> curl --data @- -X PATCH --dump - http://localhost:8529/_api/graph/graph1/edge/edge1
{"optional3" : "val3"}

HTTP/1.1 200 OK
content-type: application/json; charset=utf-8
etag: 57595398

{
  "edge": {
    "_id": "e/edge1",
    "_rev": "57595398",
    "_key": "edge1",
    "_from": "v/vert2",
    "_to": "v/vert1",
    "$label": null,
    "optional2": "val2",
    "optional3": "val3"
  },
  "error": false,
  "code": 200
}