anchor.diff:      }],
       "metric": {
         "precision": {
  +        "k" : 20,
           "relevant_rating_threshold": 1,
           "ignore_unlabeled": false
         }
  
positive.code: {
      "requests": [ ... ], <1>  
      "metric": { <2>
        "reciprocal_rank": { ... } <3>
     }
  }
  ------------------------------
  
negative.code: returns typical information retrieval metrics like _mean reciprocal rank_,
  _precision_ or _discounted cumulative gain_.
  
  [float]
  === Overview
  
  