libphonenumber\PhoneNumberUtil::initExtnPatterns PHP Method

    protected static function initExtnPatterns()
    {
        // One-character symbols that can be used to indicate an extension.
        $singleExtnSymbolsForMatching = "xｘ#＃~～";
        // For parsing, we are slightly more lenient in our interpretation than for matching. Here we
        // allow a "comma" as a possible extension indicator. When matching, this is hardly ever used to
        // indicate this.
        $singleExtnSymbolsForParsing = "," . $singleExtnSymbolsForMatching;
        static::$EXTN_PATTERNS_FOR_PARSING = static::createExtnPattern($singleExtnSymbolsForParsing);
    }