The index seeks to track the investment results of an index composed of investment-grade U.S. municipal bonds expected to mature or be redeemed before December 2, 2031. The fund will invest at least 80% of its assets in the component securities of the underlying index, and the fund will invest at least 90% of its assets in fixed income securities of the types included in the underlying index that BFA believes will help the fund track the underlying index. The fund is non-diversified.