What the difference and usage of encodings UTF-8 and UTF-8-MAC in iconv?

What the difference and usage of encodings UTF-8 and UTF-8-MAC in iconv? I thought it was the difference between \n and \r(MAC OS 9) at first. But I tried iconv -f UTF-8 -t UTF-8-MAC filename > filename2 The file content doesn't change in hex view.