Directory provision is a statutory or contractual sentence or paragraph in which a directory requirement appears. A directory requirement is one that is optional as opposed to a mandatory provision. It is a statutory or contractual instruction that is desirable but not absolutely necessary.
Generally put, mandatory provisions are essential to the substance of the law to which they relate. Such provisions may be ordered in the statute to be done in a certain way or at a certain time, and in no other; or their omission may incur consequences that are themselves set forth in the statute. The converse characterizes directory provisions: lack of strict compliance does not injure any substantive right, and the underlying proceeding is not invalidated by the lack of compliance. Thus the distinction between mandatory and directory statutory provisions is not simply whether the provision must be performed. More often, the distinction turns on whether the manner or time of performing the act is so critical to the statutory subject matter that any deviation can "injuriously affect" the rights of interested persons.[Exxon Chem. Patents v. Lubrizol Corp., 935 F.2d 1263, 1268 (Fed. Cir. 1991)]