Describe symbolism in Master Class by Terrence McNally

In Master Class, the stage of the theatre symbolically and literally represents the stage of a theatre—the recital hall at the Juilliard School, where Maria Callas gave a series of master classes in 1971 and 1972 before a full house of students and spectators. In the theatre, when Master Class is performed, it is, of course, not really 1971 but the present; it is not Juilliard but (for the play's Broadway run) the Golden Theatre; and the audience is comprised of paying theatregoers, not advanced voice students. But the audience is there, as an audience, in both the reality of the theatrical event and the fiction of the play.