The investment seeks to track the investment results of the BofA Merrill Lynch U.S. High Yield Constrained Index. The fund generally will invest at least 90% of its assets in the component securities of the underlying index and may invest up to 10% of its assets in certain futures, options and swap contracts, cash and cash equivalents, including shares of money market funds advised by BFA or its affiliates, as well as in securities not included in the underlying index. The underlying index is designed to provide a broad representation of the U.S. dollar-denominated high yield corporate bond market. The fund is non-diversified.