The investment seeks to track the investment results (before fees and expenses) of the ICE ® US Municipal AMT-Free VRDO Constrained Index. The fund generally invests at least 80% of its total assets in the components of the underlying index. The underlying index tracks the performance of U.S. dollar denominated tax-exempt variable rate demand obligations that are publicly issued by U.S. states and territories, and their political subdivisions, and that have interest rates that reset daily, weekly or monthly.