anchor.diff:  }
   --------------------------------------------------
   // CONSOLE
  -<1> The `default_field` uses the `classic` similarity (ie TF/IDF).
  -<2> The `bm25_field` uses the `BM25` similarity.
  -
  +<1> The `default_field` uses the `BM25` similarity.
  +<2> The `classic_field` uses the `classic` similarity (ie TF/IDF).
  
positive.code:         "default_field": { <1>
            "type": "text"
          },
          "bm25_field": {
            "type": "text",
            "similarity": "BM25" <2>
          }
        }
      }
  
negative.code: The only similarities which can be used out of the box, without any further
  configuration are:
  
  `BM25`::
          The Okapi BM25 algorithm. The algorithm used by default in Elasticsearch and Lucene.
          See {defguide}/pluggable-similarites.html[Pluggable Similarity Algorithms]
          for more information.
  
  `classic`::
          The TF/IDF algorithm which used to be the default in Elasticsearch and
          Lucene. See {defguide}/practical-scoring-function.html[Lucene’s Practical Scoring Function]
          for more information.
  
  
  