Is it legal to extend the xml-stylesheet DTD ?

This may seem like going back to basics, but I've discovered I've missed
something very elemental in the scheme of things...

After studying section 18 and the references from the spec, (and then
discovering this 'feature' had a spec all to itself) I still can't make
out... is a syntax like this totally illegal or what?

<?xml-stylesheet 
	type="text/xsl" 
	media="html" 
	title="Developers Job Summary (Slate)" 
	href="../../xsl/slate.xsl" 
	alternate="yes" 
	suffix=".html" 
?>


Here I've created the attribute "suffix" which is not in the spec, and
used it for purposes of my own. 

<reference> http://www.w3.org/TR/xml-stylesheet/ </reference>

I'm used to unrecognised parameters being ignored by the interpreters,
and, coming from HTML, haven't been too concerned.

Reading the spec I can't see anywhere where the DTD specifically
excludes unnamed parameters. This is mainly because I'm not that clear
on DTD syntax. If it doesn't say, do I assume it's banned? This may be a
silly question, similar to one I heard 2 months ago (this list of things
that are NOT allowed is infinite) but... does it actually make it
illegal?

It says the tag can contain pseudo attributes (why pseudo?)
and then says
"The following pseudo attributes are defined".
In English, this reads as an inclusive grouping, not an exclusive one.
How does it read if you speak DTD natively?

It arises because I've finally got back to testing on Cocoon at it barfs
on that directive.
IE (updated of course) doesn't. This is indicative of nothing, I know.
;-)

I guess I can fudge it later in the document with a look-up table:

<SAVE-AS title="Developers Job Summary (Slate)" suffix=".html" />
<SAVE-AS title="Developers Job Summary (Print)" suffix=".txt" />

But I think that [expletive deleted].

So, word from the wise? Am I breaking something to add my own info tags?

.dan.

PS: Is there actually a definitive reference for the "media" types, or
is everyone still making it up as they go along?

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