This section (http://jsonapi.org/format/#document-structure-top-level) tell:

A document's top level MAY also have the following members: "meta", "links", "linked"
No other members should be present at the top level of a document.

But the errors node (http://jsonapi.org/format/#errors) is missing from this authorized list:

Error objects SHOULD be returned as a collection keyed by "errors" in the top level of a JSON API document

Also, adding a full example of response with an error could be nice.