Restore note about contentMediaType

I did not mean to remove this.

Author: handrews

versions/3.0.4.md

@@ -1750,6 +1750,8 @@ Note also that `Content-Transfer-Encoding` is deprecated for `multipart/form-dat
 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.
 
+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.
+
 See [Appendix E](#percentEncodingAndFormMediaTypes) for a detailed examination of percent-encoding concerns for form media types.
 
 ###### Example: Basic Multipart Form