For example, a production script might include the following scene heading:
```
INT. APARTMENT - DAY
IN: A young woman sits on the couch, reading a book.
```
This indicates that the scene takes place inside an apartment during the day. It begins with a shot of a young woman sitting on the couch, reading a book.
The "in" is used to distinguish the beginning of this scene from the previous one. It also helps to create a visual impression of the scene and to set the tone for the action that follows.