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Re: XHTML m12n XSD

From: Curt Arnold <Curt.Arnold@hyprotech.com>

> Substitution groups (especially if the common ancestor and single
> restrictions were removed per LC-96) could effectively replace parameter
> entities for content models.

I don't think it could.  The first reason is that the XHTML M12n people's
system works by redefining groups, so substitution groups don't seem to fit
the bill.  The second is the technical reason that XHTML M12n allows you to
change optionality of elements in a content model and add required or
optional ones everywhere. I don't think there is any simple way, currently,
to declare that there is a kind of abstract element which is only required
if there is an element declared to be part of its substitution group.  (And,
if there is some tortuous way to do it, I doubt very much that it would be
straightforward enough to be  to anyone's taste or not explode or look like

However, in the XS XHTML M12n approach, I do use substitution groups to
implement the .class parameter entity, which I seems to be very close.

The problem is that there needs to be two levels of schema activity; one
says "these items cohere together, because they don't make sense other wise"
and the other says "I have chosen to couple these items together in the
process of cobbling together my language".  The first level is not
well-served by grammar-based schemas, the second often is.   (IMHO the first
is where Schematron fits in, the second is where XML Schemas fits in.)

Rick Jelliffe