What is the docbook equivalent to HTML <div>?

[Alan Ezust <alan.ezust@gmail.com>]

I would like to group elements which are marked as "solutions" to exercises.

Each group of elements  could be 0 or more paragraphs mixed with
bridgeheads, orderedlists and unorderedlists.

In the HTML generated version, I'd like a <div class="solutions"> to
end up around this grouping, and something equivalent the FO version
too.

Is there a docbook element which one would use to this end? What is
the right way to group together these elements?