transition.tween(name[, value])
For each selected element, assigns the tween with the specified name with the specified value function. The value must be specified as a function that returns a function. When the transition starts, the value function is evaluated for each selected element, in order, being passed the current datum d and index i, with the this context as the current DOM element. The returned function is then invoked for each frame of the transition, in order, being passed the e