(1)    The auditorium board shall regulate and control the use of said institution, and fix the terms and conditions of its use; and shall do all things necessary for the maintenance and operation thereof.

   (2)   Said institution shall be used primarily for public meetings, conventions, expositions, and other purposes of a public nature, which are hereby declared to be public purposes; but not for exhibits or trade shows if a charge is made for space occupied by any exhibitor or when an admission fee is exacted.

   (3)   When not in use for any of said primary purposes, the board may rent said institution, or any part thereof, on such terms and for such purposes as may be deemed advisable and not inconsistent with said primary purposes.

   (4)   

      (a)    In this subsection:

         1.    “Convention” means a county, state, or national assembly of authorized, chosen, or elected delegates or representatives meeting to accomplish some specific commercial, industrial, labor, civil, social, scientific, or educational object.

         2.    “Patriotic affairs” means affairs given for the encouragement and support of the government in time of war, or for the benefit and support of soldiers, sailors, or marines who have been, or are in the service of the United States, including memorial exercises, exhibitions, fairs, reunions, entertainments, or barracks for such persons, and to all of which affairs the public is admitted without charge.

      (c)    When not in use for any of its primary purposes, the common council of said city may authorize the gratuitous use of said institution, or any part thereof, for the purposes of conventions, or for offices, class rooms, studios, gymnasiums, lodge rooms, or accommodations for any industrial, commercial, scientific, educational, fraternal, musical, or labor organization which in its opinion will prove a public benefit to the city and promote the welfare and public interests of its citizens and to which said citizens are admitted without charge; and said purposes are hereby declared to be public purposes.

      (d)    Whenever the common council shall approve the gratuitous use of the institution for the particular conventions and purposes specified in this subsection, said common council shall appropriate to the auditorium fund the usual and customary rentals charged therefor. The aggregate amount to be so expended may be made a part of the annual budget, as provided by ch. 65, 1943 stats.