Keywords

Verbs

RFC2119 defines the meaning of common verbs:

• MUST, REQUIRED, SHALL: absolute requirement of the specification.

• MUST NOT, SHALL NOT: absolute prohibition of the specification.

• SHOULD, RECOMMENDED: there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed.

• SHOULD NOT, NOT RECOMMENDED: there may exist valid reasons in particular circumstances when the particular behavior is acceptable or useful, but the full implications must be understood and carefully weighted.

• MAY, OPTIONAL: the item is truly optional. Implementations must be ready to accomodate for the missing item.