diff --git a/02.md b/02.md
index 3eaf992e..f92e5b37 100644
--- a/02.md
+++ b/02.md
@@ -65,4 +65,4 @@ If no user is logged in or the current user context is not relevant, an absolute
 ~carol@names.com/erin/charlie
 ```
 
-
+In order to qualify for petname resolution they must have only ASCII letters, numbers or `_`.