docs: public static final List<Float> parsePercentiles(final String spec) {
      List<Float> rs = new ArrayList<Float>();
      int start_pos = spec.indexOf('[');
      int end_pos = spec.indexOf(']');
      if (start_pos == -1 || end_pos == -1) {
        throw new BadRequestException("Malformated percentile query paramater: " + spec);
      }
      
      String [] floats = Tags.splitString(spec.substring(start_pos + 1, end_pos), ',');
      for (String s : floats) {
        String trimed = s.trim();
        rs.add(Float.valueOf(trimed));
      }
      return rs;
    }