docs: @Override
      public String tagKey(String key) {
          String conventionKey = delegate.tagKey(key);
  
          conventionKey = START_UNDERSCORE_PATTERN.matcher(conventionKey).replaceAll(""); // 2
          conventionKey = SF_PATTERN.matcher(conventionKey).replaceAll(""); // 2
  
          if (!START_LETTERS_PATTERN.matcher(conventionKey).matches()) { // 3
              conventionKey = "a" + conventionKey;
          }
          return StringUtils.truncate(conventionKey, KEY_MAX_LENGTH); // 1
      }