The optional UserWriteMask Attribute exposes the possibilities of a client to write the Attributes of the Node taking user access rights into account. It uses the AttributeWriteMask DataType which is defined in 8.60.

The UserWriteMask Attribute can only further restrict the WriteMask Attribute, when it is set to not writeable in the general case that applies for every user.

Clients cannot assume an Attribute can be written based on the UserWriteMask Attribute.It is possible that the Server may return an access denied error due to some server specific change which was not reflected in the state of this Attribute at the time the Client accessed it.