* - ISO control characters and space characters are treated as spaces.
         * - Alphanumeric characters (0-9, A-Z, a-z) are appended to the buffer.
         * - Symbol characters (!-/, :-@, [-`, {-~) are appended to the buffer.
         * - Duplicate terms can be removed based on the `duplicateTermRemoved` flag.

    /**
     * Appends a filter to an existing filter chain.
     *
     * @param filter the filter to append
     * @param chain the existing filter chain to append to
     * @return a new filter chain that includes the appended filter
     */
    protected FilterChain appendFilterChain(final Filter filter, final FilterChain chain) {
        return (context, query, boost) -> filter.execute(context, query, boost, chain);
    }

    /**

     * Adds search highlighting for HTML and PDF documents.
     *
     * @param document the document data map
     * @param url the base URL
     * @return the URL with appended query parameters
     */
    protected String appendQueryParameter(final Map<String, Object> document, final String url) {
        final FessConfig fessConfig = ComponentUtil.getFessConfig();