anchor.diff:  
   [source,js]
   --------------------------------
  -{
  +GET /index/type/_rank_eval
  +{
  +    "requests": [
  +    {
  +        "id": "JFK query", 
  +        "request": { "query": { "match_all": {}}},
  +        "ratings": []  
  +    }],
       "metric": {
           "reciprocal_rank": {}
       }
   }
   --------------------------------
  -
  +// CONSOLE
   
   === Normalized discounted cumulative gain
   
  
positive.code: 
  [source,js]
  --------------------------------
  {
      "metric": {
        "precision": {
          "relevant_rating_threshold": 1,              <1>
  
negative.code:                         "query": "{{query_string}}"}}}}},  <1>
    "requests": [
    {
        "id": "JFK query",
        "ratings": [
          {
            "rating": 1.5,
  