ob <span class="keyword">of</span> <span>string option</span></code></td></tr></table><code> ]</code></dt></dl><dl><dt class="spec value" id="val-to_yojson"><a href="#val-to_yojson" class="anchor"></a><code><span class="keyword">val</span> to_yojson : <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> Yojson.Safe.t</code></dt><dt class="spec value" id="val-of_yojson"><a href="#val-of_yojson" class="anchor"></a><code><span class="keyword">val</span> of_yojson : Yojson.Safe.t <span>&#45;&gt;</span> <spa