Each line must have an identifier that is unique within the document to make it possible to reference the line. For example, from other documents.

Namespace
cbc urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2
Example value
1
Rules
Identifier/Error message Flag
EUGEN-T68-B08901
Document MUST NOT contain elements not part of the data model.
fatal