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How? There is no documentation for this property what so ever and my attempts have yielded very bad results. Lack of documentation is starting to show some lack of drive on the control suite. The documentation related to this property that I did find was for WP8x, kind of concerning that if this control is a port/carry over that you would include that information with present documentation.
What is more concerning is that this the only solution I have right now for using with an in development app that CalendarView from Windows 10 can't fill since you can't add custom content to that control