anchor.diff:    },
     "upsert": {}
   }
  ---------------------------------------------------
  +----
   // TEST[s/"id": "my_web_session_summariser"/"source": "ctx._source.page_view_event = params.pageViewEvent"/]
  -// TEST[continued]
   
   [discrete]
   [[doc_as_upsert]]
  
positive.code: value:
  
  [source,console]
  --------------------------------------------------
  POST test/_update/1
  {
    "doc": {
  
negative.code:     }
    }
  }
  ----
  
  You could also remove a tag from the list of tags. The Painless
  function to `remove` a tag takes the array index of the element
  