code: @Nonnull
      static String headerLetter(final int i) {
          final int flags = DATA_MODEL.getDataFlags(i);
  
          // TODO: The "magic" of how to interpret flags must be in DataModel, not here.
          if (((flags >> 7) & 3) == 1) {
              return Character.toString(ENCODE_CHARS[(flags >> 11) & 31]);
          }
          return "";
      }
docs: TODO: What does this method do? What is parameter i (rename)?