MouseEvent is an event triggered by mouse gestures. In contrast to the fundamental html.MouseEvent class it can represent the mouse events in a drag operation. Instead of a bare bone 'mouse move' event it can represent a 'mouse hover' or a 'mouse drag' event.

class MouseEvent {
 static const int CLICK = 0;
 static const int DOUBLE_CLICK = 1;
 static const int DRAG_START = 2;
 static const int DRAG = 3;
 static const int DRAG_END = 4;
 static const int HOVER = 5;

 /// the type of the mouse event 
 final int type;
 
 /// the underlying DOM mouse event 
 final html.MouseEvent event;
 
 /**
  * Create a mouse event of type [type] connected to the 
  * underlying DOM mouse [event].
  */
 MouseEvent(this.type, this.event);
 
 String get _typeAsString {
   switch(type) {
     case CLICK: return "CLICK";
     case DOUBLE_CLICK: return "DOUBLE_CLICK";
     case DRAG: return "DRAG";
     case DRAG_START: return "DRAG_START";
     case DRAG_END: return "DRAG_END";
     case HOVER: return "HOVER";
   }
 }

 /// returns true if this mouse event is a drag event
 bool get isDragEvent => type == DRAG_START || type == DRAG ||
     type == DRAG_END;

 @override
 toString() => "{MouseEvent: type=${_typeAsString}, x=${event.offset.x},"
    " y=${event.offset.y}";
}