title: How do you set kCGImagePropertyExifUserComment on a CGImageMetadataRef?
body: <p>How do you set kCGImagePropertyExifUserComment on a CGImageMetadataRef in iOS?  These are the only functions I have found and they are only for MacOS</p>
  
  <p><a href="https://github.com/phracker/MacOSX-SDKs/blob/master/MacOSX10.9.sdk/System/Library/Frameworks/ImageIO.framework/Versions/A/Headers/CGImageMetadata.h" rel="nofollow noreferrer">https://github.com/phracker/MacOSX-SDKs/blob/master/MacOSX10.9.sdk/System/Library/Frameworks/ImageIO.framework/Versions/A/Headers/CGImageMetadata.h</a></p>