[docs] Updated.

docs/lua-api-block.md

@@ -47,6 +47,12 @@ Example:
 draw_type = "solid" -- this is the default value
 ```
 
+### `groups`
+
+Groups of the block. They can be used in recipes, and can also filter Lua-defined inventory widgets.
+
+See [Item#Attributes#groups](/lua-api-item#groups) for more details.
+
 ### `hardness`
 
 Hardness of the block, affects mining speed.

docs/lua-api-gui-inventory.md

@@ -23,6 +23,15 @@ gui:inventory {
 
 ## Attributes
 
+### `filter`
+
+Use a group as a filter for this inventory widget.
+
+Example:
+```
+filter = "group:om_fuel"
+```
+
 ### `inventory`
 
 Details of the inventory to use.

docs/lua-api-recipe.md

@@ -59,7 +59,7 @@ result = {
 Possible attributes:
 
 - `id`: String ID of the item created.
-- `amount`: Amount of items in the created stack
+- `amount`: Amount of items in the created stack.
 
 #### `pattern`
 
@@ -78,6 +78,8 @@ pattern = {
 
 Mapping of the characters used in `pattern` to actual item string IDs.
 
+**Note:** Keys can also be groups. See [Item#Attributes#groups](/lua-api-item#groups) for more details.
+
 Example:
 ```lua
 keys = {
@@ -103,7 +105,9 @@ input = {
 Possible attributes:
 
 - `id`: String ID of the item created.
-- `amount`: Amount of items in the created stack
+- `amount`: Amount of items in the created stack.
+
+**Note:** `id` can also be a group. See [Item#Attributes#groups](/lua-api-item#groups) for more details.
 
 #### `output`