.</p>
<p>If a class is not intending to implement the feature, it should throw
an <a href="../dart-core/UnsupportedError-class.html">UnsupportedError</a> instead. This error is only intended for
use during development.</p>
    </section>
    
    <section>
      <dl class="dl-horizontal">
        <dt>Inheritance</dt>
        <dd><ul class="gt-separated dark clazz-relationships">
          <li><a href="../dart-core/Object-class.html">Object</a></li>
          <li><a href="../dart-core/Error-class.html">Error