Newbie docbook-xsl question: how to customiseuser.header.navigation?

Hello.

I'm using xsltproc (packaged on Debian Sarge, if this is relevant) to
convert a DocBook source to HTML. I wish to add some user navigation
links to the tops of generated pages. The docs talk about
user.header.navigation, but I'm not clear on how to actually set this.

- Using --stringparam appears to have no effect.

- Using --param variously generates xpath errors, or has no effect.

- Copying chunk.xsl and docbook.xml from /usr/share, tweaking them
directly, and then messing about with a lengthy --path option generated
several message like "duplicate name 'dbhtml-attribute'", which I really
don't get.

Am I on the right path here? Is there a simpler way?

- Raz