MIME-type conventions, standards or limitations?

Question

Given a new, proprietary file format that cannot currently be handled by any known application, I assume you can just invent a new MIME type value as follows:

Content-Type: application/my-arbitrary-format

Assuming this is the way to go, are there any limitations (format, syntax, length, reserved words, or otherwise), standards (IETF, ISO, W3C, IEEE, etc), or conventions (like the slash type/format)?

Note that I do NOT want to use a known MIME type value, because the browser and/or OS should not make assumptions about what can or cannot open the file.

Answer 1

To do this correctly, you can register your new type with IANA. http://www.iana.org/assignments/media-types/