Universität Bremen TZI This document formalizes and consolidates the definition of the Extended Diagnostic Notation (EDN) of the Concise Binary Object Representation (CBOR), addressing implementer experience. Replacing EDN's previous informal descriptions, it updates RFC 8949, obsoleting its Section 8, and RFC 8610, obsoleting its Appendix G. It also specifies registry-based extension points and uses them to support text representations such as of epoch-based dates/times and of IP addresses and prefixes. // (This cref will be removed by the RFC editor:) The present -23 is // intended as reference material during the 2026-04-29 CBOR interim, // a complete specification that reacts to discussion on previous // draft revisions and that can be used to confirm the results in a // WGLC. Among other concerns, the discussion revealed that some // additional editorial content was required; the attempt was to // address this need without making technical changes.