text: import json
  import six
  
  from .bot import Bot
  
  
  class Element(dict):
      __acceptable_keys = ['title', 'item_url', 'image_url', 'subtitle', 'buttons']
  
      def __init__(self, *args, **kwargs):
          if six.PY2:
              kwargs = {k: v for k, v in kwargs.iteritems() if k in self.__acceptable_keys}
          else:
              kwargs = {k: v for k, v in kwargs.items() if k in self.__acceptable_keys}
          super(Element, self).__init__(*args, **kwargs)
  
      def to_json(self):
          return json.dumps({k: v for k, v in self.iteritems() if k in self.__acceptable_keys})
  
  
  class Button(dict):
      # TODO: Decide if this should do more
      pass
  
  # class Receipt:
  #     pass
  