Poppables present information on demand in a given context. This is an abstract base class for Popup menus and other contextual information like image highlights. It's main purpose is to ensure that only one poppable at a time can be shown in a given context. Note that in an application multiple poppables can be shown in different context at the same time.
Let's look at an example of a popup class. In this class the register method is called by the constructor. The class also implements a close method which is called if the second poppable is registered.