anchor.diff:      return _convert(_data, (k,v) => v is ConfigMap ? v.toMap() : this[k]);
     }
   
  +  /**
  +   * Accessing keys using this operator evaluates the computation on requested position
  +   */
     operator[](key) {
       _data[key] = (_data[key] is ComputedValue) ?
                        _data[key].getValue(root) :
  
positive.code:   }
  }
  
  class Configuration {
  
    final Map<String, Map > _configurations = {};
  
    /**
     * Register configuration under [name].
     */
    void add(String name, Map configuration, {String parent: null}) {
      configuration['__name__'] = name;
  
negative.code:    * Name of the configuration is stored under key "__name__".
     * Throws [ArgumentError] if configuration with [name] does not exists.
     */
    Map get(String name) {
      return new ConfigMap(_get(name)).toMap();
    }
  
    Map _get(String name) {
      if (!_configurations.containsKey(name)) {
        throw new ArgumentError("Configuration with name '$name' does not exist.");
      }
  