anchor.diff:  
     var spans = querySelectorAll(".preview form span");
     for (HtmlElement span in spans) {
  -    span.onClick.listen(headTextClick);
  +    span.onClick.listen(onDimensionLabelClick);
     }
     var inputs = querySelectorAll(".preview form input");
     for (HtmlElement input in inputs) {
  -    input.onBlur.listen(formBlur);
  +    input.onBlur.listen(onDimensionInputBlur);
     }
   
   }
   
  -void headTextClick(Event e) {
  +void onDimensionLabelClick(Event e) {
     var target = (e.target as HtmlElement);
     var parent = target.parent;
     parent.querySelectorAll("span").style.display = 'none';
  
positive.code: 
  void main() {
    container = querySelector('#container');
    querySelector('#refresh').onClick.listen(refreshPreviewContent);
    querySelector('#url').onChange.listen(refreshPreviewContent);
    createPreview(0, 0, 1024,768,0.5);
    createPreview(520, 0, 320, 480 ,0.8);
    createPreview(0, 420, 1920,1200,0.4);
  
negative.code: }
  
  
  void onRefreshClick(Event e) {
    var iframes = querySelectorAll('iframe');
    for(var i=0; i<iframes.length; i++) {
      iframes[i].setAttribute('src', 'about:blank');
  