anchor.diff:                 "doc_count": 2,
                  "sales": {
                     "value": 60
  -               },
  -               "sales_deriv": {
  -                  "value": -490 <2>
                  }
               },
               {
  
positive.code: [[search-aggregations-reducer-max-bucket-aggregation]]
  === Max Bucket Aggregation
  
  A parent reducer aggregation which calculates the derivative of a specified metric in a parent histogram (or date_histogram) 
  aggregation. The specified metric must be numeric and the enclosing histogram must have `min_doc_count` set to `0`.
  
  The following snippet calculates the derivative of the total monthly `sales`:
  
  [source,js]
  --------------------------------------------------
  {
      "aggs" : {
          "sales" : {
              "date_histogram" : {
                  "field" : "date",
                  "interval" : "month"
  
negative.code:                "doc_count": 3,
                 "sales": {
                    "value": 550
                 }
              },
              {
                 "key_as_string": "2015/02/01 00:00:00",
  