Better document how form submit callbacks should be called

Thanks for opening this. I'm not even really sure *where* to document this. 😅 I guess that's one of the remaining tasks...

Wouldn't this be in form.api.php? It is for "Callbacks and hooks related to form system.".

How does this work for Hooks that use dependency injection and autowiring?

@catch had this question:

It would be good to open a follow-up to discuss whether there's a DI-friendly option for form callbacks. Could we use service notation maybe?

📌 Use CallableResolver for form callbacks Active

Yes CallableResolver supports the service notation.