@Override
    public String toString() {
        return "trace [level: " + level + ", explainLevel: " + explainLevel + ", timestamps: " + timestamps + ", query: " + query + "]";
    }
Traces how properties was resolved and from where. Done after the fact to avoid special handling
of tracelevel, which is the property deciding whether this needs to be done
container-search/src/main/java/com/yahoo/search/query/Trace.java