Message

The validity period end date may not be earlier than the issue date.

Context
/ubl:Catalogue
Test
(cac:ValidityPeriod/cbc:EndDate) and (number(translate(cac:ValidityPeriod/cbc:EndDate,'-','')) >= number(translate(cbc:IssueDate,'-','')))
Usage
/ ubl:Catalogue / cac:ValidityPeriod / cbc:EndDate