Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values used in these fields do not have conflicting uses, and to promote interoperability, their allocation is often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA) Services. To make assignments in a given registry prudently, guidance is needed for describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226.