I found that Swift doesn't specify an RFC in the documentation like the other specs sometimes do. I am pretty sure from the implementation and the options that we're using RFC 4648. Is that correct?
Second, is it worth it to put this information in the documentation? Since RFC 4648 is the "current" (as of this post) version we may not need it right now, but if it is further changed in the future, I believe that the documentation would be helpful in de-conflicting RFC versions.