anchor.diff:  returns typical information retrieval metrics like _mean reciprocal rank_,
   _precision_ or _discounted cumulative gain_.
   
  -experimental[The ranking evaluation API is new and may change in non-backwards compatible ways in the future, even on minor versions updates.]
  -
   [float]
   === Overview
   
  
positive.code: [cols="<,<",options="header",]
  |=======================================================================
  |Parameter |Description
  |`relevant_rating_threshold` |Sets the rating threshold above which documents are considered to be
  "relevant". Defaults to `1`.
  |`ignore_unlabeled` |controls how unlabeled documents in the search results are counted.
  If set to 'true', unlabeled documents are ignored and neither count as relevant or irrelevant. Set to 'false' (the default), they are treated as irrelevant.
  
negative.code: [cols="<,<",options="header",]
  |=======================================================================
  |Parameter |Description
  |`k` |sets the maximum number of documents retrieved per query. This value will act in place of the usual `size` parameter 
  in the query. Defaults to 10.
  |`relevant_rating_threshold` |Sets the rating threshold above which documents are considered to be
  "relevant". Defaults to `1`.
  |=======================================================================
  