docs: def is_json_file(abspath):
      """Parse file extension.
  
      - *.json: uncompressed, utf-8 encode json file
      - *.gz: compressed, utf-8 encode json file
      """
      abspath = abspath.lower()
      fname, ext = os.path.splitext(abspath)
      if ext in [".json", ".js"]:
          is_json = True
      elif ext == ".gz":
          is_json = False
      elif ext == ".tmp":
          return is_json_file(fname)
      else:
          raise JsonExtError(
              "'%s' is not a valid json file. "
              "extension has to be '.json' for uncompressed, '.gz' "
              "for compressed." % abspath)
      return is_json