Re: Media, charset, title attributes for xsl-stylesheet PI

["Paul W. Abrahams" <abrahams@xxxxxxxxxxx>]

     Date: Fri, 13 Aug 1999 09:59:01 +0700
     From: James Clark <jjc@xxxxxxxxxx>
     Subject: Re: Media, charset, title attributes for
     xsl-stylesheet PI

     "Paul W. Abrahams" wrote:

     > The semantics of the xsl-stylesheet processing instruction
     appear to be
     > derived from HTML used with CSS.  The pseudo-attributes of
     that PI are
     > `type', `href', `title', `media', `charset', and
     `alternate'.  It's
     > clear to me now how `type' and `href' are used with XSLT
     stylesheets:
     > `type' should have the value ``text/xsl''

     That hasn't been decided yet.

I've seen it written down somewhere, but I can't remember where,
unfortunately.  I do believe you; if you say it hasn't been decided,
then some committee has yet to make up its collective mind, no matter
what unofficial emanations have escaped from their container.


     > and `href' should point to the
     > XSLT stylesheet file.
     >
     > But what is not clear is what significance if any the rest
     of the
     > pseudo-attributes have or even might have for XSLT.    I've
     played
     > around with IE5, which seems to silently ignore them.   It's
     possible
     > that `title' and `alternate' would be used by a user agent
     to select a
     > stylesheet, I suppose,

     Yes: the user agent can use them to allow a user to select
     between
     multiple stylesheets.

     > but the CSS cascade isn't applicable to XSLT.

     XSLT can blend together multiple stylesheets.  The obvious way
     to apply
     a sequence of XSLT stylesheets A.xsl, B.xsl, C.xsl is to treat
     it as
     equivalent to applying a single stylesheet that imports A.xsl,
     then
     B.xsl, then C.xsl.

Yes, that's certainly the obvious way.  But is it specified anywhere
that it *should* be the way, similarly to how it's specified for the
HTML/CSS combination?   Is it likely that it will ever be pinned down?
The approach you suggest is a highly educated and reasonable guess, but
still a guess.


     > And given that XSLT is one level removed from its result
     namespace, I
     > can't see how `media' or `charset' would apply at all.

     charset is not useful for XSLT because XSLT uses the standard
     XML way of
     specifying the charset of the stylesheet. media allows you
     have to
     specify different stylesheets for different media (ie one
     stylesheet for
     print and one for screen).

The problem I see with `media' is that it's one level removed from the
place the information is used, namely, the XSL tree of formatting
objects.  XSLT itself knows nothing about media.  Is the idea that the
user agent selects the XSLT stylesheet based on the media to be used for
the rendering?  That's a plausible model, but not the same one used for
CSS as far as I can tell; in the CSS model the selection takes place
within CSS itself.

Paul



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