code: def multi_choice(choices=[], message='Pick as many items as you like.', default=None, title=''):
      
      return backend_api.opendialog("multi_choice", dict(choices=choices, message=message, default=default, title=title))
docs: Present the user with a list of choices.
      allow him to select multiple items and return them in a list.
      if the user doesn't choose anything from the list, return the empty list.
      return None if he cancelled selection.
  
      :ref:`screenshots<multi_choice>`
  
      :param choices: a list of the choices to be displayed
      :param message: message to be displayed.
      :param title: window title
      :param default: default list of strings
      :rtype: None or list of strings