   _UInt32 == UInt32
 {
   associatedtype _UInt32 = UInt32
-  static func _isScalar(_: Encoding.CodeUnit) -> Bool
   func _parseMultipleCodeUnits() -> (isValid: Bool, bitCount: UInt8)
   var buffer: Encoding.EncodedScalar { get set }
   func _bufferedScalar(bitCount: UInt8) -> Encoding.EncodedScalar

  }
}

extension UTF16.ReverseDecoder : _UTF16Decoder {
  public typealias Encoding = Unicode.UTF16

  public // @testable

  }
}

extension Unicode.UTF16.ForwardDecoder : _UTFDecoder {
  public typealias Encoding = Unicode.UTF16
  
  public // @testable
