Yes, the rules are:
- A callback can have only ONE output
- An element can only be used ONCE as output (you can’t have two callbacks using the same output)
For example, if you need to change the text of 3 different elements, you might need 3 callbacks. I’m currently looking into “loop over callbacks” for when I need to do the exact same action on several elements of the page. I’ve bookmarked topics of interests:
- Handel multiple callback outputs programmatically
- https://github.com/plotly/dash/issues/59#issuecomment-313214212
I’ll probably work on it in a few weeks