javascript Class Set ?

Question

Is there a javascript class/object name set? In a raphael demo i saw this code

var targets = r.set();
                targets.push(r.circle(300, 100, 20),
                   r.circle(300, 150, 20), ...

and i didnt know js can use object that way. So i looked into the source and it looks like i am calling this

paperproto.set = function (itemsArray) {
    arguments[length] > 1 && (itemsArray = Array[proto].splice.call(arguments, 0, arguments[length]));
    return new Set(itemsArray);
};

But i googled and found nothing about a class called set nor seen anything in code.

Where can i find more about Set?