public static function formattingRuleHasFirstGroupOnly($nationalPrefixFormattingRule)
    {
        $firstGroupOnlyPrefixPatternMatcher = new Matcher(static::FIRST_GROUP_ONLY_PREFIX_PATTERN,
            $nationalPrefixFormattingRule);

        return mb_strlen($nationalPrefixFormattingRule) === 0
            || $firstGroupOnlyPrefixPatternMatcher->matches();
    }