ap</code></a> and
   <a href="String.html#VALmapi"><code class="code"><span class="constructor">String</span>.mapi</code></a> functions to cover most cases of building
   new strings. You should prefer those over <code class="code">to_string</code> or
   <code class="code">unsafe_to_string</code> whenever applicable.</p>

<p>2. Temporarily giving ownership of a byte sequence to a function
   that expects a uniquely owned string and returns ownership back, so
   that we can mutate the sequence again after th