@Override
    public int compareTo(BucketValue rhs) {
        if (comparator.compare(to, rhs.from) <= 0) return -1;
        if (comparator.compare(from, rhs.to) >= 0) return 1;
        return 0;
    }
Returns the exclusive-to value of this bucket.

@return The to-value.
container-search/src/main/java/com/yahoo/search/grouping/request/BucketValue.java