The example demonstrates how to create a menu to display collections of geo objects on the map.
To create such a menu, you must create two representations of a geo object: its API-representation (in the form of placemarks on the map) and its DOM representation (i.e. the menu item).
These representations can be linked inside the event handler for the DOM representation (click on menu item) by calling specific methods in the API representation of the geo object (adding/removing placemarks on the map).
In this example, the menu is based on the data array that is defined in the file groups.js.
The example is discussed more in the developers' club.