title: What does sender is in prepareForSegue:sender call?
body: <p>Suppose I perform a segue change when a button is tapped as given in the code below. </p>
  
  <pre><code>- (IBAction)btnTapped:(id)sender {   
      [self performSegueWithIdentifier:@"login" sender:self];
  }
  </code></pre>
  
  <p>I'm wondering the purpose of the "sender" part. Does it make difference if I make the call with the parameter <code>sender:sender</code>, <code>sender:@{@"foo",@"bar"}</code> or <code>sender:nil</code> ??</p>
  
  <p>Edit1:</p>
  
  <p>Can I get this <code>sender</code> at the destination ViewController for instance at <code>ViewDidLoad()</code> function? </p>