title: Switching containerView content from within viewController
body: <p>I have three viewControllers <strong>Main</strong>, <strong>A</strong>, <strong>B</strong>. <strong>Main ViewController</strong> holds <strong>ContainerView</strong> and other content as well does all transactions in containerView. <strong>ViewControllerA</strong> has <strong>ButtonA</strong> when pressing it content of container has to change to <strong>ViewControllerB</strong>
  how can I do that? I cannot find any similar examples.</p>
  
  <p><a href="https://i.stack.imgur.com/jwdWi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jwdWi.png" alt="enter image description here"></a></p>