D is a college town that became concerned about the deterioration of its rental housing stock. The deterioration was believed to be caused by landlords' neglect of health and safety regulations. D promulgated two ordinances. The Building Officials & Code Administrators International, Inc.'s (BOCA's) 1996 National Property Maintenance Code became section 23.16(b) of chapter 23. The second ordinance created a procedure for the periodic inspection and licensure of rental property. Section 23.13(b) now forbids landlords to rent out residential property that does not comply with the minimum standards established by the BOCA code and any other standards adopted by D. Chapter 22 of the housing code already contained a provision limiting the number of unrelated persons who may live in a single-family dwelling to four. A 'Commentary' that was promulgated with the amended sections lists the 'Duties of the Tenant' which quotes the multiple occupancy provision of chapter 22. Chapter 23 now divides rental property into three classes. Class A properties are those found to be fully compliant with the housing code. Licenses permitting the rental of units in such properties are issued for three years. Class B properties are those with only minor infractions of the ordinance's minimum standards, and such properties are licensed for one year. Class C properties are in serious violation of the standards, and they may not be licensed for rental purposes at all. D's building inspector inspects each rental property. If a landlord or tenant refuses to permit the inspection, the building inspector can apply to a Wisconsin court for a 'special inspection warrant' for real property. The application for the warrant and the warrant itself declare the search to be for the purpose of determining compliance with sections 23.13(b) and 23.16 of the housing code. The inspector's practice in executing such warrants was to search for violations of the multiple occupancy provision as well. This involved his looking in closets or bureau drawers for evidence that more than four unrelated persons are living in the apartment. The building of any landlord who refused to permit inspection was placarded with notices that it was unfit to be inhabited. This practice was abandoned in favor of utilizing the warrant procedure. Ps sued D to enjoin enforcement of the ordinance permitting periodic inspections. P argued there was not probable cause under the Fourth Amendment. The district court granted an injunction against the occupancy searches, and both parties appealed.