Extend/modify DocBook Schema?

Hello,

I used a modified version of DocBook for an API documentation effort,
adding programmer, maintainer, and packagename to methodsynopsis. 
I was working from the 4.2 DocBook DTD (docbookx.dtd,v 1.13 2002/07/17)
and I followed the examples in the online documentation. [1]

Now I'd like to prepare to try this with the Office 11 Beta (whenever it 
arrives), and need to implement my customization layer in WXS. I had 
changed the order of elements in methodsynopsis by putting 
packagename right before methodname, and by adding a language
attribute.  (I also added some names to the end of the content model, but
I don't think they're a big problem.) I've appended a snippet of the XML. 
[2]

I'm very new to WXS, and based on the reading I've done so far, I don't 
think I can support the existing API XML documents with my custom DTD 
and with a customized Schema, because I don't see how I can change 
the order of elements in methodsynopsis to insert my packagename.

Is there a way to customize the DocBook Schema through a customization
layer as I did for the DTD? Or should I change the XML to match a content 
model that I can support  using import? Am I overlooking namespace issues 
that can make this easier (or more difficult)?

 TIA,

 Joe


[1] Customizing DocBook http://www.docbook.org/tdg/en/html/ch05.html

[2]
<methodsynopsis language="PL/SQL">
   <void/>
   <packagename>header_link_footer</packagename>
   <methodname>FOOTER</methodname>
   <methodparam>
       <type>varchar2</type>
       <parameter>screen_level</parameter>
   </methodparam>
   <programmer>
       <personname>
           <firstname>Joe</firstname>
           <surname>Gilvary</surname>
       </personname>
   </programmer>
   <maintainer>
       <personname>
       <firstname>Joe</firstname>
       <surname>Gilvary</surname>
       </personname>
   </maintainer>
</methodsynopsis>