How to create custom "node.labels" for swarm 1.12

According to document for create swarm service that reference to create “node.labels” for custom special labels for node in swarm 1.12 with command “docker node update” (Ref: Anyway as check with document for “docker node update” (Ref: It not any option for update custom node.labels as required. I’m try to check other KB and document but still not found any relate for this topic. So please kindly advise for this purpose.

Now as Docker 1.12 RC5 had been release. Now i can see option "docker node update --label-add for support this purpose. Thanks so much,