anchor.diff:    render() =>
        div({'className': selectorClass}, [
           span({"className": "round-selector-text"}, selectorText),
  -        showFirstLast ? _renderFastLeftArrow() : div(),
  +        showFirstLast ? _renderFastLeftArrow() : div({}),
           _renderArrow(true),
           div({"ref": "itemsDiv", "className": "round-list-fixed-width"},
               div({
  
positive.code:     ss.add(window.onResize.listen((_) => _scrollToCentroid()));
      _scrollToCentroid();
      redraw();
    }
  
    componentWillUnmount() {
  
negative.code: 
    get _visibleItemsWindowSize => ref('itemsDiv') != null ? ref('itemsDiv').marginEdge.width : null;
    get _shownItemCount => _visibleItemsWindowSize ~/ _spanWidth;
    get _minMarginLeft => _visibleItemsWindowSize - (items.length * _spanWidth);
    get _shouldDrawLeft => true;
    get _shouldDrawRight => true;
    get _scrollListWidth => _spanWidth*(lastIndex-firstIndex);
  