This event occurs when the user starts modifying a cell in a grid control. EVENT-DATA-1 contains the column number of the cell, and EVENT-DATA-2 contains its record number. For convenience, the properties X and Y are set to the cursor's cell for the duration of this event (that is, they are set to the cursor's location at entry to the event procedure and restored to their prior values at exit). This allows you to get a before image of the cell easily by simply doing an INQUIRE on CELL-DATA.
You can prevent the entry from occurring by setting EVENT-ACTION to EVENT-ACTION-FAIL.