anchor.diff:                 "doc_count": 2,
                  "sales": {
                     "value": 60
  -               },
  -               "sales_deriv": {
  -                  "value": -490 <2>
                  }
               },
               {
  
positive.code: --------------------------------------------------
  {
     "aggregations": {
        "sales": {
           "buckets": [
              {
                 "key_as_string": "2015/01/01 00:00:00",
  
negative.code:                "doc_count": 2,
                 "sales": {
                    "value": 375
                 }
              }
           ]
        },
        "max_monthly_sales": {
            "keys": ["2015/01/01 00:00:00"], <1>
            "value": 550
        }
     }
  }
  --------------------------------------------------
  
  <1> `keys` is an array of strings since the maximum value may be present in multiple buckets
  
  