Clarify data / errors top-level members.

* Primary data can also be a single link object. * Errors may be included at the top level instead of primary data.
json-api · wycats · Feb 18, 2015 · Dec 24, 2014 · Jan 7, 2015 · Jan 9, 2015
commit 87d2828ffa94b13ffe7a335303da3a3ce2a06f1c
diff --git a/format/index.md b/format/index.md
@@ -61,12 +61,15 @@ called out below.
 A JSON object **MUST** be at the root of every JSON API response. This object
 defines a document's "top level".
 
-The document's "primary data" is a representation of the resource or
-collection of resources primarily targeted by a request.
+The document's "primary data" is a representation of the resource, collection
+of resources, or resource relationship primarily targeted by a request.
 
-The primary data **MUST** appear under a top-level key named `"data"`. The
-primary data **MUST** be either a single resource object or an array of
-resource objects.
+A document **MUST** contain either primary data or a collection of error
+objects.
+
+Primary data **MUST** appear under a top-level key named `"data"`. Primary
+data **MUST** be either a single resource object, an array of resource
+objects, or a value representing a resource relationship.
 
 ```javascript
 {
@@ -78,6 +81,8 @@ resource objects.
 }
 ```
 
+Error objects **MUST** appear under a top-level key named `"errors"`.
+
 A document's top level **MAY** also have the following members:
 
 * `"meta"`: non-standard meta-information about the primary data.