anchor.diff:  * copy targets of updated fields, if any, are also non-indexed, non-stored single valued numeric docValues fields.
   
   To use in-place updates, add a modifier to the field that needs to be updated.
  -The content can be updated or incrementally increased.
  +The content can be updated or incremented/decremented.
   
   `set`::
   Set or replace the field value(s) with the specified value(s).
   May be specified as a single value.
   
   `inc`::
  -Increments a numeric value by a specific amount.
  -Must be specified as a single numeric value.
  +Increments or decrements a numeric field's value by a specific amount, specified as a single integer or float.
  +Postive amounts increment the field's value, and negative decrement.
   
   [TIP]
   ====
  
positive.code: ----
  {"id":"mydoc",
   "price":99,
   "popularity":62,
   "categories":["kids","toys","games"],
   "sub_categories":["under_5","under_10"],
   "tags":["buy_now","clearance"]
  
negative.code: ----
  {"id":"mydoc",
   "price":{"set":99},
   "popularity":{"inc":-7},
   "categories":{"add":["toys","games"]},
   "sub_categories":{"add-distinct":"under_10"},
   "promo_ids":{"remove":"a123x"},
  