small docbook customization layer for business letters

[Craeg Strong <cstrong@arielpartners.com>]

Hello:

Below please find my first cut at a RELAXNG schema that provides an 
extremely
thin customization layer on top of Docbook 5.0b1 for business letters.

I hope you might find it interesting.  Any and all comments welcome.

I myself was quite pleased with how easy it is to create such 
Docbook-based schemata (less than 50 LOC)!
All my custom elements are in the "l:" namespace, and the docbook 
references start with "db."

My biggest issue right now is trying to figure out if there is a RELAXNG 
validator out there
with XML catalog support, so I can keep my schema files separate from 
thirdparty ones....

--Craeg

<grammar>
  <include href="docbook.rng">
    <start>
      <element name="l:letter">
        <a:documentation>A business letter</a:documentation>
       <ref name="db._info"/>
       <element name="l:sender">
          <a:documentation>The person sending the letter</a:documentation>
          <ref name="db.personname"/>
          <ref name="db.affiliation"/>
          <ref name="db.address"/>
       </element>
       <element name="l:addressee">
          <a:documentation>The party to whom the letter is 
addressed</a:documentation>
         <choice>
            <group>
               <ref name="db.personname"/>
               <ref name="db.affiliation"/>
             </group>
            <ref name="db.orgname"/>
          </choice>
         <ref name="db.address"/>
        </element>
       <optional>
          <element name="l:regarding">
             <a:documentation>A short summary of what this letter is 
about, usually printed in the form of "RE: blah"</a:documentation>
            <oneOrMore><ref name="db.all.blocks"/></oneOrMore>
          </element>
        </optional>
         <element name="l:salutation"><text/></element>
       <element name="l:body">
          <a:documentation>The main body of the letter</a:documentation>
         <oneOrMore><ref name="db.all.blocks"/></oneOrMore>
    </element>
    <element name="l:closing"><text/></element>
    <element name="l:signature">
        <ref name="db.personname"/>
         <optional><ref name="db.affiliation"/></optional>
      </element>
      </element>
    </start>
  </include>
</grammar>