docs: public int compareTo(ReadableDuration other) {
          long thisMillis = this.getMillis();
          long otherMillis = other.getMillis();
          
          // cannot do (thisMillis - otherMillis) as it can overflow
          if (thisMillis < otherMillis) {
              return -1;
          }
          if (thisMillis > otherMillis) {
              return 1;
          }
          return 0;
      }