Dear Diary: My friend Leslie, a retired teacher, invited me to the New York Public Library for the Performing Arts one Saturday to watch a film of a Broadway musical. I told her if it was being shown at the Theater on Film and Tape Archive, it was restricted to researchers and professionals. I found the title in the online catalog, and verified that “all viewers must have a valid reason for viewing and a library card.” But Leslie insisted, and I agreed to meet. Before entering the screening room, I stopped to quietly caution her. “Volunteer no information,” I...