The NodeController relays user-commands through to the current node. It also routes messages the other way: accepting commands from the current node and relaying them through to the application-housing. A NodeController can be physically implemented in any way, but for ease of comprehension let us assume a toolbar implementation: It is up to the application programmer to decide on a per-node basis which buttons exist on this toolbar and when they are enabled/disabled, added or removed, and what user-processes they trigger. This specification can be done as part of the initial definition of a node in the model and/or in the triggers file. For instance the Copy and Paste buttons above are created in the setup code for the triggers file.