The fund's main objective is to provide a high and steady flow of current income that is not subject to federal personal income taxes. Although there are no specific limits on the maturity of individual securities within the portfolio, it is structured to maintain a value-weighted average maturity typically ranging from 10 to 25 years. A substantial portion, at least 75%, of the fund's investments are in municipal bonds that are highly rated—meaning they fall into the top three credit-rating tiers from nationally recognized agencies, or are judged to be of equivalent quality by the fund's advisor if unrated.