code: @Override
      public int writeComment(String data)
          throws IOException
      {
          writeAscii("<!--");
          int ix = writeCommentContent(data);
          if (ix >= 0) { // unfixable '--'?
              return ix; 
          }
          writeAscii("-->");
          return -1;
      }
docs: Method that will try to output the content as specified. If
  the content passed in has embedded "--" in it, it will either
  add an intervening space between consequtive hyphens (if content
  fixing is enabled), or return the offset of the first hyphen in
  multi-hyphen sequence.