Under normal market conditions, the fund invests at least 80% of its net assets (plus borrowings for investment purposes) in a portfolio of bonds, including but not limited to corporate, government and mortgage bonds, which, at the time of purchase, are rated investment-grade (e.g., rated at least BBB- by S&P Global Ratings or Baa3 by Moody's Investors Service, Inc.) or have an equivalent rating by a nationally recognized statistical rating organization ("NRSRO"), or are of comparable quality if unrated.