}

    /**
     * Retrieves an extractor for the specified key.
     * If multiple extractors are associated with the key, returns a composite extractor
     * that tries each extractor in order until one succeeds.
     *
     * @param key the key to look up
     * @return the extractor for the key, or null if not found
     */
    public Extractor getExtractor(final String key) {