tart+len</code> are valid
   positions in <code class="code">s</code>.</p>

<p>Byte sequences can be modified in place, for instance via the <code class="code">set</code>
   and <code class="code">blit</code> functions described below.  See also strings (module
   <a href="String.html"><code class="code">String</code></a>), which are almost the same data structure, but cannot be
   modified in place.</p>

<p>Bytes are represented by the OCaml type <code class="code">char</code>.</p>

<p>The labeled version 