ActionChange is called automatically when the associated action changes. It updates the button control to reflect the action's current Checked state. Then it calls the inherited method, which checks the associated properties for that client type. 

The Sender parameter is the associated action. The CheckDefaults parameter specifies whether properties and event handlers should be changed if they differ from the default values. When CheckDefaults is true, properties and event handlers are only changed when the current values are the default values (that is, when the values have not been previously changed). When CheckDefaults is false, properties and event handlers are changed, regardless of their current values. 

TCustomAction