A radio component is a special type of menu component, in which one, and only one, menu item is active at any time. For any radio component,
for one item , and
for all the others. The menu item that was selected last is the one that returns
Radio components are used to group together items, only one of which may be chosen at a time.
Click Radio Component in the button bar of the Interface Builder to add a radio component to the current interface. Radio components must be added as the children of a menu, and, like standard menu components, are not visible in the interface skeleton until items have been added. To add an item to a radio component, click Item . New items are automatically of the correct type for radio components. Note that you cannot add a submenu as an item in a radio component.
The way that a selected radio component is indicated on-screen depends on the operating system or window manager you are running; for example it may be a dot or tick to the left of the selected item. On some systems, a diamond button is placed to the left of every item, and this is depressed for the item which is currently selected.
Like standard menu components, separators divide radio components from other items or components in a given menu.
LispWorks IDE User Guide (Windows version) - 25 Nov 2011