anchor.diff:  		start_date :: pos_integer() | undefined,
   		end_date :: pos_integer() | undefined,
   		type :: price_type() | undefined,
  -		period :: valid_period() | undefined,
  +		period :: recur_period() | undefined,
   		units :: unit_of_measure() | undefined,
   		size :: integer() | undefined,
   		amount :: integer() | undefined,
  
positive.code: 		start_date :: '_' | pos_integer() | undefined,
  		end_date :: '_' | pos_integer() | undefined,
  		is_bundle = false :: '_' | boolean() | undefined,
  		status :: product_offering_status() | '_' | undefined,
  		specification :: string(),
  		price :: '_' | [#price{}],
  		characteristics = [] :: [tuple()],
  
negative.code: 		{product :: string(),
  		start_date :: pos_integer(),
  		termination_date :: pos_integer(),
  		status :: product_status(),
  		characteristics = [] :: [tuple()],
  		last_modified :: tuple() | '_' | undefined}).
  
  