Also called Universal Business Language, OASIS UBL
Universal Business Language is an OASIS XML standard covering business documents, and it is the second of the two syntaxes EN 16931 can be expressed in. Most PEPPOL traffic is UBL, and it carries exactly the same invoice content as the CII a Factur-X file embeds.
UBL dominates PEPPOL and a lot of European public sector invoicing. If you are exchanging invoices over a network rather than emailing PDFs, you are probably handling UBL.
It is noticeably less verbose than CII and easier to read unaided, which matters when you are debugging at four in the afternoon.
A UBL invoice and a CII invoice carrying the same EN 16931 content are the same invoice. The business terms are identical, because the terms belong to the standard rather than to either syntax.
What differs is element naming and nesting, which is why converting between them is mechanical but not trivial, and why our validator detects which one it has rather than asking you.
Detected from the file. The EN 16931 rules apply to both syntaxes.
