code: private static String appendVerticalBorder(String msg) {
      StringBuilder borderedMsgBuilder = new StringBuilder(msg.length() + 10);
      String[] lines = msg.split(SystemCompat.lineSeparator);
      for (int i = 0, N = lines.length; i < N; i++) {
        if (i != 0) {
          borderedMsgBuilder.append(SystemCompat.lineSeparator);
        }
        String line = lines[i];
        borderedMsgBuilder.append(VERTICAL_BORDER_CHAR).append(line);
      }
      return borderedMsgBuilder.toString();
    }
docs: Add {@value #VERTICAL_BORDER_CHAR} to each line of msg.
  
  @param msg the message to add border
  @return the message with {@value #VERTICAL_BORDER_CHAR} in the start of each line