anchor.diff:  import "package:dnd/dnd.dart";
   
   void main() {
  -  var box = boxManager.create(128, 128);
  -  box.appendTo(document.body);
  -  box.setColor("blue", background: true);
  -  box.enableDragging(new Dropzone(document.body));
  +  var mainBox = boxManager.create(64, 64);
  +  mainBox.appendTo(document.body);
  +  mainBox.setColor("blue", background: true);
  +  mainBox.enableDragging(new Dropzone(document.body));
   
     boxManager.moveApart(20);
     document.onKeyPress.where((it) => it.keyCode == 67).listen((e) {
  -    var newBox = boxManager.clone(box);
  +    var newBox = boxManager.clone(mainBox);
       var e = newBox.element;
       
       int i = 0;
  
positive.code:     }
      
      void callbackStart(_) {
        if (i == 5) {
          window.requestAnimationFrame(callbackEnd);
          return;
        }
  
negative.code:     
      window.requestAnimationFrame(callbackStart);
    });
    
    document.onKeyPress.where((e) => e.keyCode == 82).listen((e) {
      var boxes = new List.from(boxManager.boxes);
      boxes.forEach((box) {
        if (mainBox != box) {
          boxManager.remove(box);
        }
      });
    });
  }