nbsp;explain&nbsp;:&nbsp;<span class="constructor">Bson</span>.t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="constructor">Bson</span>.t<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;hint&nbsp;:&nbsp;<span class="constructor">Bson</span>.t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="constructor">Bson</span>.t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="constructor">Bson</span>.t<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;returnKey&nbsp;