anchor.diff:      return index;
   
     }
  +
   
     List retrieve(source) {
       int index = -1;
  
positive.code:   int maxObjects = 10;
    int maxLevels = 4;
    int level = 0;
   
    Bounds bounds = null;
  
    List<dynamic> objects = new List<dynamic>();
  
    List<QuadTree> nodes = new List<QuadTree>(4);
  
  
negative.code:     var i = this.nodes.length;
  
      while (i-- > 0) {
        if (this.nodes[i] != null) {
          this.nodes[i].clear();
          this.nodes[i] = null;
        }
      }
  
  