The Fund seeks to achieve its investment objective primarily through investments in municipal debt securities whose interest payments generally are exempt from U.S. federal income taxes. Under normal circumstances, the Fund invests at least 80 percent of its net assets (plus the amount of any borrowings for investment purposes) in municipal debt securities. For these purposes, municipal debt securities include debt obligations issued by state and local governments, their political subdivisions, agencies, and public authorities, and certain other governmental issuers (such as the U.S. territories of Puerto Rico, Guam, and the U.S. Virgin Islands). Municipal debt securities in which the Fund may invest also include participations or other interests in municipal securities backed by banks, insurance companies, and other financial institutions. The Fund may invest up to 30 percent of its net assets in municipal securities subject to the federal alternative minimum tax. The federal alternative minimum tax is a separate U.S. federal tax system that operates in parallel to the regular federal income tax system but eliminates many deductions and exclusions. The federal alternative minimum tax system treats as taxable certain types of income that are nontaxable for regular income tax purposes, such as the interest on certain private activity municipal bonds, which are bonds issued by state or local governments to fund projects that primarily benefit private businesses or individuals rather than the general public.