diff --git a/data/builtin.lua b/data/builtin.lua
index 3a38b60a..b8891c06 100644
--- a/data/builtin.lua
+++ b/data/builtin.lua
@@ -359,6 +359,7 @@ minetest.nodedef_default = {
 	type="node",
 	-- name intentionally not defined here
 	description = "",
+	groups = {},
 	inventory_image = "",
 	wield_image = "",
 	wield_scale = {x=1,y=1,z=1},
@@ -418,6 +419,7 @@ minetest.craftitemdef_default = {
 	type="craft",
 	-- name intentionally not defined here
 	description = "",
+	groups = {},
 	inventory_image = "",
 	wield_image = "",
 	wield_scale = {x=1,y=1,z=1},
@@ -435,6 +437,7 @@ minetest.tooldef_default = {
 	type="tool",
 	-- name intentionally not defined here
 	description = "",
+	groups = {},
 	inventory_image = "",
 	wield_image = "",
 	wield_scale = {x=1,y=1,z=1},
@@ -452,6 +455,7 @@ minetest.noneitemdef_default = {  -- This is used for the hand and unknown items
 	type="none",
 	-- name intentionally not defined here
 	description = "",
+	groups = {},
 	inventory_image = "",
 	wield_image = "",
 	wield_scale = {x=1,y=1,z=1},
diff --git a/data/mods/default/init.lua b/data/mods/default/init.lua
index f0e6b6dc..d0733737 100644
--- a/data/mods/default/init.lua
+++ b/data/mods/default/init.lua
@@ -308,6 +308,12 @@
 -- Item definition options (register_node, register_craftitem, register_tool)
 -- {
 --     description = "Steel Axe",
+--     groups = {}, -- key=name, value=rating; rating=1..3.
+--                     if rating not applicable, use 1.
+--                     eg. {wool=1, fluffy=3}
+--                         {soil=2, outerspace=1, crumbly=1}
+--                         {hard=3, brittle=3, spikes=2
+--                         {hard=1, metal=1, spikes=1}
 --     inventory_image = "default_tool_steelaxe.png",
 --     wield_image = "",
 --     wield_scale = {x=1,y=1,z=1},