The fund invests, under normal circumstances, at least 80% of its net assets (plus any borrowings for investment purposes) in municipal debt securities that (1) pay interest that is excluded from gross income for federal income tax purposes, and (2) do not produce income that will be considered to be an item of preference for purposes of the alternative minimum tax. At least 80% of its net assets will normally be invested in investment grade municipal debt securities. The advisor will attempt to maintain a dollar-weighted average effective portfolio maturity of five years or less.