Universität Bremen TZI The Concise Binary Object Representation, CBOR (STD 94, RFC 8949), defines a "diagnostic notation" in order to be able to converse about CBOR data items without having to resort to binary data. RFC 8610 extends this into what is known as Extended Diagnostic Notation (EDN). This document sets forth a further step of evolution of EDN, and it is intended to serve as a single reference target in specifications that use EDN. It specifies how to add application-oriented extensions to the diagnostic notation. It then defines two such extensions for text representations of epoch-based date/times and of IP addresses and prefixes (RFC 9164). A few further additions close some gaps in usability. It modifies one extension specified in Appendix G.4 of RFC 8610 to enable further increasing usability. To facilitate tool interoperation, this document specifies a formal ABNF definition for EDN as defined today, and it adds media types.