func_detail

Ericw-tools qbsp supports detail brushes which are similar in concept to Quake 2’s detail brushes.

They don’t seal the map. To be compatible with existing Quake 1 mapping editors, detail brushes can be added by creating an entity with classname func_detail. When qbsp reads the map file, it will add any brushes included in a func_detail entity into the worldspawn as details and remove the func_detail entity. Any number of func_detail entities can be used (useful for grouping) and all included brushes will be added to the worldspawn.

This classname used on brushes textured with alphatested textures will alpha-mask the #255 colored parts of that texture rendering those parts invisible.

func_detail variants

func_detail_wall : This func_detail variant doesn’t split world faces. Useful for when you want a decoration touching a floor or wall to not split the floor/wall faces (you’ll get some overdraw instead.) If it completely covers up a world face, that face will get clipped away, so it’s not suitable for fence textures; see func_detail_fence instead.

func_detail_fence : Similar to func_detail_wall, but never clips away . It is suitable for fence textures, never clips away world faces. Useful for dense fences, grates, etc., that are solid and block gunfire.

func_detail_illusionary : Similar to func_detail_fence, but with no collision (players / monsters / gunfire), and doesn’t cast shadows unless enabled with "_shadow" "1". Useful for creating hanging vines or spiderwebs.
Combine with a clip brush for fences that can be shot through with hitscan weapons, but blocks movement and projectiles; suitable for Half-Life-style fences and 2D railings.

Regular func_detail is analogous with detail brushes in Quake II, whereas func_detail_wall is analogous with the func_detail in Source 1 (roughly) or func_detail with zhlt_detaillevel 1 in VHLT (closely).