PKPString::substr_replace PHP Method

    static function substr_replace($string, $replacement, $start, $length = null)
    {
        if (extension_loaded('mbstring') === true) {
            $string_length = self::strlen($string);
            if ($start < 0) {
                $start = max(0, $string_length + $start);
            } else {
                if ($start > $string_length) {
                    $start = $string_length;
                }
            }
            if ($length < 0) {
                $length = max(0, $string_length - $start + $length);
            } else {
                if (is_null($length) === true || $length > $string_length) {
                    $length = $string_length;
                }
            }
            if ($start + $length > $string_length) {
                $length = $string_length - $start;
            }
            return self::substr($string, 0, $start) . $replacement . self::substr($string, $start + $length, $string_length - $start - $length);
        }
        return is_null($length) === true ? substr_replace($string, $replacement, $start) : substr_replace($string, $replacement, $start, $length);
    }