docs: public int[] getChildIndexes(int index) {
      if (index == 0) {
        if (isConstant()) {
          return new int[0];
        } else {
          int[] result = new int[subexpressions.size()];
          int startIndex = 1;
          for (int i = 0; i < subexpressions.size(); i++) {
            result[i] = startIndex;
            startIndex += subexpressions.get(i).size();
          }
          return result;
        }
      } else {
        int[] parts = findSubexpression(index);
        int[] result = subexpressions.get(parts[0]).getChildIndexes(parts[1]);
        for (int i = 0; i < result.length; i++) {
          result[i] += parts[2];
        }
        return result;
      }
    }