framework/i18n/MessageFormatter.php
private static function tokenizePattern($pattern)
    {
        $charset = Yii::$app ? Yii::$app->charset : 'UTF-8';
        $depth = 1;
        if (($start = $pos = mb_strpos($pattern, '{', 0, $charset)) === false) {
            return [$pattern];
        }
        $tokens = [mb_substr($pattern, 0, $pos, $charset)];
        while (true) {
            $open = mb_strpos($pattern, '{', $pos + 1, $charset);
            $close = mb_strpos($pattern, '}', $pos + 1, $charset);
            if ($open === false && $close === false) {
                break;
            }
            if ($open === false) {
                $open = mb_strlen($pattern, $charset);
            }
            if ($close > $open) {
                $depth++;
                $pos = $open;
            } else {
                $depth--;
                $pos = $close;
            }
            if ($depth === 0) {
                $tokens[] = explode(',', mb_substr($pattern, $start + 1, $pos - $start - 1, $charset), 3);
                $start = $pos + 1;
                $tokens[] = mb_substr($pattern, $start, $open - $start, $charset);
                $start = $open;
            }

            if ($depth !== 0 && ($open === false || $close === false)) {
                break;
            }
        }
        if ($depth !== 0) {
            return false;
        }

        return $tokens;
    }
private static function tokenizePattern($pattern)
    {
        $charset = Yii::$app ? Yii::$app->charset : 'UTF-8';
        $depth = 1;
        if (($start = $pos = mb_strpos($pattern, '{', 0, $charset)) === false) {
            return [$pattern];
        }
        $tokens = [mb_substr($pattern, 0, $pos, $charset)];
        while (true) {
            $open = mb_strpos($pattern, '{', $pos + 1, $charset);
            $close = mb_strpos($pattern, '}', $pos + 1, $charset);
            if ($open === false && $close === false) {
                break;
            }
            if ($open === false) {
                $open = mb_strlen($pattern, $charset);
            }
            if ($close > $open) {
                $depth++;
                $pos = $open;
            } else {
                $depth--;
                $pos = $close;
            }
            if ($depth === 0) {
                $tokens[] = explode(',', mb_substr($pattern, $start + 1, $pos - $start - 1, $charset), 3);
                $start = $pos + 1;
                $tokens[] = mb_substr($pattern, $start, $open - $start, $charset);
                $start = $open;
            }

            if ($depth !== 0 && ($open === false || $close === false)) {
                break;
            }
        }
        if ($depth !== 0) {
            return false;
        }

        return $tokens;
    }
Tokenizes a pattern by separating normal text from replaceable patterns.
@param string $pattern patter to tokenize
@return array|bool array of tokens or false on failure