Using the Dialog class in Interactive Statements
The Dialog class provides methods that can only be called from
        within an interactive instruction (dialog) such as MENU,
            INPUT, INPUT ARRAY, DISPLAY ARRAY and
            CONSTRUCT. 
The methods are called through the predefined variable DIALOG, which
            automatically provides a reference to the Dialog object.
Tutorial Chapter 5 Enhancing the
                Form illustrates the use of Dialog class methods to
            disable/enable actions during a MENU interactive statement.