The UserAttribute allows an application to store extra infomation in a Node object through key/value pairs. This extra information is saved with the domain and can be retrieved after loading the domain from both net and hkb format. If an application tries to read a user attribute which is unspecified, an hErrorSvrNoSuchUserAttribute error is raised. To avoid reading non-existing user attributes, use the HasUserAttribute property. To delete a user attribute, use the RemoveUserAttribute method. Key strings must have a format similar to C identifiers.