A VB form supports many events to help you efficiently manage
the phases of a form's lifetime within the application.
It's useful to know about programming form events because they
often mark important moments in an application's runtime session, such as:
When a form first becomes available in memory
When a user changes attention between forms
When a form leaves memory
These events can become quite important for tying together parts
of your application, for startup and cleanup operations, and for providing more
global validation of user changes to controls on a form.