By local law, a legislative body may specify in a zoning law the allowable modifications that may be made by a variance. The modifications in a variance: may be only of density, bulk, dimensional, or area requirements of the zoning law; may be only allowed where, owing to conditions peculiar to the property and not because of any action taken by the applicant, a literal enforcement of the zoning law would result in unnecessary hardship or practical difficulty as specified in the zoning law; and may not be contrary to the public interest.