- Updates [[RFC2119]] - [RFC 2119](https://tools.ietf.org/html/rfc2119) specifies common key words, such as "MUST", "SHOULD", and "MAY", that may be used in protocol specifications. It says that the key words "are often capitalized," which has caused confusion about how to interpret non-capitalized words such as "must" and "should". This document updates [RFC 2119](https://tools.ietf.org/html/rfc2119) by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document is part of [BCP 14](https://tools.ietf.org/html/bcp14). - Guidance becomes the following: - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [BCP 14](https://tools.ietf.org/html/bcp14) [[RFC2119](https://tools.ietf.org/html/rfc2119)] [[RFC8174](https://tools.ietf.org/html/rfc8174)] when, and only when, they appear in all capitals, as shown here.