IPython/html/static/notebook/js/widgets/view_container.js

var ContainerView = IPython.WidgetView.extend({
    
    render : function(){
        this.$el.html('');
        this.$container = $('<div />')
            .addClass('container')
            .addClass(this.model.comm.comm_id);
        this.$el.append(this.$container);
    },
    
    update : function(){},
});

IPython.notebook.widget_manager.register_widget_view('ContainerView', ContainerView);