title: when a search hits a document, how can ES only return parts of that document?
body: <p>I have a document with nested types and I use nested query to search on the nested part.
  Now I get a hit and the search result returned is the whole doc.
  Could anyone tell me how can I get only this nested part or the part of document which contains this nested part?
  Should I use parent-child? Or using nested types can also meet my requirement?
  Thanks!</p>