sBlock                                        (Assignable)

        Contains an optional code block that, when present, is evaluated
        immediately after the ListBox object's selection changes.  The code
        block takes no implicit arguments.  Use the ListBox:buffer variable
        to determine the current selection.

        This code block is included in the ListBox class to provide a method
        of indicating when a state change event has occurred.  The name
        "sBlock" refers to state block.