BEAst: Not a part of version 3.1, but use this code instead of the text if possible. An example is "174" for DrawingNumber (T6222) Peppol: The type of reference. Must me part of UNCL1001. 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
udt:CodeType
Example value
380
Code lists
Document name code, full list (UNCL1001)
Rules
Identifier/Error message Flag
PEPPOL-T120-R031
AdditionalDocumentReference SHALL contain a Document Type Code or a Document Type.
fatal
PEPPOL-T120-B01401
Value MUST be part of code list 'Document name code, full list (UNCL1001)'.
fatal