title: What does setting the UIWindow's rootViewController do?
body: <blockquote>
    <p>Assigning a view controller to this property (either programmatically
    or using Interface Builder) installs the view controller’s view as the
    content view of the window.</p>
  </blockquote>
  
  <p>The above quote is from the UIWindow's reference.  My question is about the particular phase : </p>
  
  <blockquote>
    <p>"installs the view controller’s view as the
    content view of the window"</p>
  </blockquote>
  
  <p>What does exactly content view refer to ? </p>
  
  <p><a href="http://developer.apple.com/library/ios/#documentation/uikit/reference/UIWindow_Class/UIWindowClassReference/UIWindowClassReference.html" rel="noreferrer">http://developer.apple.com/library/ios/#documentation/uikit/reference/UIWindow_Class/UIWindowClassReference/UIWindowClassReference.html</a></p>