docs: def validate_one_format(jupytext_format):
      """Validate extension and options for the given format"""
      if not isinstance(jupytext_format, dict):
          raise JupytextFormatError('Jupytext format should be a dictionary')
  
      for key in jupytext_format:
          if key not in _VALID_FORMAT_INFO + _VALID_FORMAT_OPTIONS:
              raise JupytextFormatError("Unknown format option '{}' - should be one of '{}'".format(
                  key, "', '".join(_VALID_FORMAT_OPTIONS)))
          value = jupytext_format[key]
          if key in _BINARY_FORMAT_OPTIONS:
              if not isinstance(value, bool):
                  raise JupytextFormatError("Format option '{}' should be a bool, not '{}'".format(key, str(value)))
  
      if 'extension' not in jupytext_format:
          raise JupytextFormatError('Missing format extension')
      ext = jupytext_format['extension']
      if ext not in NOTEBOOK_EXTENSIONS + ['.auto']:
          raise JupytextFormatError("Extension '{}' is not a notebook extension. Please use one of '{}'.".format(
              ext, "', '".join(NOTEBOOK_EXTENSIONS + ['.auto'])))
  
      return jupytext_format