String spec() {
            var builder = new StringBuilder();
            builder.append('[');
            builder.append(spec.substring(0, pos));
            builder.append(']');
            builder.append('[');
            builder.append(spec.substring(pos));
            builder.append(']');
            return builder.toString();
        }
Decide if sortorder is ascending or not.
container-search/src/main/java/com/yahoo/search/query/Sorting.java