Peppol makes use of a subset of the UBL 2.1 specification. UBL is an open standard maintained by OASIS. The official website is https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=ubl. It offers downloads for for XML schema files and code lists for UBL 2.1 (56 MB).
E-RECHNUNG.GV.AT supports the Peppol-UBL format not only when used via the Peppol transport infrastructure but also when using the invoice upload or the web service delivery.
Invoices with UBL document type
Invoice can be delivered in version 2.1. Credit notes with UBL document type
CreditNote can also be deliver in version 2.1.