Let's talk about PostScript first. PostScript has documented, standardized,
and commonly used facilities for identifying the version of PostScript in
use directly in the PostScript data itself. Moreover, this information does
not map cleanly to a single number or group of parameters. It is complex
information that cannot distilled in the manner you specify. Moreover, if you
attempt to do this the result will not be useful -- it only introduces a
number of silly states where the parameter claims one version but the
document claims another.
Thus, this proposal does not make sense for PostScript. It has in fact been
proposed before and rejected for the reasons given.
Now, on to GIF. GIF also has an internal identifier. It is even stronger than
PostScript in one sense -- the identifier is a REQUIRED part of the data. There
are presently only two values it can take; I suppose new ones might appear
in the future.
Once again, reproducing information, especially information that is a mandatory
part of the format, in the header is not clearly desireable. It would be
one thing if the information was separable and representable like it is
with some formats. But these things don't apply to these data types.
Finally, there's TIFF. TIFF is not mentioned in the current MIME draft. I
don't know what, if any, parameters it would be appropriate for it to accept.
I believe that once again it is internally self-identifying, but I'm not sure
about this. In any case, it is a moot point since there's no standard for it
in MIME anyhow. If you want to argue about how TIFF is parameterized you can
either write a specification for it or go argue with the NETFAX folks, who are
using a specific profile of TIFF for their work.
Ned