docs: function HeadlessEvent(type, opt_bubbles, opt_preventable) {
        this.type = type;
        this.bubbles = (opt_bubbles !== undefined ?
            !!opt_bubbles : false);
        this.cancelable = (opt_preventable !== undefined ?
            !!opt_preventable : false);
  
        this.defaultPrevented = false;
        this.cancelBubble = false;
      }