49 CFR § 1500.5 - Rules of construction.
(a) In this chapter, unless the context requires otherwise:
(1) Words importing the singular include the plural.
(2) Words importing the plural include the singular.
(3) Words importing the masculine gender include the feminine.
(b) In this chapter, the word:
(1) “Must” 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”.