Unnumbered Chapters in HTML Stylesheet?

[Michael Urban <urban@panix.com>]

I would like the Prologue and Epilogue chapters of a novel to be
unnumbered.  I arbitrarily used  role="simple"  for those chapters,
and was able to coerce the HTML stylesheet to produce unnumbered headers.
But the other chapters compute their number based on the actual
count of <chapter> elements, so the first chapter after the Prologue
is still Chapter II, rather than the desired Chapter I.

Is there some other way to go about this?  It is not terribly
important, but if there's a Clever Trick I am missing, I would
be delighted to hear about it.