* The value is, e.g. digest <br>
     * comment: Field name for digest in the index.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getIndexFieldDigest();

    /**
     * Get the value for the key 'index.field.title'. <br>
     * The value is, e.g. title <br>
     * comment: Field name for title in the index.