title: Xcode auto layout constraints - why defaulting to negative padding?
body: <p>I am simply adding a UIView into the main view of a view controller. I want the height to always be 64px, but the width to stretch to the width of the screen.</p>
  
  <p>However, when I go to add constraints, the left and right padding default to -16, even though the view is stretched all the way across its parent view. Even if I set these back to 0, when I run the app the -16 padding is added back in. What is going on here?</p>
  
  <p><img src="https://i.stack.imgur.com/aZ73e.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/T88Ue.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/H1hkN.png" alt="enter image description here"></p>