def _get_substitutions(dset):
    """Get substitution mapping

    Parameters
    ----------
    dset : Dataset
      Providing the to-be-queried configuration.

    Returns
    -------
    dict
      Mapping substitution keys to their values.
    """
    return {
        k.replace("datalad.run.substitutions.", ""): v
        for k, v in dset.config.items("datalad.run.substitutions")
    }