One XAML for UWP, Windows 8.1 and Windows Phone 8.1

I was recently involved in a conversation on how to have the easiest way to maintain a XAML view across a UWP (Universal Windows Project) a Windows 8.1 and Windows Phone 8.1 projects. There are a few options and the most straight forward way to do it with a UserControl residing in a Portable Class Library. However… What…