docs: protected static void checkMetricLabelName(String name) {
      if (!METRIC_LABEL_NAME_RE.matcher(name).matches()) {
        throw new IllegalArgumentException("Invalid metric label name: " + name);
      }
      if (RESERVED_METRIC_LABEL_NAME_RE.matcher(name).matches()) {
        throw new IllegalArgumentException("Invalid metric label name, reserved for internal use: " + name);
      }
    }