Using <h1> for chapter titles in HTML output

I am trying to customize HTML output so that MS Word will open the HTML
files in a way that produces consistent paragraph styles.  In
particular, I want chapter titles in the DocBook content to become <h1>
elements so that they eventually map to the default "Heading 1"
paragraph style in MS Word.  By default, the chapter title is output in
an <h2> element.

My searching the docbook-apps archives, HTML parameter documentation,
and experimenting with XSL customizations has not turned up an answer
for me.

Can anyone point me to a configuration that will cause chapter titles to
appear in the HTML <h1> element?

In case it matters, the DocBook content uses <section> elements rather
than <sect1>, <sect2>, and so on.  Also, I don't mind that the <book>
title is already <h1>.  Having both the book and chapter titles use <h1>
is not a problem for me.

Thanks for your help.

Peter Desjardins