code: @Override
      public void validate(ValidationHelper helper, Context context, String key, Object t) {
  
          if (key != null) {
              if (!key.startsWith("x-")) {
                  final String message = Tr.formatMessage(tc, "invalidExtensionName", key);
                  helper.addValidationEvent(new ValidationEvent(ValidationEvent.Severity.ERROR, context.getLocation(), message));
              }
          }
      }
docs: {@inheritDoc}