> I think there was a push for all "underlying" ranges to be made public, and named source (just like for retro). so this way, a user could (not that I know a use case for it), write myTee.source.

It has been brought before, but I don't think that it's ever been discussed in depth. The main problem with it is that it completely bypasses the range. For instance, if you did it with `filter`, then what's in `source` wouldn't necessarily have much relation to what `filter` was iterating over, because `filter` skips at least some of the elements. I'd argue that no new ranges should make their source public without it being thoroughly discussed in the newsgroup first.

The thing that's off here is `TeeRange` isn't a Voldemort type, which is almost always how we do it now. There isn't much reason to declare `TeeRange` outside of tee if it's `private`.