voku / portable-utf8

      self::checkForSupport();

    }

    if (self::$support['mbstring'] === true) {

      // INFO: this is only a fallback for old versions

      if ($encoding === 'UTF-8' || $encoding === true || $encoding === false) {

        $encoding = 'UTF-8';

      } else {

        $encoding = self::normalize_encoding($encoding);

      }

      return \mb_strpos($haystack, $needle, $offset, $encoding);

    }

    if (self::$support['iconv'] === true) {

      // ignore invalid negative offset to keep compatility

      self::checkForSupport();

    }

    if (self::$support['mbstring'] === true) {

      // INFO: this is only a fallback for old versions

      if ($encoding === 'UTF-8' || $encoding === true || $encoding === false) {

        $encoding = 'UTF-8';

      } else {

        $encoding = self::normalize_encoding($encoding);

      }

      return \mb_substr($str, $start, $length, $encoding);

    }

    if (self::$support['iconv'] === true) {

      return (string)\grapheme_substr($str, $start, $length);