nchor"></a><code><span><span class="keyword">val</span> empty : <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p>returns an empty element</p></div></div><h2 id="variables-management"><a href="#variables-management" class="anchor"></a>Variables management</h2><div class="odoc-spec"><div class="spec value anchored" id="val-add_var"><a href="#val-add_var" class="anchor"></a><code><span><span class="keyword">val</span> add_var : <span><a href="#type-t">t</a> <span class="arrow">&#45;&gt;</spa