This fund is structured so that, under normal circumstances, at least 80% of the income it generates is exempt from federal income taxation. While it maintains the flexibility to acquire securities with any maturity date, the fund primarily focuses on municipal debt instruments with extended maturities. The majority of its holdings are in investment-grade securities; these are defined as those rated within the top four credit categories by at least one prominent credit rating agency, or, if unrated, assessed by T.