# W-INV237

Source: https://xmlvalid.com/rules/W-INV237

> ID must be unique within the document instance

- Level: warning
- Rule sets: OIOUBL 2.1 Invoice rules (Denmark) 1.17.2
- Context: `doc:Invoice/cac:InvoiceLine`
- Test: `cbc:ID = ./following-sibling::*/cbc:ID`

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