fBlock                                       (Assignable)

        Contains an optional code block that, when present, is evaluated each
        time the CheckBox object receives or loses input focus.  The code
        block takes no implicit arguments.  Use CheckBox:hasFocus to
        determine if the check box is receiving or losing input focus.  A
        value of true (.T.) indicates that it is receiving input focus;
        otherwise, a value of false (.F.) indicates that it is losing input
        focus.

        This code block is included in the CheckBox class to provide a method
        of indicating when an input focus change event has occurred.  The
        name "fBlock" refers to focus block.