diff --git a/customizing.md b/customizing.md
index eaf9e6f..f9c20c7 100644
--- a/customizing.md
+++ b/customizing.md
@@ -4,7 +4,8 @@
 
 RecordBuilder can be customized in a number of ways. The types of customizations will change over time. See
 [@RecordBuilder.Options](record-builder-core/src/main/java/io/soabase/recordbuilder/core/RecordBuilder.java)
-for the current set of customizations and their default values. 
+for the current set of customizations and their default values. For example, the `useImmutableCollections` option
+adds special handling for record components of type `java.util.List`, `java.util.Set`, `java.util.Map` and `java.util.Collection`. When the record is built, any components of these types are passed through an added shim method that uses the corresponding immutable collection (e.g. `List.copyOf(o)`) or an empty immutable collection if the component is `null`.
 
 You can: