Section 1.3 - Rules of construction(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