The fund seeks to achieve its investment objective by investing under normal circumstances at least 80% of its assets in debt securities whose interest is, in the opinion of bond counsel for the issuer at the time of issuance, exempt from federal income tax. It may invest up to 30% of its total assets in high yield securities. The average portfolio duration of this fund normally varies within (negative) 2 years to positive 2 years of the portfolio duration of the securities comprising the Bloomberg Municipal Bond Index.