ys be viewed as a simpler index on any prefix of its indexed fields; for example, see
 <a href="Index2.html#asIndex1()"><code>Index2.asIndex1()</code></a>.

 <p>
 <b>Complex Sub-Fields</b>

 <p>
 Only simple fields may be indexed, but the indexed field can be either a normal object field or a sub-field of
 a complex <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/Set.html" title="class or interface in java.util" class="external-link"><code>Set</code></a>, <a href="https://doc