It is commonly used for tweening powered by css. This is all well and good, but what if you want to tween a dom element attribute such as viewBox on a SVG element? Well, the animation method can handle that as well. Take a look.
Also, see a working example here. (Works in all modern browsers)
The “duration” is the amount of milliseconds the tween will last. “step” will be called at every step of the tween which is where you will put your animation logic of course, and finally “complete” will be called once the tween if finished. Tween on.