unix> curl --header 'if-none-match: "29110874"' --dump - http://localhost:8529/_api/document/products2/29110874

HTTP/1.1 200 OK
content-type: application/json; charset=utf-8
etag: "29110874"

{ 
  "hallo" : "world", 
  "_id" : "products2/29110874", 
  "_rev" : "29110874", 
  "_key" : "29110874" 
}