title: Where does animated come from when calling super.viewWillAppear(animated)?
body: <p>In the examples I see of overriding viewWillAppear(_ animated: Bool), I'm confused with the parameter passed for calling the super function: </p>
  
  <pre><code>super.viewWillAppear(animated)
  </code></pre>
  
  <p>I assume that "animated" is a Bool that is set to true, but where did this Bool come from? It's not declared elsewhere in my UIViewController and it isn't a property of the UIViewController. </p>