Is it possible to create a subscription with a filter for activity type group?

Hi,

We are trying to create a subscription where we would like to add a filter to select or ignore activity types in the group "Internal" (in order to avoid having to list all activity types in that group and also avoid having to add new internal activity types as they are created). However we don't seem to be able to use activity type groups. Does anybode know if it is possible and if so, what is the syntax?

We tried both:
activityDetails.activityType in ['internal']
and
activityDetails.activityTypeGroup in ['internal']

I remember trying to perform a similar question in API search-function some time ago, unsuccessfully. So if anybody knows if it is possible in the search-request I would like to know the syntax.