anchor.diff:  @Inject @Updated Event<Document> anotherDocumentEvent;
   -------------------------------------------
   
  -If the observer does specify qualifiers, it will be notified of an event if the event 
  -object is assignable to the observed event type, and if the set of observed event 
  +If the observer does specify qualifiers, it will be notified of an event if the event
  +object is assignable to the observed event type, and if the set of observed event
   qualifiers is a subset of all the event qualifiers of the event.
   
   The observer method may have additional parameters, which are injection
  
positive.code:    }
  }
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negative.code: if (document.isBlog()) blogEvent.select(new AnnotationLiteral<Updated>(){}).fire(document);
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  The above shown event is fired with two qualifiers - `@Blog` and `@Updated`.
  An observer method is notified if the set of observer qualifiers is a subset of the fired event's qualifiers.
  Assume the following observers in this example:
  
  