Q. I’m editing a textbook that references a play. Should it be “Act 3,” “act three,” or “act 3”? A solution to this mystery would be greatly appreciated. I’ve looked at CMOS a hundred times for help with this issue.

A. Wow—a hundred times? If you can suggest how we can make CMOS 8.184 more clear, we’ll try to do better in the next edition: “Words denoting parts of long poems or acts and scenes of plays are usually lowercased, neither italicized nor enclosed in quotation marks . . . act 3, scene 2.”