1) Function names are misleading or not descriptive enough. E.g. isAlpha(). I assumed this meant is alphanumeric, but it actually means isAlphabetic (as in no numeric values at all). isAlphanumeric() clears this up, but just call the first isAlphabetic and remove any ambiguity. 2) Explicit binary inverts; e.g. isUppercased(), isLowercased(). This leads to bad coding style as conditionals that point in the affirmative usually leads to easier to read code. If it's not uppercased of course its lowercased, so why keep a function around to point this out? Save on the cognitive load on the users and just keep one around. Let them negate it for the desired result.
Otherwise, thank you for contributing what looks to be a pretty handy library that isn't tied to just MacOS/iOS and Xcode. I'm really starting to enjoy Swift and am curious to use it in non-client environments soon and a library like this is a pretty nice tool to have.