anchor.diff:      int length,
       // QUESTION: This accepts 128, 192, 256, should we use an enum instead?
       //           (obviously, more values might be acceptable in the future)
  +    //           Or would separate methods be better, downside is that it
  +    //           deviates from how other generateKey methods work.
     ) {
       ArgumentError.checkNotNull(length, 'length');
   
  
positive.code:   //           identity on all platforms? HmacSecretKey can only accept the
    //           implementations defined in this library. When passing to webcryto
    //           we must pass as a string.
  
    /// Compute a cryptographic hash-sum of [data] stream using this [Hasher].
    ///
  
negative.code: // QUESTION: Should these Hasher implementations be `const` or `final`?
  // QUESTION: Should these Hasher implementation be top-level elements or static
  //           properties on the `Hasher` class?
  //           (is this perhaps easier to find, as they would be namespaced)
  //           NOTE: factory constructors might be cool.
  
  /// Key for signing/verifying with HMAC.
  ///
  