I think you are right. I thought that the author was meaning that it is possible to use \n and \t in values because UTF8 would encode them in multibyte sequenc

I think you are right. I thought that the author was meaning that it is possible to use \n and \t in values because UTF8 would encode them in multibyte sequences (like Modified UTF8 encodes \0 as 0xC0,0x80). What he was actually meaning is that if a codepoint is > 127 its multibyte encoding won't contain any \n or \t. Sorry for the confusion.