docs: def install(application, default_content_type, encoding=None):
      """
      Install the media type management settings.
  
      :param tornado.web.Application application: the application to
          install a :class:`.ContentSettings` object into.
      :param str|NoneType default_content_type:
      :param str|NoneType encoding:
  
      :returns: the content settings instance
      :rtype: sprockets.mixins.mediatype.content.ContentSettings
  
      """
      try:
          settings = application.settings[SETTINGS_KEY]
      except KeyError:
          settings = application.settings[SETTINGS_KEY] = ContentSettings()
          settings.default_content_type = default_content_type
          settings.default_encoding = encoding
      return settings