diff --git a/OpenRA.Mods.RA/World/DomainIndex.cs b/OpenRA.Mods.RA/World/DomainIndex.cs
index 2c7def6793..2e6dbdbf76 100644
--- a/OpenRA.Mods.RA/World/DomainIndex.cs
+++ b/OpenRA.Mods.RA/World/DomainIndex.cs
@@ -18,7 +18,8 @@ using OpenRA.Traits;
 
 namespace OpenRA.Mods.RA
 {
-	// Identify untraversable regions of the map for faster pathfinding, especially with AI
+	[Desc("Identify untraversable regions of the map for faster pathfinding, especially with AI.",
+		"This trait is required. Every mod needs it attached to the world actor.")]
 	class DomainIndexInfo : TraitInfo<DomainIndex> {}
 
 	public class DomainIndex : IWorldLoaded