shell> curl -X PUT --header 'If-Match: "2228639132"' --data-binary @- --dump - http://localhost:8529/_api/document/products/2228311452 <<EOF
{"other":"content"}
EOF

HTTP/1.1 412 Precondition Failed
content-type: application/json; charset=utf-8
etag: "2228311452"

{ 
  "error" : true, 
  "code" : 412, 
  "errorNum" : 1200, 
  "errorMessage" : "precondition failed", 
  "_id" : "products/2228311452", 
  "_rev" : "2228311452", 
  "_key" : "2228311452" 
}