BEAst: Used for T6004 - use value "ProjectReference". In other cases - T6473 Document type external. Peppol: The type of reference that cannot be specified by a code. At least one of Document Type Code and Document Type must be used.

Namespace
cbc urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2
Data type
Text
udt:TextType
Example value
Photo
Business terms
tir16-p050
Rules
Identifier/Error message Flag
PEPPOL-T128-R031
AdditionalDocumentReference SHALL contain a Document Type Code or a Document Type.
fatal