Subject to the provisions of a district charter, the electors of a district may, from time to time, and in exercise of their power of the initiative, or by approving a proposition referred to them by the governing body of the district, authorize the district to assume additional functions. [1969 c.700 § 11; 1977 c.95 § 18; 1977 c.665 § 11; 1997 c.516 § 7; 1997 c.833 § 10; 2005 c.22 § 192; 2007 c.173 § 4]