title: Rune vs byte ranging over string
body: <p>According to <a href="https://blog.golang.org/strings" rel="noreferrer">https://blog.golang.org/strings</a> and my testings, it looks like while we <code>range</code> a string, the characters we get are <code>rune</code> type, but if we get it by <code>str[index]</code>, they will be <code>byte</code> type, why is it?</p>