function substring($string = '',$limit = 10,$suffix='...',$from = 0){
	if(isset($string)&&is_string($string)){
		if(mb_strlen($string,'UTF-8')>$limit){
			//removing characters according to limit and UTF-8 encoding
			$string = preg_replace('#^(?:[\x00-\x7F]|[\xC0-\xFF][\x80-\xBF]+){0,'.$from.'}'.'((?:[\x00-\x7F]|[\xC0-\xFF][\x80-\xBF]+){0,'.$limit.'}).*#s','$1', $string);
			return $string.$suffix;
		}else{
			return $string;
		}
	}else{
		return null;
	}
}