(a) In Subchapters A through K of this chapter, unless the context requires otherwise:

(1) Words importing the singular include the plural;

(2) Words importing the plural include the singular; and

(3) Words importing the masculine gender include the feminine.

(b) In Subchapters A through K of this chapter, the word:

(1) Shall is used in an imperative sense;

(2) May is used in a permissive sense to state authority or permission to do the act prescribed, and the words “no person may *  *  *” or “a person may not *  *  *” mean that no person is required, authorized, or permitted to do the act prescribed; and

(3) Includes means “includes but is not limited to”.

[Doc. No. 1150, 27 FR 4590, May 15, 1962, as amended by Amdt. 1-10, 31 FR 5055, Mar. 29, 1966]