49 C.F.R. § 1500.5 Rules of construction.
Title 49 - Transportation
(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”.
Title 49: Transportation
PART 1500—APPLICABILITY, TERMS, AND ABBREVIATIONS
§ 1500.5 Rules of construction.