Invoice line period start date (ibt-134).
ibr-030
cac:InvoiceLine/cac:InvoicePeriod | cac:CreditNoteLine/cac:InvoicePeriod
(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))