function score example that checks for words in a multi valued field and adds 1 if the word was found.

gistfile1.txt

curl -XPOST "http://localhost:9200/scorescripttest/test/" -d'
{
   "tags": [
      "dressing room",
      "zebrawood",
      "wood",
      "oak",
      "on your person",
      "seating",
      "chair",
      "home",
      "sophisticated",
      "furniture",
      "mahogany"
   ]
}'

curl -XPOST "http://localhost:9200/scorescripttest/test/_search" -d'
{
   "query": {
      "function_score": {
         "query": {
            "match": {
               "tags": "chair"
            }
         },
         "functions": [
            {
                
               "script_score": {
                   "params": {
                       "tags": ["seating", "chair", "mahogany"]
                   },
                  "script": "score = 0;foreach (value : doc[\"tags\"].values){if(tags contains value){score+=1};} return score;"
               }
            }
         ],
         "boost_mode": "replace"
      }
   }
}'

If you want the original score to be added to the script score, replace "boost_mode": "replace" with "boost_mode": "sum".