 has been downloaded and stored locally in the
          `DataSource` directory.
        - a remote URL that has not been downloaded, but is valid and
          accessible.

        Parameters
        ----------
        path : str
            Can be a local file or a remote URL.

        Returns
        -------
        out : bool
            True if `path` exists.

        Notes
        -----
        When `path` is an URL, `exists` will return True if it's either
        stored locally in the `DataSource` directory, or is a valid remote
        URL.  `DataSource` does not discriminate between the two, the file
        is accessible if it exists in either location.

        Tr