Illegal or art?

At issue is the Minneapolis Park Board ordinance called Proper Attire Required. It reads: "No person 10 years of age or older shall intentionally expose his or her own genitals, pubic area, buttocks or female breast below the top of the areola, with less than a fully opaque covering in or upon any park or parkway. ... This provision does not apply to theatrical, musical, or other artistic performances upon any park or parkway where no alcoholic beverages are sold."