Merge branch '5.4' into 6.2

* 5.4:
  minor
  Clarify how `CollectionType` entries are indexed

Author: OskarStark

reference/forms/types/collection.rst

@@ -11,6 +11,9 @@ 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                                      |
 +---------------------------+--------------------------------------------------------------------------+