Fascinating. http://www.onstageblog.com/columns/2017/4/17/8-ways-to-respect-the-importance-of-stage-etiquette?rq=Etiquette
"Noel [Coward] and I were in Paris once. Adjoining rooms, of course. One night, I felt mischievous, so I knocked on Noel's door, and he asked, 'Who is it?' I lowered my voice and said 'Hotel detective. Have you got a gentleman in your room?' He answered, 'Just a minute, I'll ask him.'" (Beatrice Lillie)