anchor.diff:    if(urlInput.value.isEmpty) {
       urlInput.value = 'http://';
     } else {
  -    refreshPreviewContent(null);
  +    onRefreshClick(null);
     }
   
     SortableGroup sg = new SortableGroup();
  
positive.code: 
    var spans = querySelectorAll(".preview form span");
    for (HtmlElement span in spans) {
      span.onClick.listen(headTextClick);
    }
    var inputs = querySelectorAll(".preview form input");
    for (HtmlElement input in inputs) {
      input.onBlur.listen(formBlur);
    }
  
  }
  
  void headTextClick(Event e) {
    var target = (e.target as HtmlElement);
    var parent = target.parent;
    parent.querySelectorAll("span").style.display = 'none';
  
negative.code: 
  void main() {
    container = querySelector('#container');
    querySelector('#refresh').onClick.listen(onRefreshClick);
    querySelector('#url').onChange.listen(onRefreshClick);
    createPreview(0, 0, 1024,768,0.5);
    createPreview(520, 0, 320, 480 ,0.8);
    createPreview(0, 420, 1920,1200,0.4);
  