anchor.diff:    bool removeItem(String path, value) {
       List list = get(path);
       var index = list.indexOf(value);
  +
       /// Assumes the lists are in sync! We are in lots of trouble if they aren't
       /// though, and verifying it is a lot more expensive.
       jsElement.callMethod('splice', [path, index, 1]);
  
positive.code: 
    /// Inserts `elements` at position `index` to the list at `path`.
    void insertAll(String path, int index, Iterable elements) {
      jsElement.callMethod(
          'splice',
          [path, index, 0]..addAll(elements.map((element) => jsValue(element))));
    }
  
  
negative.code:   /// affect the values of custom properties.
    void updateStyles() => jsElement.callMethod('updateStyles');
  
    /// Sets a value on an attribute path, and notifies of changes.
    void set(String path, value) =>
        jsElement.callMethod('set', [path, jsValue(value)]);
  
    /// Add `item` to a list at `path`.
    void add(String path, item) {
  