Just a quick note about the big picture here: The new number formatting facilities are conceptually a wrapper around the existing NumberFormatter class. NumberFormatter is focused on localised strings, which is why NumberFormatter.Style has no .hexadecimal value. In contrast, String.init(_:radix::uppercase:) produces a non-localised string. To my mind trying to mix these two seems like a type error.
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Quinn “The Eskimo!” @ DTS @ Apple