[ibr-030]-If both self-billed invoice line period start date (ibt-134) and self-billed invoice line period end date (ibt-135) are given then the self-billed invoice line period end date (ibt-135) MUST be later or equal to the self-billed invoice line period start date (ibt-134).
ibr-030cac: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))