Under normal market conditions, the fund invests at least 80% of its net assets in investment grade municipal bonds rated BBB/Baa or higher at the time of purchase by at least one independent rating agency, or, if unrated, judged by the fund's sub-adviser to be of comparable quality. It may invest up to 20% of its net assets in below investment grade municipal bonds, commonly referred to as "high yield" or "junk" bonds.