xml-dev - XHTML & Schemas

[Paul Prescod <paul@prescod.net>]

Let me try to put this argument on a practical footing.

Namespaces are triggers for various things. Stylesheets, validators,
etc.

For better or worse XHTML has three different grammars. I could probably
be convinced that this is a bad idea (and on another day might even
argue vociferously that way). But anyhow, XHTML has three grammars. This
probably has more to do with politics than technology: "our mandate is
to blah blah blah".

That means that when we get namespace-aware validators there will be
three schemas. Schemas are namespace-triggered:

 * not "version attribute" triggered
 * not DOCTYPE triggered

They are namespace triggered. (and for good reason...trying to bring
attributes into it makes the validation model much more complicated)

It follows that we need three namespaces to attach the three grammars
to.

Next year we will want to introduce parts of XHTML into our various
other document types. By that time we will hopefully have a schema
language that allows us to validate "HTML islands." Great! But which
grammar do we validate against? With only one namespace we either have
no choice or we must use the most loose of the three.

Now as a purist I don't think that it should be possible to use the
XHTML namespace until the W3C describes what conformance means. So I
would vote to do away with the namespaces altogether until that time
comes around. But given that this is not politically feasible I think
that the current status of three namespaces makes sense as a required
hook for future schema-based validation.

The alternative is to let "loose" become the defacto standard! Ack.
Better that we should either (temporarily) banish namespaces, banish
"loose" or make three namespaces so that we do not paint ourselves into
a corner.

 Paul Prescod

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