The input focus determines what graphic control receives keyboard input. Like Microsoft Windows™, only one graphic control can receive keyboard input at a time. Each graphic item changes it display to indicate it has the focus. For example, a button shows a dashed line around its label. Pressing the return key while an item has the focus is the equivalent of clicking the mouse on it with the correct button combination (specified in its Button parameter).
Each graphic function that can receive the focus has a number called a focus ID number. The focus number is usually (but not necessarily) unique. NextFocusID automatically sets the focus to the next item with a certain focus ID number; FocusID returns the focus ID number of the item that is currently has focus.