[tei-council] heresy or heroic?

[Syd Bauman]

What do people think of putting @validUntil on <rng:ref> to express
the idea that an element's use in a particular content model is
deprecated? E.g.
   <content>
     <!-- ... -->
     <rng:choice>
       <rng:ref name="altIdentifier" validUntil="2015-11-01"/>
       <rng:ref name="msIdentifier"/>
     </rng:choice>
     <!-- ... -->
   </content>

I'm not planning on writing code to make that work now, but I'm
thinking about it, and think I see how to make it work.

For now I'm planning to hand-write a Schematron check for this
particular case. (As per decision in Oxford on FR 294, FR 459.) But
having a general-purpose deprecation method would be better; but
adding an attribute to an element in another namespace might involve
a bit. We may have to modify the RELAX NG schema in order to get
validity, e.g. Hmm ...