In this section, we will look at three classes in the OpenLayers library that we won't often work directly with, but which provide an enormous amount of functionality to most of the other classes in the library. The first two classes, Observable and Object, are at the base of the inheritance tree for OpenLayers—the so-called super classes that most classes inherit from. The third class, Collection, isn't actually a super class but is used as the basis for many relationships between classes in OpenLayers—we've already seen that the Map class relationships with layers, overlays, interactions, and controls are managed by instances of the Collection class.

Before we jump into the details, take a look at the inheritance diagram for the components we've already discussed:

As you can see, the Observable class, ol.Observable, is the base class for every component of OpenLayers that we've seen so far. In fact, there are very few classes in the OpenLayers library that do not...