DOCBOOK-APPS: multiple tocs in website

What is the purpose of having multiple <toc>s in website? I have experimented with it and can see how it works; it is almost as if it builds two completely separate websites, but with the same "look and feel." Under what circumstances are multiple <toc>s within a single <layout> preferable to two completely different <layout>s?

Having asked these questions, I can imagine that it would be convenient to maintain one set of xsl stylesheets. But it would also be nice to be able to specify different homebanners, banners, and css stylesheets for the two navigational heirarchies. I don't see how this can be done since they are specified under <layout> and seem to apply to any <toc> inside the <layout>.

I notice, for example, that the docbook.sourceforge.net website and the example website are two distinct websites, not multiple tocs within the same website.

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Kevin M. Dunn
Professor of Chemistry
Hampden-Sydney College
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