Section 90.5. Mandatory Rules, Permissive Rules, and Explanatory Material.

(A) Mandatory Rules.

Mandatory rules of this Code are those that identify actions that are specifically required or prohibited and are characterized by the use of the following terms:

(1) for imposing a duty or condition precedent, "shall" or "must", and

(2) for prohibiting action, "shall not", "may not", or "no ... may".

(B) Permissive Rules.

Permissive rules of this Code are those that identify actions that are allowed but not required, are normally used to describe options or alternative methods, and are characterized by the use of the following terms:

(1) for discretionary authority, "shall be permitted", "is permitted", or "may", and

(2) for negating a duty or condition precedent, "shall not be required", "is not required", or "need not".

(D) Informative Annexes. {As in NEC}