Improve warning message for registration table reuse

doc/lua_api.md

@@ -5895,16 +5895,23 @@ Call these functions only at load time!
 
 ### Environment
 
-* `core.register_node(name, node definition)`
-* `core.register_craftitem(name, item definition)`
-* `core.register_tool(name, item definition)`
+* `core.register_node(name, nodedef)`
+    * register a node with its definition
+    * Note: you must pass a clean table that hasn't already been used for
+      another registration to this function, as it will be modified.
+* `core.register_craftitem(name, itemdef)`
+    * register an item with its definition
+    * Note: (as above)
+* `core.register_tool(name, tooldef)`
+    * register a tool item with its definition
+    * Note: (as above)
 * `core.override_item(name, redefinition, del_fields)`
     * `redefinition` is a table of fields `[name] = new_value`,
       overwriting fields of or adding fields to the existing definition.
     * `del_fields` is a list of field names to be set
       to `nil` ("deleted from") the original definition.
     * Overrides fields of an item registered with register_node/tool/craftitem.
-    * Note: Item must already be defined, (opt)depend on the mod defining it.
+    * Note: Item must already be defined.
     * Example: `core.override_item("default:mese",
       {light_source=core.LIGHT_MAX}, {"sounds"})`:
       Overwrites the `light_source` field,
@@ -5912,7 +5919,7 @@ Call these functions only at load time!
 * `core.unregister_item(name)`
     * Unregisters the item from the engine, and deletes the entry with key
       `name` from `core.registered_items` and from the associated item table
-      according to its nature: `core.registered_nodes`, etc.
+      according to its nature (e.g. `core.registered_nodes`)
 * `core.register_entity(name, entity definition)`
 * `core.register_abm(abm definition)`
 * `core.register_lbm(lbm definition)`