#562 Change description of TEI Header and simplify content model of TEI

[Lou Burnard]

It seems time to rethink the definitions of the teiHeader element in
line with expanded applications of it as a generic metadata
container. At the same time, it would be useful to simplify the
content model of the <TEI> element itself.

This ticket proposes the following changes:

1. Change the description of <teiHeader> from "supplies the
   descriptive and declarative information making up an electronic title
   page for every TEI-conformant document." to "supplies descriptive and
   declarative metadata associated with a digital resource or set of
   resources". This change makes it easier to use the teiHeader to
   document an <fsdDecl> (as is currently proposed) and also to use it
   with the proposed new <standOff> element.

2. Change the description for the class model.resourceLike from
   "groups non-textual elements which may appear together with a header
   and a text to constitute a TEI document" to "groups separate elements
   which constitute the content of a digital resource, as opposed to its
   metadata."

3. Change the content model of <TEI> from

  <content>
    <group xmlns="http://relaxng.org/ns/structure/1.0">
      <ref name="teiHeader"/>
      <choice>
        <group>
          <oneOrMore>
            <ref name="model.resourceLike"/>
          </oneOrMore>
          <optional>
            <ref name="text"/>
          </optional>
        </group>
        <ref name="text"/>
      </choice>
    </group>
  </content>
~~~~~~
to

<content>
<group xmlns="http://relaxng.org/ns/structure/1.0">
<ref name="teiHeader">
<choice>
<oneormore>
<ref name="model.resourceLike">
</ref></oneormore>
</choice>
</ref></group>
</content>
~~~~~

and (of course) add <text> to model.resourceLike</text>

The only possible downside of this change is that if you have an ODD
in which model.resourceLike is deleted for some reason, you will now
thereby delete the <text> element. But deleting model classes is an
intrinsically dangerous procedure which should only be undertaken by
the fully aware.

[Martin Holmes]

I don't see any actual objection yet, but this is such a rudimentary change we should probably test it in a branch.

[Laurent Romary]

I vote for this immediately.

[Hugh A. Cayless]

I'm in favor of this (though it warrants discussion, obviously). I agree with Martin too, though that it needs testing, so I'm going to suggest we use this as a way to experiment with testing Git branches.