Outline
In Internet standards document, often there will be some level of expressed demand keywords. They are often used to represent the function (characteristics) level of importance, the standard implementation can decide whether to add these features in their implementation, according to the meaning of these words.
According to the update RFC8174, these words only in the case that has the all caps represent the role of demand levels, in other cases, only ordinary English semantics.
Specific Keywords
- MUST, REQUIRED, SHALL must, must mean, very positive, specific implementation requirements must include these keywords modified characteristics.
- MUST NOT, SHALL NOT, entirely negative, with MUST and other opposition expressed by these keywords modified characteristics banned, must not have.
- SHOULD, RECOMMENDED, in some cases, people may realize there are good reasons not to implement this feature, but before making a decision, we must fully consider all the consequences. The implication is that these features are optional, but standard recommendation implement this feature, if you choose to not implement all the consequences.
- SHOULD NOT, NOT RECOMMENDED, and SHOULD opposition, in some cases, to achieve personnel may have good reasons to implement these functions are beneficial, but before implementation, to fully consider the consequences. The implication of these features are optional, the standard is not recommended to achieve this function, if you must do so at your own risk.
- MAY, OPTIONAL optional, compared with SHOULD, SHOULD NOT, there are more neutral, standards and no clear preference, with full implementation requirements of personnel may be, want to do, not do not want to use. Achieve interoperability need to consider: contains the implementation of this feature is to be able to work together to achieve and do not contain this feature.