Add rubric element

[th-we]

Here's a first suggestion for the <rubric> element. @pe-ro, do the classes and content make sense like that?

[pe-ro]

Yes, what you've done makes sense, but I think it's better if we emulate <dir> in terms of model classes and content. So, I'd put <rubric> in the same attribute and model classes as <dir> and add model.paracontentPart --

<classes>
  <memberOf key="att.common"/>
  <memberOf key="att.facsimile"/>
  <memberOf key="att.lang"/>
  <memberOf key="model.controlEventLike"/>
  <memberOf key="model.paracontentPart"/>
</classes>

I'd also use the same content model as <dir> --

<content>
  <rng:zeroOrMore>
    <rng:choice>
      <rng:text/>
      <rng:ref name="model.textPhraseLike.limited"/>
      <rng:ref name="model.graphicPrimitiveLike"/>
      <rng:ref name="model.editLike"/>
      <rng:ref name="model.transcriptionLike"/>
    </rng:choice>
  </rng:zeroOrMore>
</content>

Finally, the content model of <layer> should be modified to contain <rubric> --

<rng:zeroOrMore>
  <rng:choice>
    <rng:ref name="model.annotLike"/>
    <rng:ref name="model.appLike"/>
    <rng:ref name="model.editLike"/>
    <rng:ref name="model.graphicPrimitiveLike"/>
    <rng:ref name="model.layerPart"/>
    <rng:ref name="model.milestoneLike.music"/>
    <rng:ref name="model.transcriptionLike"/>
    <rng:ref name="rubric"/>
  </rng:choice>
</rng:zeroOrMore>

These changes have the result of making <rubric> available within <syllable>, <layer>, and <p> without creating an ambiguous content model that confuses an XSD schema.

I'm not completely happy with this, however, because I think <rubric> should be made available at the textual phrase level instead of within <p>. But, there has to be something for us to work on next week. 😄