docs: def load_index(self, version_string):
          """Load the completion index for a given CLI version.
  
          :type version_string: str
          :param version_string: The AWS CLI version, e.g "1.9.2".
  
          :raises: :class:`IndexLoadError <exceptions.IndexLoadError>`
          """
          filename = self._filename_for_version(version_string)
          try:
              contents = self._fslayer.file_contents(filename)
          except FileReadError as e:
              raise IndexLoadError(str(e))
          return contents