When you connect two components by an edge, it is gray and dashed.

After assigning metadata to the edge, it becomes solid, but still remains gray.

When you click any metadata item in the Outline pane, all edges with the selected metadata become blue.

If you click an edge in the Graph Editor, the selected edge becomes black and all of the other edges with the same metadata become blue. (In this case, metadata are shown in the edge tooltip as well.)

Figure 27.4. Metadata in the Tooltip