title: How to size and position an embedded UIViewController using Auto Layout constraints?
body: <p>Here is what I wanna do:
  My storyboard contains a <code>UIViewController</code> with just a few controlls. It's height is less than half a screen. For simplicity, let's call it the <code>DataViewController</code>. 
  The <code>DataViewController</code> is embedded inside other <code>UIViewControllers</code> through a "<code>Container View</code>". </p>
  
  <p>Although "<code>Container View</code>" displays the <code>DataViewController</code>, it still needs to have an explicit <code>height</code> set. Otherwise interface builder complains about ambiguous constraints. </p>
  
  <p>Now, how can I tell "<code>Container View</code>" that it's size should be what's required by <code>DataViewController</code>? I.e. without setting a hard coded, explicit <code>height</code> in Interface Builder (which, I fear, would break the layout if the font size changes)? </p>
  
  <p>Or in other words: How do you size/position embedded <code>UIViewControllers</code> in Interface Builder?</p>