I'm reading Agatha Christie's Murder on the Orient Express, and one line says "She had on a shingle cap and I only saw the back of her head.” Googling around, I found "shingle caps" that are beaded and look like you'd wear them out on the town, as well a pattern for a more modest, crocheted one. I'm guessing it's like a boudoir cap to keep your hair nice while you sleep, so it would be more like the crocheted one. Can a vintage fashion expert confirm this for me?