To pursue its goals, the fund normally invests at least 80% of its net assets, plus any borrowings for investment purposes, in municipal bonds that provide income exempt from federal income tax. Municipal bonds are debt securities or other obligations issued by states, territories and possessions of the United States and the District of Columbia and their political subdivisions, agencies and instrumentalities, or multistate agencies and authorities, and certain other specified securities.

The fund normally invests at least 50% of its assets in municipal bonds rated BBB/Baa or lower or the unrated equivalent as determined by Insight North America LLC, the fund's sub-adviser. Municipal bonds rated below investment grade (BB/Ba or lower) are commonly known as "high yield" or "junk" bonds. These bonds typically offer higher yields than investment grade bonds, but involve greater risks, including the possibility of default, and increased market price volatility. The fund may invest up to 10% of its assets in defaulted municipal bonds. The fund may invest up to 50% of its assets in higher quality municipal bonds (those rated AAA/Aaa to A or the unrated equivalent as determined by the fund's sub-adviser).

The dollar-weighted average maturity of the fund's portfolio normally exceeds ten years, but the fund may invest without regard to maturity. A bond's maturity is the length of time until the principal must be fully repaid with interest. Dollar-weighted average maturity is an average of the stated maturities of the bonds held by the fund, based on their dollar-weighted proportions in the fund.

The fund's portfolio managers focus on identifying undervalued sectors and securities. To select municipal bonds for the fund, the portfolio managers use fundamental credit analysis to estimate the relative value and attractiveness of various sectors and securities and actively trade among various sectors based on their apparent relative values.

Although the fund seeks to provide income exempt from federal income tax, income from some of the fund’s holdings may be subject to the federal alternative minimum tax.