Groups
A group is who a group-scoped event is about. A static group keeps a list you add to; a dynamic group holds whoever's attributes contain its filter, so nobody keeps it up. Beside the groups somebody keeps are temporary lists, picked by a person for one send: you can see them, but a key cannot change one and an event cannot name one. In the Standard lens a group is, for example, “Group A”.
DELETETake someone out of a group
Requires groups:write. Named by Raven's id for the subject or contact, not by a membership id. Membership is who is in the group now, so this really removes; what was sent to them while they were in it is untouched. The one DELETE in the API.
204 with no body. 404 when they are not in this group. 409 on a temporary list.
None: success is 204. On failure the body is { error, code }.