가끔씩 문서를 보다보면 "MUST", "SHOULD", "REQUIRED" 같은 용어들이 같이 사용되는데 이것이 "꼭" 해야 하는 것인지, 아니면 "하면 좋은 것" 인지 구분이 안될 때가 많다. 그래서 이것에 대해서 정리한 RFC 2119 Requirement level 문서를 요약하기로 했다.
정리
1. Must / Required / Shall: 절대 준수
2. Must not / Shall not: 절대 금지
3. Should / Recommended: 하는 것을 권유, 추천
4. Should not / Not recommended: 하지 않는 것을 권유, 추천
5. May: 하던 말던
단계
1. MUST (+ required, shall)
This word, or the terms "REQUIRED" or "SHALL", mean that the definition is an absolute requirement of the specification.
절대적인 요구 사항, 꼭 따라야 함.
2. MUST NOT (+ shall not)
This phrase, or the phrase "SHALL NOT", mean that the definition is an absolute prohibition of the specification.
절대 금지.
3. SHOULD (+ recommended)
This word, or the adjective "RECOMMENDED", mean 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.
하는 것을 권유. 이유가 있는 경우 무시 가능. 그러나, 이의 영향력에 대해서 이해하고 있어야 하며 신중하고 고민해야 함.
4. SHOULD NOT (+ not recommeded)
This phrase, or the phrase "NOT RECOMMENDED" mean that there may exist valid reasons in particular circumstances when the particular behaviour is acceptable or even useful, but the full implications should be understood and the case acrefully weighed before implementing any behaviour described with this label.
하지 않는 것을 권유. Should와 동일하게, 하는 것을 막지 않으나 신중하게 고려하길 바람.
5. MAY (+ optional)
This word, or the adjective "OPTIONAL", mean that an item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because the vendor feels that it enhances the product while another vendor may omit the same item. An implementation which does not include a particular option MUST be prepared to interoperate with another implementation which does include the option, though perhaps with reduced functionality. In the same vein an implementation which does include a particular option MUST be prepared to interoperate with another implementation which does not include the option (except, of course, for the feature the option provides.)
옵션. 해도 되고 안 해도 되고.