On_Select userexit in Select menus/button-areas or On_Event userexit in element selection state.
In update mode of mask edit state you can arrive and edit all fields of the previously selected record of the mask. If the mask in the active widget contains elements of data base tables in the foreign format, DataView will not check for record locking or the existence of depending elements.
Example:
In DataView itself the userexit is used for the standard function update in the Select menu.