What's the "rekordboxdj://" custom protocol for?

I recently discovered there's a custom protocol that can be used to start Rekordbox from a web browser or a shortcut.

I have several question about it:

1. Since when is it available ?
2. Can it be used to always start the latest Rekordbox DJ version installed ?
3. What's the purpose of the command line argument ? What options are available ?
4. Does it exist on Mac as well?

Thanks for your answers.