-must_be_valid_reason">must_be_valid_reason</a> <span>&#45;&gt;</span> bool</code></dt></dl></div></div></div><dl><dt class="spec value" id="val-pp_must_be_valid_reason"><a href="#val-pp_must_be_valid_reason" class="anchor"></a><code><span class="keyword">val</span> pp_must_be_valid_reason : <a href="index.html#module-F">F</a>.formatter <span>&#45;&gt;</span> <span><a href="index.html#type-must_be_valid_reason">must_be_valid_reason</a> option</span> <span>&#45;&gt;</span> unit</code></dt><dt class="spec val