private void prepareNow(Freshness freshness) {
        if (freshness == null) return;
        // TODO: See what freshness is doing with the internal props and simplify
        if (rankProperties.get("vespa.now") == null || rankProperties.get("vespa.now").isEmpty()) {
            rankProperties.put("vespa.now", "" + freshness.getRefTime());
        }
    }
Sets sorting from a string. See {@link Sorting} on syntax
container-search/src/main/java/com/yahoo/search/query/Ranking.java