title: What is "Constrain to margin" in Storyboard in Xcode 6
body: <p>I am Working with autolayout and constraints and found there is a <code>Constrain to margins</code> option in Xcode 6 which was not present in Xcode 5 and is checked by default.</p>
  
  <p>I created a test project then I added a <code>UITableView</code> on a ViewController with the frame set to the same size as view and added constraints</p>
  
  <p><strong>Xcode 6</strong>
  You can see here even though tableview has the same frame as view Xcode suggests to add -16 as constraint whereas Xcode 5 would suggest adding spacing 0.</p>
  
  <p><img src="https://i.stack.imgur.com/aZF5T.png" alt="With Constrain to margin checked"></p>
  
  <p>Now when you uncheck "Constrain to margin" option it behaves same as Xcode 5 and would suggest adding 0 as constraint </p>
  
  <p><img src="https://i.stack.imgur.com/ncu1i.png" alt="With Constrain to margin UnChecked"></p>
  
  <p>Also, I found that once I add constraint with Constrain to margin checked, I am no longer able to open the storyboard file in Xcode 5 so it's definitely something new in Xcode 6</p>
  
  <p>Hopefully, I am able to explain my question properly. I would like to understand what "Constrain to margin" actually does and when I should and should not use it. I do apologize if it's something very simple and obvious.</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>I found something about layout margins in <a href="https://developer.apple.com/LIBRARY/PRERELEASE/IOS/documentation/UIKit/Reference/UIView_Class/index.html#//apple_ref/occ/instp/UIView/layoutMargins" rel="noreferrer">discussion here</a> , I wonder if it's related to this.</p>