title: ( iOS ) What is superview and what is subviews
body: <p>What is superview and what is subviews?</p>
  
  <p>When I add this code:</p>
  
  <pre><code>[self.view addSubview:self.frontView];
  // what does that mean ?
  </code></pre>
  
  <p>And...</p>
  
  <pre><code>@property (nonatomic, strong) IBOutlet UIImageView *frontView;
  [self.frontView superview] != nil // means ?
  </code></pre>
  
  <p>what is in superview?</p>