   /// Because of buffering, it is impossible to find the corresponding position
   /// in the generator for a given returned `UnicodeScalar` or an error.
   ///
-  /// - parameter next: A generator of code units to be decoded. Repeated
+  /// - parameter next: A generator of code units to be decoded.  Repeated
   /// calls to this method on the same instance should always reuse the same
   /// generator.  Failing to do so will result in undefined behavior.
   public mutating func decode<

              _decodeBuffer = UInt32(codeUnit)
              _bitsInBuffer = 8
            }
          } else {
            _atEnd = true
            return .EmptyInput
          }

  /// consume a certain byte before looking at it.
  var _decodeBuffer: UInt32 = 0

  /// The number of bits in `_decodeBuffer` that are current filled.
  var _bitsInBuffer: UInt8 = 0

  /// Whether we have exhausted the generator.  Note that this doesn't mean
  /// we are done decoding, as there might still be bytes left in the buffer.
  var _atEnd: Bool = false

  /// Start or continue decoding a UTF-8 sequence.
