I try to do this :
I have books, books have many tags. It's a nested relation !
When a user search "starwars vador", I search in all books to find books with this tags.
If a book has tags "starwars" and "vador" it's the best match ! And that's I try to do.
In my case, if a book has 2 tags, he has not a best score than books with only one tag matched.
Is it possible to increase the score according to the number of nested documents matched ?