extra.put("reloadable_keyword_marker", ReloadableKeywordMarkerFilterFactory::new);
        extra.put("reloadable_stop", ReloadableStopFilterFactory::new);
        extra.put("flexible_porter_stem", FlexiblePorterStemFilterFactory::new);
        extra.put("alphanum_word", AlphaNumWordFilterFactory::new);
        extra.put("disable_graph", DisableGraphFilterFactory::new);
        return extra;
    }