I am not entirely fond of this word "supertext," but sometimes one needs to put a name on a concept. It caught on amongst my students because it suggests something in contrast to the character's "subtext," and operating on a higher plane. Psychologists have a term for something similar, "meta-cognition." Sorry, that probably doesn't help...
Anyway, "supertext" refers to the actor’s attitude toward being on the stage, including everything from career goals, to love of the playwright’s words, to surprise at where the audience laughed, to irritation with one's colleagues. It will always find some form of expression in a production, no matter how naturalistic the intended style, so should not be ignored. In fact, in a healthy production, a shared supertext is the very source of its style. It is a micro culture growing out of the actors’ attitudes and needs, not something imposed from above.
An over-simplified example:
Emma is cast as Juliet. Larry is cast as Romeo. Juliet's subtext is: "What a hunk! Too bad he was born into that family." Juliet's text is: "Romeo, Romeo, wherefore etc..." Emma's supertext is: "If Larry forgets his lines again, I'll murder him."
No matter how deeply an actor goes into character, she unmistakably carries her attitudes and reasons for being an actor with her. It's best when the nature and expression of this can be an integral part of the production and not something she is fighting to hide from the audience.
When a group of actors share much the same supertext, an ensemble style becomes possible. When it is manifested as the actors taking ownership of the production and carrying that attitude with them on to the stage, they are more than halfway to a success.
Many chronic acting problems such as self-consciousness are explainable in terms of supertext. However, trying to eliminate the supertext is not the solution.
"Hey guys, all those tissues! Clean up the dressing room, please! Take care of the show. One can always see the state of the dressing room reflected in your work out there on the stage!"
- Pablo Vela