You set the Callback property when you're working with a modeless balloon. A modeless balloon is one that allows the user to switch back to the application in which they're working without first closing the balloon. A modeless balloon may be useful if you're creating help that the user will want to leave open while performing several steps in the application. To make a balloon modeless, set the Mode property of the Balloon object to msoModeModeless.
The Callback property specifies a function or a macro to run when the user clicks a button on a balloon. If you write a function to be called by the Callback property, you can use that function to determine which button was clicked.
You set the Callback property to the name of a function or macro. For example, the following line of code sets the Callback property:
Assistant.NewBalloon.Callback = "EvaluateCheckboxes"Note that you must set the Callback property to the name of a Function procedure; you can't set it to the name of a Sub procedure. The Function procedure must be public.