anchor.diff:      "properties" : {
         "title" : { "type" : "string", "copy_to" : "meta_data" },
         "abstract" : { "type" : "string", "copy_to" : "meta_data" },
  -      "meta_data" : { "type" : "string" },
  +      "meta_data" : { "type" : "string" }
       }
   }
   --------------------------------------------------
  
positive.code: {
    "book" : {
      "properties" : {
        "title" : { "type" : "string", "copy_to" : ["meta_data", "article_info"] },
      }
  }
  --------------------------------------------------
  
negative.code:     "tweet" : {
          "properties" : {
              "image" : {
                  "type" : "binary"
              }
          }
      }
  