anchor.diff:  
   In this example, the `HtmlFormatter` is only subscribed to poem events for the duration of the call to `#recite`. After that it is automatically detached.
   
  -=== Replacing return values with events
  +### Replacing return values with events
   
   *This is interesting. I can see this being useful for more than just traditionally event-generating objects*
   
  
positive.code: 
  You can run the proof-of-concept benchmark for yourself! It's in the `scripts` directory.
  
  === Managing subscription lifetime
  
  *You know, it occurs to me that in the `Poem` example, it really doesn't make sense to have an `HtmlFormatter` plugged into a `Poem` forever. Is there a way to attach it before the call to `#recite`, and then detach it immediately after?
  
  
negative.code: 
  For convenience, the event name, source, and arguments are all bundled into an `Event` object before being disseminated to observers.
  
  ### Making an object observable
  
  *OK, say I have an object that I want to make observable. How would I go about that?*
  
  