nking functions.</p>
</li>
<li><p><code>controller</code> - the directive&#39;s required controller instance(s) - Instances are shared
among all directives, which allows the directives to use the controllers as a communication
channel. The exact value depends on the directive&#39;s <code>require</code> property:</p>
<ul>
<li>no controller(s) required: the directive&#39;s own controller, or <code>undefined</code> if it doesn&#39;t have one</li>
<li><code>string</code>: the controller instance</li>
<li><code>