Strategy. The Fund seeks to track the investment results of the Bloomberg U.S. CMBS (ERISA Only) Index (the Underlying Index ), which measures the performance of investment-grade (as determined by Bloomberg Index Services Limited (the Index Provider or Bloomberg )) commercial mortgage-backed securities ( CMBS ), which are classes of securities (known as certificates ) that represent interests in pools of commercial mortgages. The Underlying Index includes only CMBS that are Employee Retirement Income Security Act of 1974, as amended ( ERISA ) eligible under the underwriters exemption, which will deem ERISA eligible the certificates with the first priority of principal repayment, as long as certain conditions are met, including the requirement that the certificates be rated in one of the … Show more… The Fund seeks to track the investment results of the Bloomberg U.S. CMBS (ERISA Only) Index (the Underlying Index ), which measures the performance of investment-grade (as determined by Bloomberg Index Services Limited (the Index Provider or Bloomberg )) commercial mortgage-backed securities ( CMBS ), which are classes of securities (known as certificates ) that represent interests in pools of commercial mortgages. The Underlying Index includes only CMBS that are Employee Retirement Income Security Act of 1974, as amended ( ERISA ) eligible under the underwriters exemption, which will deem ERISA eligible the certificates with the first priority of principal repayment, as long as certain conditions are met, including the requirement that the certificates be rated in one of the three highest rating categories by Fitch Ratings, Inc., Moody's Investors Service, Inc. or S&P Global Ratings. The Underlying Index includes investment-grade CMBS that are ERISA eligible with $300 million or more of aggregate outstanding transaction size. In addition, the original aggregate transaction must be $500 million or more and the tranche size must be $25 million or more. CMBS certificates must have an expected life of at least one year and must be either fixed-rate or subject to an interest rate cap equal to the weighted average coupon of the underlying asset pool. Excluded from the Underlying Index are non-ERISA eligible securities and privately issued securities, including those which may be resold in accordance with Rule 144A under the Securities Act of 1933, as amended (the 1933 Act ). The securities in the Underlying Index are updated on the last calendar day of each month. BFA uses an indexing approach to try to achieve the Funds investment objective. The Fund does not try to beat the index it tracks and does not seek temporary defensive positions when markets decline or appear overvalued. Indexing may eliminate the chance that the Fund will substantially outperform the Underlying Index but also may reduce some of the risks of active management, such as poor security selection. Indexing seeks to achieve lower costs and better after-tax performance by aiming to keep portfolio turnover low in comparison to actively managed investment companies. BFA uses a representative sampling indexing strategy to manage the Fund. Representative sampling is an indexing strategy that involves investing in a representative sample of securities or other instruments that collectively has an investment profile similar to that of an applicable underlying index. The instruments selected are expected to have, in the aggregate, investment characteristics (based on factors such as market value and industry weightings), fundamental characteristics (such as return variability, duration ( i.e. , an instrument's price sensitivity to a change in interest rates), maturity or credit ratings and yield) and liquidity measures similar to those of an applicable underlying index. The Fund may or may not hold all of the components of the Underlying Index. 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 will invest no more than 10% of its assets in futures, options and swaps contracts that BFA believes will help the Fund track the Underlying Index as well as in fixed income securities other than the types included in the Underlying Index, but which BFA believes will help the Fund track the Underlying Index. Cash and cash equivalent investments associated with a derivative position will be treated as part of that position for the purposes of calculating the percentage of investments included in the Underlying Index. The Fund seeks to track the investment results of the Underlying Index before fees and expenses of the Fund. The Underlying Index is sponsored by Bloomberg, which is ? independent of the Fund and BFA. The Index Provider determines the composition and relative weightings of the components of the Underlying Index and publishes information regarding the market value of the Underlying Index. Industry Concentration Policy. The Fund will concentrate its investments ( i.e. , hold 25% or more of its total assets) in a particular industry or group of industries to approximately the same extent that the Underlying Index is concentrated. For purposes of this limitation, securities of the U.S. government (including its agencies and instrumentalities), repurchase agreements collateralized by U.S. government securities, and securities of state or municipal governments and their political subdivisions are not considered to be issued by members of any industry. Show less