Swift-3 error: ‘-[_SwiftValue unsignedIntegerValue]: unrecognized selector

I ran into the same problem:

let attributedOptions : [String: AnyObject] = [
            NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType as AnyObject,
            NSCharacterEncodingDocumentAttribute: String.Encoding.utf8 as AnyObject
        ]

Here the String.Encoding.utf8 the type check fails. Use NSNumber(value: String.Encoding.utf8.rawValue)