Directory
A provision in a statute, rule of procedure, or the like, that is a mere direction or instruction of no obligatory force and involves no invalidating consequence for its disregard, as opposed to an imperative or mandatory provision, which must be followed. The general rule is that the prescriptions of a statute relating to the performance of a public duty are so far directory that, though neglect of them may be punishable, it does not affect the validity of the acts done under them, as in the case of a statute requiring an officer to prepare and deliver a document to another officer on or before a certain day.
Generally, statutory provisions that do not relate to the essence of a thing to be done, and as to which compliance is a matter of convenience rather than of substance, are directory, while provisions that relate to the essence of a thing to be done, that is, matters of substance, are mandatory.
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Law Library - American Law and Legal InformationFree Legal Encyclopedia: Directed Verdict to Do Not Attempt Resuscitation order (DNAR order)