I would like it if actors could establish and practice this protocol with one another. I do it with my fellows. I find something about their performance that works and tell them about it. Then, I vary from the old workshop rules by NOT offering harder criticism, unless the actor asks for it. Sometimes they do, sometimes they don't. Sometimes they do much later. Not only is offering positive feedback a kindness, it's also as important as offering 'negative' feedback. The information alone is just as important, as an actor tries to gauge his or her own work. One downside of this approach is that, actors' egos being what they are, sometimes the actor thinks that my positive feedback is all there is; they think, in my eyes, they've done only great work. And then, when they see ME work, and tune themselves to the problems in my performance, they don't give ME feedback on what specifically worked, and instead of then giving me 'negative' feedback, they don't say anything to me at all... which leaves me feeling terrible. And resentful about having taken such care with them, when it was their turn in the spotlight. I think I've unwittingly over fed two or three egos to near obesity in this way, lately, and sorta feel like they've been stealing food off my plate when it's been my turn to dine. Grrrrr.
Grump, Grump, Humph, Pshaw.
I've not heard anyone in theater offer a protocol for criticism as I often heard creative writing instructors do, usually on the first day of class. If I teach again, it will be lesson number one.