anchor.diff:  
   The above result includes the `_index`, `_type`, and `_id` of the
   document we wish to retrieve, including the actual source of the
  -document that was indexed.
  +document that was indexed if it could be found (as indicated by the
  +`found` field in the response).
   
   The API also allows to check for the existence of a document using
   `HEAD`, for example:
   
   [source,js]
   --------------------------------------------------
  -curl -XHEAD 'http://localhost:9200/twitter/tweet/1'
  +curl -I 'http://localhost:9200/twitter/tweet/1'
   --------------------------------------------------
   
   [float]
  
positive.code:     "_index" : "twitter",
      "_type" : "tweet",
      "_id" : "1", 
      "_source" : {
          "user" : "kimchy",
          "postDate" : "2009-11-15T14:12:12",
  
negative.code: 
  [source,js]
  --------------------------------------------------
  curl -I 'http://localhost:9200/twitter/tweet/1/_source'
  --------------------------------------------------
  
  [float]
  