Certain words and phrases used in this Zoning Code are defined for the purpose thereof as follows. Words used in the present tense include the future. The singular number includes the plural, and the plural the singular. The word "lot" includes the word "plot". The word "occupied" includes the word "designed or intended to be occupied". The word "used" includes the words "arranged", "designed" or "intended to be used". The word "shall" is a mandatory requirement, the word "may" is a permissive requirement and the word "should" is a preferred requirement.