Referencing HTML sub-pages?

[Karl Eichwalder <ke gnu franken de>]

I learned that you can nicely reference HTML index files from a Mallard
index page; e.g., href="help:opensuse-manuals" finds
opensuse-manuals/index.html in /usr/share/help/C/ .

opensuse-manuals/index.html is a set of book.  Now I'd like to know
whether you can directly link to arbitrary files in
/usr/share/help/C/opensuse-manuals?  There we have sub-books such as
book.opensuse.startup.html.  I tried
"help:opensuse-manuals/book.opensuse.startup.html" without success.

-- 
Karl EICHWALDER