[NTG-context] extending the value of a key

Hello, I remember, that there is a new mechanism to extend the value of a key, but I forgot how it works. Example to show what I'm searching for: Instead of writing "\setuptyping[style=\doresetattribute{spacing}\tt]" I would prefer something like "\setuptyping[style+=\doresetattribute{spacing}]" Could someone help please? Cheers, Peter -- http://pmrb.free.fr/contact/