MSG-BEGIN-HEADING-MENU-POPUP This event is fired when the user starts changing the check-box value of a menu item in a heading menu popup of a Grid control. The EVENT-DATA-1 and EVENT-DATA-2 data items contain the column number and the current value (respectively) of the check box menu item corresponding to the column. Setting EVENT-ACTION to EVENT-ACTION-FAIL inhibits the change of the check-box menu item value.
