Scenario:
4 Entry Fields in Form - three mandatory, one optional. Optional can be filled by choosing en entry from multi-coloumn Auswahlliste.

-> Fill the three mandatory fields with other entries from the Auswahlliste, when non-mandatory field is picked by user.

Example:
Public form to drop a onsite report.
Customer, Customer No. and Onsite Order Number are mandatory, transaction no. is optional.
Transaction No. is linked with the other information in an Auswahlliste.

User can now manually enter the three mandatory infos, or by entering the correct Transaction No, the fields are autofilled.