anchor.diff:  you don't know much about. For example, this allows creating a histogram
   aggregation with meaningful intervals based on the min/max range of values.
   
  +For the following examples, lets assume the following indexed data:
  +
  +[source,js]
  +-------------------------------------------------
  +PUT /github/user/1?refresh
  +{
  +    "user": "kimchy",
  +    "project": "elasticsearch",
  +    "rating": "great project"
  +}
  +
  +PUT /twitter/tweet/1?refresh
  +{
  +    "user": "kimchy",
  +    "message": "you know, for search",
  +    "rating": 10
  +}
  +------------------------------------------------
  +// CONSOLE
  +// TESTSETUP
  +
  +
   The field stats api by defaults executes on all indices, but can execute on
   specific indices too.
   
  
positive.code: 
  [source,js]
  --------------------------------------------------
  curl -XPOST "http://localhost:9200/_field_stats?level=indices" -d '{
     "fields" : ["rating"]
  }'
  --------------------------------------------------
  
  This is equivalent to the previous request.
  
  
negative.code:          }
        }
     }
  }
  --------------------------------------------------
  // CONSOLE
  <1> Custom date format
  