 class="code">bytes</code> and <code class="code">string</code>. They do not copy the internal data;
    used improperly, they can break the immutability invariant on
    strings provided by the <code class="code">-safe-string</code> option. They are available for
    expert library authors, but for most purposes you should use the
    always-correct <a href="Bytes.html#VALto_string"><code class="code"><span class="constructor">Bytes</span>.to_string</code></a> and <a href="Bytes.html#VALof_string"><code cl