Section 390.7 - Rules of construction(a) In part 325 of subchapter A and in this subchapter, unless the context requires otherwise: (1) Words imparting the singular include the plural;(2) Words imparting the plural include the singular;(3) Words imparting the present tense include the future tense.(b) In this subchapter the word- (1)Officer includes any person authorized by law to perform the duties of the office;(2)Shall is used in an imperative sense;(3)Must is used in an imperative sense;(4)Should is used in a recommendatory sense;(5)May is used in a permissive sense; and(6)Includes is used as a word of inclusion, not limitation.53 FR 18052, 5/19/1988, as amended at 60 FR 38744, 7/28/1995; 83 FR 16226, 6/15/2018