# F-INV304

Source: https://xmlvalid.com/rules/F-INV304

> AdditionalDocumentReference class must be excluded

- Level: error
- Rule sets: OIOUBL 2.1 Invoice rules (Denmark) 1.17.2
- Context: `doc:Invoice/cac:InvoiceLine/cac:BillingReference`
- Test: `count(cac:AdditionalDocumentReference) = 0`

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