anchor.diff:              {
                   "links": {
                       "memberships.user_group": {
  -                        "href": "/groups/{memberships.user_group}",
  +                        "href": "/user_groups/{memberships.user_group}",
                           "type": "user_groups"
                       },
                       "memberships.user": {
  
positive.code: 
  + Response 204
  
  ## Add a link [/groups/{id}/links/users]
  Only links to users may be added.
  
  ### Add user links [POST]
  
negative.code:                     "projects": "/projects",
                      "workflows": "/workflows",
                      "subject_sets": "/subject_sets",
                      "groups": "/user_groups",
                      "classifications": "/classifications",
                      "memberships": "/memberships",
                      "collections": "/collections",
  