function CompositionEvent(ev) {
    // [Constructor(DOMString typeArg, optional CompositionEventInit compositionEventInitDict)]
    // interface CompositionEvent : UIEvent {
    //     readonly    attribute DOMString data;
    // };

    UIEvent.call(this, ev);

    /**
     * @name CompositionEvent#data
     * @type String
     */
    this.data = ev.data;
}
See [UI Events (formerly DOM Level 3 Events)](http://www.w3.org/TR/2015/WD-uievents-20150428/#events-compositionevents).

@class CompositionEvent
@augments UIEvent

@param {Event} ev The native DOM event.