anchor.diff:  
       revision_history = [] :: [subscriptions:rev()]
   }).
  -
   
   %% Model for caching handle details fetched from OZ
   -record(od_handle, {
  
positive.code:     users :: undefined | sets:set(od_user:id())
  }).
  
  
  %% Identity containing user_id
  -record(user_identity, {
      user_id :: undefined | od_user:id(),
      provider_id :: undefined | oneprovider:id()
  }).
  
  
  %% User session
  -record(session, {
  
negative.code:     revision_history = [] :: [subscriptions:rev()]
  }).
  
  %% Local, cached version of OZ group
  -record(od_group, {
      name :: undefined | binary(),
  