> Well, this is begging the question. Yes if you consider validity
> against schematron constraints to be a necessary part of TEI
> conformance. No if it isn't.
And I do consider validity against constraints (Schematron or
otherwise) that are errors (as opposed to just warnings) to be
a necessary part of TEI conformance.
> This is all well and good. But am I wrong in thinking that
> occasionally schematron constraints are introduced which do not
> cause any component to be "deprecated" in the sense that they gain
> a @validUntil attribute which sets in train the scenario you
> describe? Constraints which just say "up till now the Guidelines
> may have permitted this because the schema wasn't expressive
> enough, but it's always been wrong and now we're going to check for
You are (of course) completely correct. There exist quite a few such
"now we can check for it" constraints. (And there will probably be
more as time goes on.)