Both start date and end date of line period must be within invoice period.
cac:InvoiceLine/cac:InvoicePeriodxs:date(cbc:StartDate) >= xs:date(../../cac:InvoicePeriod/cbc:StartDate) and xs:date(cbc:EndDate) <= xs:date(../../cac:InvoicePeriod/cbc:EndDate)