For the following: ```swift import RegexBuilder let r = Regex { CharacterClass.anyUnicodeScalar } _ = try! r.wholeMatch(in: "x") ``` Crashes with: ``` Fatal error: Should have been handled by tree conversion ``` However it's not clear this API should still exist, as it was removed from https://github.com/apple/swift-evolution/blob/main/proposals/0363-unicode-for-string-processing.md.