A. Key words for use in RFCs to Indicate Requirement Levels

According to RFC 2119 Key words for use in RFCs to Indicate Requirement Levels , we specify how the main keywords used in RFCs should be interpreted. Authors who follow these guidelines should incorporate this phrase near the beginning of their document:

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT;", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.