Got that, thank you.
Any hint for good approach to format those group_title? I looked through the code a bit and it seems the group_title is only built within js on the frontend, is it?
I was just playing around with the hooks/filters for default / meta calls and didnt come to a reasonable approach. Also I was thinking about creating a helper field and wondered if I could dynamically create default values. sanitize hooks are only called upon save not on changes within the form, are they?