The Fund seeks to achieve its investment objective by investing at least 80% of its assets (exclusive of collateral held from securities lending) in securities included in its underlying index. The Fund also has a policy to invest, under normal circumstances, at least 80% of its net assets plus any borrowings for investment purposes (measured at the time of purchase) (Net Assets) in municipal securities, the interest on which is exempt from regular federal income tax (i.e., excluded from gross income for federal income tax purposes). The Index is a rules-based index that is designed to measure the performance of the municipal securities market with remaining maturities between one and fifteen years with screens that take into account certain social or environmental factors. These screens may exclude negative sectors, sources of funds and use of proceeds and include securities with potentially environmentally or socially beneficial outcomes. Municipal securities include fixed income securities issued by or on behalf of states, territories and possessions of the United States (including the District of Columbia) and the political subdivisions, agencies and instrumentalities, the interest on which is exempt from regular federal income tax.