th the
callback.</p>
<p>Returns the callback that should be used in place of the provided
<code>callback</code>. Frequently zones simply return the original callback.</p>
<p>Custom zones may intercept this operation. The default implementation in
<a href="dart-async/Zone/root-constant.html">Zone.root</a> returns the original callback unchanged.</p>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span></h2>
      <pre class="language-dart"><code class