Listing information like this is always problematic because code can change and we can't keep docs updated. Instead of this, let's tell the reader to run this command $ php bin/console debug:container session.storage. to know the exact storages available in their app.

There you go :-) I see your point, but on the other hand I think there should be a detailed explanation of all those storages somewhere. What do you think?

And I don't quite understand the difference to handler_id - its description is exactly the same:

The service id used for session storage.

But in fact, handler_id is about the storage location (Symfony folder, PHP folder, Redis)? But what is save_path then?

Thanks Thomas! Let's merge this now and the pending question can be tackled in another issue or PR. Thanks!