Clarify interaction of format: byte and Content-Transfer-Encoding header definition

Author: mikekistler

versions/3.0.4.md

@@ -1753,8 +1753,9 @@ It is not currently possible to correlate schema properties with unnamed, ordere
 Note that there are significant restrictions on what headers can be used with `multipart` media types in general ([RFC2046 §5.1](https://www.rfc-editor.org/rfc/rfc2046.html#section-5.1)) and `multi-part/form-data` in particular ([RFC7578 §4.8](https://www.rfc-editor.org/rfc/rfc7578.html#section-4.8)).
 
 Note also that `Content-Transfer-Encoding` is deprecated for `multipart/form-data` ([RFC7578 §4.7](https://www.rfc-editor.org/rfc/rfc7578.html#section-4.7)) where binary data is supported, as it is in HTTP.
-Using `format: byte` for a multipart field is equivalent to setting `Content-Transfer-Encoding: base64`.
-If `format: byte` is used along with setting a different `Content-Transfer-Encoding` value with the `headers` field, the result is undefined.
+
+Using `format: byte` for a multipart field is equivalent to specifying an `encoding` object with a `headers` field containing `Content-Transfer-Encoding: enum: ["base64"]`.
+If `format: byte` is used for a multipart field that has an encoding object with a `headers` field containing `Content-Transfer-Encoding` with a schema that permits values other than "base64", the result is undefined.
 
 Per the JSON Schema specification, `contentMediaType` without `contentEncoding` present is treated as if `contentEncoding: identity` were present.  While useful for embedding text documents such as `text/html` into JSON strings, it is not useful for a `multipart/form-data` part, as it just causes the document to be treated as `text/plain` instead of its actual media type.  Use the Encoding Object without `contentMediaType` if no `contentEncoding` is required.