Jirka's suggestion is the best approach. It gives you all the flexiblity
in the world with no extra work. Here's how it might look:
...
<tr>
<td>
<para>
<info>
<vadim:metadata xmlns:vadim="http://somedomain-you-own/some-namespace-you-makeup">
<vadim:somefield>somedata</vadim:somefield>
</vadim:metadata>
</info>
Ipsum lorem. Stuff readers see goes here.
</para>
</td>
...
DocBook's info element and its contents are already ignored by the xslts.
You can encode your data in xml as complex as it needs to be in a namespace
of your invention. Here's another way of doing it if you don't like namespace prefixes:
<tr>
<td>
<para>
<info>
<metadata xmlns="http://somedomain-you-own/some-namespace-you-makeup">
<somefield>somedata</somefield>
</metadata>
</info>
Ipsum lorem. Stuff readers see goes here.
</para>
</td>
