I wonder how many libraries correctly handles the date 1712-02-30 in the Swedish calendar (according to Wikipedia the only official 30th of February in history)?

https://en.wikipedia.org/wiki/List_of_non-standard_dates#Feb...

Tried using ncal like in the examples in that blog post, but it did not work correctly using either Julian or Gregorian. Of course the Swedish calendar from 1700-1712 was neither, but somewhere in-between, because of the (failed) attempt to gradually move from one to the other.