code: @Override
    public int compareTo(SAXRecord o) {
      int a = this.occurrences.size();
      int b = o.getIndexes().size();
      if (a == b) {
        return 0;
      }
      else if (a > b) {
        return 1;
      }
      return -1;
    }
docs: This comparator compares entries by the length of the entries array - i.e. by the total
  frequency of entry occurrence.
  
  @param o an entry to compare with.
  @return results of comparison.