# ibr-co-20

Source: https://xmlvalid.com/rules/ibr-co-20

> If Invoice line period (ibg-26) is used, the Invoice line period start date (ibt-134) or the Invoice line period end date (ibt-135) MUST be filled, or both.

- Level: error
- Rule sets: PINT Billing rules 1.1.3, PINT Billing rules (as shipped with PINT AE) 1.0.4
- Context: `cac:InvoiceLine/cac:InvoicePeriod | cac:CreditNoteLine/cac:InvoicePeriod`
- Test: `exists(cbc:StartDate) or exists(cbc:EndDate)`

Validate a document against these rules: https://xmlvalid.com/validate