The fund seeks to provide diversified investment exposure to the U.S. high yield bond market. While the fund is not an index fund and does not attempt to replicate any index, the fund normally invests substantially all of its assets in bonds that, at the time of purchase, are included in the Bloomberg US Corporate High Yield Total Return Index (Index), ETFs providing exposure to securities included in the Index and derivatives with economic characteristics similar to such bonds, ETFs or the Index. The fund's derivatives investments may include futures, total return swaps, structured notes and credit default swap indexes. Under normal circumstances, the fund will invest at least 80% of its net assets, plus any borrowings for investment purposes, in high yield securities and ETFs providing exposure to such securities. The fund's policy with respect to the investment of at least 80% of its net assets may be changed by the fund's board, upon 60 days' prior notice to shareholders. The fund considers high yield securities to be securities with ratings that qualify for inclusion in the Index.