code: private static String makeHHString(int i)
      {
          String s = Integer.toHexString(i).toUpperCase();
          if (s.length() == 1)
          {
              s = "0" + s;
          }
          return s;
      }
docs: Make an integer into an HH hex value.
  Does no checking on the size of the input, since this
  is only meant to be used locally by writeAttrURI.
  
  @param i must be a value less than 255.
  
  @return should be a two character string.