In Blender’s Freestyle, a line set filters which edges are drawn using criteria like visibility, face marks

http://ratten-wiki.de/index.php?title=What_Makes_a_High-Quality_HVAC_Line_Set_Worth_It

In Blender’s Freestyle, a line set filters which edges are drawn using criteria like visibility, face marks, and material boundaries, allowing separate stroke styles for silhouettes and creases.