Some related questions around Display P3 (wide gamut) image handing:
Or...
The answers, from Apple, are here: https://developer.apple.com/videos/play/wwdc2016/712/ with PDF here: http://devstreaming.apple.com/videos/wwdc/2016/712ugi7vg8jznn3pc3u/712/712_working_with_wide_color.pdf
Some notes:
Photoshop:
Xcode:
Way more info in that WWDC session.
Naming: