Eri is the Japanese word for collar, which is the place you grab to control your opponent. Technically speaking, you don't want to limit yourself to grabbing the collar. What if he is wearing a shirt? Or nothing at all?
For those circumstance there are techniques called Ratai Dori: "Naked techniques".
Considering this Tanto Dori - positioning is important so that you can also apply certain Ratai Waza.