anchor.diff:  
     static const hour = TimeAggregation._internal('hour');
     static const day = TimeAggregation._internal('day');
  +  static const week = TimeAggregation._internal('week');
     static const month = TimeAggregation._internal('month');
     static const year = TimeAggregation._internal('year');
     static const term = TimeAggregation._internal('term');
  
positive.code:       case 'day':
          out = day;
          break;
        case 'month':
          out = month;
          break;
  
negative.code:   static final _allowed = <String>{
      'hour',
      'day',
      'week',
      'month',
      'year',
      'term',
  