Rules of regulatory construction.

(a) As used in this part: (1) Includes means including but not limited to; (2) May means is permitted to or is authorized to; (3) May not means is not permitted to or is not authorized to; and (4) Shall or must is used in the mandatory and imperative sense. (b) In this part: (1) Words importing the singular include the plural; and (2) Words importing the plural include the singular.