[tei-council] tricky situations for using @validUntil

[Syd Bauman]

I think you may be on to something here, Martin, but my mind is a bit
fuzzy right now. I'm going to talk it through (aloud) in the hopes of
straightening myself out.

1) On 2015-02-14 we put a validUntil=2016-04 on the <pi> elementSpec
   (which had been introduced back in version 3.14 of the
   Guidelines). 

2) On the 2015-05 build, the P5 build process
   a. notices that 2015-05 < 2016-04 and does not fail,
   b. transforms the validUntil=2016-04 into a Schematron test[1]
      which gets put into p5odds.isosch.
   In 2015-06 Project Circle generates their customization against
   the current Guidelines and get that same Schematron test in their
   .isosch file. When they validate their instances that have <pi>,
   they get the warning.

3) On the 2017-05 build, the P5 build process notices 2017-05 >
   2016-04, and fails. The release technician cusses, goes in and
   removes the elementSpec for <pi>, regenerates, and all is well.

4) In 2017-10 project Circle makes a change to their customization
   and re-generates schemas against the 2015-05 version. (This is the
   situation you were worrying about, yes?) Their customization process
   puts the Schematron test into their .isosch file. When they
   validate their instances that have <pi>, they get the warning.

I don't think I see a problem for the average Circle project, here,
but I may be missing something.

On the other hand, if on 2018-10-20 TEI-C Council member Art Tangent
wants to *build* a 2017-flavored version of P5 itself, he will get a
build error and it will fail. Is that what you're worried about?

Part of me says that's a serious problem, and we have to sort through
how to fix it. And part of me says we keep built copies of the
Guidelines around, why would Art need to rebuild it? And on the rare
occasion he really does need to, he should change his system clock.
(Blasphemy!)
   
Notes
-----
[1] <sch:pattern xmlns:sch="http://purl.oclc.org/dsdl/schematron">
      <sch:rule context="tei:pi">
        <sch:report test="true()" role="nonfatal">
          WARNING: use of deprecated element — The TEI-C may drop support for the <sch:name/> element as early as 2016-04. 
        </sch:report>
      </sch:rule>
    </sch:pattern>
    (perhaps with a better worded message).

> Thanks Syd for the summary. I don't recall anyone having raise this
> additional issue:
> 
> We've been telling people that they can build their TEI project
> against any TEI version in the Vault if they want to. However, once a
> validUntil date expires, even if they're building against an old
> version in dating from a period when it had not expired but was only
> deprecated, they'll still get an error, won't they?
> 
> If so, I think this is unfortunate. I wonder if we ought to be
> thinking of our @validUntil in terms of TEI version numbers rather
> than dates.
> 
> Or am I missing something?