* The value is, e.g. fess.search <br>
     * comment: document index
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getIndexDocumentSearchIndex();

    /**
     * Get the value for the key 'index.document.update.index'. <br>
     * The value is, e.g. fess.update <br>