<h1> headers in html and webhelp output of <book>

Hi, 

We produce single-page HTML and chunked webhelp output from our DocBook files. I have noticed that for books, the title of high-level elements (chapter, appendix, and so on) receives an <h1> tag. Is there a way to change it to <h2>? I suspect that the components.xsl is responsible for calculating the header levels, but couldn't customize it to work for me.

Thanks a lot, 

Robert