he specification for a forked zone.</p>
<p>When forking a new zone (see <a href="dart-async/Zone/fork.html">Zone.fork</a>) one can override the default
behavior of the zone by providing callbacks. These callbacks must be
given in an instance of this class.</p>
<p>Handlers have the same signature as the same-named methods on <a href="dart-async/Zone-class.html">Zone</a> but
receive three additional arguments:</p><ol><li>the zone the handlers are attached to (the "self" zone).</li><li>a <a href="dart-async/Zo