Question
Adding a DS record with a blank domain value in Plesk returns the message This required field is empty. You need to specify a value.
Why is it not possible to add a DS record to the root domain?
Answer
DS records are used to establish trust from a parent zone, but the root zone is at the top of the DNS hierarchy, so there is no parent zone to create a DS record in. Such records should be added on the registrar's end.