Merge pull request #423 from vbatts/image-layout_anchors

image-layout: organize for anchors

Author: 7c00d

image-layout.md

@@ -9,6 +9,8 @@ Given an image layout and a ref, a tool can create an [OCI Runtime Specification
 * [Applying the filesystem layers](layer.md#applying) in the specified order
 * Converting the [image configuration](config.md) into an [OCI Runtime Specification `config.json`](https://github.com/opencontainers/runtime-spec/blob/v1.0.0-rc2/config.md)
 
+# Content
+
 The image layout MUST contain two top level directories:
 
 - `blobs` contains content-addressable blobs.
@@ -25,6 +27,8 @@ The image layout MUST also contain an `oci-layout` file:
     - The `imageLayoutVersion` value will align with the OCI Image Specification version at the time changes to the layout are made, and will pin a given version until changes to the layout are required
 - It MAY include additional fields
 
+## Example Layout
+
 This is an example image layout:
 
 ```
@@ -49,16 +53,9 @@ $ shasum -a 256 ./blobs/sha256/afff3924849e458c5ef237db5f89539274d5e609db5db935e
 afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51 ./blobs/sha256/afff3924849e458c5ef237db5f89539274d5e609db5db935ed3959c90f1f2d51
 ```
 
-Object names in the `refs` 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 `_`.
+## Refs
 
-Object names in the `blobs` subdirectories are composed of a directory for each hash algorithm, the children of which will contain the actual content.
-A blob, referenced with digest `<alg>:<hex>` (per [descriptor](descriptor.md#digests-and-verification)), MUST have its content stored in a file under `blobs/<alg>/<hex>`.
-The character set of the entry name for `<hex>` and `<alg>` MUST match the respective grammar elements described in [descriptor](descriptor.md#digests-and-verification).
-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.
-
-The blobs directory MAY be missing referenced blobs, in which case the missing blobs SHOULD be fulfilled by an external blob store.
+Object names in the `refs` 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 `_`.
 
 No semantic restriction is given for object names in the `refs` subdirectory.
 Each object in the `refs` subdirectory MUST be of type `application/vnd.oci.descriptor.v1+json`.
@@ -70,7 +67,7 @@ For example, an image may have a tag for different versions or builds of the sof
 In the wild you often see "tags" like "v1.0.0-vendor.0", "2.0.0-debug", etc.
 Those tags will often be represented in an image-layout repository with matching refs names like "v1.0.0-vendor.0", "2.0.0-debug", etc.
 
-This illustrates the expected contents of a given ref, the manifest list it points to and the blobs the manifest references.
+### Example Ref
 
 ```
 $ cat ./refs/v1.0 | jq
@@ -81,6 +78,21 @@ $ cat ./refs/v1.0 | jq
 }
 ```
 
+This illustrates the expected contents of a given ref, the manifest list it points to and the blobs the manifest references.
+
+## Blobs
+
+Object names in the `blobs` subdirectories are composed of a directory for each hash algorithm, the children of which will contain the actual content.
+A blob, referenced with digest `<alg>:<hex>` (per [descriptor](descriptor.md#digests-and-verification)), MUST have its content stored in a file under `blobs/<alg>/<hex>`.
+The character set of the entry name for `<hex>` and `<alg>` MUST match the respective grammar elements described in [descriptor](descriptor.md#digests-and-verification).
+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.
+
+The blobs directory MAY be missing referenced blobs, in which case the missing blobs SHOULD be fulfilled by an external blob store.
+
+### Example Blobs
+
 ```
 $ cat ./blobs/sha256/e692418e4cbaf90ca69d05a66403747baa33ee08806650b51fab815ad7fc331f | jq
 {