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

https://mag-wiki.win/index.php/HVAC_Line_Set_Planning_for_Single-Zone_vs_Multi-Zone_Systems

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.