add(feedback = new FeedbackPanel("feedback").setOutputMarkupId(true));
List<IGridColumn<DataSource, Rule>> columns = new ArrayList<IGridColumn<DataSource, Rule>>();
columns.add(new CheckBoxColumn("checkbox"));
columns.add(new PriorityColumn(new ResourceModel("priority"), "priority").setInitialSize(60));
columns.add(new EditablePropertyColumn(new ResourceModel("pathPrefix"), "pathPrefix"));
columns.add(new EditablePropertyColumn(new ResourceModel("extensions"), "extensions").setInitialSize(100));
columns.add(new TypeColumn(new ResourceModel("type"), "type").setInitialSize(90));
columns.add(new TemplateColumn("template", new ResourceModel("template")).setInitialSize(250));