hor"></a><code><span><span class="keyword">val</span> string_of_config_usage_extra : <span><span class="optlabel">?len</span>:int <span class="arrow">&#45;&gt;</span></span> <span><a href="#type-config_usage_extra">config_usage_extra</a> <span class="arrow">&#45;&gt;</span></span> string</span></code></div><div class="spec-doc"><p>Serialize a value of type <a href="#type-config_usage_extra"><code>config_usage_extra</code></a> into a JSON string.</p><ul class="at-tags"><li class="parameter"><span class="at-t