2. Conventions

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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

Key Word Meanings

• MUST / REQUIRED / SHALL - Indicates an absolute requirement
• MUST NOT / SHALL NOT - Indicates an absolute prohibition
• SHOULD / RECOMMENDED - Indicates that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course
• SHOULD NOT / NOT RECOMMENDED - Indicates that there may exist valid reasons in particular circumstances when the particular behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label
• MAY / OPTIONAL - Indicates that an item is truly optional