Freestyle > Adding Detail to the Control Mesh > Splitting Mesh Elements > Example: Splitting Edges
  
Example: Splitting Edges
Original Shape
Split Shape
Inserting two splits to a single edge highlighted in green
Adding 3 splits to a single edge highlighted in green
Adding a split to a single edge highlighted in green. The split propagates through the quad faces in a loop and ends before it runs into a non-quad face.