We're dealing with linking to/from apps now - on iOS it is a HUGE mess, littered with edge cases. They basically made like 5 breaking changes from iOS 8 until 10. And nothing is compatible with the other. Some of the "link" websites (for like marketing etc) even have to have tables where it says "this link will work in this webview, but not in this app, and sometimes in that app depening on the moon position".