anchor.diff:  "function_score": {
       "query": {},
       "boost": "boost for the whole query",
  -    "FUNCTION": {},
  +    "FUNCTION": {}, <1>
       "boost_mode":"(multiply|replace|...)"
   }
   --------------------------------------------------
  +<1> See <<score-functions>> for a list of supported functions.
   
   Furthermore, several functions can be combined. In this case one can
   optionally choose to apply the function only if a document matches a
  
positive.code: --------------------------------------------------
  
  
  
  ===== Detailed example
  
  Suppose you are searching for a hotel in a certain town. Your budget is
  limited. Also, you would like the hotel to be close to the town center,
  
negative.code:     }
  }
  --------------------------------------------------
  <1> The `DECAY_FUNCTION` should be one of `linear`, `exp`, or `gauss`.
  <2> The specified field must be a numeric, date, or geo-point field.
  
  In the above example, the field is a <<mapping-geo-point-type>> and origin can be provided in geo format. `scale` and `offset` must be given with a unit in this case. If your field is a date field, you can set `scale` and `offset` as days, weeks, and so on. Example:
  
  
  [source,js]
  --------------------------------------------------
      "gauss": {
          "date": {
                "origin": "2013-09-17", <1>
                "scale": "10d",
                "offset": "5d", <2>
                "decay" : 0.5 <2>
          }
      }
  --------------------------------------------------
  <1> The date format of the origin depends on the <<mapping-date-format>> defined in
      your mapping. If you do not define the origin, the current time is used.
  <2> The `offset` and `decay` parameters are optional.
  
  [horizontal]
  `origin`::
  