Menu sensitivity
Menu sensitivity is the fact that menu options may be made available in certain situations, and unavailable in others. When they are unavailable, their text prompt appears in a greyed-out colour.
You can determine under what circumstances a menu option must be available by setting and unsetting Sensitivity properties. You can see these properties when you right-mouse-click the menu option and then choose Properties. Use the Property Inspector's Show Help button to learn more on what each sensitivity property does.
Menu sensitivity propagates to the menu toolbar (the icon ribbon). When a menu option is available, any corresponding icon is also clickable. When a menu option is unavailable, any corresponding icon appears in a non-clickable state.
You can also make a menu option state-sensitive by using the action:
MenubarSetItem(<itemname>,{'ON'|'OFF'}