anchor.diff:            //recurse
             _extractElements(value);
           }
  -        
  +
         });
       }
       else if (data is Collection) {
  
positive.code:       return _objectData.remove(key);
      }
      else {
        throw new UnsupportedOperationException("JsonObject is not extendable");  
      }
    }
  
  
negative.code:       return _objectData[key] = value;
      }
      else {
        throw new UnsupportedOperationException("JsonObject is not extendable");
      }
    }
  
    ///If [isExtendable] is true, or the key already exists,
    ///then allow the edit.
    ///Throw [UnsupportedOperationException] if we're not allowed to add a new
    ///key
    putIfAbsent(key,ifAbsent()) {
  