anchor.diff:    set date(DateTime dt) {
       _showDate = dt;
       navText.text = _dateToString(_showDate);
  -    _table.children.clear();
  +    table.children.clear();
       var d = dt.subtract(new Duration(days:dt.day + ((dt.weekday - dt.day) % 7) - 1));
  -    while (_table.children.length < 6) {
  -      var row = _table.addRow();
  +    while (table.children.length < 6) {
  +      var row = table.addRow();
         for (var i = 0;i < 7;i++) {
           row.append(_createCell(d));
  -        d = d.add(new Duration(days:1));
  +        d = new DateTime(d.year, d.month, d.day+1);
         }
  +      table.append(row);
       }
   
     }
  
positive.code: 
      nav..append(leftNav)..append(rightNav)..append(navText)..classes.add('calendar_nav');
  
      element..append(nav)..append(_table)..classes.add('calendar');
    }
  
    bool get showNav => nav.hidden;
  
negative.code: class Calendar {
    DateTime _showDate, _now = new DateTime.now();
  
    final DivElement element, nav , leftNav , rightNav;
  
    final SpanElement navText;
  
    final TableElement table;
  
    Map<int, TableCellElement> _cellMap = new Map<int, TableCellElement>();
  
    Calendar() : element = new DivElement(), nav = new DivElement(), leftNav = new DivElement(), rightNav = new DivElement(), table = new TableElement(), navText = new SpanElement(){
      date = _now;
      leftNav.classes..add('nav')..add('left_nav');
      leftNav.append(new DivElement());
  