text:   /**
     *  Checks access to the observer for grammar violations. This includes checking for multiple OnError or OnCompleted calls, as well as reentrancy in any of the observer methods.
     *  If a violation is detected, an Error is thrown from the offending observer method call.
     *  
     * @returns An observer that checks callbacks invocations against the observer grammar and, if the checks pass, forwards those to the specified observer.
     */    
    Observer.prototype.checked = function () { return new CheckedObserver(this); };
  
    /**
     * Schedules the invocation of observer methods on the given scheduler.
     * @param {Scheduler} scheduler Scheduler to schedule observer messages on.
     * @returns {Observer} Observer whose messages are scheduled on the given scheduler.
     */
    Observer.notifyOn = function (scheduler) {
      return new ObserveOnObserver(scheduler, this);
    };  