The SEC Investor Bulletin on Exchange-Traded Funds (ETFs) (mirror) divides ETFs into two classes: Index-Based ETFs and Actively Managed ETFs. As its name indicates, index-Based ETFs track some indexes. Unlike Index-Based ETFs, Actively managed ETFs are required to publish their holdings daily.
Does the SEC have the list or definition of indexes that an ETF is allowed to track to be classified as an Index-Based ETF? Motivation of the question: an Actively Managed ETF could try to be regarded as an Index-Based ETFs by creating some ad hoc index.