anchor.diff:  where `DECAY_FUNCTION` can be "linear", "exp" and "gauss" (see below).
   The `offset` and `decay` parameters are optional.
   
  +[horizontal]
   `offset`::
       If an `offset` is defined, the decay function will only compute a the
       decay function for documents with a distance greater that the defined
       `offset`. The default is 0.
  +
   `decay`::
  -
  -The `decay` parameter defines how documents are scored at the distance
  -given at `scale`. If no `decay` is defined, documents at the distance
  -`scale` will be scored 0.5.
  +    The `decay` parameter defines how documents are scored at the distance
  +    given at `scale`. If no `decay` is defined, documents at the distance
  +    `scale` will be scored 0.5.
   
   For example, your documents might represents hotels and contain a geo
   location field. You want to compute a decay function depending on how
  
positive.code:         }
      ],
      "max_boost": number,
      "score_mode": "(mult|max|...)",
      "boost_mode": "(mult|replace|...)"
  }
  --------------------------------------------------
  
  
negative.code: Finally, the newly computed score is combined with the score of the
  query. The parameter `boost_mode` defines how:
  
  [horizontal]
  `multiply`::    query score and function score is multiplied (default)
  `replace`::     only function score is used, the query score is ignored
  `sum`::         query score and function score are added
  