diff --git a/reference/forms/types/collection.rst b/reference/forms/types/collection.rst
index c5572f93c6b..ab537de89ab 100644
--- a/reference/forms/types/collection.rst
+++ b/reference/forms/types/collection.rst
@@ -11,6 +11,8 @@ forms, which is useful when creating forms that expose one-to-many
 relationships (e.g. a product from where you can manage many related product
 photos).
 
+When rendered, existing collection entries are indexed by the keys of the array that is passed as the collection type field data.
+
 +---------------------------+--------------------------------------------------------------------------+
 | Rendered as               | depends on the `entry_type`_ option                                      |
 +---------------------------+--------------------------------------------------------------------------+