Usually you only must write what will be heart completly.
- If a character is interrupted, you stop the text when the other is starting speaking.
Then if you wanna know for you and for the actor, what’s the intended speech, you have to take notes for you. Cause of course it seems more natural for the actor to say the whole text, and be really interrupted. Otherwise, he’ll stop suddently cause he doesn’t know what to say later.
- If one tells not very audible conversations, you can still write it, but you must write it so :
CHARACTER 1
(whispering, or not quite audible)
Blabla, Blabla, Blabla
Do you got any other situations ? Cause I can explain you other solutions.
But one thing I can tell you, is that, you can break the rules, and have your own, to have your own coherence. You can find an original system.