I have 6 fields in a custom tab added in tcode me21n. This custom tab is a subscreen. My 1st field is a dropdown field with value yes/no. If user selects yes then next 2 fields will become mandatory for user to give values else it will remain normal like other 3 fields. I have used badi to do this screen enhancement. It may be a simple question but please help me to achieve this. I dont know where to validate this either in pbo or any other badi method.