title: When do I have to use Priority in iOS AutoLayout?
body: <p>Using iOS AutoLayout you will do something like: </p>
  
  <pre><code>self.view.addConstraint(NSLayoutConstraint(item: label, 
     attribute: .Width, 
     relatedBy: .Equal, 
     toItem: self.view, 
     attribute: .Width, 
     multiplier: 0.3, 
     constant: 0))
  </code></pre>
  
  <p>You can also use a priority for each layout constraint.</p>
  
  <p><strong>When do I have to use Priority in iOS AutoLayout?</strong></p>