Enumerates the various reasons for raising the ToolBarNotify event.
Values:
| IG_ARTX_GUI_TOOLBAR_BUTTON_SELECTED | A button has been selected. |
| IG_ARTX_GUI_TOOLBAR_NONE_SELECTED | No button is selected. |
| IG_ARTX_GUI_TOOLBAR_HIDDEN | A button on toolbar caption is clicked. |
| IG_ARTX_GUI_TOOLBAR_DESTROYED | The toolbar is about to be destroyed. |