Regions of nodes and edges can be folded (see grouping of nodes). As a result, a summary node is displayed for all nodes of a region of nodes. In addition, summary edges to this summary node are displayed for sets of edges to nodes of the region. It is possible to specify the attributes for these summary nodes and edges that come from a folding operation. This allows folded regions to be given a different appearance than normal nodes and edges. The attributes for these summary nodes or replacement edges are specified as follows: