private Set<String> parseFieldList(String fieldList) {
        if (fieldList.startsWith("[f:") && fieldList.endsWith("]")) {
            String content = fieldList.substring(3, fieldList.length() - 1);
            String[] parts = content.split(",");
            return new TreeSet<>(Arrays.asList(parts));
        }
        return Set.of();
    }
resolve summary class to use when none provided
container-search/src/main/java/com/yahoo/prelude/fastsearch/PartialSummaryHandler.java