The investment seeks to provide investment results that correspond to the total return performance of fixed-income securities in the aggregate, as represented by the ICE BofA US Municipal Securities Index. The fund generally invests at least 80% of its assets, plus the amount of any borrowings for investment purposes, in securities or other financial instruments that are components of or have economic characteristics similar to the securities in the index. The index tracks the performance of U.S. dollar denominated investment grade tax-exempt debt publicly issued by U.S. states and territories, and their political subdivisions, in the U.S. domestic market.