clarification about nested index

Signed-off-by: Akihiro Suda <[email protected]>

image-layout.md

@@ -199,7 +199,11 @@ Those tags will often be represented in an image-layout repository with matching
 }
 ```
 
-This illustrates an index that provides two named manifest references and an auxiliary mediatype for this image layout.
+This illustrates an index that provides two named references and an auxiliary mediatype for this image layout.
 
+The first named reference (`stable-release`) points to another index that might contain multiple references with distinct platforms and annotations.
+Note that the [`org.opencontainers.image.ref.name` annotation](annotations.md) SHOULD only be considered valid when on descriptors on `index.json`.
+
+The second named reference (`v1.0`) points to a manifest that is specific to the linux/ppc64le platform.
 
 [descriptors]: ./descriptor.md

img/media-types.dot

@@ -6,6 +6,7 @@ digraph G {
     layer [shape=note, label="Layer tar archive\napplication/vnd.oci.image.layer.v1.tar\napplication/vnd.oci.image.layer.v1.tar+gzip\napplication/vnd.oci.image.layer.nondistributable.v1.tar\napplication/vnd.oci.image.layer.nondistributable.v1.tar+gzip"]
   }
 
+  imageIndex -> imageIndex [label="1..*"]
   imageIndex -> manifest [label="1..*"]
   manifest -> config [label="1..1"]
   manifest -> layer [label="1..*"]