The most important Sophtalk network used by Centaur is the variable network. This network has been constructed around the
activities of the variable structure, namely tree and selection
modification. Signals that circulate in this network include modified, which means the source tree has been modified, and selection-modified, which means that a selection has changed. To
illustrate how these signals might be interesting to a listening
network member, consider the following scenario. Each time the current
selection changes, the clipboard reacts to the selection-modified signal and decides whether the operator of the
subtree it contains matches the phylum of the currently selected
subtree. The clipboard responds by announcing which editing operations
are valid. The ctview listens to these signals and makes unavailable
editing operations truly unavailable by disactivating the
corresponding buttons in the Edit pulldown and turning the
button titles gray.
A variable usually participates in many variable networks, at least as many as there are ctedits that manipulate it. Thus, to recover the variable network for a given ctedit, call the function {ctedit}:network (described in the environment manual).