docs: def v1_subfolder_list(request, response, kvlclient, fid):
      '''Retrieves a list of subfolders in a folder for the current user.
  
      The route for this endpoint is:
      ``GET /dossier/v1/folder/<fid>/subfolder``.
  
      (Temporarily, the "current user" can be set via the
      ``annotator_id`` query parameter.)
  
      The payload returned is a list of subfolder identifiers.
      '''
      fid = urllib.unquote(fid)
      try:
          return sorted(imap(attrgetter('name'),
                             ifilter(lambda it: it.is_folder(),
                                     new_folders(kvlclient, request).list(fid))))
      except KeyError:
          response.status = 404
          return []