An object that receives notification events from a notifier object with which it is registered. See notification event. Contrast with notifier.

an object that monitors changes to the data in an observable object

an object that tracks changes to other objects

carries Objective connotations (somebody else observing somebody who observes something). At this site, it is used as a kind of bridge towards orthodox way of thinking. Reality is a no-no word at this site just as Objective and Objectivity are. It should be replaced with Out There or Commonly Agreed Description of the World and Ourselves within It. The whole concept is based on the fact that we can not perceive the "out there" directly. Variants like real and really are tolerated as long it is clear that they refer to Cultural Imprint, Commonly Agreed Description... or Common Perceptual Base. However, an effort should be made to avoid them. It is important to notice that existence of reality in classical sense is not denied. What it used to annotate, is divided between these more suitable forms.

Receives notification from an agenda model's observer controller whenever an entry or to-do list is added, updated or deleted in the agenda model. See also: observer controller