Does the `MouseEvent` constructor really take two arguments?

My reading of the DOM level 2 spec that `MouseEvent` is [an interface, not a constructor](http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-MouseEvent), and that instances should be [created with `createEvent`](http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-DocumentEvent), but I might have misunderstood.