tened to, it starts listening to the
input <code>stream</code>.</li>
<li>Subscriptions of the returned stream forward (in a reasonable time)
a <a href="dart-async/StreamSubscription/pause.html">StreamSubscription.pause</a> call to the subscription of the input
<code>stream</code>.</li>
<li>Similarly, canceling a subscription of the returned stream eventually
(in reasonable time) cancels the subscription of the input <code>stream</code>.</li>
</ul>
<p>"Reasonable time" depends on the transformer and stream. 