title: What is the purpose of UIControl.sendAction's selector?
body: <p>What is the purpose of UIControl.sendAction's selector argument? It makes sense that UIControl.addTarget takes the selector argument that represents the function that is to be called when an action is sent, but why would the controller that's sending the event specify a function to be called? There's something that I'm missing. For some context, here's a piece of code from the custom button that I'm trying to implement:</p>
  
  <pre><code>override func touchesEnded(touches: Set&lt;UITouch&gt;, withEvent event: UIEvent?) {
      self.pressed = false
      if self.bounds.contains(touches.first!.locationInView(self)) {
          // sendAction(???, to: nil, forEvent: UIControlEvents.TouchUpInside)
      }
  
      super.touchesEnded(touches, withEvent: event)
  }
  </code></pre>