Hello @abhinav, thanks for your answer!
My configuration matches your example, so it seems I managed to understand how FTS works in couchbase 
I have more questions though :
Using fuzziness, to much matches. For instance : amfkenfjemfjn (i just typped random letters) matches “Alfred”.
Adding the highlight option, it shows me that alf is the part that matches. I understand that, but I would think that adding random letters after would not match at all.
Second question: trying to get rid of the accents in French names, I was looking for an ascii folding filter and found this merged PR on bleve github (add ASCII Folding Filter by Funzinator · Pull Request #1070 · blevesearch/bleve · GitHub). It is not yet available in Couchbase, do you know if it will be soon ?
Third question (related to the previous one) : without an ascii folding filter, I tried using character regexp filters, to transform “éèÉÈëËêË” to “e”, but it seems to transform it to “ee”. I found this post (Character Filter) where the person has a similar problem and asks :
Or could it be that is a problem of utf8, because ü ist a 2 byte character, while u is 1 byte?
Can it be the reason ?
@sreeks : I’ll tell you more about my experience with couchbase FTS when I’ll have use it a little more
Thanks a lot
Jérémie