voku / portable-utf8

   * will be returned, unless either the <b>ENT_IGNORE</b> or

   * <b>ENT_SUBSTITUTE</b> flags are set.

   */

  public static function htmlspecialchars(string $str, int $flags = ENT_COMPAT, string $encoding = 'UTF-8', bool $double_encode = true): string

  {

    if ($encoding !== 'UTF-8' && $encoding !== 'CP850') {

      $encoding = self::normalize_encoding($encoding, 'UTF-8');

    }

    return \htmlspecialchars($str, $flags, $encoding, $double_encode);

  }

  /**

   * Checks whether iconv is available on the server.

   *

   * @return int

   */

  public static function strwidth(string $str, string $encoding = 'UTF-8', bool $cleanUtf8 = false): int

  {

    if ($encoding !== 'UTF-8' && $encoding !== 'CP850') {

      $encoding = self::normalize_encoding($encoding, 'UTF-8');

    }

    if ($cleanUtf8 === true) {

      // iconv and mbstring are not tolerant to invalid encoding

      // further, their behaviour is inconsistent with that of PHP's substr

      $str = self::clean($str);

    }

    // fallback to "mb_"-function via polyfill

    return \mb_strwidth($str, $encoding);

  }

  /**

   * Get part of a string.