Nope, that's not private and not restricted. Essentially everyone in the world is invited and everyone in the world (even those who don't speak) can listen. In

Nope, that's not private and not restricted. Essentially everyone in the world is invited and everyone in the world (even those who don't speak) can listen. In practice the number of participants is much larger; at a table you probably have 2 <= N <= 10. And there's no presence information: if someone "gets up from the table" (stops looking at the thread) you don't know that. There's no visible distinction between being silent and not being there at all.