ss="hljs-attr">"mandatory"</span>: <span class="hljs-literal">false</span>,
        <span class="hljs-attr">"default"</span>: <span class="hljs-string">""</span>
      }
    ]
  }
}
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="define-the-listener"></a><a href="#define-the-listener" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1