diff --git a/docs/world api.md b/docs/world api.md
index 2df7b12744..4e23549304 100644
--- a/docs/world api.md	
+++ b/docs/world api.md	
@@ -491,9 +491,10 @@ class MyGameWorld(World):
     base_id = 1234
     # instead of dynamic numbering, IDs could be part of data
 
-    # The following two dicts are required for the generation to know which
-    # items exist. They could be generated from json or something else. They can
-    # include events, but don't have to since events will be placed manually.
+    # The following two dicts are required for the generation to know which items exist.
+    # They can be generated with arbitrary code during world load, but keep in mind that
+    # anything expensive (e.g. parsing non-python data files) will delay world loading.
+    # They can include events, but don't have to since events will be placed manually.
     item_name_to_id = {name: id for
                        id, name in enumerate(mygame_items, base_id)}
     location_name_to_id = {name: id for