typedef void __fastcall (__closure *TTBCustomizeQueryEvent)(TToolBar* Sender, int Index, bool &Allow);
TTBCustomizeQueryEvent is the type of event handlers that allow a toolbar to decide whether to allow a user customization.
Sender is the customizable toolbar that the user is trying to modify.
Index is the index of the button to be deleted or the index where a new button is to be inserted.
Allow returns an indication of whether the user can proceed with the operation. On entry, Allow is True, indicating that the user can add or delete the button. The event handler can change Allow to False to block the change to the toolbar.