new_contents: from tw.api import Widget
  
  class IFrameWidget(Widget):
      params = ['id', 'url']
      template = """
        <iframe id="${id}" src="${url}" width="100%" height="100%">
          <p>Your browser does not support iframes.</p>
        </iframe>
      """
      engine_name = 'mako'
  
subject: Add a simple iframe widget