/** The key of the configuration. e.g. _version */
    String INDEX_FIELD_VERSION = "index.field.version";

    /** The key of the configuration. e.g. _seq_no */
    String INDEX_FIELD_seq_no = "index.field.seq_no";

    /** The key of the configuration. e.g. _primary_term */
    String INDEX_FIELD_primary_term = "index.field.primary_term";

    /** The key of the configuration. e.g. lang */