anchor.diff:  ----
   {"id":"mydoc",
    "price":{"set":99},
  - "popularity":{"inc":20},
  + "popularity":{"inc":-7},
    "categories":{"add":["toys","games"]},
    "sub_categories":{"add-distinct":"under_10"},
    "promo_ids":{"remove":"a123x"},
  
positive.code: May be specified as a single value, or as a list.
  
  `inc`::
  Increments a numeric value by a specific amount.
  Must be specified as a single numeric value.
  
  === Field Storage
  
  
negative.code: ----
  {"id":"mydoc",
   "price":99,
   "popularity":35,
   "categories":["kids","toys","games"],
   "sub_categories":["under_5","under_10"],
   "tags":["buy_now","clearance"]
  