Cocoa/OSX tagging UI

I'm looking to implement a tagging interface on OSX that lets users type text "tags" to attach to an object. Ideally, I'd like to implement a fancy UI like the screenshot below:

-

Note: This shows multiple states

This UI lets the user type tags, then groups them into a rounded shape when enter is pressed. They can be deleted by dragging over to highlight (shown in dark blue) and p开发者_开发问答ressing delete. I think this is a slick interface for quickly jotting down a bunch of tags without having to repeatedly press form buttons.

I've seen this interface in Mail.app and a few other places in OSX, so that makes me wonder if there's some sort of cocoa class out there for this. Anyone know of one? If not, I guess I'm looking at a custom opengl view.

---

Take a look at NSTokenFieldCell.