Merge pull request #137 from runcom/regexp-ref

image-layout.md: fixes

Author: vbatts

image-layout.md

@@ -7,7 +7,7 @@ Given an image layout a tool can convert a given ref into a runnable OCI Image F
 The image layout has two top level directories:
 
 - "blobs" contains content-addressable blobs. A blob has no schema and should be considered opaque.
-- "refs" contains descriptors pointing to an image manifest list
+- "refs" contains descriptors pointing to an image manifest
 
 It also contains a file that is used to identify the layout version:
 
@@ -20,6 +20,7 @@ $ cd example.com/app/
 $ find .
 .
 ./blobs
+./blobs/sha256-e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f
 ./blobs/sha256-afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51
 ./blobs/sha256-5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270
 ./blobs/sha256-e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f
@@ -36,7 +37,7 @@ $ shasum -a 256 ./blobs/sha256-afff3924849e458c5ef237db5f89539274d5e609db5db935e
 afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51 ./blobs/sha256-afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51
 ```
 
-Object names in the `refs` and `blobs` MUST NOT include characters outside of the set of "A" to "Z", "a" to "z", the hyphen `-`, the dot `.`, and the underscore `_`.
+Object names in the `refs` and `blobs` subdirectories MUST NOT include characters outside of the set of "A" to "Z", "a" to "z", "0" to "9", the hyphen `-`, the dot `.`, and the underscore `_`.
 Hash algorithm identifiers containing the colon `:` will be converted to the hyphen `-`.
 For example `sha256:5b` will map to the layout `blobs/sha256-5b`.
 The blobs directory MAY contain blobs which are not referenced by any of the refs.
@@ -50,7 +51,24 @@ This illustrates the expected contents of a given ref, the manifest list it poin
 
 ```
 $ cat ./refs/v1.0
-{"size": 4096, "digest": "sha256:afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51", "mediatype": "application/vnd.oci.image.manifest.v1+json"}
+{"size": 4096, "digest": "sha256:e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f", "mediatype": "application/vnd.oci.image.manifest.list.v1+json"}
+```
+```
+$ cat ./blobs/sha256-e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f
+{
+  "schemaVersion": 2,
+  "mediaType": "application/vnd.oci.image.manifest.list.v1+json",
+  "manifests": [
+    {
+      "mediaType": "application/vnd.oci.image.manifest.v1+json",
+      "size": 7143,
+      "digest": "sha256:afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51",
+      "platform": {
+        "architecture": "ppc64le",
+        "os": "linux"
+      }
+    },
+...
 ```
 ```
 $ cat ./blobs/sha256-afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51