This genre is unique because of its unusual format. Only scripts and screenplays show the dialogue with little emotion. In a script, you don’t necessarily write out that a character says something or yells it or whispers it unless you are positive it needs to be there. Otherwise, it depends on the director’s and cast’s interpretation of the character, which will come later.
When you are writing script to screenplays, you are writing the bare bones of the show to come. You are only writing in the minimal information needed to bring your vision, with just the details needed to keep the storyline the way you see it. You are like the original director, writing down or typing the scenes as you see them.
Of course, then the big director will probably come along and mark up and even rewrite parts of your script, so once someone has it, you need to be careful and not take any changes personally.