code: public static function rtrim($str, $charlist = false)
  	{
  		if (empty($charlist) && $charlist !== false)
  		{
  			return $str;
  		}
  
  		if ($charlist === false)
  		{
  			return utf8_rtrim($str);
  		}
  
  		return utf8_rtrim($str, $charlist);
  	}
docs: UTF-8 aware replacement for rtrim()
  
  Strip whitespace (or other characters) from the end of a string. You only need to use this if you are supplying the charlist
  optional arg and it contains UTF-8 characters. Otherwise rtrim will work normally on a UTF-8 string.
  
  @param   string  $str       The string to be trimmed
  @param   string  $charlist  The optional charlist of additional characters to trim
  
  @return  string  The trimmed string
  
  @link    https://www.php.net/rtrim
  @since   1.3.0