anchor.diff:  % Define the data structures used throughout the app.
   
  --type(time() :: {pos_integer(), non_neg_integer(), non_neg_integer()}).
  +-type(time() :: {pos_integer(), non_neg_integer(), non_neg_integer()} | 'undefined').
   
   -record(user_group, {
   	id :: 'undefined' | pos_integer(),
   	name :: binary(),
   	permissions = [] :: [atom()],
  -	created = os:timestamp() :: time(),
  -	updated = os:timestamp() :: time()
  +	created :: time(),
  +	updated :: time()
   }).
   
   -record(user, {
  
positive.code: 	grid_opacity = 0.5 :: float(),
  	zones = [] :: [pos_integer()],
  	combatants = [] :: [pos_integer()],
  	created = os:timestamp() :: time(),
  	updated = os:timestamp() :: time()
  }).
  
  -record(zone, {
  
negative.code: 	fill_color = <<"green">> :: binary(),
  	stroke_mode = gappy :: 'gappy' | 'solid',
  	path = <<>> :: binary(),
  	created :: time(),
  	updated :: time()
  }).
  
  -record(combatant, {
  