 
   public var failureHandler: FailureHandler?
 
+  /// Sets up the success handler.
   public func onSuccess(successHandler: SuccessHandler) -> Self {
     self.successHandler = successHandler
     return self
   }
 
+  /// Sets up the failure handler.
   public func onFailure(failureHandler: FailureHandler) -> Self {
     self.failureHandler = failureHandler
     return self

  /// some representation along the path which does not contain a relation
  /// matching the expected relation.
  func nest(representation: Representation, env: Env) {
    representations.append(representation)
    if hasRel {
      response = responseForRel

    return representation.linkFor(rel)
  }

  /// Runs a new request-response cycle for the next nested representation.
  /// - returns: a new unfinished response for the next nested fetch. The fetch
  ///   starts automatically and runs concurrently when the getter returns.
  var responseForRel: Response? {
