The fund normally invests at least 80% of its net assets (plus any borrowings for investment purposes) in municipal obligations that are exempt from regular federal income tax. It may invest up to 50% of its net assets in obligations rated below investment grade. The fund may invest up to 20% of its net assets in other debt obligations, including (but not limited to) taxable municipal obligations, U.S. Treasury securities and obligations of the U.S. government, its agencies or instrumentalities.