I do not see any difficulties to implement this similar with the way we implemented the xml-styelsheet PI support. However, it will be great if instead of an oXygen specific PI we would be able to use something more generic.

I am curious how much interest is in having such a PI. I remember that I was pro having a PI to associate a Relax NG schema with an XML document and there was a strong reaction against making a proposal for such a PI on the Relax NG list. So what people think about such a PI?
Abel Braaksma (online) wrote:

Thanks for your answer, George,

oXygen detects automatically the xml-stylesheet PI if you try to
execute the transform action on a file and in that case it will ask
you if you want to use that stylesheet for the transformation.

My point wasn't very clear perhaps (and I intermingling with the OP
here...). When i write a stylesheet, that stylesheet often has a
couple of test XMLs that go with it for unit tests etcetera. Not the
other way around: when i write an XML document, it is not defined to
run with a particular stylesheet (and often, these documents come
from other sources and meddling with them seems inappropriate).

So, what I'd actually like is a way to associate XML files with
stylesheets, not stylesheets with XML files:

<?sample-xml-list test-one.xml test-two.xml ?>

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.ww3...etc
  ....
</xsl:stylesheet>

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