A grid cell was double-clicked (text or numeric matrix). This might be used to generate more detailed information on the chosen cell. For the cell co-ordinates see 2†4‡¾.
Note that you will get this event if the user double-clicks on the grid headers – the row/column index will be ¯1 in this case (¯1 ¯1 is the top corner). These co-ordinates are always reported in ŒIO=1.