Table of Contents structure

[waldron.Navix@canon.co.jp]

Hi,
New to the list, and this is my first question.
I've been doing XML work for the last several years now, using my own structure
designs for each job. This is the first time though I've tried marking up a doc
using Docbook (customer requires it). My problem is in the TOC Preface section.
There does not seem to be enough depth there to do what I need. I have a preface
with multiple levels (sections). The Tocfront elements don't allow sublevels
(children), and I don't want to use the Tocchap elements until I get into the
main body (chapters) of the TOC. Tocpart seems to be limited to just Tocentry
too...
So may Preface would look something like this normally (by my own design...):
<toc>
  <title>Contents</title>
  <preface>
    <tocA>A-title</tocA>
    <tocA>A-title
       <tocB>B-title</tocB>
       <tocB>B-title</tocB>
    </tocA>
    <tocA>A-title
       <tocB>B-title</tocB>
       <tocB>B-title</tocB>
    </tocA>
   </preface>
   <chapter value="1">
       ... and so on.

Could someone offer a logical method of markup for a TOC preface with multiple
levels?
Thanks in advance!
Cheers,
Dee Waldron
Navix Ltd
Tokyo Japan