You can see how silhouette edge detection goes, which edges from ManifoldEdges (2 neighbors) are qualified as silhouette and which edges were detected as BorderEdges. This is available in view3dscene by View -> Fill mode -> Silhouette and Border Edges menu item.

Figure 8.1. Fountain level, no shadows

Figure 8.2. Fountain level, shadows turned on

Now, turn edges on. Silhouette edges detected are drawn yellow (these depend on light position relative to the model). Blue edges are BorderEdges (these are independent from light position, they are simply edges with only 1 neighbor triangle).

Figure 8.3. Fountain level, edges marked

Figure 8.4. Fountain level, only edges