docs: def do_struct(self, subcmd, opts, message):
          """${cmd_name}: get the structure of the specified message
  
          ${cmd_usage}
          ${cmd_option_list}
          """
          client = MdClient(self.maildir, filesystem=self.filesystem)
          as_json = getattr(opts, "json", False)
          client.getstruct(message, as_json=as_json, stream=self.stdout)