Strategy. Main investments. Under normal circumstances, the fund invests at least 80% of net assets in securities issued by municipalities across the United States and in other securities whose income is free from regular federal income tax. The fund may invest up to 20% of net assets in securities whose income is subject to the federal alternative minimum tax (AMT). Due to regulatory changes, effective June 11, 2026, the fund will replace the 80% investment policy and related disclosures set forth in this prospectus. Specifically, effective June 11, 2026, under normal circumstances, the fund will invest at least 80% of net assets, plus the amount of any borrowings for investment purposes, in securities issued by municipalities across the United States and … Show more… Main investments. Under normal circumstances, the fund invests at least 80% of net assets in securities issued by municipalities across the United States and in other securities whose income is free from regular federal income tax. The fund may invest up to 20% of net assets in securities whose income is subject to the federal alternative minimum tax (AMT). Due to regulatory changes, effective June 11, 2026, the fund will replace the 80% investment policy and related disclosures set forth in this prospectus. Specifically, effective June 11, 2026, under normal circumstances, the fund will invest at least 80% of net assets, plus the amount of any borrowings for investment purposes, in securities issued by municipalities across the United States and in other securities whose income is free from regular federal income tax. Derivative instruments that provide exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the funds 80% investment policy, consistent with the funds investment policies and limitations with respect to investments in derivatives. The fund can buy many types of municipal securities of all maturities and duration. These may include revenue bonds (which are backed by revenues from a particular source) and general obligation bonds (which are typically backed by the issuer's ability to levy taxes). They may also include municipal lease obligations and investments representing an interest therein. The fund may invest without limit in high yield debt securities. High yield debt securities (commonly referred to as junk bonds) are those rated below the fourth highest credit rating category (i.e. grade BB/Ba and below) and may include debt securities not currently paying interest and debt securities in default. Compared to investment-grade debt securities, junk bonds generally pay higher yields, have higher volatility and higher risk of default on payments of interest or principal. The fund generally intends to invest approximately 40% - 60% in high yield debt securities, although the fund may invest without limit in such securities. The fund may use forward delivery bonds, which are bonds priced on a determined date but that are not issued and settled until a later period (ranging from several weeks to more than a year). The fund may also engage in tender option bond transactions. In a tender option bond transaction, the fund transfers fixed-rate long-term municipal bonds into a special purpose entity (a TOB Trust), which then typically issues two classes of beneficial interests: short-term floating rate interests (TOB Floaters), which are sold to third party investors, and residual inverse floating rate interests (TOB Inverse Floater Residual Interests), which are generally held by the fund. Forward delivery bonds with settlement dates greater than 35 days and tender option bond transactions are treated as derivatives by the fund and are subject to the fund's policies and procedures with respect to derivatives. Forward delivery bonds with settlement dates greater than 35 days generally are used for non-hedging purposes to seek to enhance potential gains. The fund may leverage its assets and seek to enhance potential gains through the use of proceeds received from TOB Floaters. Management process. Portfolio management looks for securities that appear to offer the best opportunity to meet the fund's objective. In making its buy and sell decisions, portfolio management typically weighs a number of factors against each other, from economic outlooks and possible interest rate movements to changes in supply and demand within the municipal bond market. When evaluating any individual security and its issuer, portfolio management may consider a number of factors including the securitys credit quality and terms, such as coupon, maturity date and call date, as well as the issuers capital structure, leverage, and ability to meet its current obligations. Portfolio management generally also considers financially material environmental, social, and governance (ESG) factors, when available. Such factors may include, but are not limited to, exposure to climate change risks, income levels and unemployment data, and an issuers governance structure and practices. Derivatives. The fund may invest in derivatives, which are financial instruments whose performance is derived, at least in part, from the performance of an underlying asset, security or index. In particular, portfolio management may use futures contracts for duration management (i.e., reducing or increasing the sensitivity of the fund's portfolio to interest rate changes). The fund may also use other types of derivatives (i) for hedging purposes; (ii) for risk management; (iii) for non-hedging purposes to seek to enhance potential gains; or (iv) as a substitute for direct investment in a particular asset class or to keep cash on hand to meet shareholder redemptions. Show less