s="keyword">sig</span> ... <span class="keyword">end</span></code></div><div class="spec module" id="module-Head"><a href="#module-Head" class="anchor"></a><code><span class="keyword">module </span><a href="Head">Head</a> : <span class="keyword">sig</span> ... <span class="keyword">end</span></code></div><div class="spec module" id="module-Header"><a href="#module-Header" class="anchor"></a><code><span class="keyword">module </span><a href="Header">Header</a> : <span class="keyword">sig</span> ... <span cla