code: private String extractAttributes(SoyMsg msg) {
      StringBuilder attributes = new StringBuilder();
      Matcher matcher = MESSAGE_ATTRIBUTE_PATTERN.matcher(msg.getDesc());
      while (matcher.find()) {
        attributes.append(matcher.group());
      }
      return attributes.toString();
    }
docs: Extracts message attributes from the message description. Returns an empty {@link String} if
  the description doesn't contain any message attribute.