I agree with you. I don't think that returning a range is necessary.
Even if call position and assignment weren't handled separately, it would still be possible to work off of the length of the argument and the index, without needing a range.
The question is whether or not pg agrees with us enough to add it to arc3 ;)
True. And I do. Unfortunately, I'm busy working on several other things at once right now. If you want to start working on it, be my guest. Hopefully I'll be able to share what I've been doing soon.