anchor.diff:  
   class CheckmarkFormatter extends Formatter {
     void call(dom.HtmlElement target, int row, int cell, dynamic value, Column columnDef, /*Map/Item*/dynamic  dataContext) {
  +    target.children.clear();
       if(value != null && value is bool && value) {
  -      target.appendHtml('<img src="packages/bwu_datagrid/asset/images/tick.png">'); // : '';
  +      target.append(new dom.ImageElement(src:'packages/bwu_datagrid/asset/images/tick.png'));
       }
     }
   }
  
positive.code: 
  class DefaultFormatter extends Formatter {
    void call(dom.HtmlElement target, int row, int cell, dynamic value, Column columnDef, /*Map/Item*/ dynamic dataContext) {
      if (value != null) {
        //return "";
      //} else {
  
negative.code:       color = 'green';
      }
  
      target.children.clear();
      target.append(
          new dom.SpanElement()
              ..classes.add('percent-complete-bar')
              ..style.background = color
              ..style.width= '${value}%');
    }
  }
  
  