(a) In this subchapter, unless the context requires otherwise:
(1) Words imparting the singular include the plural;
(2) Words imparting the plural include the singular; and
(3) Words imparting the masculine gender include the feminine;
(b) In this subchapter, the word: (1) ``Shall'' is used in an imperative sense;
(2) ``Must'' is used in an imperative sense;
(3) ``Should'' is used in a recommendatory sense;
(4) ``May'' is used in a permissive sense to state authority or permission to do the act described, and the words ``no person may* * *'' or ``a person may not* * *'' means that no person is required, authorized, or permitted to do the act described; and
(5) ``Includes'' is used as a word of inclusion not limitation. [Amdt. 171-32, 41 FR 15996, Apr. 15, 1976, as amended by Amdt. 171-32A, 41 FR 40630, Sept. 20, 1976; Amdt. 171-121, 58 FR 51528, Oct. 1, 1993; 75 FR 60338, Sept. 30, 2010]