It just works.
And the moment it doesn’t – your doomed. As a developer and as a user. I’ve recorded a little film demonstrating what happens if it’s not working:
And this also works the other way round. It happens all the time that the complete data is gone. Just gone. With no chance to get it back and no – it’s not the developer’s or the user’s fault. It was just erased by iCloud without any predictable reason and there is no chance to debug it or to narrow it down or to avoid it.
All I can do is automatically create a local backup for any possible change and add a ‘feature’ to restore from such a backup. But this doesn’t mean that iCloud will not directly overwrite it again.
Apple, please ask Google for help with your web based things. You simply suck at it!