Class IV. Other citizens of the Borough, to be appointed by the Mayor. Members of Class IV shall hold no other municipal office, position or employment except that one member may be a member of the Historic Preservation Commission, if established pursuant to N.J.S.A. 40:55D-1, and one member may be a member of the Board of Education. If there is an Environmental Commission, the member of the Environmental Commission who is also a member of the Planning Board as required by N.J.S.A. 40:56A-1 shall be a Class IV member unless there be among the Class IV or alternate members of the Planning Board a member of the Board of Education, in which case the member common to the Planning Board and Environmental Commission shall be deemed a Class II member of the Planning Board. For the purposes of this section, membership on a Borough board or commission whose function is advisory in nature, and the establishment of which is discretionary and not required by statute, shall not be considered the holding of a Borough office.