ence of length <code class="code">len</code>,
    containing the subsequence of <code class="code">s</code> that starts at position <code class="code">pos</code>
    and has length <code class="code">len</code>.</p>
</div>
<ul class="info-attributes">
<li><b>Raises</b> <code>Invalid_argument</code> if <code class="code">pos</code> and <code class="code">len</code> do not designate a
    valid range of <code class="code">s</code>.</li>
</ul>
</div>

<pre id="VALsub_string">val sub_string : bytes -&gt; pos:in