l-message" class="anchor"></a><code><span class="keyword">let</span> message: <a href="index.html#type-t">t</a> <span>=&gt;</span> option(string);</code></dt><dd><p>Human_readable message indicating details about last transition.</p></dd></dl><dl><dt class="spec value" id="val-reason"><a href="#val-reason" class="anchor"></a><code><span class="keyword">let</span> reason: <a href="index.html#type-t">t</a> <span>=&gt;</span> option(string);</code></dt><dd><p>Unique, one_word, CamelCase reason for the conditio