Hi,
Selection screen is different from the normal screen. These events are specific to Selection Screen. If you want to validate any field in normal screen. You do it in PROCESS AFTER INPUT event of flow logic of your screen.
If you want any value help or input help you can use PROCESS ON HELP-REQUEST (POH) and PROCESS ON VALUE-REQUEST (POV) These events.
For more info on These events Please check in SAP HELP PORTAL (help.sap.com).
Regards,
Aswath.