    <dd>Join sequences of messages in a variety of ways.</dd>
        <dt>reduce sequence</dt>
        <dd>Apply an expression against all messages in a sequence to reduce it to a single message.</dd>
    </dl>
    <h3>Inputs</h3>
    <dl class="message-properties">
        <dt class="optional">parts<span class="property-type">object</span></dt>
        <dd>To automatically join a sequence of messages, they should all have
        this property set. The <b>split</b> node generates this property but it
     