<Match> uses the exactly prop while <MatchRoutes> routes have an exact property. This should be consistent. I prefer exactly if for no other reason than that <Match> came first.
Marking this as a "bug" in the sense that it's a bug of the API surface.
+1 for exact, not many var names uses '*ly' in my experience
However <Match exactly pattern='whatever'...> reads better than <Match exact pattern='whatever'...>
But only by a tiny bit.
It's too early to nit-pick prop names in v4. We're just exploring some new possible API. Please rest assured we won't ship the final release with two props that are supposed to do the same thing but with different names :)
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+1 for exact, not many var names uses '*ly' in my experience