diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 462b3066ab1e9aeac7848b3f859ca5e5f80a64ac..f6d8e8a342a63327797ed57bfadb4b1590e6e0bc 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1164,6 +1164,7 @@ module ClassMethods
       #   Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
       #   Note that this operation instantly fires update SQL without waiting for the save or update call on the
       #   parent object, unless the parent object is a new record.
+      #   This will also run validations and callbacks of associated object(s).
       # [collection.delete(object, ...)]
       #   Removes one or more objects from the collection by setting their foreign keys to +NULL+.
       #   Objects will be in addition destroyed if they're associated with <tt>dependent: :destroy</tt>,