anchor.diff:  }
   --------------------------------------------------
   
  -<1> The `stack` key means it contains all field stats for the `stack` index.+<1> The `stack` key means it contains all field stats for the `stack` index.
  +
  +==================================================
  
positive.code: --------------------------------------------------
  
  <1> The `_all` key indicates that it contains the field stats of all indices in the cluster.
  
  With level set to `indices`:
  
  [source,js]
  --------------------------------------------------
  curl -XGET "http://localhost:9200/_field_stats?fields=rating,answer_count,creation_date,display_name&level=indices"
  --------------------------------------------------
  
  [source,js]
  
negative.code: `sum_doc_freq`::
  
  The sum of each term's document frequency in this field, or -1 if this
  measurement isn't available on one or more shards.
  Document frequency is the number of documents containing a particular term.
  
  `sum_total_term_freq`::
  
  The sum of the term frequencies of all terms in this field across all
  documents, or -1 if this measurement isn't available on one or more shards.
  Term frequency is the total number of occurrences of a term in a particular
  document and field.
  
  