An event handler is a public method of a класс that is called each time an event is raised by an object having an observer of the same класс.

The name of the event handler is the "event name" of the object, followed by an underscore, and the name of the event.

The event name of an object is usually the name you define in the development environment, but can be anything you want. This name is attributed at object creation by the NEW instruction.