anchor.diff:  
   === Error Handling
   
  -In many circumstances we found, that exception is raised inside the event. For
  -this case *potok* comes with the built-in mechanism for handling errors.
  +In many circumstances we found, that exception is raised inside the
  +event. For this case *potok* comes with the built-in mechanism for
  +handling errors.
   
   Let's see some code:
   
  
positive.code: 
  ==== Watch Event
  
  Apart from the simple state transformations, applications usually
  need to perform asynchronous operations such as call remote API, access
  local database, etc. This is where the *watch* events play their
  role. They are designed to handle asynchronous operations.
  
  
negative.code:     (update state :counter (fnil inc 0))))
  ----
  
  You may be thinking, the signature of the `update` function is very
  similar to a reduce function. And in fact, it does just that the state
  reduction, and it can be defined using a plain ClojureScript function:
  
  [source, clojure]
  ----
  