Enclose all tag elements in a request generated by a client application.
(Optional) One or more attributes of the form attribute-name="value". This feature
can be used to associate requests and responses if the value assigned
to an attribute by the client application is unique in each opening
<rpc> tag. The NETCONF server echoes the attribute
unchanged in its opening
<rpc-reply> tag, making it simple to map the response to the initiating request.
The NETCONF specification assigns the name
message-id to this attribute.