anchor.diff:    );
   }
   
  +@sealed
   abstract class Pbkdf2SecretKey {
     Pbkdf2SecretKey._(); // keep the constructor private.
   
  
positive.code:   Future<Map<String, dynamic>> exportJsonWebKey();
  }
  
  abstract class HkdfSecretKey {
    HkdfSecretKey._(); // keep the constructor private.
  
  
negative.code:     if (dart.library.js) 'src/webcrypto_impl_js.dart' as impl;
  
  /// Thrown when an operation failed for an operation-specific reason.
  @sealed
  abstract class OperationError extends Error {
    OperationError._(); // keep the constructor private.
  }
  
  /// A key-pair as returned from key generation.
  @sealed
  abstract class KeyPair<S, T> {
    KeyPair._(); // keep the constructor private.
  
  