coded string can be multiple bytes, you have to walk over the -->

<!-- string to find the nᵗʰ letter of a string. This is a significantly more -->

<!-- expensive operation, and we don’t want to be misleading. Furthermore, ‘letter’ -->

<!-- isn’t something defined in Unicode, exactly. We can choose to look at a string as -->

<!-- individual bytes, or as codepoints:-->

<p>普通、ベクタへの <code>[]</code> を用いたアクセスはとても高速です。
しかし、UTF-8でエンコ�