[uf-new] Separating File Content from File Format

Manu Sporny msporny at digitalbazaar.com
Fri Apr 6 09:27:01 PDT 2007

Charles Iliya Krempeaux wrote:
>> Hmm, reading that gives me the impression that parameters are defined
>> when media types are registered, and aren't something we can add to
>> suit our needs.
> I don't believe that is the case.
> I believe (according to the spec) you are free to create your own
> Content Type parameters.

I disagree, you could break backwards compatibility if you start tacking
on parameters that are not defined in the MIME-type (which is used in
the Accept and Content-Type fields):

"When sending data to older HTTP applications, implementations SHOULD
only use media type parameters when they are required by that
type/subtype definition."[1]

I can't find any statement in the literature that says that you can add
parameters that are not in the "Required" or "Optional" listing.
Furthermore, RFC 2045 states:

"Use of non-registered media types is discouraged." [1]

"MIME implementations must ignore any parameters whose names they do not

I believe this means that web browsers should ignore any parameters
whose names they do not recognize. That means if it isn't in the
MIME-Type specification, it should be ignored by any implementation
reading a field containing the MIME-Type.

In short - if it isn't registered with the Mime-Type - you shouldn't be
using it.

-- manu

[1] http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.7
[2] http://rfc.net/rfc2045.html#p10

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