/** The key of the configuration. e.g. 10 */
    String SUGGEST_POPULAR_WORD_SIZE = "suggest.popular.word.size";

    /** The key of the configuration. e.g. 30 */
    String SUGGEST_POPULAR_WORD_WINDOW_SIZE = "suggest.popular.word.window.size";

    /** The key of the configuration. e.g. 10 */
    String SUGGEST_POPULAR_WORD_QUERY_FREQ = "suggest.popular.word.query.freq";