Peppol: An identification of the specification containing the total set of rules regarding semantic content, cardinalities and business rules to which the data contained in the instance document conforms.

Namespace
cbc urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2
Data type
Identifier
udt:IdentifierType
Example value
urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0
Business terms
BT-24
Rules
Identifier/Error message Flag
PEPPOL-EN16931-R004
Specification identifier MUST have the value 'urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0'.
fatal
BR-01
[BR-01]-An Invoice shall have a Specification identifier (BT-24).   
fatal