CLIPS defines seven primary message-handlers that are attached
to the class USER. These handlers cannot be
deleted or modified.
9.4.4.1 Instance Initialization
9.4.4.2 Instance Deletion
9.4.4.3 Instance Display
9.4.4.4 Directly Modifying an Instance
9.4.4.5 Modifying an Instance using Messages
9.4.4.6 Directly Duplicating an Instance
9.4.4.7 Duplicating an Instance using Messages