The specific properties applicable to the Button control are:
Default Button: Set to True to make this button the “default button” for the control. The default button is the one which is triggered when the user pushes the Return key. If you have the automatic OK button enabled in the dialog properties, normally that button would be the default.
Close Dialog: Set to True to make this button close the dialog when it’s clicked. If set to False, nothing will happen automatically when the user clicks the button, but your script will be notified.
Return Value: If Close Dialog is set to True, this lets you specify the value that the dialog returns when it closes. For example, you might have a three buttons that all close the dialog – specifying a different return value lets you tell which one the user clicked after the dialog closes.