title: Positioning content in a CALayer
body: <p>How do I position content in a CALayer so that it scales to fit the width (preserving aspect ratio) and is positioned at the top of the layer?</p>
  
  <p>More specifically, I'm trying to achieve this positioning with an AVCaptureVideoPreviewLayer.  If I set the preview layer's videoGravity to AVLayerVideoGravityResizeAspectFill then it fills the width but centers the content vertically in the frame (cutting off the top and bottom).</p>