title: How to disable touch input to all views except the top-most view?
body: <p>I have a view with multiple subviews.  When a user taps a subview, the subview expands in size to cover most of the screen, but some of the other subviews are still visible underneath.</p>
  
  <p>I want my app to ignore touches on the other subviews when one of the subviews is "expanded" like this.  Is there a simple way to achieve this?  I can write code to handle this, but I was hoping there's a simpler built-in way.</p>