# F-LIB096

Source: https://xmlvalid.com/rules/F-LIB096

> When using ExternalReference, URI is mandatory

- Level: error
- Rule sets: OIOUBL 2.1 Invoice rules (Denmark) 1.17.2, OIOUBL 2.1 Credit Note rules (Denmark) 1.17.2, OIOUBL 2.1 Reminder rules (Denmark) 1.17.2
- Test: `cac:Attachment/cac:ExternalReference and not(cac:Attachment/cac:ExternalReference/cbc:URI != '')`

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