shell> curl -X PATCH --data-binary @- --dump - http://localhost:8529/_api/graph/graph/edge/edge1
{ 
  "optional3" : "val3" 
}

HTTP/1.1 202 Accepted
content-type: application/json; charset=utf-8
etag: 1301243350

{ 
  "edge" : { 
    "_id" : "edges/edge1", 
    "_key" : "edge1", 
    "_rev" : "1301243350", 
    "_from" : "vertices/vert1", 
    "_to" : "vertices/vert2", 
    "$label" : null, 
    "optional1" : "val1", 
    "optional3" : "val3" 
  }, 
  "error" : false, 
  "code" : 202 
}