A check box is a labelled box which is either checked or unchecked.
Whenever a check box is clicked by the user, the check box's value is toggled and its callback procedure is invoked. A callback procedure is provided as an initialization argument when each check box is created.
Creates a check box with a string or bitmap label. If label is a bitmap, then the bitmap must be valid (see ok? in bitmap%) and not installed in a bitmap-dc% object; otherwise, an exn:application:mismatch exception is raised.
If an ampersand (``&'') occurs in label (when label is a string), it is specially parsed; under Windows and X, the character following an ampersand is underlined in the displayed control to indicate a keyboard mnemonic. (Under MacOS, mnemonic underlines are not shown.) The underlined menumonic character must be a letter or a digit. The user can effectively click the check box by typing the mnemonic when the control's top-level-window contains the keyboard focus. The user must also hold down the Meta or Alt key if the keyboard focus is currently in a control that handles normal alphanumeric input. The ampersand itself is removed from label before it is displayed for the control; a double-ampersand in label is converted to a single ampersand (with no mnemonic underlining). Menumonic keyboard events are handled by on-traverse-char (but not under MacOS).
The callback procedure is called (with the event type 'check) whenever the user clicks the check box.
The style argument is provided for future extensions. Currently, style must be the empty list.